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Old 01-03-14, 11:38 AM
  #19  
Racer Ex 
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The chart is sort of a "Dick and Jane" primer, don't take it as gospel. Aerodynamics isn't a set piece, it's really interactive and interdependent. Depending on the person I could put you in a skin suit/helmet/whatever that would be slower than your regular kit. How you're built, your position, all play into whether a helmet or suit will work for you.

Bike hardware tends to be less contingent on the individual, but the word "tends" is certainly a qualifier.

I've been through 4 different test facilities and including field and track testing have a hundred plus hours doing this kind of thing. I've been fortunate enough to have worked with some of the big brains on aero stuff and the mantra is mostly "test it".

What is pretty much absolutely correct is that for track the bang for the buck is all on the aero side.

400g on a wheel over the course of a mass start race might cost you a watt on your average power over 60 minutes. The difference in aerodynamics of your wheel might cost you 20 or more, both depending on how you ride the race. And considering most races are won in a high speed sprint, a bad wheel choice might cost you the race; drag goes up exponentially as you go faster.

The quick practical example is to have someone put two wheels in a stand, one heavy, one light. Spin them by hand blindfolded with the same force and you'd be hard pressed to tell the heavy wheel from the light wheel, and the force would get both wheels to close to the same RPM.

Now take those wheels and stick them out a car window at 35 MPH. After a few tries you'll quit watching them fly out of your hands and quickly tell which wheel has less drag

Talking about the disc vs. other wheels in another thread, you also have rotational drag created from spokes as they go through the air. A lot of long, thick spokes are going to take more power to spin at (pick your RPM) than a few short, thin spokes, again, going up exponentially as the speed increases. This is part of the reason those old box 32's are slow.

A disc has virtually no rotational aero drag. The five spoke has very low rotational drag because at some point the wheel reaches an RPM where the spokes are essentially drafting each other in cleanish air.

The openings in the 5 spoke allow it to be turned a bit easier than a disc, where you're moving a solid wall against the air flow vs. a perforated one. If you've ridden a disc front you'll be nodding your head.

All 50mm wheels are not alike. Spoke count, rim shape, and tire can all move the number. A really well designed 60mm might stomp all over an 88mm of a different design. Throw a little bit of wind at an angle and a rock star wheel can become a slug. So you either test or find someone who has. Be sure to look at the protocol...testing one wheel with X tire and another with Y might hide reality.

One of the really nice things about using Jim's facility at VSC is you get an actual bike ridden so you get a sum of all the parts compared to a wind tunnel. And it's neat watching numbers change sometimes as people go from cruise mode to race pace. And because it's a sum of the parts number, it will sometimes tell you the wind tunnel was wrong.

Last edited by Racer Ex; 01-03-14 at 11:47 AM.
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