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Rahal Letterman ALMS GT car

The Ultimate Guide to Suspension and Handling Part IV: Reduce Weight Transfer

by Mike Kojima

Now that we have reduced body motion and improved steering response, and tuned out under or oversteer to improve the chassis balance, our next step is to reduce weight transfer. Weight transfer is the movement of weight from the inside to the outside wheels of a car under cornering.

Check out part one of the series here!

Check out part two of the series here!

Check out part three of the series here!

 

Grip goes up with load but the relationship rolls off at a certain point.

Excessive lateral weight transfer hurts handling. It is caused by centrifugal force working on the chassis’ center of gravity which loads the outside wheels and unloads the inside wheels reducing mechanical grip.  Increased load on the outside wheels increases grip but not as much as decreasing the load on the inside wheels reduces their grip.

Weight transfer = ( Lateral acceleration  x  Weight  x  Height of CG ) / Track width

In case you didn't know, a car's center of gravity is the point where the car's mass is centered about,  If you were balancing a car on your finger tip, the point it balances at is the lateral center of gravity. If you were balancing it on its side, that point would be the car's vertical CG location.

 

body roll
Contrary to popular belief, body roll does not contribute very much to weight transfer.  The car's CG will only move laterally a fraction of an inch, not conducive to shifting weight.  Typically this is only 1-1.5 percent.

Contrary to popular belief, very little weight transfer can be attributed to lean in a corner. Even at large roll angles weight transfer due to roll is quite small. So, lowering a car’s center of gravity and widening its track width will reduce weight transfer much more effectively than reducing roll angle by an order of magnitude.  You can calculate the amount of weight transfer due to body roll thusly.

Distance of CG lateral displacement= Height of CG x sin x degrees of body roll°

Total weight tranfer= Weight of car- (Weight of car x ( one half of track width / Distance of CG lateral displacement) / track width)

A typical performance street car might roll 3-4 degrees at maximum cornering speed.  A modified high performance car will roll about 2-3 degrees.  A race car might roll .7-1.5 degrees.  So if you crunch some numbers on your car you will see that lowering the CG or making the track width wider affect weight transfer a lot more than limiting roll.

CG shift
This grossly exaggerated example shows how load transfer is affected by body roll.

 

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Comments
538
538link
Thursday, July 29, 2010 9:07 PM
Great article as always!
Big J
Big Jlink
Friday, July 30, 2010 1:37 AM
sometimes all I need is the equation to spell everything out. I guess it's time for Lexan windows.
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