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

[Andy Bettencourt]

FYI: Current process

ITA, ITB and ITC FWDers get a 50lb deduction just for being FWD.

ITS and ITR FWDers get a 100lb deduction.

Straight up, off the top, no questions asked.

[lateapex911]

So, is the answer to grab a "median" car, assign it a weight value, say 100 pounds as it's 'adder', then apply it to other weights via a percentage?

So a car that would hit the class at say 2500 gets a 100 pound break, but a car that is 2800 before adders gets 112 pounds?

[tom_sprecher]

I think real men drive RWD race cars and weight breaks for FWD is affirmative action.

While you jest, there is still a certain, albeit small, underlying truth to this statement.

[hondaracer48]

Andy,
Are you saying that SCCA is working on giving the ITS GSR's another 100lbs off in addition to the 100lbs it received in 2007? I love the sound of that.

I do have some comments on what I read earlier on this thread. First, someone please explain why with everything mathematically pointing to the RWD as being superior, that the FWD cars are able to out brake the RWD cars? And I don't think that is just a personal opinion either. Second, I think the most important advantage to a road race car, whether it be a 1500lb or 3500lb one, is the balance of the car (with comparable horsepower of course). The more balanced the weight, the less amount of weight transfer that can push the tire beyond its cornering limits, at the same time the longer or earlier the driver will be able to accelerate. The longer the acceleration, the faster lap times. Lastly, I do believe that math is a priceless tool we can use in preparing a car or predicting its tendencies, but there is no one formula that will be consistant. There are just too many factors, which explains why many pro teams take their winning formula back to the same track, try all weekend making adjustments, and still end up in the back. It is however, our best shot, by repeating success. I think the current method of taking an educated guess, group these cars together, and see what happens works just fine. Until someone does come up with a 100% built ITS GSR (I'm almost there, but moving is forcing the sale of the car), it would be wasted time to argue about FWD/RWD advantages. I still personally believe that a 100% built ITS GSR at 2590lbs will be a dominating car.

Ed Chang
San Francisco Region

[ekim952522000]

Since were all just brain storming how about just modifying the power to weight ratio for each class for FWD cars.

Example: Let's take four ITR cars and run them through the regular process.

ITR cars
93-96 Prelude 190*1.25*11.25 = 2671 - 100 = 2571
00-01 Type R 195*1.20*11.25 = 2633 - 100 = 2533
00-02 Celica 180*1.25*11.25 = 2531 - 150 (fwd w/struts) = 2381
91-95 Legend 230*1.25*11.25 = 3235 - 100 = 3135
02-03 RSX 200*1.25*11.25 = 2813 - 150 (fwd w/struts) = 2663

Now what if we took those same cars and kept everything the same but used a pw/wt ratio of 10.75 for fwd instead of 11.25

93-96 Prelude 190*1.25*10.75 = 2553
00-01 Type R 195*1.20*10.75= 2515
00-02 Celica 180*1.25*10.75 = 2418 - 50 (struts) = 2368
91-95 Legend 230*1.25*10.75 = 3090
02-03 RSX 200*1.25*10.75 = 2687 - 50 (struts) = 2637

So with just a quick guess of .50 adjustment of pw/wt ratio for FWD I got these results. The HP numbers are for projected IT HP

Celica 225hp
2381 - 2368 = 13

prelude 237.5hp
2571 - 2553 = 18

Type R 234hp
2533 - 2515 = 18

RSX 250hp
2663 - 2637 = 26

Legend 287.5hp
3135 - 3090 = 45

Anyways this was just a exercise to see what would happen as you can see it got pretty close to the existing ITR weights but as the FWD cars get more powerful the get slightly more of a weight break. Which seems to make since.

[JoshS]

Holy cow everyone ... can't we keep it simple?

Sure, we can use a formula based on weight or horsepower or something to figure out the FWD subtractor, but if our baseline for a typical car is 50lbs or 100lbs (depending on class), then the new formula will still end up pretty darn close to the fixed subtractor we already have.

I say, keep it simple ... fixed numbers per class are close enough. Argue all you want if the fixed number is right or not, but please, can't we just keep the process SIMPLE? It's all an approximation anyway.

Changing the process might move some weights around +/- 50lbs (see Mike's math just above) but we'd have to assign new weights to every FWD car for not much adjustment. It's not worth it.

[ekim952522000]

Holy cow everyone ... can't we keep it simple?

Sure, we can use a formula based on weight or horsepower or something to figure out the FWD subtractor, but if our baseline for a typical car is 50lbs or 100lbs (depending on class), then the new formula will still end up pretty darn close to the fixed subtractor we already have.

I say, keep it simple ... fixed numbers per class are close enough. Argue all you want if the fixed number is right or not, but please, can't we just keep the process SIMPLE? It's all an approximation anyway.

Changing the process might move some weights around +/- 50lbs (see Mike's math just above) but we'd have to assign new weights to every FWD car for not much adjustment. It's not worth it.

Exactly.

I think the current deduct is close enough. The simpler the process is the better. We don't want ITAC members to have to be math majors to class a car.

[JeffYoung]

I totally agree with keep it simple.

I would also need a good answer to "what's broken" and "why are we doing this" before I would support it. If we need a good reason "why" in order to respect a member's request to remove a washer bottle, I think we need as much or more in order to change the fundmentals of the process.

[Andy Bettencourt]

Andy,
Are you saying that SCCA is working on giving the ITS GSR's another 100lbs off in addition to the 100lbs it received in 2007? I love the sound of that.

No. Just describing how it works currently.

[Greg Amy]

I hate marathon quoting sessions, but unfortunately this is the only way I can see to efficiently address multiple points, quickly.

I think real men drive RWD race cars and weight breaks for FWD is affirmative action.

Why do you hate the handicapped, Dick? We're not a different race, Dick, we're "special".

In order for their to be a change, we need to understand why 100lbs is 'wrong', and why your 150lbs is 'right'. Until we can make an educated decision on that...The current 100lbs is subjective. Your 150lbs is subjective....but that is just my gut.

Agreed, Andy. I can't justify it mathematically, I can only give you a process to make it easier. Further, anything I offer will seem to be tainted with a selfish agenda (with the idea that it may actually require more than 150 pounds in the long run, but sometimes you only get one bite at the apple...) But, my gut has one extra "bit" that yours doesn't, and that's more years of the experience and education you're looking for, mostly in front-wheel-drive cars but a lot in RWD as well.

I can easily understand how lack of experience with FWD, coupled to having seen FWD perform well in some classes, would increase your skepticism. But you will have to resolve among yourselves how much of my stated judgment and opinion is potentially clouded with a selfish agenda. I see the same thing when opposed by those whose experience is primarily RWD. I'd like to think you'd understand how little of this actually is selfish, as I try to do as well for you.

after reading the differences and advantages between RWD and FWD, i feel like an idiot for racing fwd.

No need to. Understanding what you're up against is 3/4 of the battle, covered by, hopefully, reasonable breaks for the shortcomings of the platform.

also, is there any perceived straight line braking advantage to either car?

Not simply due to FWD versus RWD. Braking is a function of weight transfer, brake size, and tire patch size, not drive location. It's one of the areas where neither platform, per se, has a distinct advantage. In fact, one could argue that because of the larger distribution of weight towards the back of the car, a RWD, mid-engine, or rear-transaxle car would have a significant weight transfer advantage (see Miata, Toyota MR-2, Porsche 911 and 944, etc).

Honestly, I've never heard, nor experienced, any braking advantages solely due to FWD. In fact, I always thought that with all that weight up front already it was a distinct disadvantage (which is why FWD cars have such piddly rear brakes; ain't much weight back there to begin with keep the tires on the ground; imagine transferring it all forwards and making only the front brakes and tires work...)

No, I suggest any perceived advantages are due primarily to the installed equipment (e.g., brake and tire sizes, weight), not the drive platform.

I will say that what ever anal grab bag these numbers came from, its at least in the right ball park. Otherwise you'd never have anything even close.

I would agree -- to a degree. But I suggest that your statement above comes from observation of ITA, ITB, and ITC which have numerous FWD cars entering. Further note that my discussion above focuses primarily on need for change within the higher-horsepower of ITS and ITR ranks, classes that have had very few FWD entries to use for illustrative comparison. As such, what I'm offering is predictions for change based on experience, knowledge, and education.

Go get yourself some vehicle like the Mitzu Eclipse or 3000GT which was offered in pretty much same trim but w/ FWD or AWD.

Did that in Firehawk in the early 90s (which was pretty close to IT prep at the time). Once you add in all the extra equipment to make it FWD it becomes too heavy and robs too much power. Except in the rain, the FWD cars were always faster. Besides, adding AWD to a FWD car usually makes it a heavy, slow FWD car.

It's not a fair comparison. And, I'm unaware of any valid direct same-chassis FWD v RWD platforms.

Curb weight/race weight is going to have a significant impact as well, just like horsepower. A heavier FWD car 'suffers" more, right, regardless of power?

Of course. Remember, it's all about those two patches of rubber up front. You're asking those same-size two patches to do a helluva lot more work on a FWD car than a RWD car.

...why with everything mathematically pointing to the RWD as being superior, that the FWD cars are able to out brake the RWD cars?

See above. I don't know where you got that contention. If you're talking about one-on-one personal comparison to specific competititors, I suggest you let one of us drive whatever RWD car you out-braked and let's see what happens....

To make a fair comparison, compare the braking hardware, weight, and tires.

I would also need a good answer to "what's broken" and "why are we doing this" before I would support it.

Then, once again, I've wasted my time here. If I've failed to impress upon you the differences in technology, dynamics, mechanics, and driving requirements for a FWD car versus a RWD car, and you (a RWD'er and part of the voting bloc of the ITAC) don't understand the functional differences and still wonder why a FWD car needs a significant break to compete fairly (and 90 pounds doesn't cut it in ITS), then there's no point in spending further time on this discussion...

GA

[Chip42]

First, someone please explain why with everything mathematically pointing to the RWD as being superior, that the FWD cars are able to out brake the RWD cars? And I don't think that is just a personal opinion either.

1 - they weigh less, due the the -100/-50lb "adder" for FWD.
2 - dynamics, spring rates, and static mass are very different, usually.
3 - apex may differ slightly, especially for low speed corners, exagerating the accordian effect - watch the exits of the same corners where the FWD cars appear to be outbraking all the RWD cars...
4 - not always true, anyhow.

Until someone does come up with a 100% built ITS GSR (I'm almost there, but moving is forcing the sale of the car), it would be wasted time to argue about FWD/RWD advantages. I still personally believe that a 100% built ITS GSR at 2590lbs will be a dominating car.

Scott Seck in the CFR has a very good GSR. one of the Ira brothers does too, somewhere in the Carolinas, I think. I believe that both would agree that a built to the hilt GSR can't compete over a race length at most tracks with the RX7s and Miatas - they may get a lap, but pretty much can't get the race. just too much work for the tires over the long run. a weight break would help, but this info is available now - there's no one holding a gun to anyones head demanding that they build these cars. the club gives us a place to race with no promisses as to the competitiveness of the car as classified (though they do try)

EDIT - I just read greg's post above and wanted to add the following about FWD in braking:
most of the cars built that fit into ITA/B/C over the past 20 years or so have been FWD. this is a fact of market conditions and industry paridigm. new cars have MUCH better braking systems than older ones, and more sorted suspension geometries as well. this could go a long way to making the FWD cars look better in braking. not that the miata, as greg points out, has great brakes. it's really the only modern RWD ITA car in the same power/wt range as the good FWD cars in the class... and it often walks all over them.

[Chip42]

It's not a fair comparison. And, I'm unaware of any valid direct same-chassis FWD v RWD platforms.

Greg - the newer Nissan Altima and Z/G-series use the same engine family and chassis core. there are a LOT of differences, but there's a start.

in the more affordable and very different chassis realm - there are the toyota AW11 MR2 (mid engine/RWD)/AE86 Corolla SR5 (front engine/RWD)/AE89 carolla FX16 (FWD) that all use the same motor (slighlty different intake on the AE86) and could be made to run the same weight and very simillar overall gear ratios. the FX16 and MR2 are very simillar in terms of frontal area, wheelbase, and Cd, and have many of the same brake and suspension components, too. very much apples to apples comparison, but good luck finding a well build FX16 for your tests...

sorry for the double post.

[JeffYoung]

I understand theoretically why FWD has some detriment to RWD. What I am saying is I need a "why" -- a mathematical why that you keep telling us about but won't give us -- for justifying 150 lbs or more as opposed to the 100 lb break FWD cars presently get vis a vis RWD cars.

That's all. You've been asked several times to give us the formula or some math to support the 150 or more, and we're still waiting. When you are prepared to share it, I will listen.

Then, once again, I've wasted my time here. If I've failed to impress upon you the differences in technology, dynamics, mechanics, and driving requirements for a FWD car versus a RWD car, and you (a RWD'er and part of the voting bloc of the ITAC) don't understand the functional differences and still wonder why a FWD car needs a significant break to compete fairly (and 90 pounds doesn't cut it in ITS), then there's no point in spending further time on this discussion...

GA

[Greg Amy]

Thump, thump, thump <<<====Greg's head hitting against a wall...

Jeff, you're missing the point. Please read my stuff again, carefully.

The point is...based on my knowledge, education, and considerable FWD experience, I think the subtractors for FWD are a bit too low in ITS and ITR; to explain why I think this, I spent consierable time trying to make sure everyone understands how FWD works and why it is not directly comparable - in simple power-to-weight terms - with RWD, particularly as you increase the weights and horsepower level above general levels.

So the outstanding -- though, I agree, not explicitly-stated -- questions is, are you willing to consider increasing the FWD subtractors in ITS and ITR, possibly at the same time being supported with an easy math defense? Or is this all wasted time?

If you want a formula "justifying" my position, you got it. Just tell me where the numbers are that you'll vote "aye" for and I'll give you mathematical justification (my favorite one, of course, is "Classified weight of whatever Greg's at the time driving minus 500"... hey, it's "math", so it must be right, right?)



GA

I understand theoretically why FWD has some detriment to RWD. What I am saying is I need a "why" -- a mathematical why that you keep telling us about but won't give us -- for justifying 150 lbs or more as opposed to the 100 lb break FWD cars presently get vis a vis RWD cars.

That's all. You've been asked several times to give us the formula or some math to support the 150 or more, and we're still waiting. When you are prepared to share it, I will listen.

[Knestis]

Okay, Greg - I'm really into this idea.

Let's assume, in the very broadest terms, that more mass exacerbates the issues you've described. (I think that's a fair starting point.) Make whatever other assumptions you want, and see if you can get your line to hit a couple of common examples at their current FWD-adder adjusted weight (e.g., the GolfIII in B, and the GSR in S, maybe?).

How might the math look...?

K

[JeffYoung]

Kirk, thanks. That is exactly what I would like to see.

Greg, not trying to turn this into a Jeff Young v. Greg Amy thread, truly I'm not, and I don't think you are either.

But, this can't work this way: "accept my theory, and then I'll give you my math to back it up."

Like Kirk said, assume we agree with your theory -- because we mostly do -- and run some numbers. Show us what a non-linear subtractor would look for B cars v. A cars v. S cars v. R cars.

Kirk, question for you. If we allow this, then as a matter of theory and consistent practice, what do we do with the guy who runs similar formulas for brake performance based on swept area and weight? Do we start generating deducts for him? Or aero?

I don't disagree with Greg's theory. But I see a slippery slope here in classification rules creep that is in my view far more dangerous than removing washer bottles and passenger glass. If we end up with a 10 page classing document on how to class cars with various formulas, we are in big trouble.

Okay, Greg - I'm really into this idea.

Let's assume, in the very broadest terms, that more mass exacerbates the issues you've described. (I think that's a fair starting point.) Make whatever other assumptions you want, and see if you can get your line to hit a couple of common examples at their current FWD-adder adjusted weight (e.g., the GolfIII in B, and the GSR in S, maybe?).

How might the math look...?

K

[Andy Bettencourt]

Greg,

You have to understand where we are coming from. You state, as fact, that it's too low. You state that we won't listen. You state that 'proving it' is basically impossible for a variety of reasons. Yet the adders are 'a bit too low'.

How the heck are we supposed to take an action item on something like this?

[Greg Amy]

How might the math look...?

Let's take a simplistic, linear example (only an example, not a proposal!!), applicable to ITS and ITR only at this point**:

y = x-20

x = stock hp
y = subtractor

Stock hp/subtractor:
100/90
120/100
130/110
150/130
170/150
200/180
230/210

The above simplistic example takes into account some of the current norms, along with my contention that the higher in HP you go, the more "break" a FWD car needs. Using a logarithmic/exponential function would be nicer, because it's non-linear and asymptotic. The current practice of a fixed value serves only the middle, not the extremes.

**I don't recommend using the same formula for ITB and ITC because of the difference in tire sizes, and the fact that these cars rarely make enough power to "spin the wheels" (an admittedly simplistic symptom for less-available traction).

[Z3_GoCar]

[quote=Greg Amy;281188
.... I'm unaware of any valid direct same-chassis FWD v RWD platforms.....

GA[/quote]

Have you considered the Toyota Corolla's

Fx-16 vs. the GT-S or even the 1st gen MR-2?

[lateapex911]

My gut reaction, admittedly to the results, is that (while you state it's for ITS/R only) the lower numbers get too much of a break, (although no 120hp car is in S or R), and the higher numbers get too much of a break, yet the middle is closer to ok..
The cars in the 200 hp range are getting nearly double the break from what they currently have.

IF I were king, I'd think it could be simple, like:

ITC...no break...doesn't matter
ITB 50 off
ITA 100 off
ITS 140 "
ITR 180 "

If you want to get fancy, chose the median car in each class, assign it the number above, then adjust the adder as a percentage of it's weight. Heavier cars get a bit more help, lighter ones, a bit less.

That way, it's not just about hp. If that calc were done at the end, all other factors which play into it are accounted for.