tholub said:If short cranks and crazy-high cadence were more efficient for racing
than long cranks, higher gearing and lower cadence, Tour de France
riders would be running 110mm cranks, and lower gears, too. The fact
that they don't, after 100+ years of equipment refinement, says
something about human physiology.
I think the fact that crank lengths for bikes vary between 165mm to
180mm stems more from the fact that bike manufacturers don't like
having 10 different crank lengths to produce, rather than optimising
efficiency for riders. There is less than 10% difference in crank
lengths, yet I'm sure Tour de France riders vary in heights by much
more than that. Think Pantani vs Ullrich or suchlike. There are many
more gears to choose from and probably that makes up for some of it.
I'm keen to shorten the cranks on my bike to 150mm because I think with
my height and short legs, I'm better off spinner at high cadence. And
long cranks are hard to spin even in a low gear.
From my experience, I feel much less tired spinning a Coker with 110mm
cranks for extended periods, than riding the longer 170mm cranks on my
roadbike for the same amount of time, even though I always use a low
gear on my roadbike. I'm sure the short cranks are much more efficient
for my short legs.
As far as RTL gearing goes, you really have to think of the geared 29"
Schlumpfs as a 43.5" gear, not as a two geared unicycle. In 29" mode,
it is practically useless for road racing unless you go with Japanese
style 50mm cranks. It is likely faster than a fixed Coker only for
steep inclines (say 15% or more). Of course you could try pushing a
43.5" gear with 50mm cranks on- but it would work well only on a
downhill, as there is not enough leverage to get good speed on it even
on the flat. For most people though, I think if you stuck, say, 125mm
cranks on a 29" Schlumpf, you're going to be stuck in the 43.5" gear
the whole time. Even if the terrain changes constantly, you're going
to lose a lot of time shifting- I estimate that you'd drop about 10
secs on a group if you had to shift. The 43.5"/125mm gear is
definitely faster than say a Coker with 110mm or even 100mm cranks on
the flat, but if the incline goes up to say 5%, I reckon a Coker would
be faster.
So the choice would be between 36" fixed Coker, 29" Schlumpf in high
gear (ie 43.5"😉, and the Coker Schlumpf (36" and 54"😉. I've not had
enough experience on the Coker Schlumpf to say if it is faster in high
gear mode on the flat. I think if you were to ride a 54" gear, you
would really only be using it on the gentle downhills or on the flat.
But you would need longish cranks which kind of cancels out a lot of
the advantage you had with a short cranked Coker. The fact that there
were riders favouring fixed Cokers over their Coker Schlumpfs at the
Unicon marathon kind of gives me the impression that you would need to
be very confident in the 54" mode to make it go faster than a fixed 36"
Coker/short cranks on the flat.
If I was in a team, I would use a fixed Coker 110mm for general
terrain, fixed Coker 125mm for very hilly terrain, and a Schlumpf
29"/125mm cranks in high gear for completely flat terrain.
My 2c worth.
Ken
--
GizmoDuck
The Uninam Tour 2008.....Hanoi to Saigon!!!
www.uninam.net
Email me for details.
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