After reading much of supposed benefits, especially for the knees, I
wanted to try shorter cranks. After much searching the web I finally
ordered the shortest set of
Thorns cranks (140mm) from St John Street Cycles
(highly recommended shop, and they delivery worldwide) and installed
them with 40/28T first on my Pashley
PDQ. I adjusted the boom length so that my legs where still only
just bent at the furthest point of the pedal stroke.
After a short period of acclimatising I am hooked. Spinning is much
easier (100rpm is easy compared with 90rpm before) and my knees feel
much better, but of course YMMV, and it is also still early days for
me. Speed at the moment seems the same as before, however since my
spring cycling I have had a 4.5 week holiday without cycling and also
fitted new tyres to the PDQ so the comparison may not be fair.
And I have bought another identical crankset for my
UPDATE August 2013: I fitted them to my PDQ in August 2010, then my
Zox in February 2012: see those pages for what I thought. And I kept
them for my Vortex 2012 and am still happy with them.
UPDATE Decemeber 2015: still in permanent use on Kett and
Vortex. Still loving them after 5 years !
UPDATE October 2016: still in permanent use on Kett but
experimenting with 155 cranks with low Q factor
Pros and Cons
Benefits: higher cadence and less knee bend, more clearance for
fairing, less risk of front wheel strike (SWB) or derailleur strike
(FWD lowracer). With less knee bend OSS handlebars can be set
lower. On a tadpole trike less risk of heal strike.
Negatives: cost: to buy new crankset or re-drilling existing
cranks and then propagate to all bikes you own.
- Before ordering first check how much boom and/or seat adjustment is
available on your bike: you will probably want to extend the distance,
e.g. 170 - 140 = 3cm further. If you are near the limit you may have
- You may want to choose a crankset that allows a good variety of
chainring sizes to experiment with what gearing works for you (some
people seem to stay with the same chainring sizes, other make
adjustments because of faster cadences). So far "Gain Ratios" have
worked for me.
Articles/forums threads (short cranks):
Articles (crank length in general):
Suppliers (esp. short cranks):
Maybe you have found a good crank, but need an extra chainring (triplizer) (can also be used to make a single to a double):
Suppliers (esp BMX 140mm (usually single chainring)):
- Thorn (UK): 38T BCD130, then fit any 74BCD ring
- IRD (US): 36T or 34T BCD110, then fit any 74BCD ring
- Red Clover (US): 42T BCD144 or BCD122, then fit any 74BCD ring (to 8 speed only)
- Also seen referred to online, but do not seem to be avilable now (maybe you can find them 2nd hand !): TA Triple Convertor, White Industries Limbo Spider, Avid Micro Convertor
- Sinz Racing "Export cranks":
ISIS (155mm up) and square taper (115mm up) / US based / I read the cranks can support 2 chainrings
- TURN3 Racing: 100-155mm, ship worldwide, single chainring ?, BMX, many colours!
- DansComp: US shop: various BMX cranks
- redline Microline Race / 110mm rings / 130mm up
- AC Mini LE / 110mm rings / 140/145
- (SJSC - UKP72 (Eur90) + P&P)
- Nimbus Giraffe Crankset: Unicycle chainset, 140mm / single chainset
- Nimbus Singlechain Giraffe: Unicycle chainset, 125mm / single chainset
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