Drilling cranks for Dual holes

I think the sizes that Kris has now are sufficient.

What would be more useful is for Nimbus to make some dual hole square taper cranks (I don’t expect Kris to, as all his products are ISIS based now).

I messed up the threads on the one side but love the 137/114 combo I made.

The park taps cut fine with a 1/2" hole.


hey, I stumbled on this little find today, it’s a pricey solution to different crank sizes, and it would raise the Q factor quite a bit, but boy, look at all those beautiful options :smiley:

also, it looks like you could make one pretty easily if you wanted to switch it around quite a bit.

anybody used these things? I wonder how they would take to a unicyclist’s abuse

109/127/150mm Cranks

This is an older thread but the info is still good. Today I added a third hole on my 127/150mm KH Spirit cranks. I now have 109/127/150mm cranks. I’ve been riding the 36er with 127/150mm cranks in the 127mm hole for a couple years and thousands of miles. I wanted to try shorter cranks for level road riding so I add the third 109mm hole on my cranks.

More pics and details here.

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And now the important question. How does it feel/compare with 127 to you?

such a pity you need to get off the uni and spend 10 mins to “change gear”

Jim, That is fantastic! your pictures would make a great “how to” for anyone interested in doing a similar project and it looks like you avoided all the silly mistakes that I made.

Well done sir!

As for taking 10 minutes to change gear… really it should take less than a minute. Much faster than swapping out cranks :smiley:

I did same some years ago (110/127/150) as Kris didn’t want to make them

I’ve put about 20 miles around the neighborhood on the 109mm cranks. I’ve only rode the 36er with 127mm in the past. Compared to the 127’s the 109’s are definitely faster but do require more pressure on the pedals, especially on hills and rough ground. I guess that my cursing speed increased about 10% and my all time fastest speed has increased too. On the road I can pull a 12% grade with no problem and shorter runs up to 17%. Free mounting is not a problem but does benefit from a slight adjustment in timing for a rolling mount.

I think for flat, smooth and long runs it is worth moving from 127 to 109mm. The 109’s also have an added training benefit, I can put more of a load/workout on my legs in a shorter time with the shorter cranks. On very long rides I would guess that moving from shorter to longer cranks may be needed when I start to get tried.

I’ve never tried the 150mm position, maybe I should do that sometime. I also did not change my seat height when I changed crank length, I might try that too.

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Great! I always wanted to increase my cursing speed.

10 posts were split to a new topic: Multi hole cranks - crank length for a 36er

How about another tyre with less roll-resistance? Like the slick road tyre vs the nightrider.

Im planning the exact same thing. I have a 9/17 but unsure at what drill to use?

I’d suggest using a 1/2" bit (assuming you don’t have a 33/64") in a drill press with some sort of vice or clamping device to hold the crank in place.

Getting the tap strait is just as important. If you use a drill press with a vice to drill the hole you can leave crank clamped and swap out the 1/2" bit with a small one to center the back of the tap.

1/2 x what?
And what drill size should I use?

1/2" by all the way through the crank.

1/2" would be the diameter of the hole a 1/2" bit will make. You then need to cut the treads with a set of 9/16" thread taps. Both right hand and left hand thread. You run the taps through the hole by hand using a T handle.

The size of the drilling machine doesn’t matter. A 6" drill press will work just fine, a bigger one would be better, and a milling machine would be better yet. I don’t suggest trying this with a hand-held drill.

If you don’t already have the equipment and cranks it would probably be cheaper to just buy multi-hole cranks. They weren’t very common with very limited choices in 2009.

I have the 9/16 tap - I remembered wrong with the 9/17 (imperial isn’t helping me). So I just need a ½" drill, right?

There isn’t a 110/137/165 crank out there. I would request the unicycle.com make lots of varieties as one can have too many to pick from :slight_smile:

You want to drill progressively bigger holes ending with 1/2"

using bits that look like this:

with a drill that looks like this:

with the crank held in place with a vice that looks like this:

Then thread them with taps that look like this:

They need to be 9/16, 20 tpi in both right and left hand thread. I’m sure there are other ones out there but the only readily available ones for the consumer market are made by Park Tool.

Typically you turn the tap using a T handle like this:

Haha thanks, thanks. But I know all that. I just want to be sure about the tap and drill sizes :slight_smile:

You most assume that I’m american? The 9/16 fine thread is an old British size, but I found a set.