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

[Knestis]

Depends. What other adders and how do they theoretically act to influence the car's performance?

I have to disclose my bias that the suspension and brake adders aren't particularly important. The influence of the allowances we can apply to the suspension overcomes stock design deficiencies to the point (I believe) that they fall into the "pick your poison" kind of factors.

That's just me, tho.

K

[tnord]

Depends. What other adders and how do they theoretically act to influence the car's performance?

I have to disclose my bias that the suspension and brake adders aren't particularly important. The influence of the allowances we can apply to the suspension overcomes stock design deficiencies to the point (I believe) that they fall into the "pick your poison" kind of factors.

That's just me, tho.

K

so.......how about we get rid of them? i mean hell, we're already trying to change the the way power adders and FWD allowances are calculated, why not go all the way and change the whole bloody thing?

[Andy Bettencourt]

Depends. What other adders and how do they theoretically act to influence the car's performance?

I have to disclose my bias that the suspension and brake adders aren't particularly important. The influence of the allowances we can apply to the suspension overcomes stock design deficiencies to the point (I believe) that they fall into the "pick your poison" kind of factors.

That's just me, tho.

K

Lead the charge!!! I'll gladly take my 50lbs back for double wishbones.

[ddewhurst]

[Eagle7]

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.

My formula was not based on weight, but on HP. Your data that I looked at was linear with HP, given a constant starting-point weight.

The reason I picked HP is that I was trying to be class-neutral. Everyone is saying that a 2500 lb ITR car needs a larger reduction than a 2500 lb ITA car. Using HP accomplishes that. Using weight would require a different formula for each class.

[tnord]

My formula was not based on weight, but on HP. Your data that I looked at was linear with HP, given a constant starting-point weight.

The reason I picked HP is that I was trying to be class-neutral. Everyone is saying that a 2500 lb ITR car needs a larger reduction than a 2500 lb ITA car. Using HP accomplishes that. Using weight would require a different formula for each class.

tire wear increases with power across all platforms, it doesn't sit well with me to base weight reductions on that.

[Knestis]

But if we were to determine the FWD subtractor as a function of weight, and we set the weight as a function of power (which we already do), then it's toe-may-toe, toe-mah-toe...

K

[Eagle7]

But if we were to determine the FWD subtractor as a function of weight, and we set the weight as a function of power (which we already do), then it's toe-may-toe, toe-mah-toe...

K

Yup, that's why I went down that road.

[tnord]

But if we were to determine the FWD subtractor as a function of weight, and we set the weight as a function of power (which we already do), then it's toe-may-toe, toe-mah-toe...

K

yes....i know.

i'm just having a real hard time accepting that a FWD 200whp 2500lb ITR car should get a 200lb break but a FWD 150whp 2500lb ITA car should get 50lbs when a RWD platform experiences increased tire loads with increases in power just the same. regardless of what lapsim says.

a little voice in the back of my head says that if this program really is all that it wouldn't be free for the general public to use.

[Andy Bettencourt]

But those loads are balanced out between the front and rear so the impact is far less.

When I look at a ITS GSR and a ITA Integra RS, and I take into account the torque, the only increase in 'work' is under braking. Significantly higher straight line speeds should result in more work for those front tires.

The %'s I posted are a function of power and weight. Isn't that as close as we can reasonably get - or WANT TO TRY AND GET TO?

[PSherm]

I have been reading thru this discussion with some amusement. I'm not planning on an ITS/ITR car, but it seems to me it's boiling down to somewhere between 50lbs and 100lbs difference in the FWD subtractor. All the other discussion regarding subtractors is just noise to me. The IT formula seems to be working pretty well for all the other classes, so why not just pick a number and move on? Since the great IT rules change, is it not possible to adjust the weight of a car afterwards? Seems to me that was one of the reasons for the rules rewrite. Sorry if this just seems naive, but I get the feeling the topic is getting wrapped around the axles (FWD vs RWD not withstanding).....

[lateapex911]

One thing that I *think* is being missed here is that while we're talking about weight and hp as the major factors, the desire to have ONE formula/method that applies to ALL classes (yea, it would be nice!) gets derailed when we remember that wheel and tire size vary from class to class.

So, the upper classes get more tire, which knocks the linearity aspect a bit.

That's why, I think, that the same adder works in ITB and ITA even though the power goes up, yet we seem to have issues in ITS, where they run on the same tires as ITA.

That's why I've got this feeling that finding a sweet spot for each class then varying the weights as a percentage makes sense.

Is there a way to get LapSim to account for the tire differences? If we could build a model for ITA that works, and in general tracks the pattern of the current weights, then I would have a lot of confidence in what it spit out for ITS.

[ekim952522000]

.....

......a little voice in the back of my head says that if this program really is all that it wouldn't be free for the general public to use.

Bosch Lapsim currently sells for $7,084 and that's just for the chassis lincense. it is a additonal $7,084 if you want the engine license to go with that.

With the free version you can adjust 26 parameters if you buy the expert version you can adjust a total of 242 parameters for the chassis (more if you buy the engine lincense). Including shocks, suspension design, roll centers, weights at all four corners of the car, brakes, simulation driver settings, camber curves, etc....

[ekim952522000]

One thing that I *think* is being missed here is that while we're talking about weight and hp as the major factors, the desire to have ONE formula/method that applies to ALL classes (yea, it would be nice!) gets derailed when we remember that wheel and tire size vary from class to class.

So, the upper classes get more tire, which knocks the linearity aspect a bit.

That's why, I think, that the same adder works in ITB and ITA even though the power goes up, yet we seem to have issues in ITS, where they run on the same tires as ITA.

That's why I've got this feeling that finding a sweet spot for each class then varying the weights as a percentage makes sense.

Is there a way to get LapSim to account for the tire differences? If we could build a model for ITA that works, and in general tracks the pattern of the current weights, then I would have a lot of confidence in what it spit out for ITS.

In this version the only tire setting I have is the amount of grip at the front and back axle I have been using 1.08 for both. The system automatically adjust that as you vary the weight of the car.

[Eagle7]

One thing that I *think* is being missed here is that while we're talking about weight and hp as the major factors, the desire to have ONE formula/method that applies to ALL classes (yea, it would be nice!) gets derailed when we remember that wheel and tire size vary from class to class.

Agreed, so if we were to continue down the "one formula" road, it would need a wheel size factor. It still seems feeasible to me, but I think we need quite a few "accepted" data points to try to generate the formula.

[ekim952522000]

Agreed, so if we were to continue down the "one formula" road, it would need a wheel size factor. It still seems feeasible to me, but I think we need quite a few "accepted" data points to try to generate the formula.

So I think something we need to do is choose a "bogey" for each class that would help give us data point targets.

I think we should use the Integra's for the bogey's for ITR - ITA. since that give us the least amount of variables.

ITR - Type R - 195hp*1.20=234

ITS - GSR - 170hp*1.25=212.5

ITA - LS/RS- 142hp*1.27=180.34


ITR - 234*11.25=2633-175=2483
ITS - 212.5*12.9=2741-150=2591
ITA - 180.34*14.5=2615-50=2565

I can't for the life of me find one formula to make that work I am trying to think of a way to factor in wheel width since I think that might be the key.

[Jeremy Billiel]

But those loads are balanced out between the front and rear so the impact is far less.

When I look at a ITS GSR and a ITA Integra RS, and I take into account the torque, the only increase in 'work' is under braking. Significantly higher straight line speeds should result in more work for those front tires.

The %'s I posted are a function of power and weight. Isn't that as close as we can reasonably get - or WANT TO TRY AND GET TO?

I am not so sure about that... Coming out the corners is a differentiation as well.

[Knestis]

Agreed, so if we were to continue down the "one formula" road, it would need a wheel size factor. ...

I'm not sure how much sense that makes. Remember that the wheel size - and the amount of tire we tend to carry - goes up from class to class.

K

[Andy Bettencourt]

I am not so sure about that... Coming out the corners is a differentiation as well.

Not for a car that has as much or LESS torque...no?

[Eagle7]

I'm not sure how much sense that makes. Remember that the wheel size - and the amount of tire we tend to carry - goes up from class to class.

K

Exactly. A 200 HP ITS car needs a different amount of weight subtracted than a 200 HP ITR car because the wheel widths are different. If we used a single formula for all classes it would need a factor for the wheel width. Whether the single formula is feasible or desirable is another matter.