33T single speed crank?

[ibie1983]

I saw this seller selling these single speed cranks on Ebay as per link below.

http://www.ebay.co.uk/itm/ALLOY-SINGLE-SPEED-BIKE-CRANKSET-SINGLE-3-32-CHAINSET-SQUARE-TAPER-FIT-CRANK-/281229806590?pt=UK_sportsleisure_cycling_bikeparts_SR&var=&hash=item417a9a4bfe

How do you go about choosing the correct number of teeth crank for your bike? Also why is he selling a 33t crank? Aren't cranks supposed to have an even number of teeth?

Thanks

[nfmisso]

The number of teeth on the chainring divided by the number of teeth on the cog at the back provides the gear ratio. There can be any integer number of teeth on either above some minimum; which around 9 teeth. Practical considerations push the minimum number of teeth higher. Even or odd does not matter. A common road double combination is 53 & 39 for an example.

Why 33T? - someone wanted it, and thought that there was sufficient market to offer more. Could be for BMX application.

Choosing - depends on fast you pedal, your strength to mass ratio, need for climbing, outside diameter of your drive tire. Here is a calculator: http://www.bikecalc.com/cadence_at_speed

You still have to determine your strength, need for climbing, etc.