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

[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.

[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]

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

[Knestis]

...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'm not proposing we consider any new variables in the process (either here or in the other discussion):

** We already use "big chunk" FWD subtractors, applied objectively (Y/N) but the values were picked subjectively - I'm looking here at figuring out a way to be more granular about it.

** We already apply different "IT power factors," based on "what we know," best guesses, informal standards of engine architecture, history, etc. In the other thread, the "Nordquist Proposition" suggests that we could make those completely objective, based on physical attributes of the car. That's always been my gold standard.

I'm on record as believing that diminishing returns sets in pretty damned quickly after the factors we already worry about. That doesn't change.

K

[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).

[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.

[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?

[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?

[hondaracer48]

There is a difference to speak of between 70% brake force on a driven axle and 70% brake force on a free rolling axle. The momentum of the flywheel raises the threshhold where the brakes would lock up. An experienced FWD driver would use this to his advantage.