Aspect Ratios & The Spirit of Cycling As A Sport

One of the key aerodynamic design variables for fairings and streamlined bodies is the Length to Width ratio (also called Aspect Ratio in some literature). There is an optimum length for a fairing intended to minimize the total drag on a body moving through the air. At low speeds (Reynolds number below about 100,000), the optimum ratio of the length of the fairing to its maximum width is about 5:1. If the fairing is made shorter, pressure drag will increase faster than the surface friction is reduced. Conversely, if the fairing is made longer, friction drag increases faster than pressure drag is reduced. The situation changes at high speed (Reynolds numbers above about 1 million). Turbulence at these speeds significantly increases friction drag relative to pressure drag, and optimum fairings are shorter.


An a example, the WW2 De Havilland Mosquito has an elongated tear drop shape profile and a length to width fuselage ratio of 6:1. This is to maximize the efficiency of flight and fluid flow in the Reynold's number regime encountered by the aircraft.

Last week, the UCI said that since 2010, they'll be enforcing their 3:1 length to width ratios for any extension or streamlining of a section of a competing bicycle, be it aerobars, seatposts, crankarms, frames, or forks.

Courtesy : UCI Code 1.3.025

I totally welcome the enforcement of this rule by the UCI. You might think in a different way. But I say we shouldn't want bicycles looking like aircrafts, at least in the competition arena. As beautiful as they might be, that'll be a silly thing in sport, won't it? If someone has to introduce such extreme aids to empower themselves in pedaling, how do you differentiate between technological prowess and their true potential as a rider? I think this thought process is best stated through UCI's own 'Preamble' for bicycles :

"The bicycle shall comply with the spirit and principle of cycling as a sport. The spirit presupposes that cyclists will compete in competitions on an equal footing. The principle asserts the primacy of man over machine."

Hence, it is nice to have a governing body overlook these matters, or soon we would have bicycles looking so aerodynamically morphed that when they're ridden, the lift force will be so great that they'll take off no lesser than airplanes. For safety, bicycle designers would incorporate into them cockpits, oxygen systems and ejection seats. And that, I fear, will be the new doping in cycling.

It is interesting that today, there are a variety of aero forks that go over this 3:1 rule. For a few examples, check out this table compiled by BikeTechReview.

So does this mean that these forks in question are now UCI illegal since 2010? I certainly can't answer that 100%, but looking at the way UCI wants to enforce this rule, it seems very likely that these forks won't be accepted in competition unless some kind of exception is made (one could tell the UCI, oh please excuse me, my ratios are still very close to your limit, see?)

Lets keep this sport unadultered, pure and true to its spirit. No more BS. Primacy of man over machine, not the other way round.

Kestrel's UCI Illegal TT Bike