Suspension Set-up

[dhall0519]

:confused::confused:
Ok I really need help here.
My car (JDM AE86 Corolla) understeers huge on corner turn in & mid corner but then easily turns into oversteer on corner exit ( when dry)
It seems that in the wet & setting set on lowest on 4 corners that the car has huge grip & turns in better
Now I realize that the 2 conditions are at totally different but answer this:
- why ,when it's dry & I leave the soft setting the car "floats" over the bumps (rear breaks traction with acceleration)& I can't get the car to drive yet in the rain it feels fast & doesn't show the same charateristics?
- when I tighten the front up it starts to understeer right away?
Any suggestion would be greatly welcomed.
:(:mad:

[max attack]

Pm me,I've been playing with an ae86 for nearly 10 years and might be able to help out.

[1337trix]

you're the levin?


you had a rough weekend man..... the car looked like it was giving you a hard time

[Benzin!]

If both front and rear are adjustable then you should set up the front to soft or half-way and the rear stiffer in order to dial out understeer.
Here is a set up guide, go to the end of the page for you problem
http://www.wtrscca.org/tech.htm
and another table nicely done
http://www.madabout-kitcars.com/kitcar/kb.php?aid=196

[94mx6-ls]

What are your alignment settings and have you measured the temps on your tires? Also, what tires are you running? Your suspension can only do so much before it becomes dependent on your tires to keep contact.

[max attack]

If both front and rear are adjustable then you should set up the front to soft or half-way and the rear stiffer in order to dial out understeer.
Here is a set up guide, go to the end of the page for you problem
http://www.wtrscca.org/tech.htm
and another table nicely done
http://www.madabout-kitcars.com/kitcar/kb.php?aid=196

Not as easy as that with the corolla.:)

[Slowpoke]

The other aspect here is that you have to understand what the adjustment knob actually does, and how body roll is affecting your dynamic camber and toe. Does your adjuster knob change only rebound, or what proportion of rebound/compression is changed?

[MazdaMatt]

If you're still thinking in the realm of dead-basics... a good rule of thumb is this:

Corner entry - adjust the front
Corner exit - adjust the back

Entry understeer, soften the front
Exit oversteer, soften the back

Of course your alignment has a major affect as well, but this general rule will help you out. If you find you're at full soft and still lacking grip add camber.

Do you have a lot of adjustables in your suspension? The more you can adjust the better you CAN make it... but the more you can adjust the worse you CAN make it too. Many people prep their cars by buying everything adjustable and end up so far from the correct setup that they can't find their way back.

[AW11_4AGZE]

Friends don't let friends use sway bars.

I think we all have different ideas when it comes to setup. I've heard and even felt that bars will make the car act different in varying surface conditions. In my opinion, varying the dampener is a bandaid for poor springrate (read wheel rate) and will give you inconsistant results.

Personally I run 600lbs/in front 350lbs/in rear. People think that's backwards... but so is my car (mid rear). It's not perfect... my shocks are are not good enough...

Talk to Maxattack ... he know's what he's doing with the 86.

Build the spring rate/ shock/ tire/ alignment/ weight distribution from the ground up...

[Caveman]

Well I keep hearing no sway bars
Next event ill have no rear bar
????

And max is defintly the man to talk to

[dhall0519]

FRONT:Greedy coil overs with rebound/compression being adjusted at the same time but to what proportions I don't know
REAR: Greddy shocks with fully adjustable spring perches & again rebound/compression adjust equally
TIRES: RT615
I'm fustrated......

[~[MPR]~]

Yes, talk to max attack, he'll definitely help you out.

I've heard and seen this issue over and over lately on many different types of vehicles. The car doesn't give consistant handling performance on different surfaces, in the wet or dry and also seems unresponsive and inconsistant to some suspension setting changes.

The probem has been found in many cases where the sway bar is the cause of the inconsistancy because of the way it operates how it actually changes your suspension dynamics as soon as you enter a turn.

To make your car stick: Throw away your sway bars. Calculate your front and rear spring rates (this is based on a formula used developed by one of the best autocross guru's...ever). Then source a set of adjustable dampers to match those springs. Tehn dial in your ride height and alignment to complement the other settings and you car will be a weapon through the cones, on any surface, wet or dry.

We followed this formula with our 87 MR2 and the results are unbelievable from the way it was before. It is very consistant and neutral no matter what the surface or weather condition. It is still not perfectly dialed in as we know our camber and alignment are not properly set up yet. But from changing the springs and dampers alone made a world of difference.


Good luck with your car and give us and update and how you're making out.:)

[dhall0519]

Sound ok but the suspension IS a matched set. Spring rates & shocks

[~[MPR]~]

Sound ok but the suspension IS a matched set. Spring rates & shocks

The current dampers you have may match the spring rates of the springs you have now. But if they are not the right spring rates for that specific vehicle's dynamics, weight/weight distribution/drive train layout, it won't matter if the dampers match the spring rates. The car will still not handle as good as it should.

What exactly is the setup you have? Springs/rates(if you know what they are)/dampers? Also do you know the weight of your car? I'll do some calculations and try to help you figure out the best setup.

It may infact be that your springs/dampers are correct but your sway bars are the main cause of it's ill-handling characteristics.

How much body roll to you currently experience? What is the current ride height set at?

[max attack]

Oh man I'm I feeling the love,thanks guys.:)

With the corolla if the front is close it'll oversteer like nothing else,ever wonder why they are so popular with the drift crowd?

Ditch the bars,well at the least the rear bar-it'll transform it-mostly on corner exit.The right front alignment alone can get you pretty close even if the springs are whacky.

I wouldn't be surprised if the greddy dampers have way too much compression damping for the spring rate-its a trait of the japanese tuners to make the car feel responsive.Doesn't work so well imo.

Pm me specifics and I'll help get it sorted,if you could make it to the next twin lakes event that would be good.

[dhall0519]

where is the twin lakes event held?

[sjd]

where is the twin lakes event held?

Barrie Molson Centre. About 45 minutes North of the GTA. The next event is August 9th.

[MazdaMatt]

Pm me specifics and I'll help get it sorted...

Don't PM him! Lay it all out here so we can see how its done!

[~[MPR]~]

Ok, I'm gonna lay it all out for all to see. Tom (max attack) feel free to jump in if you think I'm incorrect as you have way more experience than I do with the AE86.

Here it is:

AE86 corolla/levin 3 door hatch
Assuming roughly 2130lbs/so say 2300lbs with driver total weight for a nice round number.
Weight distribution: 53/47% (front/rear)
R compound tire factor: 0.8 (this will come into play later in the calculations)

Suspension motion ratios: Front - nearly 1:1, so we'll say 1 to keep it simple.
Rear - 1:1 as the spring is pretty much acting directly on the axle. So 1 as well.

Now for the magic suspension formula:

Since the motion ratios for the front and rear are at 1:1, this can be left out of the equasion because the wheels rates will pretty much equal the spring rate.

Front spring rate:
(2300/2)x.47x.8=432in/lbs. Since this end carries more of the vehicles mass, well round up to the nearest 50in/lb so 450in/lbs (since nobody makes a 432in/lb specific spring rate).

Rear spring rate:
(2300/s)x.53x.8=488in/lbs. Since this end has less of the vehicles mass, we'll round down to 450in/lbs.

Now this should be a good base line to start, but now we must take into account the drive train layout and some other factors this vehicle has that can affect the handling dynamics:

The ae86 is front engine rear wheel drive and has a live or solid rear axle. Solid rear axles like this act like a giant anti roll bar (thus why we said to throw away the existing rear bar). Because of the effects the rear axle has on the vehicle it will always be as if there is a large rear anti roll bar. By using the spring rates we calculated above, you'll find it would turn in great but at mid corner and especially on corner exit, the ass end of the car will step out almost uncontrollably and very easily no matter what. To compensate for this issue we'll need to soften the rear spring rates. I suggest through simulations I've run and through talking to tom, dropping the rear rate calculated by roughly 100in/lbs, or even more would be a very good place to start and should give the car much more balanced handling characteristics.

So now we are at:

Front: 450in/lbs.
Rear: 300-350in/lbs.

Now with this in mind you should source some dampers to match (koni yellows would work great with these rates). And from there work on ride height and alignment to fine-tune your setup.

I'm not familiar with the ae86's chassis so I wouldn't know where to set your ride height or camber/caster/toe to. but tom can deffinitely help you out there. I know as a rule of thumb to set your ride height so that your lower contol arms at the front are almost parallel to the ground and slightly downward from the chassis toward the wheels. For the rear, since it's multi-link, I don't know the geometry to know where to set it. But I do know you'd want the radius arm (line from the center of rotation of the movement of the rear axle through it's travel tot he center of the axle) to be setup the same as the front lower control arms if that makes sense and is possible. Tom, feel free to chime in here...lol.


I hope this helps you out and it wasn't too complex to understand. I tried to explain in the simplest terms. Once you get the springs/dampers right it just comes down tot he fine tuning aspects like ride height/alignment/camber/caster etc...and oh yeah...remove and throw away the front and rear anti roll bars.

Good luck!:D

Tom, I'd love to hear your input...:)

[~[MPR]~]

Just thinking about the ride height adjustment...scratch what I said about the rear ride height.

Because it's a multi-link solid axle type rear suspension, and not a double wish-bone or macphearson strut type, it's not as important to the vehicle's handling dynamics as those other types of suspensions are. Main reason being the rear camber/toe will never change throughout it's range of travel as the front suspension and other types of suspensions do.

This is what I would do for setting the ride height: Get the front ride height set as per how I explained in my previous post and then match the rear so the car sits flat on level ground. So basically same height, front and rear.

Also, you should set the ride height first then adjust the camber/caster/toe.

[MazdaMatt]

Questions:

Why'd you use the front weight portion on the rear spring calculation and vise versa? If you didn't mean to, then you wouldn't end up with the same spring rate on both ends after your rounding.

What does R compounds have to do with the vehicle needing a total spring rate 0.8 times the total vehicle weight? From what i can tell, that sets the standing compression to 0.8 inches, but what's that got to do with R comps?

Comments:

Ride height selection has a lot to do with body roll - specifically the relation between CG and roll centre at a given end of the car. It has been a while since I was playing Forza regularly, but it as a known affect on cornering that you need to take into account.

Does anybody have a copy or a link to the guide in "Prepare to Win", the book by... Carroll Smith? (correct me if i've got the wrong guy)

Edit - one more thing: There's no way your wheel rates are 1:1... i think. It is the ratio of the distance travelled by the wheel for a given distance compressed by the spring. If you compress the spring 1 inch, does the wheel move 1 inch? Not likely unless the spring mounts to the centre of the knuckle and is oriented perfectly tangent to the arc of travel.

[darcyw]

struts type suspensions are accepted at 1:1. I've forgotten the rate for the A arm, honda type suspension...i think its .75:1.

later
darcy

[~[MPR]~]

Questions:

Why'd you use the front weight portion on the rear spring calculation and vise versa? If you didn't mean to, then you wouldn't end up with the same spring rate on both ends after your rounding.

-Yes I did this intentionally, it's part of the formula. You multiply by the percentage of the oposite end. I can back up the reasoning behind this but I'd have to find the article again, which I will do, and post it. We used this formula on the MK1 MR2 we race and it works VERY well for any type of vehicle. I have spoken to people from professional race teams who have not used this formula but simply kept trying different setups and kept tweaking until they found the best settings and when they give me the data from their vehicle, no matter what it is, and I calculated, I end up almost every time with the almost identical spring-rate (front and rear) that they use. The only exception being, somethimes, if it's say a front engine front wheel drive car, they will use a lower spring rate in the rear but with a larger anti roll bar, which, if you add the rate of that bar to the spring rate they are running (because an anti roll bar takes away and transfers spring rate from the inside spring and adds it to the outside spring), it equals the spring rate calculated with this formula (for use without anti roll bars).

What does R compounds have to do with the vehicle needing a total spring rate 0.8 times the total vehicle weight? From what i can tell, that sets the standing compression to 0.8 inches, but what's that got to do with R comps?

-Because tires have a certain spring rate them selves, you must take into account that rate and include that factor into your calculations for determining wheel rates (or in the case of the Levin with 1:1 motion ratios, the actual spring rate).

Comments:

Ride height selection has a lot to do with body roll - specifically the relation between CG and roll centre at a given end of the car. It has been a while since I was playing Forza regularly, but it as a known affect on cornering that you need to take into account.

-Exactly. Thats why I would set the ride height as I explained before. It would place the roll center in the correct position with repect to the center of gravity of the vehicle. Depending on your suspenion geometry, having your ride height too high or low can drastically affect your camber and toe within it's range of travel as well.

Does anybody have a copy or a link to the guide in "Prepare to Win", the book by... Carroll Smith? (correct me if i've got the wrong guy)

Edit - one more thing: There's no way your wheel rates are 1:1... i think. It is the ratio of the distance travelled by the wheel for a given distance compressed by the spring. If you compress the spring 1 inch, does the wheel move 1 inch? Not likely unless the spring mounts to the centre of the knuckle and is oriented perfectly tangent to the arc of travel.

-If you look at the front suspension of the ae86, the spring is acting almost directly on the point where the wheel touches the ground and is also acting very close to the tangent of the arc of motion. If you also look at the rear suspension of the ae86, the springs act pretty much straight down on the rear axle and both of those examples are almost if not exactly motion ratios of 1:1.



Tom, if you know the exact motion ratios of the front and rear suspension, please share. I could not find this information, but just by looking at pics of the front and rear suspension I can tell they are pretty darn close to 1:1.


This is great...I live for these discussions!:D Always learn something new...

[max attack]

You got most of it right on,his rates on the greddy coilovers are pretty much exactly as you've calculated.I've run my car in the past stiffer than that(won the 1st 2 regional titles with it,guess it wasn't too bad)with 550's front and as high as 500 rear but that was on r's.Trouble was it simply bounced from bump to bump rather than absorbing them.
The rear spring is quite inboard of the wheel in its stock location so there's a motion ratio but only when 1 wheel is compressed.His car is coilover all around as mine is so the rear spring rate should be reduced a bit as its much closer to the wheel.
The rear control arms I believe induce rear toe in as compressed(on 1 side-ie during cornering) due to the unequal lenght of the upper and lower arms,also when lowered the short upper arms become sharply angled which changes the geometry quite a bit.The wide bushings in those arms also bind when 1 side of the housing is compressed/extended and causes inside wheel lift(yet another reason to ditch the rear bar).I fixed both problems on mine by going to an equal lenght 3 link set-up with heims,with 1 wheel in full droop I can tuck a 20" race tire 4" into the wheel well-about a billion times better than stock.
Another pc of the puzzle is the rear roll center,when lowered it essentially remains unchanged while the front is lowered alot so this gives a steeply raked roll axis to the front.On mine I built an adjustable panhard mount that has a range of 2" to 6" lower roll center than stock,makes a very noticable difference-car will understeer in if too aggressive but sticks the rear damn good on the way out(over twice the stock power level)
Cusco I believe makes a bolt on axle mount to lower the panhard mount,only lowers it 2"(about enough to get panhard level if lowered 2",and the panhard SHOULD be level to minimize rear steer with rear compression)
At the front roll center adjusters should be used to get the lower control arm back in shape,otherwise you need mega static camber to compensate for the lack of -camber gain in a turn.Castor needs to be keep to a minimum,just enough for driver feedback and no more.
My recommandations would be to unhook both bars,leave the front springs alone for the time being(they are too stiff imo for the street tires used)and lower the rear spring rates to 250lb(also too stiff but...).For reference my car is on 350's front,175's rear and no bars and sticky tires,yes its lighter overall(and way lower) but with all the turbo stuff up front the nose is close to stock weight.
I don't like going over about -2.5 front camber,hurts braking(especially trail braking)and the turn-in can actually suffer due to the extra time it takes fot the tire to flatten and generate max grip(problem gets worse the wider the tire).Toe should be 0,I run a little toe out but its competition only.My tire wear is perfect,well the fronts wear the insides slightly more and the rears wear the outsides slightly more-rotate front to back every event and all 4 are perfect.
Hope this helps,keep us posted as to any changes made and the effects.Btw I could bring a set of springs to pop in the rear if you make it to the next tlmc event just to try,I've sold my complete suspension set-up but will have the 175's still.

Forgot to mention,when you go to adjustable rear arms adjust the nose of the diff down-it makes a surprising difference in forward bite.If it hops out of the hole you went too much-adjust it up a bit before you break something and try again.

[~[MPR]~]

Awesome write up Tom! Will take a few minutes to soak all that up...hehe.

Sounds like I was a bit off in my calculations to what you actually suggest, but not too far off. I was going based off the ae86 in forza 2. I did what I mentioned earlier and then started dropping the rear spring rate until I could step on it even before the apex and the ass would grab and hook through mid to corner exit. My rates in the simulation were lower as well given the car was at about 1800lbs and putting down 300+hp. I believe I'm running 350-400 front and 250-275 rear.

So for a ~1500lb. (if I remember correctly?) rolla like yours, 350front and 175rear sounds about right. And... for his 2300lb levin...450 front 300 rear. The formula works. I don't mean to go by what a video game is telling me, but that the game is actually acturate enough to try out different setting and get an idea of what works and what doesn't. Of course the only real way to tell is to actually go out in do it in real life...lol.

dhall0519, I hope you can come out to the next twin lakes event. I'm eger to see how you make out trying the different settings.:)

[max attack]

I'm old enough to not be to much of a gamer,do enjoy the decent driving games when I get a chance though.

I wish my car was that light,it actually a little over 1800lbs but with a much lower cg compared to an 86 of the same weight due to the composite roof and pillars and hatch.Not too mention my floor has been cut out so the seat could be even lower,damn hard to see over the cowl though.

Next car will be pretty close to exactly half the weight of the corolla,ALOT lower(approx 2.5" clearance on 20" race rubber,total height about 44" to top of cage)alot shorter overall and a shorter wheelbase(still working out exact space requirements)but think it'll be between 86 to 89 inches.I get to design and locate all pivot locations,control arm lenghts etc.Roll centers will be just above ground,current #'s have the rc's at 2" above ground but that can be lowered a touch pretty easy.

I'm outa the country on vacation as of very early tomorrow morning so I'll miss what goes on with this tread untill late next week when I get back.Look forward to it.

[AW11_4AGZE]

Mike, the reason for the .8 (or less than one anyways) multiplication for R compound is not exactly because the tire holds a spring rate. Rather, it is for G loading. If the tire is overloaded, you will lose traction.

Also, the reason for crossing the spring rates is simple; it is ment to offset the car's weight bias. If each end of the vehicle had the exact same level of grip, the front would break away first because the higher weight would overcome the available traction earlier.

Also, I believe the 86 croud suffers from bump steer if lowered too far. I would suggest RCA's for the front... Tom?

[~[MPR]~]

Mike, the reason for the .8 (or less than one anyways) multiplication for R compound is not exactly because the tire holds a spring rate. Rather, it is for G loading. If the tire is overloaded, you will lose traction.

That's right...thanks for the reminder. :p

Also, the reason for crossing the spring rates is simple; it is meant to offset the car's weight bias. If each end of the vehicle had the exact same level of grip, the front would break away first because the higher weight would overcome the available traction earlier.


^There you go, mazdamatt. Now I don't have to go look up the article. lol

Also, I believe the 86 croud suffers from bump steer if lowered too far. I would suggest RCA's for the front... Tom?

[dhall0519]

Wow this is a lot to take in........
For the record I do have rca installed & all these suggestions will be considered & tried......
STAY TUNED.......
Thanks Guys

[Caveman]

Ok no that covers a toyota
how about a 350 hp 400 ftlbs first gen rx7
aprox 2100 + me so 2400 lbs
nead forward bite as right now i spin for like 300 ft both tires on 245 45 16 ventis z214

Over steers yes but that we can fix relitvly easaly
eliminat the wats link and rear sway bar add a panhard and go from there

O and a littel less skinny pedel
These are my tire options as of right now
http://www.youtube.com/watch?v=JtK_J3CYSUM
help me please I cant launch my car anymore with the new engine

[AW11_4AGZE]

Ok no that covers a toyota
how about a 350 hp 400 ftlbs first gen rx7
aprox 2100 + me so 2400 lbs
nead forward bite as right now i spin for like 300 ft both tires on 245 45 16 ventis z214

Over steers yes but that we can fix relitvly easaly
eliminat the wats link and rear sway bar add a panhard and go from there

O and a littel less skinny pedel
These are my tire options as of right now
http://www.youtube.com/watch?v=JtK_J3CYSUM
help me please I cant launch my car anymore with the new engine


Ummmm.... Less power. It's too much Rob! ;) The same calculations apply for any car. Are you solid rear axel or independant?

You are lighter and have more power than us... You could get it to do circles around us if you set it up, and are ginger on the throttle.

[~[MPR]~]

What's your rear suspension setup, Rob? (solid axle or independent?)

Also whats the weight distribution % (front/rear)? I'm sure it's a little off from factory spec since the Wankel was thrown out and the V8 shoe-horned in...haha.

With that we should be able to help you out. And yes...lay off the throttle!!!:D

[Caveman]

Solid rear axle
still need to get it corner weighted but im thinking aprox 60%F
From what ive read thay say the small block with alum intake and no acc. just an alt and wp only adds abought 100 lbs over stock with a/c and thats what my car had

batt has moved to rear (just ahead of diff on the right)
eng was installed as far back as posabull (with firewall mods)
eng also mounted right of center to help compisate my fat but on the left

bigest isue other then forward bite (ok is forward bite) is very loose on entry. Tail tends to slip out to the right. EVERY TIME. never to the left ??? And at that point I have to throtel to control it (realy hard on tires)
Thanks Guys

If i make the twin event ill have the rear bar removed to try that.

So what do you think can i fit the 27 x 10 Cascar slicks on the back?
I might need Mike Wolfs help with that sawzall after all.

[MazdaMatt]

Is it stepping out to the right when you're straight braking, or only when you're doing a left turn-in?

[Caveman]

Any time (not brake pull) inharent fault with the first gen rx7s o.e. set up.
ive looked at a bunch of them and all have the diff off set to the right 1/2" . Thats the main reason I want to put in an adjustabull panhard rod and ditch the wats link. and pull the diff to center I think that will help

O and the front is coil over strut O.E. as of now

[~[MPR]~]

Rob, your car will be a bit of a challenge to setup. We can calculate some baseline numbers to start at, but it may take some trial and error to find the sweet spot.

With the amount of power you're putting down, you may want to use a throttle block or something so you can't apply more than say 20% throttle? Reason I say this is so you don't confuse too much power for a loose rear-end. After you know the suspension is prime, you can unblock the throttle and go nuts!

I'll do some calculations and post up the results a little later tonight.

[dhall0519]

Hey thanks for the invite to Twin Lakes.
I'm going to try & be @ aug 9 event, but no promises...

[~[MPR]~]

Ok Rob, Here's what I got for ya:

1st gen RX7 with V8.
Weight: 2400lbs w/ driver
Weight distribution: Stock is 50/50, with V8 ~55/45 est.
Motion ratios: front ~1.0, rear ~1.0 (this means the wheel rates calculated are the same as the spring rates to be used)

Calculations:

F=1200x.45x.8=432in/lbs

R=1200x.55x.8=528in/lbs (WAY too stiff for this particular car)

Given the RX7 is a solid rear axle and is so tail happy, I'd start off with 450in/lbs springs in the front (with no anti roll bar of course) and 350in/lbs springs in the rear (also no arb).

What dampers are you running Rob? They'll have to match pretty good or it'll bounce a little...

If the ass end is still sliding all over (corner entry, mid corner, exit) without being provoked by throttle input, then you'll have to try going softer in the rear spring rates. If it's pushing, go stiffer in the rear.

On top of all this, there's alignment you'll have to play with as well. And you know as well as I do, with the power you have in a vehicle that light with a solid rear axle, it's going be hard to make it stick at any point on an autocross track. You may want to run a more autocross friendly tire like RA1's or V710's which stick well even when cold vs an actual track slick which needs some heat before it starts to stick.

About the issue of the car stepping out always to the right when you hit the brakes...may I suggest adding a ballast weight on the passenger side? Also I'm sure you've done this, but check to make sure none of the calipers are seized. If you do add ballast weight, depending on how much, you may have to up the spring rates all-round.



Good luck with the car. Keep us updated!:)

[~[MPR]~]

Hey thanks for the invite to Twin Lakes.
I'm going to try & be @ aug 9 event, but no promises...

Cool, hopefully see ya there!

[MazdaMatt]

MPR - I don't get it. You used the formula, then you totally scrapped the numbers and gave him some "off the top of your head" guesses. Your guesses didn't even have the same F/R bias, let alone ratio. What's the point of the formula?

There's no such thing as too much power - only too much throttle input from the driver.

[Caveman]

as it stands I need to know how much and the weight is.
at that point I start figuring out what to buy.
for now i think the rear is to stiff right now and am goingt to soften the springs a touch
remove rear bar and tighten front bar
lower rear tire pres and add less gas
im going to melt down some wheel weight and make a ballest weight for the rear of set to the right.

We will see how it works on sunday

as for tires I run hankook ventous z214 c70 compound
40 treadware AUTOCROSS TIRE
thanks all

[AW11_4AGZE]

MPR - I don't get it. You used the formula, then you totally scrapped the numbers and gave him some "off the top of your head" guesses. Your guesses didn't even have the same F/R bias, let alone ratio. What's the point of the formula?

There's no such thing as too much power - only too much throttle input from the driver.

He isn't explaining the whole article. It was created by a gentleman by the name of Steve Hoeshler. He explained in detail, how he has setup, tested, and confirmed suspension settings and thier results.

Do not confuse wheel rate with spring rate. "Motion ratio" would be better explained as wheel leverage as well.

Think about a solid axel for a second. If you have 2 springs on opposite side, how would the rate change as the suspension loads? Because of the nature of the dependancy of the rear suspension, it would be hard to make a calculation to determine the inside spring's effect on the outside wheel rate. Also the linkage of the axel to the chassis can play a role on the effective wheel rate. Because of the cars tendancy to oversteer, I too would suggest a more trial and error apporach starting with a lower rate.

Remember, we are shooting to make the car neutral, to give the maximum amount of grip through all wheels. Just removing swaybars and having linear springs will greatly improve steering response. Having the right balance of rates will improve everything after the initial response.

I would suggest reading Steve's article. He wins.... a lot.
Here is a recent video: http://www.youtube.com/watch?v=x0psV0fmWrI&feature=channel

There is such thing as too much power ;)

[~[MPR]~]

MPR - I don't get it. You used the formula, then you totally scrapped the numbers and gave him some "off the top of your head" guesses. Your guesses didn't even have the same F/R bias, let alone ratio. What's the point of the formula?

There's no such thing as too much power - only too much throttle input from the driver.

There is a lot more to it then just the formula.

I will post up the entire article from which this formula is explained some time soon, so you can read it and hopefully come to a better understanding of how the results are derived for different types of vehicles.

As I explained before, the effect of the solid rear axle in a front engine rwd car acts like a giant anti roll bar. Anti roll bars are bad and because of their nature they take away grip from the inside and add it to the outside via transferring spring rate from the inside to the out side wheel, respectively. Make sense? You can remove the rear anti roll bar, but you can't remove the solid rear axle, which mean you still have a fairly significant anti roll bar in the rear. (unless you go with independent rear suspension, which is a much better system, but not always an option). The formula gives spring rates for the ideal independent suspension systems without the use of anti roll bars. This means you must incorporate and factor in the effect of the solid rear axle as an anti roll bar in your final calculations and estimates. Sometimes you have to "guess" as we don't know the real effect of said component(s) on the vehicles dynamic until it's actually tested.

To help you understand why I lowered the rear rate with a rwd solid axle car, here is an example: Say you have a car and your calculated spring rates are 450 front and 500 rear. Say this car has fully independent front and rear suspension. In this case we can use these springs rate with no anti roll bars and achieve maximum grip. The other alternative is to use lower rate spring rates with anti roll bars, where the rate of the anti roll bar bar plus the rate of the spring equals that of the rates calculated using the formula, and achieve similar handling characteristics. (and with a smoother ride going straight). BUT the down side to doing this is your now using those anti roll bars. In a corner they take away spring rate from the inside and add it to the outside thus, lowering the grip on the inside tire and pushing the outside tire beyond it's limit thus, lowering mechanical grip. On a car with a solid rear axle, there is no getting around removing a rear anti roll bar, because it will always be there, as the axle. So to equal out the effect of the axle, you must lower the spring rate. How much to lower it? That must be guessed and trialed to find the true answer.

The formula will get you to a certain point, then you must factor in many different variables specific to each type of vehicle. Sorry if I didn't make that very clear before. I know it looked like I just did the calculations, then changed the numbers without really explaining it fully.

There is quite a bit more to it, so it may seem at times we willjust throw a number in or change a rate without fully explaining it, but to me and others who use and understand it, it makes sense and works. To fully explain and type it all out would take a LONG time, so I'll post up the full article as soon as I get the chance.

Cheers.

Anymore questions? :)

[~[MPR]~]

^^While I was typing up my long-winded explanation, Tim basically summed it all up in a nut-shell...figures...lol.:p

[MazdaMatt]

Thanks, I totally missed the concept of the solid axel acting as a sway bar to begin with (cuz you didn't mention it!). It makes perfect sense now.

Hook up the article. I love reading this stuff.

The "other camp" of suspension design uses frequency calculation and damping ratios. Being an engineer this technique is just a reminder of second year control systems class; it has Bode plots and everything. Does the method that you are using assume a specific frequency is desired? What I mean is, would that formula always spit out results with the same spring frequency?

If you've not used the "other" method, google it. There are some excellent eye-openers in those articles.

[max attack]

Lots more good stuff,Steves video posted above is just like looking out of my civic windsheild.:rolleyes:

[~[MPR]~]

Thanks, I totally missed the concept of the solid axel acting as a sway bar to begin with (cuz you didn't mention it!). It makes perfect sense now.

Hook up the article. I love reading this stuff.

The "other camp" of suspension design uses frequency calculation and damping ratios. Being an engineer this technique is just a reminder of second year control systems class; it has Bode plots and everything. Does the method that you are using assume a specific frequency is desired? What I mean is, would that formula always spit out results with the same spring frequency?

If you've not used the "other" method, google it. There are some excellent eye-openers in those articles.

I'll have to read up on that method as I'm not too familiar with it.

[MazdaMatt]

The basic premise is that any spring and mass will have a "natural frequency". The corner weight of your sprung mass and the tension of the spring under that corner of the car determine that corner's natural frequency.

Different applications demand different frequencies. An autocross car may be 2Hz, a big cushy oldsmobile may be 0.5Hz. The natural frequency, measured in Hz, is how often in a second the mass will bounce. An oldsmobile hitting a bump lumbers up and down very slowly - it takes about 2 seconds to do a full compress, stretch and return. That car may also bounce 3-4 times before it settles - that's damping and I'll hit that next.

Damping ratio is a measure of how many cycles of compress-stretch the spring will go through before it settles. This number is inverse, so a damping ratio of 0.2 will bounce 5 times, 0.5 will bounce twice, and 1 will bounce once. If you set to 1.1 your spring will never return to center.

So spring rate in Hz is oscillations per second. Damping ratio is what fraction of motion is eliminated in each oscillation.

These two numbers together describe exactly what that corner of the car will do when it hits a bump. If it has a frequency of 2Hz and a damping of 0.5, it will do two oscillations per second and stop after 2 cycles, taking 1 second to settle completely. I think typically race cars for the track want about 1.5Hz and 0.7 damping.

This has been the Intro To Spring Frequency 101. Read about it for 10 more hours and you'll be done Spring Frequency 101. It's complicated stuff, especially when you get into roll frequency and "third spring" designs. You can control the hell out of your car with this stuff.

[max attack]

Yep,the trick is also to get the right fequency front to rear as the motion ratios are pretty much always different on the same car.

My biggest problem is I know just enough about all this to second guess every decision I ever make.:)

[AW11_4AGZE]

The basic premise is that any spring and mass will have a "natural frequency". The corner weight of your sprung mass and the tension of the spring under that corner of the car determine that corner's natural frequency.

Different applications demand different frequencies. An autocross car may be 2Hz, a big cushy oldsmobile may be 0.5Hz. The natural frequency, measured in Hz, is how often in a second the mass will bounce. An oldsmobile hitting a bump lumbers up and down very slowly - it takes about 2 seconds to do a full compress, stretch and return. That car may also bounce 3-4 times before it settles - that's damping and I'll hit that next.

Damping ratio is a measure of how many cycles of compress-stretch the spring will go through before it settles. This number is inverse, so a damping ratio of 0.2 will bounce 5 times, 0.5 will bounce twice, and 1 will bounce once. If you set to 1.1 your spring will never return to center.

So spring rate in Hz is oscillations per second. Damping ratio is what fraction of motion is eliminated in each oscillation.

These two numbers together describe exactly what that corner of the car will do when it hits a bump. If it has a frequency of 2Hz and a damping of 0.5, it will do two oscillations per second and stop after 2 cycles, taking 1 second to settle completely. I think typically race cars for the track want about 1.5Hz and 0.7 damping.

This has been the Intro To Spring Frequency 101. Read about it for 10 more hours and you'll be done Spring Frequency 101. It's complicated stuff, especially when you get into roll frequency and "third spring" designs. You can control the hell out of your car with this stuff.

I read that same theory in full, it's not overly complicated. Personally, I feel that is a great guideline to damping setup, but not as good for a spring setup.

I've talked to people who have used this as an initial guideline for setting thier spring rates, just to change them and have them closer to Steve's calculations.

Then again, there are people running even higher spring rates than that and doing quite well. All I know is Steve's setup worked quite well for us.

[~[MPR]~]

^Nice sig Tim...lol.

So I found an old issue of sport compact car (R.I.P. sport compact car mag...:( will miss it dearly.) which had an article that explained this theory. Basically the way I see this theory works is it helps you tune your car to a specific level of "comfort" and is more geared for setting up street cars that do mostly driving on the road and the occasional track day. It also mainly just focuses more on damping and less on getting the actual spring rates right. While getting the damping right is very important, more important is getting the spring rates right FIRST, THEN matching the dampers to the springs.

[~[MPR]~]

Alright here's the suspension theory article I promised to post up a couple weeks back:

(the following in 'bold' is a straight copy from Steve's installments on his race suspension setup theory)

Each installment will be a separate post.

Race Suspension Theory

MR2OC Posted by “Xhead”


“Originally Posted by XHead
We’ll take this a step at a time:

Ok, so its a pure competition car. No/little compromise. So the starting point is a target "total roll". As a general rule a strut car doesn't react well to body roll due to camber issues and lateral roll center movement. A target of 1.5~1.75 degrees total roll is typical. Total roll is a function of grip, wheel rate, moment arm length and roll stiffness. Keeping the car flat also minimized the severe bump steer issue the Mk1 chassis has.

We'll start with grip. Current generation STS tires are going to generate something in the 1.1g of grip, vs 1.3+ of say a Hoosier A6. So the STS car will require slightly less roll stiffness than a CSP car to achieve the same total roll. We need some roll to give the driver feedback and prevent the outside tires from being overloaded on turn-in and transition. Shocks will play a key roll here.

Next is ride height because that determines the length of the moment arm (the distance between the roll axis and CG). The CG acts through the moment arm (like a lever) to roll the car about the roll axis. The roll axis is the line drawn through the front and rear roll centers. The CG height is basically fixed in relation to the body but the roll axis is a function of the control arm and strut angle and therefore ride height. The roll axis height drops at a significantly higher rate than ride height. So we have to be careful about how low the car goes.

Before we can choose spring/bar rates we need to set the ride height to determine roll axis height and therefore moment arm length. Ideally, we want the roll axis to be 1 to 2 inches above ground with the rear at about 1" and the front at about 2". Since we won't be modeling the car in software, our target is to simply have the roll centers above ground level and that the front be above the rear so the roll axis is reclined toward the rear of the car.

So our starting point is to deal with the things that we can’t really change easily. Spring/bar rates are free so we can choose rates that work with the rest of the setup. Ride height is basically free so we can raise/lower the car to our advantage. What we can’t change as per the STS rules is the control arm geometry. So we need to set the control arm angle to optimize roll axis location and camber curve. In reality, its not control arm angle but instead the angle of the line between the inner control arm pivot bolt and the center of the outer ball joint. You can clearly see the front ball joint pivot is well above the centerline of the control arm. Same for the rear but somewhat less offset.

To achieve our previously stated geometry, we want the front virtual control arm (the line between the inner pivot and the ball joint center) to be roughly parallel to the ground. In the rear, the ball joint should be slightly above (maybe ¼”) the inner pivot. Unfortunately, this is likely to set the nose of the car noticeably higher than the rear. This may be adjusted later when we know the severity of the body’s rake. Actual ride height and roll center location will be effected by tire diameter. This virtual control arm angle is about the best compromise location to optimize the camber curve assuming less than 2 degrees of body roll. Its doesn’t address the bump steer problem but that will be addressed later.

-Steve”

[~[MPR]~]

“Installment #2:

Now that we have control arm angle (roll axis) set, we will address wheel rates. Realize that spring rates and wheel rates are related but not equal. The wheel rate is the result of the wheel’s mechanical advantage over the spring. This is expressed as a linkage ratio. As an example, the linkage ratio of a typical strut suspension is about 1.1:1. That is, the wheel moves 1.1” for every 1” of strut movement. Now this changes as the suspension moves through its range of travel and typically the mechanical advantage is at its maximum at full droop and goes down as the suspension compresses. While this is a generalization, it is basically the nature of the Mk1’s suspension. Its also important to remember that front and rear suspensions seldom have the same linkage ratio.

Its also important that we understand that a wheel rate includes the action of a swaybar if fitted. Swaybar rates are figured much the same. The bar’s wheel rate is the bar’s spring rate multiplied by the linkage ratio. Most Mk1 swaybars connect to the strut, so the linkage ratio is the same as that of the spring. And finally, the wheel rate is the wheel rate of the spring plus the wheel rate of the bar.

Now we return to the first installment and consider total roll rate. We targeted ~1.5 degrees of total roll. Now we need to figure a total roll rate that yields that amount of roll with the given roll axis height. Total roll rate is the total of the front and rear wheel rates. Front wheel rate + rear wheel rate = total roll rate. So how do we determine a total roll rate? I have developed my own basic starting point that is simple and effective. I have proven this method to work well for me with many different cars in both autocross and road racing. As noted previously, a favorite assumption of many people is to choose spring rates that equal corner weights. The problem with this method is it ignores actual vehicle dynamics. Most such setups would include a front (and sometimes a rear) swaybar. The front swaybar, if sized accordingly could provide enough additional front roll stiffness to give adequate handling balance. For our purposes here, we don’t care if its swaybar, spring rate or a combination of both, we are only concerned with the resulting wheel rate. Later we will decide on the split between spring and bar rates.

Back to determining total roll rates. I noted I had a simple formula for a starting point. That formula is: ½ the total vehicle weight divided by the inverse of the weight distribution. An example for a 2200 lbs car with 44/56 front to rear weight distribution (a rough estimate of your car's weight and distribution):

2200 / 2 = 1100 lbs

1100 * .56 = 616 lbs/in front wheel rate

1100 * .44 = 484 lbs/in rear wheel rate

The reason for inversing the weight ratio is to offset the car’s rear weight bias. If each end of the vehicle had the exact same level of grip, the rear would break away first because the higher weight would overcome the available traction earlier. Therefore a rear weight bias car will naturally oversteer therefore more front roll stiffness is necessary to counteract that natural tendency. How much front roll bias varies but all things being equal (and they never are) basing the offset in roll ratio on the inverse of the weight bias gets you pretty darned close.

Now you are probably stunned at the high wheel rates, but we aren’t through yet. First, remember the second paragraph regarding grip? STS tires don’t generate the same level of grip that A6 Hoosier do. As a result, lower spring rates are necessary to produce the desired amount of body roll. The difference in G loading is about 20~25%, so lets reduce our wheel rates by that amount

616 front * .8 = 492.8 lbs/in

484 rear * .8 = 387.2 lbs/in

To round off the rates: 500 lbs/in front and 400 lbs/in rear.

Now lets apply these to the MR2 chassis and its dynamics. Experience and testing are valuable here and I can apply my experience and make a couple of assumptions. First, that the low roll centers resulting from the current ride height and the high CG result in a long moment arm and a lot of body roll for a given wheel rate. Second, that the front has a longer moment arm than the rear. So we need a little more front roll stiffness and a little more total. Therefore we will bump the rates up slightly, especially in the front. I would think that using the wheel rates as spring rates would be enough of a bump and then add say 50 lbs/in to the front. The resulting spring rates:

550 lbs/in front

400 lbs/in rear.

Next we will address swaybars.

-Steve”

[~[MPR]~]

“Installment #3:

Now that we have a starting point for individual wheel rates we can now decided how we want to divide the wheel rate between spring rate and swaybar rate. To make an informed decision we must understand the function of the swaybar and how it interacts with the springs. A swaybar is nothing more than a torsion bar (spring) that has either end attached to each wheel of a single axle. It’s the twisting action of the bar that is the torsion spring. Because it only applies when a one wheel of the axle moves independently of the other, it has only moderate effect on ride quality.

To understand the swaybar’s effect on the springs and chassis we must understand how the springs interact with the chassis as well. We already understand how they affect body roll but they also effect ride quality and that is what we will now address. There are three basic principles that apply. First is ride frequency. Ride frequency is the rate at which the chassis reacts to input, a bump in the road. Ride frequency is expressed as Hz. A soft ride frequency would be about 1 Hz or one cycle per second. A cycle being the car passing over a bump, the chassis reacting and then returning to its original state. A stiff ride would be a frequency of about 2 Hz and a very stiff ride would be 2.5 to 3 Hz. We could easily calculate ride frequency based on the sprung weight of the car (total weight carried by each axle – unsprung weight of each axle = sprung weight) and the wheel rate of the springs on each axle. However, for our exercise here its only necessary that we understand the concept. The final part of the concept is that each axle has its own ride frequency based on the sprung weight and wheel rate of each axle.

Ride frequency is used to determine the second principle favored speed. Favored speed is the road speed at which the two ends of the car return to their original state after the car passes over a bump. To achieve a positive favored speed (a speed greater than zero, and yes you can have negative favored speeds) the front ride frequency must be lower than the rear so that the front returns at the same time the rear does for a given speed. Achieving this effect will produce the best ride quality for that speed and desired stiffness. The favored speed can be set at any target speed by tuning the front and rear spring rates to achieve the ride frequencies that produce the effect at the target speed. This effect works for both stiff and soft rides at most any speed and is why your stiffly sprung car feels smoother as speed increases. Most manufacturers set the favored speed using spring rate to achieve a smooth ride at their desired target speed (usually between 50 and 70 mph), then use swaybars to tune the ultimate handling balance and body roll.

The final principle we need to understand is center of suspension. Center of Suspension (CoS) is the point on the chassis at which, if weight was applied, both ends of the car would compress exactly the same amount. As an example, if the front and rear springs had exactly the same wheel rate then you could push down exactly half way between the two axles and the front and rear would compress the exact same amount. If the front springs were softer than the rear, the center of suspension point would be moved rearward to accommodate the softer front spring rate. The weight of the car then acts through the center of suspension via the Center of Gravity (CG). The difference in the car’s CG and Center of Suspension is a moment arm (which is basically a lever) just as the difference in CG and roll center. So the CG acts through the moment arm to compress the suspension in reaction to a bump. If the CG is behind the CoS, then the rear suspension is compressed more for a given load. The inverse is also true, if the CG is ahead of the CoS, the front suspension is compressed more. And like body roll, the longer the moment arm (the greater the distance between the CoS and the CG), the more the suspension on that end is compressed for a given load.

To minimize excessive body movement in response to bumps, we want the center of suspension as close to the CG as possible. This minimizes the length of the moment arm and therefore the CG's leverage over the CoS. For the Mk1, the CG is near the rear axle so we would have to have front springs that were much softer than the rear to achieve a center of suspension anywhere near the CG. Then to achieve good ride quality we set a desired favored speed and then tune the spring rates to suite. For the Mk1, setting a favored speed of say 50 mph, the front springs would have to be slightly softer, or the rear springs slightly stiffer, that that which would locate the center of suspension exactly at the CG.

This is the method the manufacturers use to tune the ride quality and handling balance of their cars. When we consider what we learned about roll ratios in the earlier installments its easy to see why the manufacturers use a hefty swaybar and soft springs on the front of the Mk1 (or most cars for that matter). Now that we understand how and why Toyota setup the stock Mk1 we can determine where we need to go to improve the car. Clearly we are not as concerned with ride quality because we are setting up a competition car. However, it is necessary that the car be able to track smoothly over bumps so as to not upset the car enough to loose traction.

-Steve”

[~[MPR]~]

“Installment #4:

Now that we understand the function of the springs and how they interact with the body to determine ride quality and body roll we can now directly address the swaybars. To achieve our target body roll and roll ratio we have chosen specific wheel rates. However, the rates we have chosen would result in a very stiff ride if we used only springs to achieve that wheel rate. To soften the ride we need to lower the spring rates, especially in the front (to achieve a positive favored speed) however, that will upset our chosen roll ratio so we add back wheel rate by supplementing spring rate with swaybar rate.

From installment #2 we had chosen 550 lbs/in front and 400 lbs/in rear spring rates. Its easy to now choose a front spring rate that will produce a more comfortable ride. Say 300 lbs/in front springs would give us a positive favored speed and move the center of suspension closer to the CG of the car, just aft of the center point between the two axles. We can then add back the spring rate by installing a swaybar with a rate of 250 lbs/in.

250 lbs/in front bar + 300 lbs/in spring = total rate of 550 lbs/in.

That looks pretty easy. However, its hard to find an off the shelf swaybar that has exactly the rate you want. In reality, unless you want to fabricate a custom bar every time you want to test a different setup, you need to calculate the rates of the available bars and then determine how much spring rate you need to achieve the desired total rate. So lets say you measure your existing swaybar and find it has a rate of 200 lbs/in. The spring rate you would want is determined by subtracting the existing bar rate from the target spring rate.

550 lbs/in target rate – 200 lbs/in bar = 350 lbs/in springs.

Easy enough. But we have a problem here. Swaybars are not the dynamic equivalent of springs. A swaybar transfers load from the inside tire to the outside tire and thus reduce mechanical grip as they add spring rate. And the effect is not linear. The stiffer the bar in comparison to the springs, the greater the effect (loss of mechanical grip). To give an example of the effect, if we set our proposed STS2 car up using the target data we have assumed above using the target spring rates without any swaybar, the car should have good balance. However, if we achieved that same target spring rate using a front swaybar, the car would tend to understeer more than if we used only springs and no swaybar. And the greater percentage of the total front spring rate the bar accounted for, the more the car would understeer. I noted as much early in the thread.

We now must choose how much bar we want to use for our final setup. As the reader may know, I don’t use swaybars on my DP car. Nor did I use swaybars on my previous racecar, a DSP X1/9. For me it is far easier to manage the setup of the car without swaybars. I also prefer the feel of the car without swaybars. It has long been my thought that; because a swaybar reduces mechanical grip, why would you want to put anything on the car that reduces mechanical grip?

With this simple method, it is easy to compare the effect of the front bar by comparing the same total spring rate using just springs and no front bar to the same total spring rate incorporating a front bar. I have done extensive testing and have proven to my own satisfaction that the theory is in fact accurate. The same total front spring rate achieved using a front swaybar will produce more understeer than the same total front spring rate achieved using springs only. In addition, the effect of the front bar changes based on the level of grip the surface offers. As a result, the car does not have consistent balance from surface to surface or even from run to run as the tires heat up from and the surface cleans and heat up throughout the day. I have found that my no-swaybar setup is very consistent on different surfaces and conditions seldom if ever requiring any changes to setup. At most, a pound or two of air pressure is all that is needed to tune the balance even in the most extreme of conditions. In fact, I don’t even change the setup for rain. All I have to do is bolt on the rain tires and the car is fine.

If one chooses to use a front swaybar, the effect resulting from the loss of mechanical grip will have to be accounted for by softening the front springs enough to bring the balance back to neutral. Choosing the amount of swaybar to use is now easy and dependant on driver taste. If the driver prefers a smoother/softer ride, use a very stiff front swaybar and subtract the front bar rate from the total spring rate to determine the required front spring rate. Testing can then determine how much less spring rate is necessary to bring the handling balance back to neutral. One could also compromise and use a very soft front bar, thus minimizing the loss of mechanical grip.

-Steve”

[~[MPR]~]

“Installment #5

Remember this number: 150%

So now is easy to see why one might choose, as I have, not to use any swaybars at all. I have spent more than 10 years working on this setup theory and testing the various permutations. Somebody else may not like the setup but I know its effective. The above method is exactly how I got to the point I am now. I came to this method by first using a spread sheet to aid in computing wheel rates and roll ratios accurately. I have since transitioned to a more scientific application of this theory using Susprog3d. I can now figure total roll based on lateral grip, ride height, CG height, roll axis and spring rates very accurately. I can also figure camber curves and roll center movement dynamically. A very powerful tool. But there is no substitute for testing and it is through testing that I have tailored my setup to suite my personal tastes. Now I will throw out much of what we have covered to this point.

I prefer a car that has slight understeer and is VERY stable in transition. I DO NOT want the car to feel loose in a slalom or fast transition. I know that a car with a significant rear weight bias, that is loose in transition, is slow. So my car has a lot of front roll stiffness to achieve my preference. So lets throw out all of the theory above and look at some simple data gathered from testing. Pulling off the swaybars and just sticking springs under the car, what works?

I decided I needed an objective comparison. I wondered if I could I derive a better, faster setup by pure testing alone, ignoring my theory. A number of test days at my favorite venue (Hunt Stage Field in Ozark, Alabama)

http://maps.google.com/maps?f=q&hl=...052872&t=k&z=14

where Wire Grass Region events are run and you can make all of the runs you want, when you want, enabled a lot of valuable data to be gathered. The basics can’t be ignored so the ride height must be set so the roll centers are close, as noted previously, and the camber curves have to be in a reasonable range. So those two elements determine ride height. What about springs? We need the car flat and we determined a total roll based on the weight of the car and potential grip. From installment #2:

2200 lbs car / 2 = 1100 lbs of total roll rate

So pulling data from my test notes. We need 1100 lbs of total roll stiffness less 20% for STS legal tires.

1100 x 80% = 880 lbs

So out came the box of springs and I started making runs. I have a spring inventory that covers a range from 300 lbs/in to 700 lbs/in in 50 lbs increments. I quickly start narrowing down the spring rate combination that produces the best balance. Once the spring rates are close, I start on roll center locations, ride height and camber curves. Then back to spring changes to further refine the balance and confirm the data. Final balance and dynamics are tuned with toe settings and tire pressure.

The testing results tell me that, for most mid-engined cars, making the front roll rate 150% of the rear is a good target. Therefore, given the above data:

350 lbs/in rear springs x 150% = 525 lbs front springs.

and

350 lbs/in rear springs + 525 lbs/in front springs = 875 lbs of total roll rate.

Close enough.

The next installment will cover shocks and dynamics.

-Steve”


So there you have it folks. Enjoy!:D

I don't believe he has finished the next installment yet.

[MazdaMatt]

~;150277']^Nice sig Tim...lol.

So I found an old issue of sport compact car (R.I.P. sport compact car mag...:( will miss it dearly.) which had an article that explained this theory. Basically the way I see this theory works is it helps you tune your car to a specific level of "comfort" and is more geared for setting up street cars that do mostly driving on the road and the occasional track day. It also mainly just focuses more on damping and less on getting the actual spring rates right. While getting the damping right is very important, more important is getting the spring rates right FIRST, THEN matching the dampers to the springs.

I very much disagree with the concept not being very complicated and with it being designed for a street car comfort level. That may have been the angle on the article that you read, but believe me it can be used for some high level race car suspension tuning. I will see if i can find the article that i read, but not bloody likely - it was a year ago. It had about 5-6 installments and was focused on setting up a formula car.

Thanks for posting that other article. I'll have to sit and read it at home when i get a chance.

[~[MPR]~]

I very much disagree with the concept not being very complicated and with it being designed for a street car comfort level. That may have been the angle on the article that you read, but believe me it can be used for some high level race car suspension tuning. I will see if i can find the article that i read, but not bloody likely - it was a year ago. It had about 5-6 installments and was focused on setting up a formula car.

Thanks for posting that other article. I'll have to sit and read it at home when i get a chance.

If you can find that article, I`d love to read it.

I`ll see what I can find and read up on it.

But I believe there is much more to it then just getting the frequency right.

[MazdaMatt]

Yes, definately. They go beyond the corner frequencies too into designing roll and dive frequencies, too. They had a car with a 3 springs in the rear, which was totally weird to me - i think the formula car guys would be more used to that.

The article isn't bookmarked on my work computer. I'll check at home because I'm pretty sure I would have bookmarked an article like this.