How close is close when balancing the weight in the car?

[Bruno]

Last year we ran with the corners of the car weighing in within 10-15 #s from each other, and the car handled great.  With the mods to the car,  we have more like 100# variance from corner to corner.  On  a 5000 # car  just how close do you need to be on the rear wheels, does a 100# deta make a difference?

[Stainless1]

Depends on which rear corner is heavier.... Consider torque... think about it...

[Bruno]

good point, stainless,  I reviewed the video of the dyno pull and the engine moves about 3/4 of an inch.  So as an estimate of this effect on the chasis,  hypothetically, If  I could  measure the force it would take to move the engine this distance I would have the total moment of inertia.  Would one then assume that this force would be spread between, the whole right side of the chasis.  Watching the dyno pull at max rpm and seeing the engine torque at max rpm was pretty convincing that one should somehow acount for this weight transfer at max speed.   

So this goes back to my original question, how close is close enough.

[Stainless1]

so you might not want the rear corners the same weight...
You might want them weighted to account for torque... 

It also may depend on how it handles...

There is no formula that covers every vehicle... at Bonneville it is trial and error... try to stay on the trial side of the line 

[hotrod]

If  I could  measure the force it would take to move the engine this distance I would have the total moment of inertia.  Would one then assume that this force would be spread between, the whole right side of the chasis.  Watching the dyno pull at max rpm and seeing the engine torque at max rpm was pretty convincing that one should somehow acount for this weight transfer at max speed. 

Billy Shope was an engineer at Chrysler Corporation and member of the original Ramchargers group.


http://www.speedwaybids.com/tech/tractiondyno.html

http://www.motorsportsvillage.com/billyshope/index.html

You might want to look over his page on using his traction dyno system to analyze what the car does under acceleration.

Larry

[akk]

On our car 920/928 GMR we use soft springs in the front with no front sway bar. In the rear we have a pretty stiff sway bar and higher rate springs to carry lead. The rear is parallel 4 bars.

The weight balance is easily adjustable with lead...the front end doesn't really get involved. Our balance with driver and all is within 10 pounds.

Cars with front air dams should not use soft front springs.

Akk

[Peter Jack]

That's an interesting combination which may again prove that the salt is different from other forms of racing. In a road race or oval application that combination would probably quickly lead to looking from whence you came!!!

Pete

[akk]

On the salt I feel very strongly about not spinning the rear tires...running on the salt is like rain racing....the coefficient of friction is like wet cement...the speeds are very high...the tire pressures are very high...the tires narrow....the driver must really concentrate and react quickly to any step out of the rear end...or around she goes.

A lot of weight and balanced loads on the rear is good to have.

I am told that 3 degrees of yaw is OK more and you are sliding!

Akk

[Richard Thomason]

When talking about weight loading for torque, think about how many cars get in trouble when they back out of it. Loss of torque can be as unsettling to a car as the initial torque. Also, I would suggest that the rate of change of torque loss is greater than torque gain. The car needs to be equally stable under acceleration, steady state and coast. If not, one glitch and you may have a problem.

[Buickguy3]

   My theory is that if Floating Mountain is more than 15 degrees off of center, the driver is now a passenger.
Doug

[SPARKY]

or was