TLMC autocross rules

[Chevettes4ever]

Hello... I hear rumors that MOD class cars now require roll cages..... is this true? I will be pretty sad if I bring my weapon to barrie only to not meet the rules... :)

[Snizzoop]

Where did you hear this rumor?

According to the CASC rules, MOD cars don't REQUIRE roll bars/cages...unless they are over 16 (I think) prep points...or are open cockpit cars. The TLMC rules are no more restrictive than that.

Looking forward to seeing this "weapon" you've built.

Cheers,

[Chevettes4ever]

Its the chevette with volvo turbo engine.

http://i1020.photobucket.com/albums/af327/chevetteman327/chevette56.jpg

Gotta lower it still....

http://i1020.photobucket.com/albums/af327/chevetteman327/chevette%20volvo%20project/turbochevette25.jpg

Not gonna make it to the first event. but I will be there for the second one.

[max attack]

Good thing the rumour you heard isn't true,no time to cage the metro untill next fall.

This picture is from today when it touched the ground for the 1st time.,as you can see it won't be ready for the 1st event-fingers crossed it might make it to the 2nd.

http://i117.photobucket.com/albums/o50/kevlarcorolla/DSC00803.jpg

[Marsh]

Looking good Tom. I think a Steward's safety check, taking the form of test run, might be in order though.;)

The regional rule book is more than a little vague on what does and does not require roll over protection. Trying to apply those same rules to club classes is like trying to apply the laws of thermodynamics to the book of Genesis without consulting anyone who actually knows the laws of thermodynamics.

Suffice it to say that you should ask the clubs solo-director as to class problems.

[max attack]

Might be able to do that Marsh,I might learn more about the car watching from the outside anyways.
Gotta figure out spring rates and order the dampers,really hope to get it close the 1st time so the calculator is going to get a workout.Trouble is I don't really want to tune with frequency,I wish I knew an FSAE guy that could back up my findings.;)

[Doug P]

Hmmm a FSAE guy that is also a driver? Where would you find one of those?

[Marsh]

Well, I would do frequency. Easiest way would be to write a spread sheet... or modify the FSAE spread sheet already written by somebody else... I'll see if I can find my old files.

[max attack]

It seems that everyone that picks rates baseed on frequency finds that the rates are too soft,my problem is the lack of experience in designing to know when something sounds right or not.Other problem is knowing what wheel rate or frequency I should actually want in the real world.

[briansexsmith]

looking good tom!

[TOYSRUS]

This picture is from today when it touched the ground for the 1st time.,
http://i117.photobucket.com/albums/o50/kevlarcorolla/DSC00803.jpg

I beleive the Region has adopted an F1 style "parc-ferme" rule Tom -

6.1.5a - "Once the car touches the ground for the 1st time, you must run the tires that are on the car for the rest of the season".....

:p

[Marsh]

Rate is frequency and frequency is rate. If it's soft that means they selected to low a frequency.

Now bare in mind that frequency doesn't include anti-roll devices. So you need to also consider roll rate separately.

[max attack]

You should've let me know earlier Bill,brand new 710's are sitting just inside the door behind the car.Spending this year sorting on DOT's before going to the hoosier slicks that its designed around for next year.

Marsh thats the confusing part for me,what frequency do I aim for with so many factors involved?. Btw roll will be controlled solely with springs,no bars for me.

[Marsh]

Milliken and Milliken (1995)

List typical ride frequencies for non-aero sedans at 1.6-2.0 Hz and aero cars at 3.0-5.0 Hz (higher the frequency the stiffer obviously)

Roll Gains are listed as 1.0-1.8 deg/g and 0.25-0.5 deg/g

In the FSAE car I designed I targeted 1deg/G and a ride frequency of 2.5 Hz. I was aiming for a higher frequency because I preferred stiffer cars at the time and we were trying to work with 2" of total suspension travel and 1.5" nominal ground clearance. It not bottoming was an issue. I was confident enough in my geometry that I didn't think a super low roll rate was necessary. In hind sight the 1 deg/G was probably a good choice but the ride frequency was a little high. It was quite drivable, but the surface we were on was really rough.
The car didn't have aero, so a higher stance and slightly softer ride rate probably would have worked better. I also didn't handle the weight transfers ideally and the car tended to understeer if any trail braking was used. Had them damndest time convincing other drivers to stop trail braking.

When I did my design I started with the roll rate and iterated checking the frequency for reference.

BTW Carol Smith recommends that anti-roll bar provide about 30-50% of the roll rate. I would agree with this, except that I think 50% is much too high unless your setting up a car with bad camber curves. 30 should be a good target.

[max attack]

Thanks Marsh,after much reading over the last few months 2.5 -3.0 hz was actually my target area but like everything else with suspension design there's so many comprimises I wasn't sure if I was on the right path or not.
My ride height is 2" clearance with 20" slicks so with the tires used this year ground clearance will be 2 3/4".I have the wing mounts welded to the chassis,won't be on the car for awhile though.
I'm a very very long ways from an expert but I'm not a fan of sways due to the manner in which they function.100% believe they are the way to go for a daily driven sedan to acheive a sporty driving car,also the easiest way to set the balance of a car on differing surfaces but essentially you tune by reducing grip.I'd rather make a quick air pressure adjustment if needed instead of carring the extra weight all the time.
I'm also a fan of relatively soft spring rates(mostly because I can't afford $1000+ ea dampers to make a stiff set-up work properly),which would go hand in hand with sways but I'm going to stick to my guns and try the no bars route-at least untill I'm proven wrong.:)(shouldn't take too long I suspect)

[Marsh]

Dislike of sway bars is common. Get over it. Sways are used on fast cars. In order to achieve an acceptable roll rate with a car as tall and with as much steel as yours, you'll have to use a really stiff ride rate. RIDE RATE IS BAD! There is nothing about stiffer springs that makes a car go faster except camber control. Camber control can come from sways too. The fastest is a compromise of both. Sway bars allow you to decouple the roll and ride rates so you can adjust one without adjusting the other. If you make the two completely dependent (no sways) then you will ALWAYS end up with too stiff a ride rate.

Essentially what you should do is determine your ride rate first and then determine the portion of roll rate coming from your springs. The difference between this and your roll-rate target is how much sway bar you need to run. If the percentage you determine is way off the exceptable margin of 30-50 percent then you screwed something up (either too stiff, too soft or unrealistic goal for one of your targets... or you made a calculation error).

What books have you been referencing BTW?

[sjd]

Dislike of sway bars is common. Get over it. Sways are used on fast cars.

When I was still with Mazda and got a tour of Dyson Racing's ALMS operation at Mosport last year the million dollar Mazda P2 Lola had sway bars. I suspect it's not the only one either.

[max attack]

Whoa there Marsh,I value your experience otherwise I wouldn't have asked-talking down to me in the form of a "get over it" does nothing more than piss me off.I don't let anyone talk down to me face to face,doing it online gets the same response.
Of course fast cars run sways,that tells me you think I've never been around motorsports at all.

The goal for this build is to go faster than any production car could take me for less than 6k all in,not to design the perfect mythical suspension set-up.In an effort to meet this target goals substancial comporimises need to be made,including the use of the relatively heavy miata parts-all of which were free.

I agree with you totally on the balanced approuch,I spent the 1st 7 years with the corolla doing just that.The car was its best the last 2 years,guess what no sways.I tested back to back several times to confirm on differing days/conditions and barless was best.There have been several scca solo national titles won in the prepared and mod classes running barless.

I started the design using inboard dampers intending to run sway mounts at the rockers,that design became overly complex and added considerable cost and fabrication time for what would be essentially minimal gain.

It wasn't all that long ago that everyone knew the earth was flat,that it was impossible for cars to exceed 1g in any direction and that huge sway bars were the hot ticket.

[AW11_4AGZE]

Swaybars AKA traction reduction devices? ;) I took advice from Steve H in the states, he just happens to have the most auto-x championships ever. I believe his occupation is setting up suspension for race application.

Besides, it's my opinion that the frequency that everyone swasses about is taken care mostly by the damper. Your total grip is hindered through swaybars by essentially stealing spring rate (and inturn wheel rate) from the inside wheel. This problem is exasterbated when there are road imperfections. Because the suspension is tied through the bar it can spike rates on both sides. I believe race team use it for trim. The majority that I have seen are very small bars, correct me if I'm wrong.

I'm sure my explanations do Steve no justice. The rates I ended up with are 600lbs/in front and 450lbs/in rear. The ride is not too stiff and cornering is excellent. The best part about the whole thing is how crisp the turn in is.

Tom, I thought the earth WAS flat. :P Nice looking project!

[Marsh]

Tom, I'm sorry I wasn't trying to insult you. I was trying to be blunt. I too thought sway bars were counter intuitive. Then I tried to actually design a car without them and wised up.

You would be amazed at the stiffness of those "small bars" because their shorter. The longer a bar is the softer it is for the same diameter. The little T-bars in open wheelers are actually pretty stiff. The problem is that your arguing for a setup that doesn't really corner better and doesn't have as much braking or acceleration grip. As I said sways are just a mechanism for decoupling the ride and roll. And honestly, you think that race teams use sways for "trim". Do you really think that the best people in the world at design suspensions are so inept that they couldn't get it right without sway bars? They aren't added after the fact to fix unforeseen problems. They are designed in. True they are adjustable for trim because not all tracks are different. But that is far from their sole purpose. They are an integral part of the roll control system of the car.

Tom you're right that the world used to be flat. Similarly cars used to not have sway bars. Then they figured out that you didn't need to take out the springs in put in solid members to eliminate body roll. You could use a secondary device to reduce roll. Then more recently they realized that you could use third elements to control pitch axis as well. Just because you don't see what looks like a sway bar on a car doesn't mean that it doesn't have an anti-roll device. Anti-roll damping and active hydraulic anti-roll systems are all over the place and have been for many years. I've seen both on FSAE cars a decade ago. And although active ride height is banned in F1, third elements are making a come back as devices for decoupling the pitch control and ride rate.

Look, it's this simple. Weight transfer must take place in a corner. Stiffer springs allow the same amount of weight transfer to result in less body roll. Sways also allow the same amount of weight transfer with less body roll. The difference is that under light lateral load a car with sways can absorb bump without being upset. A car without sways cannot because it's springs need to be stiffer. Sure sways complicate things when encountering uneven bumps. Guess what, so do stiffer springs. But stiffer springs give the same complication for EVEN bumps.

[max attack]

Thanks Marsh,I'm not really debating that the best set up is a comprimise of both as I do believe thats the way to go for the closest to optimum set-up.Just with the narrow chassis up front,outboard dampers and longish a-arms getting mounts to support the bar properly seem very awkward.
The way I see it if I tried to use say the stock miata front bar for example since its easy to come by,the chassis mounts would be too far inboard and the bar would flex at the mount with wheel movement instead of twisting as it should.
I see this adding to the spring rate instead of just roll rate and wouldn't be as effective to decouple roll resistance from wheel rate as you've mentioned,I visualize it making the car not very sensitive to changes and hard to sort.
Using a short sway would mean the end link being near the inner end of the a-arm,I don't see that being very effective with the small movement relative to wheel travel.
With limited funds having a custom bar built to try doesn't look like an option for me at this point.

[Marsh]

I'm reminded of the first time I meat Carol Smith. I answered a question he asked about why we did something a certain way with, "we couldn't find the room to do it a better way". He gave me a look that reminded me of my mother and for a brief instant I thought he was going to hit me with a shoe. His retort was something like "Packaging is the easiest part of an engineers job and if you can't get that right then you've got no business here". I'm paraphrasing, that was about 12 years ago.

From looking at the pictures I can think of one or two fairly simple designs that only require the compromise of extra long links.

[max attack]

I'm reminded of the first time I meat Carol Smith. I answered a question he asked about why we did something a certain way with, "we couldn't find the room to do it a better way". He gave me a look that reminded me of my mother and for a brief instant I thought he was going to hit me with a shoe. His retort was something like "Packaging is the easiest part of an engineers job and if you can't get that right then you've got no business here". I'm paraphrasing, that was about 12 years ago.

From looking at the pictures I can think of one or two fairly simple designs that only require the compromise of extra long links.

Haha,from my experience dealing with engineers for work it seems most are pretty good at being "blunt".:)

I'm open to ideas to try with regards to possible sway bar design,nearly all the pictures I've looked at for open designs use inboard dampers.The locost sites from both here and overseas have some decent builds but most are comprimised in that they are built essentially as street cars.

[Caveman]

Tom if your looking to build a sway bar, you can get stock car type bars that are straight with splined ends and corresponding brackets.
Contact Scott at Can Alignment he can help you out with locating or building the parts needed.

Hope to see you in may

[max attack]

Tom if your looking to build a sway bar, you can get stock car type bars that are straight with splined ends and corresponding brackets.
Contact Scott at Can Alignment he can help you out with locating or building the parts needed.

Hope to see you in may

Hi Rob,I'll be out in May for sure-it'll just be in the super duper 3cyl metro.:)

For the bars I don't think I can make that style of bar work well,I think a pc of spring steel that can be bent to run on an angle from the chassis tube to the outer ball joint area would be 1 of the ways to go.Should allow the bar to twist instead of bend but I'm not going to stress on a sway bar just yet,many other things to deal with before I can drive it at the june events.Then I'll know how many other things don't work as designed.:)