Once the scales were leveled, we decided to build four ramps so we could drive the car on the scales rather than jack the car and lower it onto the scales. The contention is that the front suspension will bind slightly if lowered onto the scales, which will affect the accuracy and repeatability of our tests. We decided to put all this to the test using the scales in all three situations. Our first test was to lower the Orange Peel Chevelle down on nonlevel scales. Next, we repeated this same test with the scales leveled and jounced the car twice on each corner to settle the springs and shocks. Then we raised the car, removed the scales, backed the car out, and drove the Chevelle up on the scales using our wooden ramps without jouncing the suspension and with the driver in the car. The first thing we noticed was that the total weight was not the same among the three tests, with the total changing by as much as 6 pounds and one corner that changed by as much as 13 pounds. After several more attempts lowering the car and using the jounce method, we found that 3,472 pounds became the most consistent figure. After leveling the scales and jouncing the car, the weight moved around a little to the rear. The ramp test moved the weight around a bit again, but the change was less than 1 percent-and the ramps frankly were a hassle. So for us, it was easier to raise and lower the car using our hoist or a floor jack, and we produced more consistent results this way compared with using the ramps. So we learned that we have to use the scales in the same spot on the shop floor and test the same way each time. A difference of a couple of pounds will not be critical in terms of vehicle performance, but it helps to be as accurate as possible. Another common solution is to build working stands the same height as the scales, which would allow us to lower the car on the stands, settle the suspension, and then roll the car onto the scales. Whichever procedure you decide to use, make sure to scale the car the same way each time.
Many racers contend that lowering the front suspension vertically on the scales (as oppose
We built these 16-inch-long wooden ramps out of 2x4s and 3/4-inch-thick particleboard cabi
We also scaled this Mustang just to look at a leaf spring car. Adding preload to the right
You can expect to become increasingly popular once your buddies discover you own a set of scales. We invited Greg Smith to bring over his 10-second nitrous'd, leaf spring '67 Mustang. The car has always launched straight, so we weren't anticipating major rear weight differences. With driver weight and half a tank of fuel, we discovered less weight in the right rear (the opposite of what we found without the driver in the car). The difference in left-to-right rear weight was 35 pounds, which is slightly more than 1 percent. Calvert Racing prefers minimizing preload, as this creates rear suspension bind, so we did not modify the weight distribution. Plus, the cross weight was within 4 pounds, which is a big reason why the car tracks straight.
||3,340 with driver (3,130 without)