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      12-29-2012, 11:41 PM   #1
splitsecond
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Benefit of lightweight front rotors?

I know that the conventional wisdom is that decreasing unsprung mass will have a substantial impact on overall performance. But how useful is it to save 3 lbs from the front axle with lightweight rotors?

I did a google search, and some of the Evo guys have found measurable increases in awhp by losing 3 lbs from each brake rotor... but I wonder if we might get a similar effect by replacing front rotors on a RWD car.

And while I'm on the topic, I've seen a lot of different numbers for the BMW Performance rotors. Some places say that they're 21 lbs (which would mean a 1-1.5 lb loss), and some places say that they're 3-4 lbs lighter than stock. Does anybody know what the right answer is?
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      12-30-2012, 11:35 AM   #2
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Quote:
Originally Posted by splitsecond View Post
the Evo guys have found measurable increases in awhp by losing 3 lbs from each brake rotor...
there's no HP gain but you gain HP/weight ratio. 3 lbs wouldn't even register on even the most sensitive of butt dynos. you can expect sharper steering response, better braking and less wear and tear on suspension bushings due to lighter unsprung weight.
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      12-30-2012, 12:43 PM   #3
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The problem is that most brake rotors that are 2 piece and claim to be lighter shave weight off the hat buy using aluminum or other lighter metals. The hat is the closest point to the hub so unsprung weight there doesn't matter nearly as much. Will it still be quicker than a heavier rotor? yes, but the difference is very hard to measure.

Last edited by MMisencik157; 12-30-2012 at 12:49 PM.
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      12-30-2012, 07:15 PM   #4
splitsecond
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So has anybody ever noticed a butt dyno difference?
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      12-31-2012, 01:02 AM   #5
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If they have its probably more of a placebo effect than anything... we are talking very small differences here.
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      12-31-2012, 03:00 AM   #6
splitsecond
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I think the main attraction for me is the fact that they don't affect your autocross class, so it's good for those of us who want to start autocrossing this summer. But if the difference isn't noticeable, then I won't bother.
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      12-31-2012, 08:36 AM   #7
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I know i definitely noticed a difference in steering. Not as dramatic as lightweight wheels and tires, but there is a noticeable difference in feel. As far a an acceleration difference I don't think you're going to find any. And FYI the hats on the OEM rotors are aluminum as well.
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