There is a common saying for drag racing that says, reducing rotating weight by 10lbs is like removing 100lbs from the car. Well, I wanted to see if this was true or not.
I did a few calculations to see what the actual effect is. The first calculation was a heavier wheel/tire combo. Lets say you bought new wheels and tires and each wheel/tire weighs 10lbs more than the origional combination, and assume that all the extra weight is at the outside, near the tire. In this situation, adding 10lbs of rotating weight has the same effect as adding 20lbs of dead weight. So for the set of 4 wheels and tires, you added an actual 40lbs, but because it is rotating weight, it is as if you added a total of 80 lbs of dead weight.
Then, I thought about the effect of a light weight driveshaft. Lets say an aluminum driveshaft is 10lbs ligher. I assumed the driveshaft is the same diameter of a steel one, and that it is 5" diameter, that 3.73 gears are being used, and that all the weight was at the outside again. In this case, removing 10.00 lbs of rotating weight from the driveshaft has the same effect as removing 26.6 lbs of dead weight from the car. It is interesting that this gain is better than the wheels/tires. The diameter is much smaller, so you'd think the weight has a much smaller effect, but actaully it spins 3-4 times faster than the wheels which makes up for the difference.
So it looks like light weight componets really do make a difference... but no where near the 10x difference in that common saying. Keep in mind, that 100lbs of dead weight is worth approximately .1 seconds in the quarter mile... so your 10lb lighter driveshaft shaves off .026 seconds and your wheel tire combo that weighs 10lbs more per wheel/tire adds nearly .1 seconds to your quarter mile.
I did a few calculations to see what the actual effect is. The first calculation was a heavier wheel/tire combo. Lets say you bought new wheels and tires and each wheel/tire weighs 10lbs more than the origional combination, and assume that all the extra weight is at the outside, near the tire. In this situation, adding 10lbs of rotating weight has the same effect as adding 20lbs of dead weight. So for the set of 4 wheels and tires, you added an actual 40lbs, but because it is rotating weight, it is as if you added a total of 80 lbs of dead weight.
Then, I thought about the effect of a light weight driveshaft. Lets say an aluminum driveshaft is 10lbs ligher. I assumed the driveshaft is the same diameter of a steel one, and that it is 5" diameter, that 3.73 gears are being used, and that all the weight was at the outside again. In this case, removing 10.00 lbs of rotating weight from the driveshaft has the same effect as removing 26.6 lbs of dead weight from the car. It is interesting that this gain is better than the wheels/tires. The diameter is much smaller, so you'd think the weight has a much smaller effect, but actaully it spins 3-4 times faster than the wheels which makes up for the difference.
So it looks like light weight componets really do make a difference... but no where near the 10x difference in that common saying. Keep in mind, that 100lbs of dead weight is worth approximately .1 seconds in the quarter mile... so your 10lb lighter driveshaft shaves off .026 seconds and your wheel tire combo that weighs 10lbs more per wheel/tire adds nearly .1 seconds to your quarter mile.