Track Cycling’s Strange Quirk

As you watch this Sundays Hour Record attempt by Bradley Wiggins, bear in mind that no part of him, or any static part of his bike has actually travelled the Hour Record distance he sets. It’s a quirk of riding on a velodrome compared to riding on the road, science gets involved & messes things up, during a quiet period of any hour attempt you can bore your family with this info, perfect cycling nerd territory. A long-legged rider has an inbuilt benefit from this, here’s why….

The Banking Effect

Let’s take a hypothetical vertical wall of death you may have seen motorbikes using as an example. This wall of death has Brad Wiggins cycling round it, but it’s quite a small diameter wall of death, so his head is sitting exactly at the centre of rotation. Even though he’s having to ride at 55kmh to keep going on this vertical wall, his head isn’t really going anywhere, he barely feels any wind there at all, it’s just rotating on the spot, causing little or no aerodynamic drag. The only point travelling at 55kmh is the point his tyre touches the wall of death. So Brad’s body or bike frame isn’t actually travelling at 55kmh, the fastest static point of his bike is his bottom bracket, which is travelling less distance than his bike computer would tell him.

A track rider, banked over on a velodrome experiences a similar, but not quite so dramatic effect. The riders body travels at a slower speed on the bankings than a computer measuring wheel rotations would indicate. Consequently, if an accurate GPS unit was affixed to the handlebars it would also read less distance & a slower speed in the bankings than the timekeepers would tell you, there’s nowhere on a bike you could fit a GPS unit that would record the exact track distance covered.

There’s aerodynamic consequences from the banking effect, Brad’s body will be causing more aerodynamic drag on the straight than it does on the bankings. His body’s air speed is slower in the bankings than on the straights, even though his track speed is the same. So as a rider gets taller, their effective body speed reduces on the bankings. It also makes wheel choice & even bottom bracket shape are more important than it originally seemed, as that as close to the point of consistently maximum speed as you can get, that point travels fastest for longest in the Hour Record.

‘Analytic Cycling’ Study

The excellent ‘Analytic Cycling‘ website, contains a wealth of information for cycling geeks, they’ve done a study using the geometry of the Dunc Gray Velodrome in Australia. The test is based on a flying 200m time trial effort, so our distance are not based on a full lap, but include a full banking & one partial banking, so our reduction in distance the centre of gravity travels per lap is more than shown here.

The model they generate shows that even though the track distance is 200m (199.99m), the distance the centre of gravity travels is about 3m less (196.7m) at a pace equivalent to a 14.166 second over 200m. This also shows that there’s a 0.3 second advantage gained on their baseline model, caused by the leaning affect & the riders centre of gravity not travelling as far as the track distance. In the next test the speed is increased & we find that the distance the centre of gravity travels reduces again, as the rider leans in more, essentially cutting the corner yet again. The final test shows that a rider sitting 200mm higher on the bike, with longer legs, also reduces the time for the 200m based on the same power & reduces the distance travelled even further.

So in summary, a taller rider (or one with longer legs to be precise) travels less distance each lap than a shorter rider, they benefit from the leaning effect of the banking, it reduces their time for the same power output. If the additional wind resistance from the longer legs can be minimised, a taller rider (such as Wiggins) has a distinct advantage. It also means that the faster you go, the more benefit you get from this reduced travel effect, which may slightly counter the huge increases in wind resistance you get from increased velocity, anything is a bonus.

The Gist Of It

This is a bit of fun for cycling nerds, but it does show a measurable improvement in speed. Those with the analytic tools to make these estimations correctly have perhaps identified an ideal body type for a pursuit/hour-record rider. But not just on the aero characteristics they display on the road, but from how their body type translates to track cycling. It may be the case that similar to rowing, a certain size of athlete is particularly gifted at these very specific disciplines in cycling. I’m pretty sure British Cycling have got this sorted already, those team pursuit riders look very similar indeed. It looks like Brad’s centre of gravity travels approx 5m less per lap than his track speed, which would mean in a 55 km Brad only travels 53.9km, while if he rode 55km in a straight line on the road, his body would also travel 55km. I was always told “you’ll go quicker on the track than anywhere else”, this may have been true, due to the reduced distance & work required caused by the banking. All this does is explain a strange quirk of track cycling, which the cycling geek may like, others, well, they stopped reading a long time ago.

 

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