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

[Greg Amy]

If the current subtractor is so far off how is the you currently hold at least 3 track records?

Because ITA is dominated by FWD cars, and the Nissan NX2000 made nearly 160 horsepower...so I held a significant advantage in horsepower.

Compare that to ITS (and to ITR, the two primary classes I'm discussing) where the FWD competitors are very much outnumbered, hold no horsepower advantage(s), and hold virtually insignificant weight advantages.

So, it should come as no surprise that when compared to other FWD cars, having a power advantage is a good thing. And, when possessing power numbers pretty much the same as your RWD competitors, FWD is a disadvantage.

Thanks for the opportunity to clarify. Next?

 

[trhoppe]

Bastard #3 here

tGA,
If the current subtractor is so far off how is the you currently hold at least 3 track records?

One of the dumber posts so far. Seriously? Does this even warrant an answer?

 

[jrvisual]

And now that you are in a new class and new car you think you should be able to dominate just like you did with a car that had a hp advantage.

In 2008, while driving a new car you still managed 2-2nds, 1-3rd, 1-4th and 2-5ths with the 5ths being your worst finish. Sounds like a pretty good 1st year in a car that has such a huge disadvantage. How many rear wheel drive cars with their inherent advantage finished behind you in those races?

The current system works, leave it be.

 

[Greg Amy]

And now that you are in a new class and new car you think you should be able to dominate just like you did with a car that had a hp advantage.

Ah, OK, I see where this is going; I apologize for thinking you had a legitimate question for me. Care to tell me who you are and why you have this "thing" for me?

BTW, you're wrong: the worst finish for me in '08 was up against the wall at Watkins Glen with a totally destroyed car, which happened while I was busting my ass trying to stay in front of two (three?) rear-wheel-drive cars that had quickly caught up to me and and were just about to pass, all while being WAAAAY in back (10 seconds or so after only 8 laps?) of yet another RWD competitor claiming to have "the same horsepower" as I did.

I'm guessing you didn't know that. And I'll have to take your word on the other results (each of which, I can only assume you are equally ignorant).

Next?

GA

 

[Chip42]

Bastard #3 here

tGA,
If the current subtractor is so far off how is the you currently hold at least 3 track records?

you might remember that his biggest gripe was with ITS, ITR where HP numbers and weight are much higher, exagerating the FWD tire-killing effect.

that said - sometimes the formula as is works, and no formual can account for the amount of time, effort, and talent that "tGA" and many others have invested in their car and driving. lap times show this. they also show when simillarly well driven, prepared, and researched cars can't keep up, if only over the long haul.

as Jeff points out, FWD is not the only reason that a fast-lap car is not a race-winner, but it is one that can be observed from afar and without bias. Where things such as brakes and aero are more make/model specific, FWD adds significantly to the demand placed upon the front tires no matter what car we are specifically referring to. physics is physics.

more weight = more work for the tires
more HP = more work for the tires
cornering = more work for the tires
braking = more work for the tires
braking and cornering loads are highest on the front tires for all cars
weight tends to go to the same end as the engine, usually the front
power loads are on the driven wheels
so FWD has to place ALL of these loads on ONE set of tires
FWD also has more of the % of total weight on a single axle, the front. if you look at axle weight/hp of a FWD car vs a RWD car, it's off by 20-30%. add to that that the tires with all of that extra weight on the FWD car are doing nearly ALL of the work, where on the RWD car they share quite a bit more of the labor.

FWD easts front tires in a rate that is roughly proportional to HP and Weight. THAT is a fact. the question is what is the fair handicap to assess, and at what level?

 

[Ron Earp]

But we don't do that, do we? No, we don't, because we have at least a passing desire to create some semblance of parity, and we recognize that there are some macro factors, such as horsepower, that really do make a difference.

And that's my whole point: second only to ponies, the drive layout is the most important factor affecting performance in otherwise-similar cars. Yet we handle the layout as nothing more than a quickie afterthought, when in fact, it has nearly as much to do with results as does the engine...

I do think there is a FWD disadvantage. How much of one, well, I just don't know.

I don't think FWD is, in all cases, second only to hp. What about the cars that lose braking effectiveness 1/3rd the way through the race? Not being able to stop and go into the braking zone with the other cars is a big disadvantage for some ITS cars. Just as having your tires go off and not being able to maintain cornering grip and acceleration is a potential problem with the FWD car. There are not always fixes for the braking issue, should there always be fixes for the FWD specific problem?

The brief results shown from the LapSim model assumed the FWD car had a 60/40 F/R distribution and the RWD car had a 50/50 distribution. As I'm sure you guys know, this 50/50 split deal for rear wheel drive cars is not always the case. It certainly isn't for my dinosaur. How do the predicted laptimes shake out with a 56/44 RWD car and the 60/40 FWD car?

All I know is if we starting using models with weight distrubtion and other parameters we'll be opening up the system to all sorts of requests based on specific allowances that a racer "needs" to have in order to compete. In a class that does not guarentee competitiveness.......

 

[JeffYoung]

This thread summed up in a nugget. No one disputes teh FWD disadvantage. The questions are: how much? how to address it? and should we address it, and not other disadvantages?

FWD easts front tires in a rate that is roughly proportional to HP and Weight. THAT is a fact. the question is what is the fair handicap to assess, and at what level?

 

[trhoppe]

This thread summed up in a nugget. No one disputes teh FWD disadvantage. The questions are: how much? how to address it? and should we address it, and not other disadvantages?

We should almost start a new thread with the two posts above and go from there.

 

[jrvisual]

The questions are: how much? how to address it? and should we address it, and not other disadvantages?

Yes we should address and we have. I am just not convinced that the 100# is not enough. Fwd is a disadvantage and it has been address.

Every car has it's advantages and disadvantages. My car once complete will never make weight. That is a disadvantage. Should I be able to remove my heater core and washer bottle? Absolutely, but not until everyone is allowed to do so.

If we get to complex with how you go about determining weights, we will open it up for all kinds of other valid arguments for why some other car should be lighter. Prove to me that 100# is not enough and I will support it. But making that point based on some software is a dangerous road.

And Greg, I have nothing against you. I was just using you as the original poster to argue my point. I did see the DNF result for WG, sorry to here about your car and I am glad you are ok.

 

[JeffYoung]

Jeff R. (above) is new to IT, just learning and local to Ron and I. He's building a RWD ITS car that is going to have a LOT of inherent disadvantages (I just noticed the 50/50 weight distribution that Ron pointed out -- that's just not true of a large portion of RWD cars).

I suspect he sees a push to reduce the weight of a competitor car -- the GSR -- that all of us have seen run at or close to the front. Give him some time to learn about our disdain for on track results, etc. -- but also understand how some of this looks to a newcomer.

Yes we should address and we have. I am just not convinced that the 100# is not enough. Fwd is a disadvantage and it has been address.

Every car has it's advantages and disadvantages. My car once complete will never make weight. That is a disadvantage. Should I be able to remove my heater core and washer bottle? Absolutely, but not until everyone is allowed to do so.

If we get to complex with how you go about determining weights, we will open it up for all kinds of other valid arguments for why some other car should be lighter. Prove to me that 100# is not enough and I will support it. But making that point based on some software is a dangerous road.

And Greg, I have nothing against you. I was just using you as the original poster to argue my point. I did see the DNF result for WG, sorry to here about your car and I am glad you are ok.

 

[jimmyc]

On track performance shouldn't be looked at like Jeff R. is.

Maybe ITS is not really that competitive in the NE? Maybe Greg is some super hero driver that is secertly an F1 friday test driver? Maybe the 9/10th build on the GSR he drivers is leaps and bounds more then anything else in the ITS feild.


In the SFR we used to have a few ITA cars that would almost always out qualify the entire ITS feild.

 

[ekim952522000]

ok I will be running a few more simulations tonight probably with a 55/45 weight for RWD cars and 70/30 for FWD.

But let me explain where I was going with it I do not think it can give us how much we need to reduce the weight but it does show the trend that the more powerful a car gets the bigger the gap opens up when comparing FWD and RWD.

Let's say that the FWD subtractor for ITA is correct. What that means then is that why'll it is possible that the subtractor for ITS is correct, it is not likely that the subtractor is correct for ITR, ITB, or ITC.

Can we all agree on one thing from the numbers presented in the simulation that it is very likely that at a minumun each class should have it's own subtractor for FWD.

Example:
ITR - 150
ITS - 100
ITA - 50
ITB - 25
ITC - 0

Doesn't the above make more logical sense then having ITA - ITC the same and ITR, and ITS the same given the above simulation results?

 

[Ron Earp]

ITR - 150
ITS - 100
ITA - 50
ITB - 25
ITC - 0

Doesn't the above make more logical sense then having ITA - ITC the same and ITR, and ITS the same given the above simulation results?

Yes, off the cuff it does make sense that as the weight and power go up then the modifier would also slightly increase.

But is this in addition to the weight break the cars already got when classed?

 

[jrvisual]

But everybody looks at on track performance. Had Greg finish on the podium every race this year, this thread would not even exist. Is it a good gauge? NO. Should it be used to make adjustment to rules? NOT in IT.

 

[JeffYoung]

My brakes are worse than a GSR's. Run them through LapSim (swept area, rotor size, etc. -- see if it even has "drum size") and post up the differences.

 

[ekim952522000]

Yes, off the cuff it does make sense that as the weight and power go up then the modifier would also slightly increase.

But is this in addition to the weight break the cars already got when classed?

I am not quite understanding Ron what I was presenting in that quickly thrown together example would be the total FWD subtractor applied to the car.

I don't really care what the exact numbers are right now.

I would just like us all to agree that as you go up to a faster class a lager subtractor should be used. we can work out what that subtractor should be next.

 

[ekim952522000]

My brakes are worse than a GSR's. Run them through LapSim (swept area, rotor size, etc. -- see if it even has "drum size") and post up the differences.

I think this would show a similar result to the FWD result. BUT Brakes sizes are all over the place and could make for a very complex formula. FWD is a simple yes or no question.

EDIT: Are you suggesting that FWD cars don't need a subtractor to be competitive?

 

[Ron Earp]

My brakes are worse than a GSR's. Run them through LapSim (swept area, rotor size, etc. -- see if it even has "drum size") and post up the differences.

Don't forget, you've got a rear axle that allows for no camber gain and is a hell of a lot of weight. You have to apply all your power through the rear tires that are never optimized for grip due to the fixed geometry. Make sure that counts in the sim.

I've got a poor front suspension compared to a GSR. My brakes are far worse than a GSR. Drums? No I doubt it has that as a choice. Plus I bet the LapSim doesn't have an option for solid discs. It probably only has vented disc rotors.

 

[Jeremy Billiel]

You guys are seriously funny. No seriously....

This is not about Greg, this is about FWD disadvantages.

Why did Greg do "ok" this year?

1. He has above average driving abilities.
2. We put a boat load of money, testing and time into the car to get it where it is.
3. The NER ITS car counts were not there this year. If we went to the ARRC it would be very easy to see how far back we would have been.

I can tell you that since I built this car it has always and will continue to have the same FWD problem that others are experiencing in ITS. The other reason that this has not been talked about previous is simple....

THERE ARE ALMOST NO ITS or ITR FWD cars running out there! Is that in indicator of something?

 

[esuvee]

The big problem I see with the LapSim results is that no changes were made beyond FWD/RWD and weight bias. I went through and 'optimized' each setup's spring and bar rates for a FWD and RWD ITR 944 and for a FWD and RWD ITA CRX. I found 112lbs needed to equalize the CRX and 250lbs needed with the 944 after working all configs to their optimal spring/bar setup. Both 'fake' setups (RWD CRX and FWD 944) took multiple iterations of roll moment distribution changes to get the best lap time and both gained more than 1 second. I'm still not sure the setups are perfect.

Imagine if you just put a RWD drivetrain in my CRX and left springs and bars alone

So, 112 and 250 are pretty different numbers, I am in the camp that this is HP related. LapSim allows you to watch the driver inputs including throttle pos. The FWD 944 spends a lot more time at part throttle than either the RWD 944 or the FWD CRX. I am also in the camp that FWD cars like mine are stupid and should be avoided at all costs so I favor no further weight brakes My next racecar will drive the right end of the car.

I also favor rules stability. We're getting close to a nice setup here, again, what specific problem do we think we have? In ITR most 'it weighs too much' complaints are already headed to the RWD rather than the FWD cars.

Alex