Perspective... and perspiration

On another thread, Sofa gave details of his amazing 30km ride with m_extreme_uni.

The ride was 30 km which is 18.65 miles.
One uni was 26 inch, 102mm cranks. (ratio 27.6%). Time: 1:44.06 = 10.78mph average.
One uni was 29 inch, 102mm cranks. (ratio 30%) Time: 1:48.30 = 10.31mph average.

So that’s two ‘medium sized’ unis comfortably beating 10mph over an 18.65 mile course, mostly off road.

Today, I put that into context with a ride of my own on the Coker.
Credentials: I consider myself fit for my age (40) and reasonably experienced and skilled. Longest ride over 50 miles, several over 30, too many to count over 10. I guesstimate I rode 750 miles in the last 12 months, on a variety of unis, not counting time spent practising and performing on the 20.

So, my comparison goes:
36 inch wheel, 150mm cranks (33% ratio). Time 1:00.00. Distance 12.44 miles.
This was in almost ideal circumstances, with all but the first mile on smooth level tarmac with no traffic (I did laps of the National Water Sports Centre main rowing course.)

So in almost ideal circumstances, I averaged 12.44mph on a Coker. In reasonably difficult circumstances, and (I quote) “less than racing”, these two heroes were only about 2mph slower over 1.5 times the distance.

I reckon that on simple cross country, I’m averaging 10mph on the Coker, and if the ground gets anywhere near my limit of ability, that drops to around 8mph.

I finished today’s ride more slowly, doing 15,89 miles in 1:25 (approx.), bringing my average down to 11.2mph for the whole ride.

Once again, I salute these two heroes. There are only three possibilities:

  1. They are gods in human form,
  2. Or I am a lousy arithmetician,
  3. Or I am a lousy unicyclist.

Are you sure about the maths, I make it that a coker with 150 cranks is significantly slower than a 29er with 102 cranks and still slower than a 26 with 102 cranks. You’re going up to a wheel size 1.2 times the 29er, with a crank size 1.4 times as long. So you should expect to be somewhat slower.

I took 3hrs45 to do a 30k last month, that was all technical singletrack on big hills and I had 150s on my 26", but even so, it isn’t anywhere near those speeds.


Thanks for the praise!

I’m gonna have to go out and try that out on the Coker. Next year I’m doing the 60 for sure!

I’m sure about the maths, and I’m also sure about yours. They’re both right as far as they go.

However, your (welcome and reassuring!) response seems to accept the so-called ‘constant foot speed hypothesis’ at face value. Put simply: if you halve the length of your cranks, you will double your rpm, or vice versa.

I don’t think it works like that, except within a fairly narrow range. I certainly found 89mm cranks no faster than 102s. Someone in this forum (John Foss?) said he’d achieved higher speeds on a 24/125 than I’ve ever achieved on any uni.

But assume the CFSH holds…
The 26 in the race had a ratio of 27.6%
My Croker has a ratio of 33.3%
Then I should go at 82% of the speed of the 26.

I managed 12.44mph in ideal conditions. Subtract, say, 30% for the conditions described in the 30km race, and I’d be averaging 8.7mph (experience shows this to be reasonable).

8.7 is 82% of 10.6, so yes, my performance on the coker is comparable to Sofa/M_extreme_uni on the 26. Almost identical, in fact.

Except that the 26 lacks the rollover factor which allows the Coker to ignore small-medium irregularities in the track, and except that maintaining a fast cadence on short cranks is more demanding than maintaining a slightly lower cadence on slightly longer cranks.

I’ve ridden a 24/102 and a 24/89, and (briefly) a 28/102. I know if I had to do 30km fast on rough ground, I’d choose the Coker/150 (or possibly a Coker/125).

Thanks for the morale boosting alternative reading of the maths, though! ;0)

Not dead yet.

I’ve done a bit of riding on a 29 with 110s and on easy terrain and on road I was a bit faster than the coker with 150s, although maybe not quite as much as I should have been.

For medium technical riding I’d ride a 29er with 125 cranks personally, I don’t have the leg strength to get shorter cranks over anything difficult and the 29er gives you a big advantage on anything twisty, it’s so much easier to turn.