Weight - Adam's favourite subject

[James Mewett]

When IPAXed times are plotted against Weight for each track the results are interesting. On all the normal tracks the advantage light cars have over heavy ones is virtually zero - meaning our classification system deals with weight fairly on these tracks.

On the Mosport GP track light cars are at a significant disadvantage, but that would be because power costs weight and almost all the light cars are underpowered for that track.

[Chris91GT]

Interesting, yes, but not useful I suspect. You've already shown that HP is one advantage at GP. The cars with high HP tend to be the heavier cars in the series, so one follows the other. Certainly, additional weight does not make a car faster. :D

[Dave]

My favorite hobby (stickin' it to Adam's theories) has become a sport! w00t w00t!

[ADAM]

see my other post on this issue on the other thread...


I dont think the data can really be that valid..I am concerned about the cars in reality

[thgear]

some thoughts:

i would like to agree with adam first and foremost that a lighter car has an advantage over a heavier car being forced to compete against each other.

for arguments sake lets make a comparison between the following two GT3cars that i have fished from the classification database:

toyota MR spyder:
weight: 2195
HP: 138

(-External dimensions: overall length (mm): 3,886, overall width (mm): 1,694, overall height (mm): 1,240, wheelbase (mm): 2,451, front track (mm): 1,476, rear track (mm): 1,461 and curb to curb turning circle (mm): 10,607

average track width in feet = 4.841 + 4.792 / 2 = 4.816

Nissan 300ZX
weight: 3405
HP: 223

(xternal dimensions: overall length (mm): 4,300, overall width (mm): 1,791, overall height (mm): 1,257, wheelbase (mm): 2,451, front track (mm): 1,496, rear track (mm): 1,534 and curb to curb turning circle (mm): 10,363 )

average track width in feet = 4.906 + 5.031 /2 = 4.968

both cars are asigned a 70% suspension rating, with nearly identical lb/hp numbers, and a final PI of 67 and 68.6 respectivly.


from a little book i picked up on suspension theory:

"it is sometimes interesting to calculate the maximum theoretical speed a car can travel in a turn without tipping over:

max speed = 2.74 X square root of [ (radius X track) / cg height) ]

let us make an assumption that both cars have their CG at 2 feet above ground

50 foot radius turn, theoretical speeds:

Toyota: root(50 x 4.816)/ 2 ) X 2.74 = 30.53 mph
Nissan: 30.53mph

the difference is in the 4th decimal points that i'm not gonna bother with, but the nissan should "theoreticaly" corner at a slightly higher speed, BUT here is the caveat tho:

" notice that weight of the car doesnt have anything to do with the tip-over speed under the stated assumptions and the further assumption that the car isnt heavier on one side than the other, and that the tires hold"

aha!

lets get into weight transfer now:

"the total weight on all four tires remains the same during this process [later weight transfer]

the amount of lateral weight transfer can be easily calculated by the following formula:

total weight transfer = (centrifugal force X cg height) / track width

centrifugal force = (weight X speed^2) / (14.97 X radius)

CF:

toyota: (2195 x 30.53^2) / (14.97 x 50) = 2733
nissan: (3405 x 30.53^2) / (14.97 x 50 ) = 4240

total weight transfer

toyota: 1134

nissan: 1706

(so far everything pans out mathematicaly, as "the maximum limit to toal weight transfer of the car is the total static weight carried by both tires, if the total weight transfer exceeds this amount both inside tires lift off the road and the car tips over)

if you multiply both of these weight transfer figures by 2 you get a number very close to the original static weight of both cars, with the difference being attributed to me not rounding numbers.)

so far so good

theoreticaly both cars could corner at an identical speed without tipping over assuming the tires hold out.

"..... is the fact that grip of a tire changes with the vertical force on the tire, If you increase the vertical force on a tire, it distorts more and its grip is reduced

it does have the ability to transmit more side force against the pavement, but not in the proportion to the increase in vertical force"

" the inside tire in a corner has a reduced vertical force on it due to the weight transfer and it gains some grip. However the increased grip of the inside tire is less than the reduced grip of the outside tire. The result is a net loss of grip. Thus increasing weight transfer at one end of the car reduces the grip at that end of the car"


there is a long passage that talks about the net effects of weight transfer on slip angles of a tire, and it uses an example that i at the moment could not fuse with my numbers here but the general theory would go something along the lines of..


if the toyota could corner at 30.5 MPH with a weight transfer of 1134 lb on to the pair of tires or 567 lb per tire

then in order for the nissan to corner at the same speed, its outside tires would have to support 1706 lb or 853lb per tire, which is 286 lb more than the toyota, or a necessary increase in the tire's capability to sustain grip of nearly FIFTY PERCENT

this means, technicaly, that the nissan WILL NOT achieve the same cornering speed as the toyota unless its tires could magicaly support such an icnrease in pressures, when the Toyota is already at the limit of adhesion.

and thats not even talking about camber changes due to geometry, and the necessity of the Nissan to employ stiffer springs which reduce mechanical grip

however none of that matters because both cars have a suspension index of 70.

and since power does not matter theoreticaly in a corner

and with the exception of the mosport GP track the benefit of added horsepower to break through aero drag is also thrown on the window

======================


HYPOTHESIS to support James claim that everything is "equal".

since the above treatsie has demonstratated an impossible demand on the nissans tires to corner at the same speed as the toyota, the only explanation for the seemingly fair competition between the two cars, is that (and this is my own theory) the skill required from the toyota driver driver over the nissan needs to be significantly (and i dare say exponentialy) greater!

since "most" of us are of average skill levels, the cornering speeds will by and large equal out

however if within a group of average racers there will be an exceptional driver in a light car, he/she will dominate.

hmmm, three names come to mind, Chris P, Jason A and Ron P, who have consitently destroyed the competion as well as pax.

Therefore i support adams claim that a lighter car in the same class as a heavier car will be faster assuming the skill levels of the drivers is at the "advanced" level

===============================


OTOH

our series is grass roots and is geared towards the average driver, and perhaps we should then simply have to "deal with the Chrispy Effect"


and now i sleep.

good night.

[msix]

Luckily there are not just corners on a race tarck (unless you drive a Go-Kart track) and there are those (more or less) longer stretches of straights inbetween the corners where the 85HP more on the Nissan comes in handy to make up that time lost in the corner ????

I am planning on doing some Solo Sprint next year ... woohooo, another BMW!!! :eek: ... but these discussions on here make me believe that some people want to have Spec cars in order to give every driver the perfectly same platform to win.

In regards to the weight advantages I like to tell you about an experience from last year at the Mosport GP track I want to share with you.

I drive an 85 325 (E30) with a 95 325 (M50) motor in it, but otherwise still have almost all the interior in it and no fancy stuff in terms of suspension. My car weights about 2800 lbs. (yeah, stop laughing now, I know I am classed somewhere in SGT2 without a chance ... but I want to have some fun)

I drove a friends car, an 88 E30 but with a stock (M20) motor, totally stripped and caged, suspension all done up etc ... and I noticed that I am doing some corners 10 - 15 km/h faster than with my car. I just could not believe the difference in the turn-in and the speed I could carry through the corners, however, going up the backstraight, I felt like I have to get out and push that sucker up the hill.
Corner 2 and 4 were about the same speed, but every other corner was much faster. Due to the lack of the power the lap times were still in the same range as with my significantely stronger, but heavier car.

.... its time to go on a weight reduction program ... :)

Klaus

[thgear]

Luckily there are not just corners on a race tarck (unless you drive a Go-Kart track) and there are those (more or less) longer stretches of straights inbetween the corners where the 85HP more on the Nissan comes in handy to make up that time lost in the corner ????


as stated at the top, the power to weight ratio of the two vehicles, and the fact that they are RWD, would conclude under our system, while not taking into account wind resistance, that both would accelerate at an identical pace.


I am planning on doing some Solo Sprint next year ... woohooo, another BMW!!! ... but these discussions on here make me believe that some people want to have Spec cars in order to give every driver the perfectly same platform to win.


spec car would be nice... but you miss understand the point of the PIP schedule and classification. The goal of which is to bring a bunch of vastly different cars to the race track and have them compete AS IF it was a spec race

and all of our bickering back and forth has to do with fine tuning the system, because quite honestly it works quite nicely in its current form, but could be improved upon.

[kmorris]

Serge, I think you are a little confused here.

"..... is the fact that grip of a tire changes with the vertical force on the tire, If you increase the vertical force on a tire, it distorts more and its grip is reduced

it does have the ability to transmit more side force against the pavement, but not in the proportion to the increase in vertical force"

The statement that the grip of the tire is reduced with increasing load does not mean that the lateral force it can transmit is reduced. The "grip" referred to here is the coefficient of friction, which is nothing more than the ratio of the maximum lateral force to the vertical load. The lateral force capacity still increases with increasing load, it just doesn't increase at the same rate, and the change is quite small, just a few percent.

" the inside tire in a corner has a reduced vertical force on it due to the weight transfer and it gains some grip. However the increased grip of the inside tire is less than the reduced grip of the outside tire. The result is a net loss of grip. Thus increasing weight transfer at one end of the car reduces the grip at that end of the car"

if the toyota could corner at 30.5 MPH with a weight transfer of 1134 lb on to the pair of tires or 567 lb per tire

then in order for the nissan to corner at the same speed, its outside tires would have to support 1706 lb or 853lb per tire, which is 286 lb more than the toyota, or a necessary increase in the tire's capability to sustain grip of nearly FIFTY PERCENT

this means, technicaly, that the nissan WILL NOT achieve the same cornering speed as the toyota unless its tires could magicaly support such an icnrease in pressures, when the Toyota is already at the limit of adhesion.

This is not at all true. The outside tires need to support more load, but their capacity to do so is not reduced significantly by load transfer. They have a limit, but they are presumably sized to the mass of the vehicle at a similar ratio to those on the Toyota.

[thgear]

The statement that the grip of the tire is reduced with increasing load does not mean that the lateral force it can transmit is reduced. The "grip" referred to here is the coefficient of friction, which is nothing more than the ratio of the maximum lateral force to the vertical load. The lateral force capacity still increases with increasing load, it just doesn't increase at the same rate, and the change is quite small, just a few percent.


races are won by 0.001 of a second, so a "a few percent" is quite large ;)

and that is the point that i have bolded out, that the increase is not linear



This is not at all true. The outside tires need to support more load, but their capacity to do so is not reduced significantly by load transfer. They have a limit, but they are presumably sized to the mass of the vehicle at a similar ratio to those on the Toyota.

presumably sized correct...

but how much larger can you fit a tire on a 300zx over that of a MR2 without, for argument sake, going outside the fenders?

[Carguy]

as stated at the top, the power to weight ratio of the two vehicles, and the fact that they are RWD, would conclude under our system, while not taking into account wind resistance, that both would accelerate at an identical pace.

More important than wind resistance is that the system doesn't take into account torque. Cars with a flat torque curve and wider powerband will accelerate from lower speeds better than cars with a steep torque curve and narrow powerband.

[thgear]

More important than wind resistance is that the system doesn't take into account torque. Cars with a flat torque curve and wider powerband will accelerate from lower speeds better than cars with a steep torque curve and narrow powerband.

i wish i had the money to build up an MK1 golf with a new age diesil engine, 100hp and 250 torque starting at 1500 rpm and ending at 4900ish, buahahaahahahahahah:D

[ScotcH]

This is not at all true. The outside tires need to support more load, but their capacity to do so is not reduced significantly by load transfer. They have a limit, but they are presumably sized to the mass of the vehicle at a similar ratio to those on the Toyota.

He has you there, Sergei ... this is the assumption taken by the CCC when coming up with a handling index. Of course the 300ZX will be able to fit bigger tires than the MR2 [edit: comes STOCK with bigger tires], effectively creating an equal ratio of "grip" to weight. This is of course an assumption, and I have no math to prove it (especially since measuring "grip" has proven impossible, therefore usurping the Uber tire rule :))

[GOLF VR6]

So Serge....If I have a huge breakfast before my first set of timed runs in the am, and then no lunch, but get to "get rid" of my breakfast before my second set of timed laps after lunch, will I have to move up a class because the overall weight of my car including driver has changed from am to pm ?? :rolleyes:

hee hee... just had to lighten this thread up a bit... lol

[ADAM]

YES YES YES... :)

100% I know the heavy cars are at a disadvantage...its not rocket science (or maybe it is :) )

the added spring rates to just equalize the roll of the heavier car is an issue as well... the "nimbleness" of a car is important...and as you can see as serge has shown.....

"ALL THINGS BEING EQUAL THE LIGHTER CAR HAS A DISTINCT ADVANTAGE OVER A HEAVIER CAR"

i just cant see how the CCC can dismiss this...I personally dont believe the "charts" we have generated, as they use flawed data that is supported by flawed class positioning...

nuff said... i cant change what people dont want to change...I will trudge on....

but when my 2700lb LS1 car, comes out with silly UBER tires and silly torque...I better not hear any whining from those who get smoked....cause your c6 vette porche 911 and wrx..are gonna get wiped :)

[thgear]

YES YES YES... :)

100% I know the heavy cars are at a disadvantage...its not rocket science (or maybe it is :) )

the added spring rates to just equalize the roll of the heavier car is an issue as well... the "nimbleness" of a car is important...and as you can see as serge has shown.....

"ALL THINGS BEING EQUAL THE LIGHTER CAR HAS A DISTINCT ADVANTAGE OVER A HEAVIER CAR"

i just cant see how the CCC can dismiss this...I personally dont believe the "charts" we have generated, as they use flawed data that is supported by flawed class positioning...

nuff said... i cant change what people dont want to change...I will trudge on....

but when my 2700lb LS1 car, comes out with silly UBER tires and silly torque...I better not hear any whining from those who get smoked....cause your c6 vette porche 911 and wrx..are gonna get wiped :)

can you help me stuff an LS1 into my porsche?

my chassis will probably be around 2500 after i'm done with it... :cool:

then we can rule the world together!

[thgear]

So Serge....If I have a huge breakfast before my first set of timed runs in the am, and then no lunch, but get to "get rid" of my breakfast before my second set of timed laps after lunch, will I have to move up a class because the overall weight of my car including driver has changed from am to pm ?? :rolleyes:

hee hee... just had to lighten this thread up a bit... lol

well actualy, its a shame we dont take weight of driver into consideration

as it stands Opal and G have a distinct advantage driving any car

even myself at 140lb, i have an advantage over some of the more "fit" racers :)

btw do you have a 944 "turbo" front bumper laying around?

[ADAM]

sure....

i think it would fit into a 944 ...no?


so far it has not been that difficult of a swap....hardest part....is getting all the little do dads and parts I need.... so many bolts ...so little time...

[ADAM]

"He has you there, Sergei ... this is the assumption taken by the CCC when coming up with a handling index. Of course the 300ZX will be able to fit bigger tires than the MR2 [edit: comes STOCK with bigger tires], effectively creating an equal ratio of "grip" to weight. This is of course an assumption, and I have no math to prove it (especially since measuring "grip" has proven impossible, therefore usurping the Uber tire rule )"


AREK
and this was a silly asumption from the start, that I did not agree with either...the weight/size of the car has 100% no bearing on how large the tires you can fit onto it....some models can fit large tires some cannot...

the 240sx that started with 195/55/15, can fit 245's on them...so what?

we have CRX"s running around with 235's and 245's

[thgear]

some cars also can naturaly fit much much larger tires than OEM under their fenders than other cars

take a 944 porsche, you can stuff a 10" rim in the rear end and it will STILL be tucked in to the fender

and whats this? i have a 55% suspension rating?? :eek: :eek: :eek:

[ADAM]

how the heck can your 944 be at 55% and my 240sx be at 60%?

[thgear]

how the heck can your 944 be at 55% and my 240sx be at 60%?

well the "turbo" and S2 models are at 60 or even 65

my old 83 non turbo 8v junker is at 55% ;) i also dont have ABS and my control and trailing arms are designed slightly different.

altho i think some of the later porsches came with stock Koni's

ohh and i also dont have LSD

or power steering

or anything...

LOL

[Carguy]

how the heck can your 944 be at 55% and my 240sx be at 60%?


I'd take the 240's IRS design over the oddball torsion bar setup of the porsche 944 any day. :cool:

[thgear]

I'd take the 240's IRS design over the oddball torsion bar setup of the porsche 944 any day. :cool:

you are SOOOO getting propositioned

[CobraStang]

More important than wind resistance is that the system doesn't take into account torque.Well, isn't HP = [torque * rpm / 5252]? Or something like that? A truck engine could have gobs of torque, but if it can't spin up very quickly, what good is it? So your lap time towing a trailer is within a second of your lap time without the trailer! Who cares? Unless your in North Carolina racing campers.

A flat powerband is where its at, for sure, but that doesn't necessarily mean that putting peak torque into the classification formulae will account for it. A wise choice of engines and/or engine mods will help flatten your powerband, and optimize your vehicle for competition.

i wish i had the money to build up an MK1 golf with a new age diesil engine, 100hp and 250 torque starting at 1500 rpm and ending at 4900ish, buahahaahahahahahah:DIf your fantasy engine makes 250 tq at 4900rpm, isn't that then 233HP at 4900rpm?

[kmorris]

can you help me stuff an LS1 into my porsche?

my chassis will probably be around 2500 after i'm done with it... :cool:

then we can rule the world together!

You can even buy a kit! (http://www.renegadehybrids.com/indexx.html)

Woo hoo!!!

[thgear]

A flat powerband is where its at, for sure, but that doesn't necessarily mean that putting peak torque into the classification formulae will account for it. A wise choice of engines and/or engine mods will help flatten your powerband, and optimize your vehicle for competition.

a diesil engine will typicaly have a flatter powerband than a gas engine for a given Horsepower rating.

[Carguy]

you are SOOOO getting propositioned

Cool, let's talk over dinner - your treat! :D

[Carguy]

A flat powerband is where its at, for sure, but that doesn't necessarily mean that putting peak torque into the classification formulae will account for it. A wise choice of engines and/or engine mods will help flatten your powerband, and optimize your vehicle for competition.

Agreed, I'm not suggesting we add peak torque into the classification - you did that all by yourself. ;) And yes, a flatter torque curve explains why the CCC re-classified Hanif's B20 engine swap up one class (or +5 pips) 2 years ago. According to the HP rating Hanif's car was in GT3 for the 2004 season, then re-classed to GT2 for the 2005 season - without any change to the HP rating.

[Chris91GT]

a diesil engine will typicaly have a flatter powerband than a gas engine for a given Horsepower rating.

I think we had this discussion 2 years ago. For your moderately flatter diesel torque curve you get:

1) Lousy throttle response
2) A very narrow band of useful power
3) A very non-linear diesel powerband

And don't quote Audi's R10... it's a 5.9L V12 that is light enough to actually rev and is capable of making power to a gasoline-comparable redline.

[ScotcH]

I think we had this discussion 2 years ago. For your moderately flatter diesel torque curve you get:

1) Lousy throttle response
2) A very narrow band of useful power
3) A very non-linear diesel powerband

And don't quote Audi's R10... it's a 5.9L V12 that is light enough to actually rev and is capable of making power to a gasoline-comparable redline.

Don't forget the new BMW 335id ... twin turbo diesel, something like 570lbs/ft ... and it handles like any other BMW :-)

[G-ForceJunkie]

Don't forget the new BMW 335id ... twin turbo diesel, something like 570lbs/ft ... and it handles like any other BMW :-)
580Nm... = 428lbs/ft :)

Leave it to the BMW guys to inflate their own ego's ;)

Source: http://www.carpages.co.uk/bmw/bmw-3-series-11-08-06.asp

[ScotcH]

580Nm... = 428lbs/ft :)

Leave it to the BMW guys to inflate their own ego's ;)

Source: http://www.carpages.co.uk/bmw/bmw-3-series-11-08-06.asp

Lol ... actually I was referring to the race car version, tweaked to over 500 lbs/ft, but hey, even the "basic" version would be just fine with me

http://www.caranddriver.com/features/12119/2006-thunderhill-25-hour-update-1.html

[Chris91GT]

Bah... you'd have to punch the throttle on turn-in just to make use of that lazy torque. :D

[thgear]

or never lift your foot off the gas!

[Rob McAuley]

Hey - We all know that certain cars do better at certain tracks. The CRX's will take Nelson, the Mustangs will take Mosport, and the BMW's will take Calabogie, Pro, and TMP.

The series used to have a wt/torque factor that was dropped a few years ago - because it was redundant. wt/hp was more meaningful.

The series was also designed to let you drop (or not run) the events at the tracks where you weren't competitive.

So quit bitchin', maximize your pips for your class, get some uber tires, and run all the events.