I just came back from watching some club races at the new mini-velodrome at Hålandsmarka, Norway. The asphalt track, which is short (125m?) with moderate banks, attracted quite a number of young riders on their road bikes. In fact, no one was riding a track bike. This made things ‘interesting’ and made me think that an article about what makes a good track bike is in order.
At first glance, one might think that a track bike is simply a road bike with a fixed-gear wheel and no brakes. This would be a natural thought. But, after watching riders hurtling around the not-steep-enough turns at Hålandsmarka, you quickly realize that something must be different. The scraping of pedals around the corners is disconcerting at best and, surely, someone must have thought that crashing hurts enough to rethink the idea of using a road frame on the track. And so it goes, a track frame is distinctly different from a road frame in a number of ways.
Bottom bracket drop
This is a measure of the vertical distance from the wheel centre to the centre of the bottom bracket. On a road bike, the drop may be about 70mm while on a track bike it may be 50mm or less. And, although 2cm may not sound like a lot, it may be enough keep us from laying our bike down in a corner.
Crank arm length
Decreasing bottom bracket drop by 2cm (from say 70mm to 50mm) gives roughly an extra 6 degrees lean potential before digging into the pavement. While this is an admirable improvement, we can do better if we also shorten our crank arms. If, for example, we move from 170mm arms down to 165mm arms then we gain yet another 1.5 degrees for a total lean improvement over a ‘std’ road bike of 7.5 degrees. Which a quick back-of-the-envelope calculation shows is equivalent to about an extra 5km/h on a small, shallow track.
So, it appears that, if you want to minimize your risk and maximize you speed at the track, you should keep a careful eye on bottom bracket drop and crank arm length when choosing a bike for the track.
