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      11-07-2012, 01:47 AM   #1
Superfly_M3
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How much merit is there to these "ultra light" rims

Ok, so I'm not new at this. I understand the concept of rotational inertia. I understand the concept of unsprung weight. I know it helps in theory BUT ...

I look at the pricing of these ultralight rims and think to myself: is this for real??? I mean, all things being equal, how much time/lap are people going to shave off by saving 2lbs/corner on the same size rim? Can someone clarify this for me? Does anyone have first hand experience or even better - concrete data that proves me wrong?

This is only an opinion so lets not start a war here.
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      11-07-2012, 09:15 AM   #2
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If you've ever swapped out a set of heavier wheels for lighter ones, you would know the difference immediately. You can feel the difference just with regular driving. As far as lap times, I can't say.
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      11-07-2012, 10:46 AM   #3
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Lighter wheels are virtually always better for performance. Whether a particular change is worth what it costs depends on the car, the price difference, and your budget.

The nice thing about weight savings is they help acceleration, braking, and handling. A pound of un-sprung, rotating mass that is out at the end of the car is worth more in savings than a pound taken out of the passenger compartment. How much more? You'd have to do a lot of calculations to come up with any reliable formula. I've heard people say it's a factor of 4, factor of 10 etc. The reality is it all depends on the vehicle and the situation.
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      11-07-2012, 11:28 AM   #4
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I agree with Ben and The Tech. I was using lightweight wheels (< 18 lb/wheel) on my track prep'd e46 M3 with Michelin PSC r-comps (F 21 lb, R 23 lb). When I switched to Nitto NTO1 r-comps each tire weighed 6-8 lb more and I could "feel" the difference on track in terms of braking (higher rotor/caliper temps with heavier setup) and accelerating. There was a change in initial turn-in but I'm not sure if that was due to different tires/compounds or increased weight (switched back to PSCs); however, my lap times were consistently lower with the lighter wheel-tire setup.
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      11-07-2012, 11:31 AM   #5
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Right ... I get it, braking, acceleration, handling. But how much difference are we really talking about?

Tech, I don't know, thats the point of this thread. Can anyone compare or relate this to say "whp" gain or how much the car would feel lighter by?

Thanks.
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      11-07-2012, 11:56 AM   #6
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Quote:
Originally Posted by Superfly_M3 View Post
Right ... I get it, braking, acceleration, handling. But how much difference are we really talking about?

Tech, I don't know, thats the point of this thread. Can anyone compare or relate this to say "whp" gain or how much the car would feel lighter by?

Thanks.
It's hard to answer your question quantitatively, especially in terms of a "whp" gain.

However, in my case, consistently lower lap times (delta depends on the track) and decreased rotor/caliper temps (firmer and consistent brake pedal, better pad wear, etc) are enough for me to justify a light wheel-tire setup. Plus being able to pickup a wheel-tire combo with one arm in the paddock sure makes changing wheels, pads and rotors a lot easier....
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      11-07-2012, 12:06 PM   #7
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Quote:
Originally Posted by Superfly_M3 View Post
Right ... I get it, braking, acceleration, handling. But how much difference are we really talking about?

Tech, I don't know, thats the point of this thread. Can anyone compare or relate this to say "whp" gain or how much the car would feel lighter by?

Thanks.
Sorry I can't answer your question directly, but perhaps you'll find some value in this data --

Going from stock brakes, wheels and tires to aftermarket (see sig) I shaved nearly 6 seconds off lap times at my regular track.

1-2 seconds of that was brakes, 3-4 seconds tires.

My Apex wheels and RS3's are actually about 3 lbs. heavier than stock wheels + tires.

My gut tells me that 18" BBS FI, for example, at ~5 lbs. less per corner than my Apex wheels may shave a couple of tenths.

With a 200 lb. passenger I lose maybe 1 second/lap. Is the disadvantage of adding that much weight in the cabin less than the advantage of a few pound decrease in unsprung weight in the wheels? I'm not certain, but I don't think so.

That said, I can understand lighter wheels from the standpoint of an overall weight reduction, and overall performance increase. (Or even if you have the $ and just like the look of a particular light weight wheel.)
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      11-07-2012, 12:13 PM   #8
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Lighter wheels definitely improves the acceleration, braking, handling and overall feel of the car. The wheels respond faster to bumps on the road too so it can improve ride quality as well. Lots of people will ask for numbers to put behind it... laptimes, g-forces, acceleration numbers. The difference in those are sometimes small but the the "feel" of the car is just that much better. Kind of hard to explain.

Modified magazine tested lighter and heavier wheels years ago in their wheel test to see what kind of effect lighter wheels had. The lighter wheels are definitely faster but not definitively so.

http://www.modified.com/tech/modp-09...t/viewall.html
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      11-07-2012, 12:23 PM   #9
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Quote:
Originally Posted by Z K View Post
Lighter wheels definitely improves the acceleration, braking, handling and overall feel of the car. The wheels respond faster to bumps on the road too so it can improve ride quality as well. Lots of people will ask for numbers to put behind it... laptimes, g-forces, acceleration numbers. The difference in those are sometimes small but the the "feel" of the car is just that much better. Kind of hard to explain.

Modified magazine tested lighter and heavier wheels years ago in their wheel test to see what kind of effect lighter wheels had. The lighter wheels are definitely faster but not definitively so.

http://www.modified.com/tech/modp-09...t/viewall.html
Am I misreading the data in that test, or did the lightest wheel (RAYS) rank 4/5 in terms of fastest lap time & average lap time, and also turn in the 2nd slowest "slowest lap time"?
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