A bit mathematical but:

We all know that at a given cadence, a bigger wheel will go faster than a small one.

We all know that for a given wheel size, smaller cranks will tend to allow a faster cadence than larger ones.

We all know that the ratio of crank size to wheel radius (or diameter) influences ease of mounting, idling and hill climbing/descending.

So, what is the best combination?

Yesterday I hit a top speed of 13mph and averaged 7.18 mph on the 24 with 102s in a ride of about 1 hour.

Today I hit a top speed of 14 mph and averaged 10.16 mph in approximately an hour on the Coker - a 26 with 125 mm cranks.

The top speed bit surprised me. As the computer only records this to a whole number, it is possible I did 13mph exactly on the 24, and 14.9 mph on the Coker, but applying the principle of mediocrity, I have to assume that the top speeds are only about 1mph apart, and that the Coker is about 7% faster. (Yes, I know skill and confidence come in here, but I feel my level of each is broadly similar on the two unis.)

The Coker averages about 41% faster, though. This is not entirely scientific, as the routes were different, and the Coker ride included a straight 10 km of level tarmac - but it also included riding across a field in the pitch dark. The rides were roughly equivalent in difficulty.

The Coker wheel is 50% bigger than the 24.

The 24’s cranks are about 19% shorter than the Cokers. Say 20%

50% minus 20% of is 40%.

The figures are near enough that it suggests to me that within certian limits, a % reduction in crank size is almost identical in effect to a % increase in wheel size for top speed.

Anyone who’s followed this far, thanks. Comments anyone?