- appropriate size taps - 9/16" x 20 left and right hand threads. I use some from XTools, but Union and Park Tool make them as well. If you've already got a 9/16" 20 TPI right hand thread tap, then just buy a 9/16" 20 TPI left hand thread tap to complete your set for pedal threading;
- appropriate size drill - 33/64" (or 13mm) for 9/16" threads (you may be able to get away with a 1/2" drill, but use a 33/64" or 13mm drill if you've got one);
- drill press (a good milling machine is even better).
Note: you must shorten the cranks by at least 23mm, so a 175mm crank will become at most a 152. This makes it difficult to produce a 160mm crank as you need to start with 180mm cranks, which are hard to come by, particularly in a design suitable for shortening.
- a great article on crank shortening including pictures of a smart DIY jig for doing the job using a drill press;
- Highpath Engineering and Bikesmith Design will shorten cranks for you;
- Shortening cranks the cut-and-shut way - cutting and welding them back together ;
Old LX cranks
I shortened some old 175mm LX cranks down to 140mm for use on my daughter's bike:
I would not recommend shortening these cranks for adult use as the crank arms narrow down. As a result, there is less meat around the new pedal hole. This is not a problem for a 30kg rider.
388g for 140mm short crank arms:
One the bike:
Truvative FiveD cranks
I've got some Truvative FiveD cranks on my tandem and they look like perfect candidates for crank arm shortening. The crank arm is a consistent width and thickness and remains perpendicular to the bottom bracket spindle for a distance that means you could shorten these down to perhaps 130mm.
I got a second hand pair of FiveD 175mm cranks and shortened them to 150mm. Worked well.
Other suitable cranks
- SRAM S600 cranks - these appear to have plenty of meat around the crank holes and look like they have parallel faces front and back. Shortening by up to 40mm looks do-able. They are available in square taper or power spline (P-spline) versions and feature 104BCD and granny mounting options.
- Shimano Zee cranks - looks like then can be shortened down to 115mm.
- Most recent Shimano Deore cranks;
- Truvaitiv Firex and Isoflow
- Suntour XCT - plenty of meat with non-tapered arms. Looks like you could quite short with these.
Three basic categories of cranks are not suitable for shortening:
- cranks with hollow crank arms. eg. Shimano Hollowtech II cranks, Stylo OCT, SRAM higher end models;
- cranks which narrow down too much or which lack sufficient material at the back of the crank arm for the pedal thread;
- carbon fibre crank arms;