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Old 01-31-2014, 08:38 AM   #11
Phat Phrog Stunt Team
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Join Date: Aug 2011
Location: Iowa
Posts: 34,205
Originally Posted by Cowracer View Post
When i raced circle track dirt cars, (hence the 'cowracer' name) I had this argument more than once. Weight distribution is critical, enough so that I spent $1300 on scales to be able to weigh the wheels individually and at the same time. In our class, we had a minimum weight of 3300#. You build them light, then add weight where you wanted to get up to minimum. I usually had 300-400 lbs of lead ballast bolted onto the car at various points.

The standard way of doing it was to hand load 45 to 70 pound lead bars onto the car and then put the car on the scale. This could make for a tiring evening going back and forth trying to trim the car up. As I had 7 or 8 hard points where I could mount lead, I figured I ought to be able to do this mathematically. I wrote a down and dirty program that factored in wheelbase, track width, and the x and y coordinates of the mounts, coupled with the weights of the bars.

Some of the 'old hands' told me there was no way that it would work because of spring rates and shock rates and etc. I said, "If i put 50# on the car, I should see a net increase of the sum of wheel weights of 50# no matter what shocks or springs. Once I got the runtime bugs out of the program, I found out that the mathematically calculated weights were within a percent or so of the actual weights. It even accounted for the fact that if you hang weight behind the rear axle (like on the bumper) you actually wind up reducing front weight and transferring it back to the rear axle. Think teeter totter.

So yes, if you put 100# exactly between two points, they will split the weight evenly.

I concur....
Retired Open wheel modified racer.


oc's buddy

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Old 01-31-2014, 08:50 AM   #12
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Join Date: Mar 2008
Location: Concord, NC
Posts: 23,910
I agree it will put 50# on the axle, but unless it is placed on the centerline of the axle and the tongue, one spring will be loaded more.

Also in dirt racing, we had 1/4", 1/2" & 3/4" spacers we could place behind the wheels to change the "side bite". We also measured tire pressure gain after each race. Ideal was to get the same pressure increase on all 4 tires.

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