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12 May

Aero wheels how much difference do they make?

Posted by Bold Apps

This post is prompted by a phone call today asking about do deep rimmed wheels make a difference. Well they do in short.

Those more at ease with the physics of this will notice what I am presenting here is a basic model but it illustrates what going on.

One common misunderstanding is that aero gain are only important at higher speeds. Not true. Power required to overcome air resistance is directly proportional to the drag coefficient.  Often people relate power to the riders velocity but since this the variable here the constant of proportionality is the drag coefficient multiplied by frontal area, CdA for short. 

So a 5% reduction in CdA results in a 5% reduction in power used at any speed. Since a slower cyclist spends more time on a course that leads to the slower cyclist saving more time in tt with aero wheels that say Alex Dowset would if one could persuade him to the Lavenham 10 on Mavic Askiums compared to the BORG50C for example. That's not the same things as saying aero wheels benefit slower riders more than faster riders as that's not true. If the same time difference were expressed in terms of a % then the faster riders see more of a % percentage benefit than the slower rider. 

So air resistance can be 

Power to overcome air resistance P(ar) = 0.5 × CdA x rho x v^3

Wheels change the CdA of the rider and bike and through that affect the riders velocity.

Rho is air density which is 1.2 kgm^-3 

for your average cyclist moving at 18 mph on mavic askiums then a set of BORG50C wheels will add 0.5 to 1kph to your speed roughly.   This may or may not be significant to you. If it isnt and for most people it isnt then your buying based on looks. Nothing wrong with that. 

 I am going to refrain from predicting time saved for particular course as such calculations are not meaningful.




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