Cut down cranks

I’ve been riding my 29er around with 125mm cranks for some time now. I like the combination really well but I’ve been curious about slightly longer cranks.

Several years ago I modified a set of 177.5 Suntour mountain bike cranks to use for MUni. I haven’t used them for a long time after discovering that I prefered 170’s for MUni so I decided to cut them down to 140’s and put them on the 29er. I’ve added a nested ablum with a couple pictures here:

There’s a big difference between 177.5mm and 140mm as you can see! I wish the cranks were wider in the area I put the new holes. It looks like there’s a chance of them cracking at the holes. I’ll just ride them till they do.

I put the cut down cranks on this evening and went for a ride on my usual route of mixed dirt, gravel and pavement but tonight with the added bonus gusty strong winds. The extra length does make for better control. Just as important though, is the greater “Q” factor, or offset, of the new cranks. They put the pedals about 3/4" farther apart than the old 125’s. This really helps me since I must be kind of “splay footed” - if that’s what it’s called when your toes point outward. My right foot more than my left. With the 125’s I had a hard time riding with the ball of my right foot on the pedal without my heel hitting the crank on every revolution. I had to either ride with my instep over the pedal or unnaturally twist my heel outward. That bothered my hip joint right away.

The new cranks with the greater “Q” are much more comforable and I’m able to easily pedal on the ball of my foot now. It’s funny that I’ve never had a problem, that I know of, being “splay footed”. All my bikes have a spot of paint worn off the right chainstay where my right heel brushes by but I’ve never actually felt my heel doing it and never really thought about it.

Steve Howard

Thanks Steve, that was really interesting.


Did you have to cut them? If you didn’t cut them, couldn’t you use both holes to vary the length? If you didn’t cut them and you tried to use it would there be any problems, ie. decreased strength because of the BIG holes, or would the extra metal get in your way?

It looks great though. I like the finish.


I suppose it would have been far too easy just to buy some 140mm or 150mm ready made cranks?:wink:

Roger at sells cut down bicycle cranks in sizes down to 89mm.

Mikefule -

MUCH too easy to just buy cranks … Besides, I really enjoy tinkering around with this kind of stuff. If my cut down cranks break at the 140mm hole I’ll just redrill them and cut them off some more. They might end up even shorter than 89mm. If they do I’ll send them to you to help further your crank length experiments!

daino149 -

I’m sure the crank arm would break at the new hole if I’d have left the crank un-cut and used the old holes at 177.5mm. The idea of multiple holes in cranks has been done and should work if the crank is properly designed.

Steve Howard