Cal Club Autocross Forums

Marshall Grice wrote:

Mako Koiwai wrote:Tom T. use to run a NSX. He told me that it's wheel base was too long for AX.

in general a longer wheel base is better.

Ok, let's hear the thinking behind that one Marshall. And in doing so please also explain why classes like AM and EM see fit to legislate a minimum legal wheelbase.

Jason Rhoades wrote:

Marshall Grice wrote:

Mako Koiwai wrote:Tom T. use to run a NSX. He told me that it's wheel base was too long for AX.

in general a longer wheel base is better.

Ok, let's hear the thinking behind that one Marshall. And in doing so please also explain why classes like AM and EM see fit to legislate a minimum legal wheelbase.

Ooh, Ooh, I want to try and answer that second part.

The concept is that a shorter car will also be lighter, better power to weight ratio. But a shorter car also means stability problems (along with too narrow of a track width) which can result in saftey problems such as roll-over. So that rule is trying to create a safer car, not necessarily limit performance.

(Did I get it right Marshall?)

Christine Berry wrote: The concept is that a shorter car will also be lighter, better power to weight ratio. But a shorter car also means stability problems (along with too narrow of a track width) which can result in saftey problems such as roll-over. So that rule is trying to create a safer car, not necessarily limit performance.

(Did I get it right Marshall?)

Last time I looked minimum weights were determined by displacement of the engine, not the chassis.

Jason Isley BS RX8 wrote:

Christine Berry wrote: The concept is that a shorter car will also be lighter, better power to weight ratio. But a shorter car also means stability problems (along with too narrow of a track width) which can result in saftey problems such as roll-over. So that rule is trying to create a safer car, not necessarily limit performance.

(Did I get it right Marshall?)

Last time I looked minimum weights were determined by displacement of the engine, not the chassis.

Yes, but a small chassis will be lighter. Smallest chassis with the biggest engine and then you can ballast up to a minimum weight and put that weight where ever you would like.

Christine Berry wrote:
Yes, but a small chassis will be lighter. Smallest chassis with the biggest engine and then you can ballast up to a minimum weight and put that weight where ever you would like.

So where will all this ballast fit on such a small chassis? Eventually you will having to start going up, which is good for your cg. I would like to see a 1,000lb shifter kart in AM.

Jason Rhoades wrote:

Marshall Grice wrote: in general a longer wheel base is better.

Ok, let's hear the thinking behind that one Marshall. And in doing so please also explain why classes like AM and EM see fit to legislate a minimum legal wheelbase.

longer wheel base means less longitudinal weight transfer, which means more braking traction and more predictable(less severe) throttle effects on corner balance. it also means greater yaw control authority and greater stablity.

I see minimum wheel base restrictions as a safety regulation. I certainly wouldn't build an AM car to the class minimum wheelbase.

Jason Isley BS RX8 wrote:

Christine Berry wrote:
Yes, but a small chassis will be lighter. Smallest chassis with the biggest engine and then you can ballast up to a minimum weight and put that weight where ever you would like.

So where will all this ballast fit on such a small chassis? Eventually you will having to start going up, which is good for your cg. I would like to see a 1,000lb shifter kart in AM.

http://www.youtube.com/watch?v=5p1ud823hFw" onclick="window.open(this.href);return false;

Jason Isley BS RX8 wrote:

Christine Berry wrote: The concept is that a shorter car will also be lighter, better power to weight ratio. But a shorter car also means stability problems (along with too narrow of a track width) which can result in saftey problems such as roll-over. So that rule is trying to create a safer car, not necessarily limit performance.

(Did I get it right Marshall?)

Last time I looked minimum weights were determined by displacement of the engine, not the chassis.

Well, when it comes to Amod.. "Cars with a minimum weight of 900 lbs, and a minimum 72 inch wheelbase." Rules for that class are barely a sentence long, haha.

I say the 72 inch wheelbase is there specifically to keep you from entering shifter karts, which need a short wheelbase and a twisty frame to turn.

Christine Berry wrote: http://www.youtube.com/watch?v=5p1ud823hFw" onclick="window.open(this.href);return false;

135kg is only 297.62lbs. Even if that did not include the driver, call him 200lbs. you still need to fit over 500lbs of ballast on that tiny chassis. Good luck. But it does look like fun.

Aaron Goldsmith wrote:
Well, when it comes to Amod.. "Cars with a minimum weight of 900 lbs, and a minimum 72 inch wheelbase." Rules for that class are barely a sentence long, haha.

I say the 72 inch wheelbase is there specifically to keep you from entering shifter karts, which need a short wheelbase and a twisty frame to turn.

It would take a lot of work to get an NSX in to AM trim. But in EM, where you could run it, displacement still bumps your minimum weight.

Jason Isley BS RX8 wrote: It would take a lot of work to get an NSX in to AM trim. But in EM, where you could run it, displacement still bumps your minimum weight.

Ugh, making an Amod car out of a production car would just be gross.

I thought that the "squarer" the wheel base, the more easily it turns ... the opposite of stability with a long wheel base ... so for AX, it would seem a shorter wheel base might be good ... unless fast transitional sections negate that? Aren't the reason that jeep like vehicles are less stable partly due to their short wheel base.

I recall some F1 teams USE to having a spacer between engine and chassis that could be removed for tight courses like Monaco.

Mako Koiwai wrote:OK ... Acura NSX:

Track: 60
Wheelbase: 99.6
Length: 174

The point I'm making is that dimensions on paper won't tell you whether a car will be really competitive or barely keeping up.

Mako Koiwai wrote:OK ... Acura NSX:

Track: 60
Wheelbase: 99.6
Length: 174

Ha, you call that a long wheelbase... RX-8: Track-59.1/59.3, Wheelbase-106.4, length-175.6.

No ... i thought the R8 had a long wheel base, considering that Tom thought the NSX has a long wheel base

Maybe all we need to do is drop a hint to Rad ... and he'll bring one out to try?

Mako Koiwai wrote:I thought that the "squarer" the wheel base, the more easily it turns ... the opposite of stability with a long wheel base ... so for AX, it would seem a shorter wheel base might be good ... unless fast transitional sections negate that? Aren't the reason that jeep like vehicles are less stable partly due to their short wheel base.

I recall some F1 teams USE to having a spacer between engine and chassis that could be removed for tight courses like Monaco.

a shorter wheelbase has a lower steering angle requirement for a given radius turn. F1 cars are steering angle limited when it comes to monaco.

I would characterize a short wheelbase car (from a theoretical perspective) as sloppy with regard to it's response to steering inputs...aka less stable. It's really difficult to prove the effects with a real car because wheelbase can't easily be changed without effecting other parameters of the car that effect the same characteristics, ie CG distribution, yaw inertia, lateral force vs steering angle curve, etc. So it's not like you can compare a miata to an f150 and say that long wheelbases are bad because the truck sucks at autoxing.


and BTW, a 99" wheel base is actually kind of short. so you're whole point of the NSX sucking because it has a long wheelbase is invalid. I would say it sucks because it has terrible snap oversteer tendencies and is generally not easy to drive.

In a given turn, the longer the wheelbase, the greater the difference between turning radius of the front vs. rear wheels. And that means to clear the apex cone with the rear wheels (which is what matters if you're doing it right), you need to swing the front end around wider, increasing your *effective* track.

In addition, that front end that you're swinging around wider is *that* much closer to the next slalom cone once the rear wheels clear the current slalom cone, making the problem worse. Body overhang will have a big effect here, too.

So I think a good case can be made for shorter wheelbase having an autocross performance advantage.

Will Kalman wrote:In a given turn, the longer the wheelbase, the greater the difference between turning radius of the front vs. rear wheels. And that means to clear the apex cone with the rear wheels (which is what matters if you're doing it right), you need to swing the front end around wider, increasing your *effective* track.

In addition, that front end that you're swinging around wider is *that* much closer to the next slalom cone once the rear wheels clear the current slalom cone, making the problem worse. Body overhang will have a big effect here, too.

So I think a good case can be made for shorter wheelbase having an autocross performance advantage.

not always true. a car that oversteers will have the rear tires track a wider radius arc then the fronts, regardless of the wheelbase. a neutral steer car (aka balanced) will track nearly true around a corner.

Marshall Grice wrote:

Jason Rhoades wrote:

Marshall Grice wrote: in general a longer wheel base is better.

Ok, let's hear the thinking behind that one Marshall. And in doing so please also explain why classes like AM and EM see fit to legislate a minimum legal wheelbase.

longer wheel base means less longitudinal weight transfer, which means more braking traction and more predictable(less severe) throttle effects on corner balance. it also means greater yaw control authority and greater stablity.

I see minimum wheel base restrictions as a safety regulation. I certainly wouldn't build an AM car to the class minimum wheelbase.

Would you build an BM to the class minimum wheelbase, it being only 8" longer? Why are there limitations in D/E Mod on how much a builder can shorten (but not lengthen) their vehicle's wheelbase (besides possibly maintaining original look)?
In a high powered RWD autocross car, is braking traction more important than corner-exit traction in an autocross setting? Is the extra tractive ability gained from additional rearward weight transfer with a shorter wheelbase worth more or less than the (not-necessarily-negative) changes to handling balance in throttle application?

I guess I just happen to disagree, I'll take a shorter wheelbase any day and any way I can get it around the cones. Superb yaw control and stability is great in Turn 8 at Willow but not what I'm looking for in the parking lot.

Jason Rhoades wrote: Superb yaw control and stability is great in Turn 8 at Willow but not what I'm looking for in the parking lot.

I thought that is why all the fast autox cars had wings?

Jason Isley BS RX8 wrote:

Christine Berry wrote:
Yes, but a small chassis will be lighter. Smallest chassis with the biggest engine and then you can ballast up to a minimum weight and put that weight where ever you would like.

So where will all this ballast fit on such a small chassis? Eventually you will having to start going up, which is good for your cg. I would like to see a 1,000lb shifter kart in AM.

Probably closer than I'd like to admit if I sat in one.

Jason Rhoades wrote: Would you build an BM to the class minimum wheelbase, it being only 8" longer? Why are there limitations in D/E Mod on how much a builder can shorten (but not lengthen) their vehicle's wheelbase (besides possibly maintaining original look)?
In a high powered RWD autocross car, is braking traction more important than corner-exit traction in an autocross setting? Is the extra tractive ability gained from additional rearward weight transfer with a shorter wheelbase worth more or less than the (not-necessarily-negative) changes to handling balance in throttle application?

I guess I just happen to disagree, I'll take a shorter wheelbase any day and any way I can get it around the cones. Superb yaw control and stability is great in Turn 8 at Willow but not what I'm looking for in the parking lot.

that's cool. I'll agree to disagreeing. no need putting everyone to sleep over it.

Marshall Grice wrote:not always true. a car that oversteers will have the rear tires track a wider radius arc then the fronts, regardless of the wheelbase. a neutral steer car (aka balanced) will track nearly true around a corner.

A car that oversteers strictly through steering inputs is going to be freakishly difficult to control. And you can't do much throttle or brake in a slalom (at least not for more than a cone or two) without Bad Things happening. FWD will understeer inherently and RWD needs to be setup with some bias towards understeer to allow critical power application and allow overhead for throttle-steering on corner exit. And it's true that there are driving techniques that can mitigate the differences. I also agree wholeheartedly with you that you can't just change the wheelbase without affecting several other variables.

I got to the point I could drift and slide the monster Dodge Intrepid around especially in rain. FWD and an oceanliner wheelbase (113"). That long wheel base slowed down the rotation and gave you time to stay ahead on the counter steering and unwinding. It was a blast. It was confidence inspiring. I don't think it was fast.