How much does rotational mass cost times?
11-24-2004, 09:41 AM
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How much does rotational mass cost times? Right now i have a 2002 SS A4 with 3.23 gear and was wondering i was looking at AR rebels with 17's in the front and 18's in the back. Would it make a huge difference in daily driving and straight line handling/cornering. The reason i ask is that my friend recently put the O.E. concepts black z06 wheels on his z06 and it still seems to perform well in straight line. And i got in a debate with my friend on how the extra weight would make a difference and he said it wouldn't. Any input is appreciated.
11-24-2004, 11:54 AM
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I remember a guy on here (not sure what his name is) who went from 18 x 9.5 Black Z06 Motorsport rims to OEM Z06 rims which are lighter (by how much I'm not sure) and said he could notice a 'significant' difference in straight line performance and handling; handling especially.
But since I don't....I like your car... it's not black by any chance is it??? 
....I just saw your signature line...it is black.....uhh ahhhhh
11-25-2004, 07:35 PM
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well now there is a rear view of it as my avatar. Well I was talking about how much of the wheel weight=rotational mass cuz is has to turn actually affects the handling/launch of the vehicle. And about the blond moment i am to so join the club.
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11-26-2004, 04:33 PM
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Originally Posted by Eugenio_SS
don't forget to take the tire weight into account... for street tires, figure 30lbs per tire... and those are what gonna kill you for rotational mass.
How much of a difference could you tell when you went to all 17x11s? I suppose the traction gained outweighed the increased rotational mass? Do you think you'd do better or worse on the track if you went to 17x9.5s?
11-27-2004, 12:26 AM
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Originally Posted by LS1_Disciple
Interesting post coming from someone with 17x11s on all 4 corners
How much of a difference could you tell when you went to all 17x11s? I suppose the traction gained outweighed the increased rotational mass? Do you think you'd do better or worse on the track if you went to 17x9.5s?
How much of a difference could you tell when you went to all 17x11s? I suppose the traction gained outweighed the increased rotational mass? Do you think you'd do better or worse on the track if you went to 17x9.5s?
if track, you mean 1/4 mile, I lost 1-2 mph... but since my priorities are on handling, yes, the traction gained outweigh the increased rotational mass... heck I have 55lbs on each corner
but worth every ounce for the handling characteristics it gives me. 
11-28-2004, 01:43 AM
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Basically, reducing 1 lb. of dead weight can reduce up to 6-7 lb. of rotational weight. For example...say a wheel/tire weighs 35 lb. If you reduce that weight by 5 lb. (lighter wheel and/or rim) you will "lose" up to 5 lb. times 7= 35 lb. of rotational weight. Multiply that times 4 wheels= 140 lbs. of rotational weight...a difference indeed in acceleration/handling/braking. Also, a 18 inch 35 lb. wheel/tire requires more energy to accelerate/brake than a 17 or 16 in. 35 lb. wheel/tire because it is further from the axis of rotation. Hope this makes sense.
11-29-2004, 08:45 PM
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Originally Posted by WindWalker
Basically, reducing 1 lb. of dead weight can reduce up to 6-7 lb. of rotational weight. For example...say a wheel/tire weighs 35 lb. If you reduce that weight by 5 lb. (lighter wheel and/or rim) you will "lose" up to 5 lb. times 7= 35 lb. of rotational weight. Multiply that times 4 wheels= 140 lbs. of rotational weight...a difference indeed in acceleration/handling/braking. Also, a 18 inch 35 lb. wheel/tire requires more energy to accelerate/brake than a 17 or 16 in. 35 lb. wheel/tire because it is further from the axis of rotation. Hope this makes sense.
we know that rotational mass will hinder more than dead mass, but depending on where the mass is in the wheels will make a difference.
getting a # such as x7 is purely speculation... and as you said... the further the mass is from the center, the worse it is... that's why I mentionned that people should consider looking at the tire weights... something that people tend to neglect when doing this kind of analysis.
11-29-2004, 11:29 PM
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[QUOTE=Eugenio_SS] getting a # such as x7 is purely speculation... QUOTE] I have read in a few sources that the 5-7 times factor does exist provided the weight is equally distributed. I believe others will agree, probably cuz they read the same thing probably. Good point on the tire weight which, being further from the axis, will be more important than rim weight. BTW, nice ride 
