Skin is slow. That’s why we’re seeing more and more cycling companies opt for longer sleeved jerseys, even for road racing. Many triathlon race suits are now made with sleeves, and of course, time trialists wear long sleeves. But what is it, exactly, that makes skin slow?

The bottom line is: skin surface is too smooth. On a blunt shape — a shape not optimised for efficient aerodynamics — the surface of an upper arm, for example, will create a smooth stream of air close to the surface. This smooth stream is not able to “make the turn” when going past the arm and will detach from the surface. This will create a large vortex region of negative pressure behind the arm.

SmoothSphere

On a rougher blunt shape, the boundary layer is turbulent, which means that it is better mixed, almost like a foamy layer of air. This turbulent layer adheres better to the surface and detaches much later than the smooth layer, thereby creating a smaller vortex behind. This reduces the drag from the negative pressure region behind the arm.

 

However, while skin may be slow, we have found that WRINKLES are even slower. ┬áSo before you go buy your aero, long – or short – sleeves, make sure it fits tight, without wrinkles when you’re in race position.

farisalsultan

At least Faris Al Sultan’s outfit doesn’t have too many wrinkles. But that’s a lot of skin.

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Luke McKenzie’s race suit was aero optimized using Alphamantis Aero Testing technologies. Note he has skin covered on the upper arm area, and no wrinkles. Photo credit: Herbert Krabel with Slowtwitch.

 

Photo: Fotoreporter Sirotti.  Note the long sleeves extend over the hands to limit potential drag area.

Photo: Fotoreporter Sirotti.
Note the long sleeves extend over the hands to limit potential drag area.