A perennial favourite argument on cycling forums is the cost-benefit of choosing a wheelset with superior aerodynamics vs a wheelset that is lighter (or an aero vs a lighter frame).
It is of course a false dichotomy that one must chose only one or the other. But that does not stop people having fun arguing the merits of each, or of holding onto beliefs/myths/folklore handed down through the generations. Of course there are a multitude of things that go into what is a suitable choice of wheels, and I'm not going to delve into those, suffice to say they involve a range of factors aside from aerodynamics and mass, including, inter alia (and not in any particular order):
- ability to stay round and true
- lateral stiffness
- repair-ability and service cost
- suitability for the purpose/race/riding situation
- braking demands
- handling characteristics
- available tyre choices
- bearing and freehub quality etc
- rules of competition
- suitability for the bike (e.g. will it fit?)
- sex appeal / bling factor
- and so on.....
So, back to weight v aero - the classic prize fight.
- air resistance (bike and rider's aerodynamics, speed and wind)
- gravity (weight of bike and rider, and gradient)
- rolling resistance (tyres and road surface)
- drive-train friction losses
- changes in kinetic energy (accelerations)
* when you really account for all the forces correctly, then the increase in power demand for an increase in sustained speed from say 40.0 to 40.8km/h (a 2% speed increase) is more like 5.5%, and you can use a exponent of 2.7 rather than 3 as a slightly better ROT.
But what about accelerations?
Some of you might recognise a few of the author's names. In summary, the equations look like this (as per a slide from one of Dr Coggan's powerpoint presentations):
A rider accelerates from a standing start with an average power of 1000 watts for 10 seconds.
A rider accelerates from 30km/h with an average power of 1000 watts for 10 seconds.
For my next trick, I will examine the shape of a typical power curve during such accelerations, and apply that variable power supply to the models, since nobody really accelerates with a flat power curve. Look out for Part II.