Tuesday, February 24, 2009

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


Jacob said...

I agree, but there's something disheartening about it, caps creativity I suppose. Then there will be a push for a racing series that does accept the aero equipment. It will be advertised like the long gone Xtreme Football League with lightning bolts and CG cyclists

Phil said...

You bring up an important point. Usually, the top contendors in the GC are just separated by seconds. Just take a look at the top 3 for the TOC. I suspect the picture will be somewhat the same for the Tour in July as well, where competitors will be obviously in top shape.

Some of how you get up there on podium is pure luck, and being at the right place at the right time apart from your power as a rider. And to get that extra edge is where technology comes in. So I have wondered : Are we seeing the limits (plateau) of human performance here? It'll definitely be interesting to watch cycling when that's the case, because every second will count.

Anonymous said...

For bikes with fewer restrictions there is always Triathlon or Road Time Trials in UK. If even they are too restrictive, there's always HPV.

I belive that rules are good, except when they are arbitary & not consistantly enforced. The UCI does not have a good record.

jimmythefly said...

Great food for thought as always!

If they want to make it about the athlete, fine by me. In that case we need a spec bike, or some sort of claiming rules. As it is there are still other advantages to be had within the rules(if you've got the budget), not to mention the minimum weight seems to discriminate against light riders.

I see what you're saying about
"If someone has to introduce such extreme aids to empower themselves in pedaling,..." but I'm reminded that clipless pedals and derailleur gears met similar resistance. That in itself is not an argument for aerodynamic excess, but certainly the equipment has made changes over time.

The spirit and principle of cycling as sport has a lot to do with equipment, whether the UCI wants to admit it or not. I'm surprised they haven't stuck to a round-tubes-only stance, but I suppose it's a bit late for that.

greg l. said...

Is Laurent Fignon behind all this?