Wheelbase for autocross formula car
I rebuilding a formula continental for auto cross and maybe hill climbing. I need to redo part of the frame and cock pit to fit me . I am debating if I should shorten part of the cockpit area to reduce my wheelbase by about 4-5 inches. This would add quite a bit to the project but it is do able. The wheelbase would either be around 88" or 84" shortened. Would this change be worth it extra work?
The shorter wheel base will reduce the cornering potential of the car. The reason is that you will transfer more of the weight of the car to the loaded tires in cornering. This in turn reduces the work that the inside tires can do. The total cornering is reduced.
Now the car may be come more responsive to cornering inputs until you over load one or both of the outside tires.
I don't know how that would affect the handling, but the minimum wheelbase is defined by the GCR rules. I am not sure what that is off the top of my head either.
A Formula Continental would be in B Modified for autocross. There is an exemption to the GCR allowing for an 80" minimum wheelbase. Eons ago, it was not uncommon for drivers to flip the front wishbones on Brabham BT-21s and, perhaps, other cars to shorten the wheelbase. Shortening the wheelbase is probably not a good idea for higher speed events such as hillclimbs.
that Chinook had the perfect wheelbase!
For reference the 85 VD FF1600 which won CM at the Solo Nationals in 2014 has an approximately 93 inch wheel base afaik (mine was). I think the Swift DB1, including the 2013 winner, is in the same range.
Dick
Former 85 VD FF autocrosser
Ummm...Originally Posted by S Lathrop
How does changing the wheelbase increase the load transferred from inside to outside while cornering?
Simply put, the further the wheels are from the CG, the less load transfer will occur or the more leverage that wheel has over the CG.
It is easily demonstrated with a mathematical model.
Sure... ...but in which axis?
Yes: while decelerating the reduced wheel base will result in greater weight transfer and thus, while decelerating (or accelerating) reduced overall grip in all directions.
But if the track width remains the same, then steady state cornering's lateral weight transfer will be no different than it was regardless of wheelbase.
When you are cornering, the weight transfer is both lateral and longitudinal. That is because the outside front tires is at an angle to the direction the mass of the war really wants to travel. The acts on the suspension system just as braking action.
Think about how much speed you loose just by turning the car.
Wheelbase for autocross formula car
Except you don't let the car decelerate. You apply throttle in order to maintain at least your cornering speed. Hence, there is no longitudinal acceleration or deceleration in steady state cornering.
No. You just add another force to the equation. Why do you think front tires ware out? When the combination of forces exceeds the performance capabilities of the tire you get push and just grind the tire to death.
Doesn't CG effectively rise when the wheelbase is shortened and no other changes are made? The angle between CG and the corners becomes steeper?
But adding that force is necessary regardless of wheelbase, so that's a wash.
I wouldn't put it that way, but when wheelbase is shortened, you will get more fore/aft weight transfer under braking and acceleration.
But you won't get any more during steady state cornering.
FYI in autocross with a formula car there is no "steady state" cornering other than "is it ever going to turn" understeer . . . which you need to tune out.
The initial post referred to the "inside tires" and hence left/right weight transfer.FYI in autocross with a formula car there is no "steady state" cornering other than "is it ever going to turn" understeer . . . which you need to tune out.
That transfer is not changed by changing the wheelbase.
Are there other factors in play? Sure.
this guy named Colin needed a variable wheelbase vehicle
he chose to alter the locations of the suspension....just saying
Figure my ignorance I come from a motocross back ground and this my first experence with cars like this. I am assuming that I will need to soften the shocks up and maybe change the reduce the rebound settings is there a guide to setting suspension up in these cars somewhere?FYI in autocross with a formula car there is no "steady state" cornering other than "is it ever going to turn" understeer . . . which you need to tune out.
My big question to you would be:
What do you want to achieve by shortening the wheelbase?
Wheelbase is a critical factor in autocross. Shorter allows a driver to steer less.
Jim
I wish I understood everything I know.
For autocross, depends on which class you want to drive in. The stock Continental could be converted to CM. If you change the frame, you would be in BM or AM and then need to deal with a much more powerful motor to be competitive. Let us know what you decide.
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
huh?
K
Based on my combination I would be forced to run Am . I am running a zx12 motorcycle engine in the chassis.
zx12 is Bmod legal also, just not at the 1020# min weight.
I also have a yamaha r1 engine that I am going to make interchange. My friends and I mostly doing this for something fun to do. I looks like we are going to be competeing with each other in the same car as most events near us only get a couple a & b mod cars
Shorten it!
Shorten it and put the ZX12 in it. I want to run against you with my 84" wheelbase GSX1300 Jedi in AM.
Marlin
Try driving through a series of cones, back and forth and back and forth. Could be a slalom or simply a series of gates. In order to set up a proper line for each ensuing cone, you have to steer more as you pass the cone before it without knocking it over.
Which will allow you steer less? Long or short wheelbase?
Jim
I wish I understood everything I know.
I don't think it's quite as simple as that.
In order to turn a car you first steer the front wheels, which creates a lateral force ahead of the centre of mass and thus creates a torque which steers the rest of the car and the rear wheels into the turn.
Reduce the wheelbase and in some cases you'll reduce the moment arm on which the lateral force at the front has to work... ...which could result in it taking longer to develop a large enough slip angle at the rear....
But then there's that whole throttle oversteer thing
"An analog man living in a digital world"
Yes, it is as simple as that. This is why you find minimum wheelbase rules in the Modified Category of the SCCA Solo rules.
Jim
I wish I understood everything I know.
Chap-man
"this guy named Colin needed a variable wheelbase vehicle
he chose to alter the locations of the suspension....just saying"
Lawrence Hayes
Hayes Cages, LLC
Sagle, ID.
I think the same guy made the a-arms shorter on one side of the car when it only needed to turn left
Wheelbase
Very entertaining listening in on this thread. Let's go back and answer the question in a different way, with a little history: The wheelbase number that occurs most often on successful solo cars over the last twenty years in amod and bmod is 80". The distribution is from a low of 80" to a high of 94". Even if you extend the data set to 30 years the only change is a group of 86" cars (FSV based). If you limit the set to the four fastest amod cars on the planet, they are 80" (both BBR cars)and 94" (Phantom cars). All of the Amod and Bmod cars have track relationships at .6-.64. This is not the best number for maximum mechanical grip, but the best compromise in solo for a car allowed a limited slip and aero loading driving in a short radius, close coupled environment. A Cmod FF will require different dimensions for track and WB to excel.
This data comes from 40 years of improving other designers cars, driving most of the above examples and producing winners for their drivers. Remember, "one test is worth 1,000 expert opinions", W. Von Braun.
Bill Gendron , Small Fortune Racing
I think you mis-typed for the Phantom. I think you meant 84". Also, I never measured the BBR Shark, but I remember Joe writing it was a footprint copy of the Phantom. Joe wrote that he designed the Vancouver Special longer than both.
so like a Segway would be the FASTEST autoxr because it has no wheelbase LOL
WB
Z, You are correct, the Phantom 1 has a WB of 84" +/-. My error.
10 in shorter than my FF.
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
You are absolutely correct. That is why there are rules specifying minimum wheelbase for AM and BM.
Leave the WB alone and build a BM car
Eric,
I don't think there is anything wrong with an 88" WB car for Solo. I doubt you will gain a measurable advantage by reducing your wheel base 4-5 inches.
Use the ZX12 engine and turn your car into a BM car. You can find events in your general area with several BM cars/drivers in attendance. Besides, you can always slap the letters AM on your car, if you choose to do so, even if it was designed to be a BM car.
Clemens
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