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Wheel weight vs. acceleration test question

5K views 8 replies 8 participants last post by  stoli  
#1 ·
Here's the thing: everyone scoffs at heavy wheels, and everyone seeks light, strong wheels, claiming that a decrease in wheel weight equals free horsepower, etc, etc.

Has anyone done a test, where they've taken the same car to the track on the same day, slapped on different wheels of different weights (with same tires) then let the acceleration timeslips be the judge?

I did just buy foose wheels and they look good yet they are 29lbs which I didn’t know until after I bought and received them. So I’m debating on selling them and buying lighter wheels, forged of course. What are your thoughts?

Thanks for the input…
Chris
 
#4 ·
lighter tires/wheels combo DOES equal better timeslips period. i tested the theory myself on an 04 street legal big turbo neon srt4. w/ no other changes....i gained between .4 and .5 seconds. used 2 different rim sizes w/ the SAME tire of the same width. factory sized rims versus a set of very light kosei rims
 
#5 ·
This website has a flywheel energy calculator. So you put in the weight, diameter, and RPM, and it says how much energy would be stored in a flywheel experiencing those conditions.

What you need to do is then choose what speed you want to figure this out, like say 100 MPH, and convert that into RPMs of your wheel. I can do this, if someone can look up what the outer diameter or circumference is of your *tire*. Then put in the wheel diameter, and then finally choose the first weight of your wheel, which you said was 29 pounds. For our purposes I think you can ignore the weight of the tire.

Then use the same numbers as above, but put in the lighter weight wheel.

The output for each calculation will be how much energy is stored in the flywheel, and so you'll know that your car will need to dump that much energy into just spinning up that wheel. Find the difference in resulting energies between the two different weight wheels, and then you'll know how much horsepower was wasted in the heavier wheel, compared to the lighter wheel. The faster speed you use, the more energy will be calculated. Choose whatever speed you like, I figure around 100 MPH is good because 1/4 mile speed. The answer will be in joules, but you can convert that to horsepower.

Rotating Mass, Available Horsepower, and Acceleration
 
#6 ·
i remember back in the day of the popular late 80"s mustang gt.....they said.....for every 100 lbs removed from the car you could expect 1/10 sec gain ( roughly a car length)
and ....for every pound you could lighten the tire/wheel assy, was equal to removing 8 pounds from the car itself in terms of gains in time. i don't know exactly how true the numbers were but i did hear it from lots of different sources. of course, WHERE the extra weight is added or removed would surely make a difference also ( as in changing the weight of the actual tire, versus a lighter, smaller diameter rim) just food for thought.
 
#7 ·
Back in the day, I had the stock wheels on my WS6 Trans Am widened from 17x9 to 17x11 and swapped from a 275 to a 315 rear tire. The weight of the wheel went up, and the inertia of the tire was higher, since all the extra weight in a wider tire is at the circumference, as far from the centerline as possible. I dynoed the difference back to back. Here are the results: 17" Modified WS6 Rims & Wheel Wells
 
#9 ·
As for switching wheels at the track; I haven't done it in the same day, but in the same week w/DA within a couple hundred feet. I went from a 19x11 Forgestar running 305/35/19 Nitto NT05r weighing in at 58lbs each to a AMR 19x10 with the same tires that weighted 64lbs each and lost about 1 tenth. It's not conclusive and it there are a lot of other factors that come into play, but I was slower in almost all runs that day than my previous 3 or 4 trips to the track on the lighter wheels.

As has been pointed out, there's a lot more to it than just cutting weight. I know guys that have gone to lightweight aluminum flywheels only to switch back to heavier steel ones. While the aluminum allowed for quicker revving, the loss of inertia made for rougher shifts at high rpm. This is fine for drag racing, but bad for road course and daily driving.