FWD vs RWD: Adders, Subtractors, and Weight, Oh my...!

[esuvee]

Two points to make now that we seem to be done with the factual side of the discussion:

1. Facts seem to show that ITS and ITR could use a bigger weight break than A, B and C. I think some earnest time on LapSim with some study of lap times (oh the horror!) to backup the LapSim models could produce and accurate number if one were desired. The laptimes wouldn't be to 'correct' the cars to equivalent laps, just to verify that the LapSim models produce the right results at the right tracks.

I feel like I missed the juicy part of this while I was away from the internets so...Rant On:

Greg seems to not desire an actual number and would rather have his vast experience pick as arbitrary a number as we currently have (what apparent idiot chose the current correction? clearly that guy was no greg). Even though in the first round of LapSim numbers Mike and I ran we came up with some backup for greg's ass numbers I don't agree with the 'vast experience' argument. It's a bit insulting to the group, the process and many of the members here who may, god forbid, know more then him on this subject but are still trying to do it the right way. Quite odd to start this whole discussion with no plan to back your position up.
Rant Off:

2. Even though I have some data to say that the current numbers might not be perfect I still have to ask what problem we are trying to solve. Is it that we have two classes not currently dominated by FWD honda products?

As an ITA CRX racer I aspire to one day build an ITR or ITS car that is more capable than my CRX. One big factor in this capability is RWD. If the GSR or a Prelude were the car to have in ITS/R I would be headed out of IT (what's the point of different classes if they have basically the same cars with a bit more motor?). The OK-ness of FWD ends when you need to take an engine's worth of weight out of the car to make it work, that's dumb and we're gaming the system if we do it.

Alex

 

[ekim952522000]

So I finshed my final Lapsim session I could fill in more but I don't think it is needed.

By calculating the percent of weight break that was needed to get the FWD cars to keep up with the RWD cars Lapsim backs up the claim that why it is possible the 2% is correct in ITA 2% would most likely be wrong for ITS and be even farther off in ITR.

 

[kophoenix32]

275/40-17 fit my 99 Firebird. Havnt done the set up work yet, I think the car will be heavy even with me at 180. Not quite done yet,but this is the car I chose so I will make it work. Testing in March!!!



Kurt Omensetter
Phoenix Auto Center
#39 ITR Firebird

 

[tnord]

so this thing says that 150whp, 2500lb car (roughly an ITA integra) needs 150lb break to be competitive? really?

 

[ekim952522000]

.........
........ One big factor in this capability is RWD. If the GSR or a Prelude were the car to have in ITS/R I would be headed out of IT (what's the point of different classes if they have basically the same cars with a bit more motor?). The OK-ness of FWD ends when you need to take an engine's worth of weight out of the car to make it work, that's dumb and we're gaming the system if we do it.

Alex

I have to respectfully disagree Alex while I do not expect a guarantee of competitiveness. I do appreciate that the ITAC is willing to try to get as close as possible. I accept at some point "it is, what it is" I just don't think we are quite there yet, close but not quite.

By "gaming the system" do you mean making it so FWD cars can race with RWD cars? Isn't that the whole point of the process to "try" to get things close? Otherwise you could say we are "gaming the system" by making it so a 180HP car can race with a 160HP car.

 

[ekim952522000]

so this thing says that 150whp, 2500lb car (roughly an ITA integra) needs 150lb break to be competitive? really?

Please keep in mind that I am not suggesting we use the exact weights the results show. Since in order to do that you would need to do tons of sims with each pw/wt ratio and optimize the spring rates bars etc.. for each weight. I am just using it to show the pattern the as the HP goes up FWD cars need a larger percentage of weight taken off.

 

[tnord]

Please keep in mind that I am not suggesting we use the exact weights the results show. Since in order to do that you would need to do tons of sims with each pw/wt ratio and optimize the spring rates bars etc.. for each weight. I am just using it to show the pattern the as the HP goes up FWD cars need a larger percentage of weight taken off.

is it saying that as power increases, FWD is at a bigger disadvantage, or is it saying that as power increases, a non-optimal setup has a larger effect?

 

[ekim952522000]

is it saying that as power increases, FWD is at a bigger disadvantage, or is it saying that as power increases, a non-optimal setup has a larger effect?

Alex ran simulations earlier where he optimized the setup for both FWD and RWD which showed similar trends.

 

[Andy Bettencourt]

why does a roughly 2% weight break work perfectly for ITA but is apparantly 100lbs or so off in ITR?

Trav:
This defines my issue with the %. Why is it 'off' Trav? Only because some have already accepted 150lbs as 'right'.

We can't use the same % for all classes because we have seemingly agreed that ITC cars need no break and ITB and ITA cars need a little and ITS and ITR cars need more.

If we used 5% for everyone (or insert your % here), there would be ITB cars getting more of a break than some ITR cars (2600lb ITB vs 2300lb ITR).

Josh:
It's about offset and how much stuff is under the fenders. FWD cars simply can't run as wide wheels are RWD cars under stock fenders as a general rule.

Kirk:
I am just listing numbers based on the LapSim piece. Here is the rub...I HAVE to use those numbers to get a target car. Here is what I get using stock crank hp numbers as a guideline:

ITR: 200hp. Base weight of 2812.5 rounded to 2815. 175lb target = 6.2%
ITS: 170hp. Base weight of 2741.3 rounded to 2742. 150lb target = 5.5%
ITA: 135hp. Base weight of 2446.8 rounded to 2447. 50lb target = 2%
ITB: 110hp. Base weight of 2337.5 rounded to 2338. 50lb target = 2.1%
ITC: 100hp. Base weight of 2355 rounded to 2355. 0lbs = 0%

So in this scenario:
Taurus SHO at 220hp would get a -192 (191.81) adder.
Contour SVT at 200hp would get a -174 (174.37) adder.
Celica GTS at 180hp would get a -157 (156.94) adder.

I applied the 6.2% right to the base weight before any additional adders were applied.

I can certainly buy this stuff. My only point was that we used our 'assumptive' target numbers as the basis. BUT - because they were derived from something like LapSim and we then try and apply it evenly, I can get behind it.

Does it pass the sniff test?

 

[JoshS]

Josh: It's about offset and how much stuff is under the fenders. FWD cars simply can't run as wide wheels are RWD cars under stock fenders as a general rule.

I get the offset thing ... but I just looked at the list of cars I've owned in my life. Not counting trucks, motorhomes, motorcycles, and Real Race Cars, I've owned 15 cars. Of those, 7 were FWD/AWD, and 9 RWD (good mix of front-engine and mid-engine). And all 15 cars had struts in the front, and they all had "FWD-type" wheel offsets in front, except for maybe the Volvo 242 and the Porsche 914, I just can't remember the wheel story on those.

Bottom line is that a strut-type car always has to squeeze the tire between the strut and the fender, and the drive equipment doesn't affect that. So we'll agree to disagree on this point.

 

[lateapex911]

Alex ran simulations earlier where he optimized the setup for both FWD and RWD which showed similar trends.

So changing the weight dist to 60/40 for FWD doesn't alter the results much??

Andy, our outputs closely mirror each others.

Let's run those numbers for ITS.

 

[tnord]

Let's run those numbers for ITS.

while you're at it....why don't you run them all with 28% power adders since FWD suffers from lower drivetrain loss than RWD. i like our process, but this is one way we can make it better.........:026:

 

[ekim952522000]

So changing the weight dist to 60/40 for FWD doesn't alter the results much??

Andy, our outputs closely mirror each others.

Let's run those numbers for ITS.

This chart showed what happened when I played with the weight dist on the right.

 

[Eagle7]

Trav:
Kirk:
I am just listing numbers based on the LapSim piece. Here is the rub...I HAVE to use those numbers to get a target car. Here is what I get using stock crank hp numbers as a guideline:

ITR: 200hp. Base weight of 2812.5 rounded to 2815. 175lb target = 6.2%
ITS: 170hp. Base weight of 2741.3 rounded to 2742. 150lb target = 5.5%
ITA: 135hp. Base weight of 2446.8 rounded to 2447. 50lb target = 2%
ITB: 110hp. Base weight of 2337.5 rounded to 2338. 50lb target = 2.1%
ITC: 100hp. Base weight of 2355 rounded to 2355. 0lbs = 0%

Still trying to get a classless equation to work.

FWD subtractor = 1.75 * (HP -100)

ITR example: 200hp. Subtractor = 175 lb
ITS example: 170hp. Subtractor = 122.5 lb
ITA example: 135hp. Subtractor = 61.25 lb
ITB example: 110hp. Subtractor = 17.5 lb
ITC example: 100hp. Subtractor = 0 lb

 

[ekim952522000]

Still trying to get a classless equation to work.

FWD subtractor = 1.75 * (HP -100)

ITR example: 200hp. Subtractor = 175 lb
ITS example: 170hp. Subtractor = 122.5 lb
ITA example: 135hp. Subtractor = 61.25 lb
ITB example: 110hp. Subtractor = 17.5 lb
ITC example: 100hp. Subtractor = 0 lb

You may be on to something but I think you need to do it against IT HP instead of stock HP.

Example with your current formula a Celica would get (225 * 1.75)-100 181 lbs off and a Legend would get (288 * 1.75) - 100 404! pounds off.

 

[Eagle7]

You may be on to something but I think you need to do it against IT HP instead of stock HP.

Example with your current formula a Celica would get (225 * 1.75)-100 181 lbs off and a Legend would get (288 * 1.75) - 100 404! pounds off.

I was just using Andy's example data points to get some thinking going about using one equation. Using IT HP sounds right to me. The 1.75 multiplier should be adjusted fit the appropriate data points. It may be that a linear equation like this doesn't fit, but I'd be surprised if a non-linear one couldn't do the job. It's just a matter of finding the equation that fits the data points.

I think you did the math wrong.
225 HP -> 1.75 * (225 - 100) = 218.75
288 HP -> 1.75 * (288 - 100) = 329

 

[Eagle7]

Mike, I looked at your data in post 242 again. LapSim shows exactly one lb/HP at 2500 lbs to equalize FWD vs. RWD - perfectly linear. I think that runs counter to the supposition that ITC doesn't need any subtractor at all. Augmenting the LapSim data with "what we know" is likely where the non-linearities will come into play.

 

[ekim952522000]

Mike, I looked at your data in post 242 again. LapSim shows exactly one lb/HP at 2500 lbs to equalize FWD vs. RWD - perfectly linear. I think that runs counter to the supposition that ITC doesn't need any subtractor at all. Augmenting the LapSim data with "what we know" is likely where the non-linearities will come into play.

Excellent points.

Actually I think it shows that it's not linear. Since as the HP goes up the cars require a higher percentage of weight to be taken off in order to equalize the lap times. If it was linear then for example a 5% weight reduction would have worked for the all the HP levels which was not the case.

and yes I really got your formula wrong ....... whoops

 

[ekim952522000]

Travis I agree with what you're saying above the reason I have been focusing more on the idea of by class. is I think it would be more likely to get the go ahead by the ITAC.

I really do think picking a "bogey" for a class then using a adjusted pw/wt ratio is a better way to do it. But am not sure if it has as good of chance of going through.

I am really liking the 150lb thing for ITR if we adjust the pw/wt for FWD cars in ITR to 10.585. it gives the celica exactly a -150lb deduct. then the legend would get a -191lb deduct. the process weight I have shown is before any adders or subtractors so it would be up to the ITAC if they still wanted to apply the -50 for struts after runing it through the process. I think this is the most fair way to handle the situation but is also a kind of radical to change to the way things have been done.


Process FWD

--------------------------------------11.25-- 10.585
Toyota Celica GTS (00-02) ------- 2531-- 2382 -150
Honda Prelude (93-96) ------------2672 -- 2514 -158
Acura Integra Type R (98-01) ----2633 -- 2477 -156
Honda Prelude (non SH) (97-01)- 2813 --2646 -166
Acura RSX-S (2002) -------------- 2813 --2646 -166
Acura Legend (91-95) -------------3234 --3043 -191

Mike, just so everyone is clear, the current process would subtract 100 fro FWD across the board on these cars.

So, what you're model proposes is a method of adjusting each model on a sliding scale. i like that, because it's rather blind.

Your result, for example, would remove an additional 66 pounds off the Prelude from it's current process weight, and 50 off the Celica, correct?

Sorry I just noticed this post. Yes the way you are reading it is correct.

So If we use the number of 150 for ITS and apply that to the civic as our bogey we would get.

ITS--------IT HP----12.9---12.15
Civic Si --- 200--- 2580----2430(-150)
GSR - ----212.5---2741---2582(-159)
Prelude --- 237.5---3064---2885(-179)

 

[Andy Bettencourt]

Further complicating the 'process'...

If a % is the right thing to do for FWD, wouldn't it be equally as correct to do it for the other adders?