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      07-07-2009, 08:32 AM   #110
GregW / Oregon

Drives: 2015 M4 Coupe, 2012 ML350
Join Date: Nov 2005
Location: Lake Oswego, OR

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Performance advantage of lighter rims

Originally Posted by Lemans_Blue_M View Post
Yes, but it's not that simple...

Yes the overall weights are close...but the effective weights are much different.

Let me explain...

The Dymag wheel has less effective weight in regards to performance, because it's Carbon Fiber outer barrel is located at the farthest point away from the center hub. That CF barrel is much lighter than that of the Volk CE28N. (i.e. the Dymag's outer barrel has less MASS)

Since a majority of the Dymags overall weight is contained in the Magnesium/Aluminum center spoke portion of the wheel, it's moment of inertia is much lower than that of the CE28N. (which is made of 6061-T6 Aluminum Alloy)

Since the Dry Carbon Fiber outer barrel on the Dymag wheel is much lighter in overall weight, it requires less energy to do the same amount of work. Which means it's easier to get the wheel to spin from a dead stop. It also improves the transitional performance during frequent accelerating and decelerating. (by reducing the load on the engine to spin up the wheel again after slowing down)

The Dymag's are a stone cold killer on the track...

Since the Dymag wheel has the lightest part of it's overall weight at the farthest point form the center bore, it's real world performance is superior to that of the CE28N.

FYI: The closer you get to the center bore, the less impact the weight will have on your overall performance. (physics 101)

But be advised...this 'advantage' in wheel technology comes at a staggering cost!
I question the amount of the advantage of a lighter rim area. The rims moment arm is less than one foot (~9.5" for a 19") Even if you have a 2 lb lighter rim, it seems that would mean 9.5/12 ft x 2 lb x 2 driven wheels = 3+ lb ft of force difference necessary to accelerate the wheels, which is only around 1% of the available torque.

Is there a flaw in my logic? Also, the distribution of the weight makes little difference to suspension action, the other key advantage to lighter wheels.

Greg Lake Oswego, Oregon, USA
2015 M4 Coupe - Silverstone/Sakhir/CF
2012 ML350