Bike Physics


Here's a quick guide on how to use this section. There are a whole bunch of numbers listed for each wheel, which I've tried to explain below. In a nutshell, lower is better for all parameters. If you'd like me to clarify the meaning of some of these numbers or debate them for that matter, just write me an email or post something to the forums.

a, b: These parameters are a measure of the bearing performance. As these numbers increase, so will the drag due to bearing friction. Conceivably, these numbers could be lowered for any wheel by using high quality bearings and ensuring that they are well aligned and adjusted.

c: This component is solely due to aerodynamic drag and is a product of the wheel design. Since the power lost due to aerodynamic drag increases with w 3, it's important to get this right.

I: The moment of inertia is really only important during accelerations. This parameter has absolutely no effect when travelling at a constant speed, even uphill.

P: The power required to keep a wheel moving at a constant speed is equal to the losses due to parameters a, b, and c. This is a very important performance characteristic. P30=power needed to keep the wheel at 30 km/h

Front Wheels
Manufacturer Model Year a b c I(kgm2) P30(W) P40(W) P50(W) Notes
Shimano 7801-SL 2007 1.8x10-3 4.81x10-4 1.80x10-5 0.034 0.62 1.25 2.19 Thin aero spokes, a light rim and good bearings make Dura Ace an unbeatable wheel. Very nice.
Shimano WH-6600 2007 8.8x10-3 3.60x10-4 2.46x10-5 0.038 0.82 1.59 2.74 A very good wheel. Ultegra is Dura Ace's little brother in every respect. Just a little heavier and less aerodynamic.
Mavic Ksyrium ES 2006 13.4x10-3 0.99x10-4 4.33x10-5 0.039 1.07 2.14 3.82 Light. Beautiful. Well built. But... big fat aluminum spokes aren't aerodynamic.
Shimano WH-540 2003 13.6x10-3 4.78x10-4 1.49x10-5 0.039 0.87 1.52 2.45 Slap some decent bearings in there and it's a winner!
Mavic Ksyrium Elite 2006 8.95x10-3 5.42x10-4 2.43x10-5 0.043 0.93 1.78 3.04 There is some drag in the bearings. The aerodynamics and MoI are excellent.
Campagnolo Scirocco 2004 6.22x10-3 3.50x10-4 3.53x10-5 0.056 0.92 1.89 3.39 The dust cover over the bearings caused some friction.
Kult ProMotion 2005 1.10x10-3 2.06x10-4 2.43x10-5 0.039 0.53 1.15 2.14 Very light rim. Great aerodynamics. Some durability issues.
custom - - 2.46x10-3 9.64x10-4 4.23x10-5 0.060 1.31 2.69 4.79 Alex DA22 rim with Shimano 105 SC hub and 15Ga spokes laced 3x
Neuvation M28 Aero 2005 0.77x10-3 1.49x10-4 3.62x10-5 0.052 0.67 1.52 2.88 Smooth bearings. Decent weight. Good Aerodynamics.
Campagnolo Eurus Carbon 2005 6.55x10-3 4.99x10-4 2.34x10-5 0.052 0.83 1.62 2.81
Campagnolo Eurus 2006 7.59x10-3 5.64x10-4 3.38x10-5 0.044 1.06 2.11 3.69
Fulcrum Racing 5 2006 4.7x10-3 10.1x10-4 3.58x10-5 0.047 1.28 2.56 4.46
Reynolds Attack 2007 0.98x10-3 5.01x10-4 3.25x10-5 0.044 0.83 1.77 3.22
Campagnolo Khamsin 2007 1.15x10-3 6.74x10-4 2.95x10-5 0.041 0.91 1.85 3.31

Rear Wheels
Manufacturer Model Year a b c I(kgm2) P30(W) P40(W) P50(W) Notes
Shimano 7801-SL 2007 6.53x10-3 6.53x10-4 2.19x10-5 0.036 0.91 1.74 2.96 Excellent aerodynamics and low moment of inertia make this a wheel to own. The bearings could use some tweaking though.
Shimano WH-6600 2007 20.4x10-3 13.8x10-4 2.85x10-5 0.063 1.81 3.25 5.27 The bearings are obviously not adjusted properly, causing excessive drag. It is also distorting the MOI calculation. Good aerodynamics, but this test should be done again.
Mavic Ksyrium ES 2006 5.27x10-3 3.60x10-4 3.45x10-5 0.043 0.89 1.84 3.31 Better aerodynamics than the front wheel, but still not good. A truly beautiful wheel.
Shimano WH-540 2003 9.42x10-3 2.14x10-4 2.36x10-5 0.046 0.73 1.41 2.45 Bad bearings and some heaviness are killing this great set of wheels.
Kult ProMotion 2005 0.63x10-3 2.34x10-4 3.08x10-5 0.040 0.64 1.41 2.63 Very light rim. Great aerodynamics. Some durability issues.
Mavic Ksyrium Elite 2006 6.03x10-3 5.26x10-4 2.58x10-5 0.049 0.88 1.72 3.00 Low MoI with amazing aerodynamics. The bearings have a bit of drag.
Zipp 404 2007 13.5x10-3 2.64x10-4 3.39x10-5 0.047 1.02 1.97 3.42