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New 03/18/2005, 3/30/05
Does anybody remember off hand what the affects of tire and wheel weight are
on whp? For instance how much HP does it cost to turn a wheel that's 2lbs
heavier or how much is freed up by a wheel that's 2lbs lighter? I remember
something like this coming up before but I didn't save that email. Thanks in
Complicated question, as it depends where the 2#s are in relation to the hub.
But yes, a 2# weight difference can be seen on a dyno.
This isn’t the best example, but a few weeks back I relayed the example that I saw on TV on the Mugen Acura that was being modified. They put on a bigger brake package that overall weighed less (most likely a much lighter caliper, with bigger rotors that weighed more) and they lost 5 WHP.
Safe to say that the lighter wheel/tire package won’t produce a butt-dyno feel at 2#s less, but combined with other small mods, it will add up.
Actually, I will be saving about 2#s per corner when I put on my new summer wheels & tires. Since I’m home, I weighed the new wheels, which are 1.5#s lighter than the stock wheels, and I suspect that the new tires (at 22#s) are lighter than the stock tires. Wish I could do before/after dyno tests, but it won’t happen.
I've heard numbers thrown around that lighter weight wheels, tires, and brake rotors all make a difference of something like 8lbs rotational weight loss per 1lb of static weight. I'm moving to centerline 17X7 rims for this summer that weigh in at sub 15lbs per rim a savings of 4.75 lbs per rim per over slicers. I also hope that I might loose a little more because of less rubber on the yokohama 245/45/17's or 225/50/17's vs the 225/55/16.
Granted I am not 100% sure about the numbers, but the lighter rotational parts means less mass for the engine to get up and moving. If I'm able to make up my 2-peice light weight rotors for 11.6 front and rear as well as the tire rim combo, I'll be looking at a static weight loss of over 10lbs per tire, which if the numbers are right and all that jazz, would translate to a lost of 320lbs or so of rotational weight. I guess that means faster acceleration.
Bruce J Malachuk
good starting point
Cam Failure #425
I don’t know its hp related effects but my memory says rotational mass is = ~3 x static, not 8.
A few years ago one of the engineers on the 911 list went through a very long and technical post of the mathematical effects of wheel weight The basics ended up being that, for wheels in the normal 15-18” range, the multiplier can be anything fro 1x to 11x, depending on where the weight is at. 4x seems to be the “generally accepted” factor, as it is close enough, and conservative enough, for most applications.
Factors in the over 5x category would have to be for taller, heavy tires that put the weight way out from the hub, not for things like brake rotors.
For Bruce’s case, the overall weight is reduced, BUT the weight moves farther out from the hub with the 17” wheels. And, with the wider 7” rim, more weight is moved out from the hub (most of the weight is in the rim of a wheel). Plus, the lower-profile 17” tires have more weight farther from the hub than with a 16” slicer and 225 tires. The “net” effect for dynamic weight could be zero, or insignificant. This assumes that the tires are the same static weight. If the new yokos are heavier than what is on there now, the effect could be worse.
Ron what tires and size? 22lbs is pretty light. The Pirelli p zero nero 225/50/16 weigh 23lbs.
4x is a good rule of thump unless you are on a bike.
215/45/17 Michelin Pilot Exalto PE2s.
Pirellis are light. When I had the P7000SuperSports in 225/50/16, they were 22.5 #s new, which is the same as the original GY RSAs.
Thanks for the helpful info. On the subject of tires I've done some more home work and am leaning strongly toward the Pirelli P Zero Nero 225-50-16. I like the weight (23lbs) and the tread compound. Any thoughts about them?
Reviews have been very good. I don’t know anyone with them yet, but I was
gonna get them before I got a great deal n the Pilot Exalto PE2s.