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Old 05-26-2008, 01:23 PM   #61
John Stranahan
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Wedge, Corner Weights
Wedge was originally applied to full size oval race cars by driving a wedge between the right rear leaf spring and the axle housing. This adds preload to the right rear. This means the right rear carries more weight as we have compressed that spring a little bit. At the same time the car tends to rock accross a diagonal line and loads up the left front wheel. Wedge increases front cornering traction at the expense of rear cornering traction. This was very helpfull on big front engine sedans that tend to push from the large amount of weight in the front.

Wedge works by preloading the left front tire (much the same as when we move weight left) This unloads the overloaded right front on the heavy sedan. As a result when weight transfers in the corner we approach that desired 50-50 weight split on the front axle that creates maximum cornering.

Now a pan car is not like a front engine sedan. It is heavy in the back to give us better forward traction. For this reason it has a natural tendency to oversteer in the corner. On the pan car oval then what we do is preload the left rear or give the car some left rear down tweak. This loads up the right front as well. You cant see this on the front scale reading because we have also put the battery on the left side. This loads up the left front enough to obscure the increase that happened at the right front. This kills some steering traction and it keeps the battery off the ground. Now that is the way I see it. We are really adding reverse wedge or negative wedge or more simply left downtweak.

The scales come in handy if you want to share setup information on your oval car with another guy. There is not another real way to say accurately how much preload you have put on the left rear without measuring it on a scale. Do you need scales to run oval. Definitely not. You are going to use this left downtweak often to fine tune the oversteer balance. You can only determine this by driving the car on the track. If you want to share your setup or be more scientific about your setup then a set of those four corner weight scales will give you a quick measure of left down tweak.

My loaner battle axe is at 11.5 ounces heavier on the left rear. From setups posted above I could increase this. To increase it substantially I will have to install that stiffer right rear spring. I have the collar already about to the end of the threads on the shock body.

To use the scales tare them all to 0 put on the car. Bounce it on the suspension. Expect some error maybe .2-.3 ounces as shock stiction will cause some friction.

Note that you need a flat surface. I am using two scales and a beam of the same height. This works as good as four scales.

That third pic shows the car with a gold spring preloaded quite heavy on the right rear. The left rear is up to 1 lb 0 ounces now for a preload of about 13.5. The right rear shock end has now failed. I'll have to screw it on a little farther.

I had to replace both shock ends to use a copper spring. I cut the ends real straight to match the length, used Losi rod ends, tapped them to reduce force putting them on and drove them on untill the end touches the caps. That aluminum threaded stud on both ends of the shock is a weak point in this type of car. The Losi XXXT rod ends will strengthen things some.

other opinions are welcome.

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Last edited by John Stranahan; 08-21-2008 at 07:13 PM.
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