As you can see, the total weight is 3,150 pounds. We can also see that the front is pretty heavy at 55.5 percent, so some weight could move to the back to help traction. In addition, the left side is heavier than the right by 1.5 percent, which isn't unusual given the car was weighed with the driver. If we were building a road race car, we would want to equalize the weight on the two front tires to make the car easier to turn in both directions.
Another popular evaluation is cross weight, which is the combined weight of opposite corners LF and RR compared with RF and LR. In our example, the cross weights reveal a difference of 1.5 percent. Ideally, we'd prefer equal cross weights. The difference is the extra 50 pounds sitting on the left front. If this were a car that we autocrossed or road raced, the additional weight on the left front would tend to make the car more efficient in lefthand turns (where the weight transfers to the right front) as opposed to a righthand turns where the weight moves to the left front that's already slightly heavy. The 50 pounds in our example is not excessive. A cross weight difference approaching 100 pounds or more would be noticeable and worth correcting.
We decided to scale our '65 El Camino and discovered the ride height on the left front was
The Checklist
As soon as you get the scale, the first thing everyone wants to do is roll a car up on it and see what it weighs. While that's understandable, it's also a bit premature. To use these scales to accurately measure your car, you need to make sure the scales are level and the car is tested the same way every time. To this end, we've made up a short checklist you should consult each time before the first weight is taken. Many of these points will not change from test to test, but they're included here so you gain an understanding of how they affect weight distribution in the car. Of these points, tire pressure is subject to the most variation. It's also critical that all nonessential items be removed from the interior and trunk. Note that the sway bar should be disconnected. It is possible to alter weight distribution with the sway bar, which is why it's best to disconnect one side of the bar. Then make sure that reconnecting the bar does not significantly change the weight distribution.
- Tire pressure
- Fuel level (full)
- Ride height
- Alignment (camber)
- All ballast positioned
- Sway bar disconnected
We used a Craftsman Laser Trac to adjust the height of all four scales to ensure our resul
Accuracy Test
The idea behind using any precision instrument is that the test procedure is consistent with every use. The point is to produce the most accurate and repeatable data. Before we could even begin weighing cars, we had to determine if our shop floor was level-and if not, what we had to do to make the scales level. My engineering accomplice, Don Young, suggested we use a laser to determine height, so we borrowed a Craftsman Laser Trac. Unfortunately, one bubble level had leaked and we discovered the other wasn't accurate, so we used a separate digital level to square the laser. Once that was accomplished, we found the slope of the shop floor was roughly 1/2 inch spanning 115 inches (the Chevelle's wheelbase), which required raising the rear scales. We also leveled the scales side to side to ensure all four were the same height.