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

[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).....

[jjjanos]

...but it seems to me it's boiling down to somewhere between 50lbs and 100lbs difference in the FWD subtractor.

Which, may I remind everyone means that the weights should not be adjusted as their current weights are within where "the process (next generation)" would place them.

Is it not at least defacto, if not dejure, ITAC policy to deny requests to adjust weight when the current weight is within that margin of error?

Now, I'm in the use the process weight camp, not the use the process weight +/- error factor camp, but it seems to me a but odd to muck about with the model when delta is within the margin of error.

[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.

[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?

[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....

[jlucas]

7pg write up so everyone can understand the differences between the free version and pro version of LapSim
http://www.tuev-sued.de/uploads/imag...van_rutten.pdf

It's a very capable program but understanding limitations & assumptions are important.
Also correlating with your DL1 data can help improve your results.

[Knestis]

Deal with grip using a tire factor...

Hoosiers = 1.0, full-tread Toyo RA1s = 0.4. Everything else is something in between. We can use mean qualifying lap times from races all across the country to come up with the numbers.

K

[Andy Bettencourt]

Deal with grip using a tire factor...

Hoosiers = 1.0, full-tread Toyo RA1s = 0.4. Everything else is something in between. We can use mean qualifying lap times from races all across the country to come up with the numbers.

K

This HAS to be your first official drunk-post of 2009.

[lateapex911]

Nice AB, now get down here and clean off my screen! Maybe Kirks been reading the wine thread on RRAX.

[ekim952522000]

Deal with grip using a tire factor...

Hoosiers = 1.0, full-tread Toyo RA1s = 0.4. Everything else is something in between. We can use mean qualifying lap times from races all across the country to come up with the numbers.

K

LOL.

The trouble I am having trying to come up with a grip variable for each class is for example. Even though a 2250lb CRX has less tire than a RSX the RSX weighs in at 2640lbs and has worse suspension it is very possible the CRX has more grip.

[ekim952522000]

Nevermind see chart below.

Jake what numbers do you need for ITS I can look them up?

[ekim952522000]

Kirk I am really starting to see the problems with using "what we know" this simulation had the exact oppsite result of what I thought would happen.

I figured as grip increased given the same weight and HP that FWD would need less weight taken off but it needs more.

[Eagle7]

LOL.

The trouble I am having trying to come up with a grip variable for each class is for example. Even though a 2250lb CRX has less tire than a RSX the RSX weighs in at 2640lbs and has worse suspension it is very possible the CRX has more grip.

I know nothing about LapSim, but would assume for the same tire compound, that its grip factor is proportional to contact patch, and contact patch is essentially proportional to wheel width.

[ekim952522000]

So Lapsim seems to indicate the higher the weight, horsepower, and grip get, the larger the percent of weight that needs to come off in order to balance FWD and RWD.

<----Why do I have a FWD car again......