Wednesday, December 1, 2010

Pedal selection and aero characteristics

It isn't very often that companies post raw wind tunnel data, but kudos to Speedplay for coming up with the goods... not only have they tested their product at one of the better tunnels, they've released the raw tunnel data that clearly shows their product outperforming competitors. While there may be some sources of error that could allow the data to show their product in a more positive light than the competitors (for example testing on a different day, with different atmospheric conditions and then not adjusting for air density), we're pretty sure that this is not the case.

The results shown indicate the following CdA's:

Speedplay4 0.237 = 11.35 m/s = 40.86 kmh (25.5mph) = 58:44 40 km (25 mi)
Speedplay3 0.242 = 11.27 m/s = 40.57 kmh (25.2mph) = 59:09 40 km (25 mi)
Shimano 0.243 = 11.26 m/s = 40.54 kmh (25.2mph) = 59:12 40 km (25 mi)
Look 0.243 = same as Shimano

That's 28 seconds faster over 40 km, and a pretty surprising result for the 4 hole cleat and 4 seconds for the 3 hole cleat. Also it isn't 33 seconds faster over 40km as claimed by Speedplay ... but that depends on the input parameters you use to do the calculations (in the above case 0.004 Crr, 85kg, 0 slope, 250w, 1.226 air density), but it is in the ball park.

With the bottom of the line speedplay retailing for around $150, this is quite good return on investment at $18 per second (4 hole), and not so good $37.50 per second for 3 hole.

Now I'm a bit intrigued as to why there is such a difference between the 3 and 4 hole mount systems... I suspect it has a lot to do with the way that the 4 hole system requires less bits to mount and therefore makes a lower profile underside to the shoe. As the following graphics (copyright Speedplay) show, there is probably at least an additional mm, perhaps more of material under the show with a 3 hole system. Which means, of course, that you may need to look at some new shoes as well to get that time difference.


You can read more about the Speedplay testing:33 seconds saved

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