ASK RIDE… Does mounting a speed sensor on your fork create more drag?

Dear Ride

Pro’s spend significant time and effort on aerodynamic setup of their bikes.  I realise this is more important on TT rigs, but (to me) it seems counterintuitive to position the speed sensor forward of the front fork on their standard racing bikes as many of them do.  Do they have data to suggest this setup creates less drag or no difference in drag (compared to positioning the speed sensor behind the front fork), or is there another reason?

Andrew (Melbourne, VIC)

Hi Andrew
I also asked myself this question, “do fork mounted speed sensors create additional aerodynamic drag?”. So during one of my cycling test sessions in the Monash University wind tunnel I tested it. The setup I tested was a typical speed sensor mounted on the front of a fork compared to the bare fork. The test was done on a bike and rider with both wheels rotating at the same speed as the tunnel air speed.
In summary the additional drag created by the unit I tested was very small, about 0.14% of the total bike and rider drag, compared to no speed sensor at all. This is equivalent to about 0.4 watts at typical race speeds when not drafting. So most of these units would typically have very little additional drag.
However it is much safer to place the sensor on the front of the fork for the simple reason that if it gets bumped the rotating spokes in the wheel will push the unit away instead of pulling it in to the wheel and maybe causing an accident.
Where the computer display is placed on the bars and its shape is a question for another time!
Having tested lots of cycling equipment and positions in the wind tunnel, I have learned that things are not always as people think and what the marketing departments would have you believe. It gets very individual with equipment and especially with position and the only way to know for sure is to test it properly. “One good test is worth a thousand opinions”
Happy (low drag) riding. Raoul
Raoul Luescher is the director of Luescher Teknik  a specialist in carbon and  sports technology.

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