Wheel weight article....

is it online yet? I seem to be 'tarded and cannot find it.

I can't find it online either. The two tire tests are, though.

Personally, the mechanical engineer in me has difficulty accepting the results of that article. Rotational inertia is real, so straight line acceleration and braking at least should be affected by wheel weight. I suppose it just wasn't enough of a change to really show in the results when tested on a turn-intensive site like the Tire Rack test course. It would be interesting to repeat that test on a race course.

I have seen another test that was similar and also confusing, but very different in nature. Most drag cars have the tires screwed to the wheels. When screwing them on, my Dad noticed that it was like 3 lbs of screws for each side of the wheel. 12 lbs total. He tried running without screws. No difference in ET or MPH.

i think that weight makes a bigger difference when you have a very low power output.

With regards to the drag racer - if you're limited by traction, your rotational inertia isn't really a factor. Once you're hooked up and your acceleration level is trailing off, the amount of inertial loss drops and becomes less significant.

I suspect the braking tests with heavier wheels also have the same "noise" from traction levels. If you're at the threshold of traction, will the rotational inertia matter? The car can only decelerate so hard. I can see how it might have an effect on the modulation behavior though.

I've felt the difference a big spike in rotating mass can make. In that case, it was a set of ludicrously sized brake rotors. Weird gyroscopic effects in the steering, where the wheels would resist turning then all of a sudden let go.

Keith wrote: With regards to the drag racer - if you're limited by traction, your rotational inertia isn't really a factor. Once you're hooked up and your acceleration level is trailing off, the amount of inertial loss drops and becomes less significant.

You're not limited by traction. Not unless you're talking about a Nitro car. Most of the time you build the thing to hook. My Dad's car made maybe 650HP and left the line at 4k or so. No lack of traction there.

Not a drag racer, so I'm not sure how much wheelspin is involved! I thought there was some.

jstein77 wrote: Personally, the mechanical engineer in me has difficulty accepting the results of that article. Rotational inertia is real, so straight line acceleration and braking at least should be affected by wheel weight.

I ran these numbers for a brake system analysis we did on the Wreck Racing miata a couple months ago. The amount of energy associated with the rotational kinetic energy of the wheels is miniscule relative to the linear kinetic energy of the chassis. There is a benefit to be had in acceleration and braking from lighter wheels but it's very small.

The biggest thing wheel weight affects is the response of the suspension during bump and rebound, and steering response.

I was a little surprised by this as well.

I would have thought the biggest change would have been to the suspension as well.

I'd ask to redo the test on a very rough surface. I know lighter wheels and tires basically revalved my shocks without ever removing them from the car.

Streetwiseguy wrote: I'd ask to redo the test on a very rough surface. I know lighter wheels and tires basically revalved my shocks without ever removing them from the car.

Yeah, I think that's exactly the type of scenario where you'd see a significant benefit.

What article was this in? I was going to go back and find it.

Tried this out twice on my Mustang. No performance numbers but the seat of the pants change was very noticable when I switched from 38# steel 17x9s to 21# alloys in the same size (included the spare) for the street. Then I swapped the race wheels from a set of 25# Simmons 16x12s to 17# Real Racing wheels. Not as revolutionary as the street set-up change but still noticably quicker. The best place to mesure this would be on a chassis dyno where you could tease out the small changes in performance due to the chages in inertia of different pairs of wheels then multiply by two (for same size F/R sets). Some tuner TV show did this on a low HP car about a decade ago and measured a 6 HP loss due to the added wheel/tire weight & diameter going (if memory servers) from 15x7 to 17x8. On a low output car 6 HP will show up in time slips or lap times, on a higher output car the change will tend to get lost in the noise (not that it might not still be worth while over time).