Bicycle Crank Length: Finding the Crank You Need

Sure, there are different length cranksets available out there. Many road cranksets come in 170 mm, 172,5 mm, and 175 mm. A few even come in a 180 mm and a 165 mm. Wow! What a range to choose from!

Hooey. If you will go get a ruler with metric markings on it and look at how much difference we're talking about, you'll see these are insignificant variations in crank length. If you happen to be an individual of nearly average size, you can find what you need; but if you are tall or short, these variations are simply a joke.

If you are very tall or very short, you have probably been stunned at the length crank called for by this formula. My own 34-inch inseam size calls for a 186 mm crankset, and I'm not exactly NBA material.  Even if you understand why such sizes are needed, just where would you get such a critter? Good question.

Long Cranks

In the case of long cranks, getting past 180 mm is a serious problem. In the 1980's, I managed to find a French TA 185 mm crankset; the length is excellent, but it's definitely a light duty crank and the chainrings were garbage -- I broke every one I installed.  I eventually made an adapter to hold Sugino chainrings, which solved that problem. Better chainrings are made by Stronglight that fit this crank without an adapter, but they are difficult to find in the US. The only place I've seen them here is fitted as original equipment on some Schwinn touring bikes. Most shops chose to carry the lousy TA chainrings as spares for the Stronglight!

The chainrings that were fitted to Viscount bicycles back in the 70's will also fit the TA crank, and are durable -- but the design is heavy to the point of being wasteful.

If you need longer than 185 mm, the options are even more limited.  Check out the High Sierra Cycle Center at  They also offer a variety of products for people with unusual problems such as one leg longer than the other.

DaVinci ( offers cranks from 150mm to 200mm.  They specialize in tandem bicycles, but their cranks will work on any bike.  They even offer a 3-hole crank that'll give you three lengths in one, just choose which hole to screw the pedals into.  That's primarily to fit children, since the difference from one hole to the next is waaay too far for any sort of minor adjustment.

Another source is Heiko Brechtel's custom crank business in Germany; you can visit it at  Heiko claims that my web site was an inspiration to start his business!

You can also visit Zinn Cycles, Inc., at; Lennard Zinn offers CNC machined cranks in any desired length.  In fact, Zinn offers entire bikes designed specifically for the taller rider (Zinn himself is 6'6" and a national champion, so he knows what he's doing).  Kieran Cox ordered a bike from Zinn and sent this report:  "Zinn's work is flawless.  The bike came out better than I thought it would.  I questioned the expenditure a few months into it, but after seeing the finished product it was worth every penny."

The advent of ATB has provided a better selection of long cranks than there used to be. Many of these long cranks are inordinately expensive, unfortunately.  They also look like ATB cranks, and that may be objectionable when mounted on a road bike.  However, they generally can be mounted on a road bike, possibly requiring the omission of an inner triple sprocket.

Profile Racing offers aluminum cranks (look like road cranks) in 160 mm to 180 mm lengths, but they also offer 4130 Chro-Moly (industrial-looking) cranks in 160 mm to 190 mm lengths plus the option of "custom lengths".

Azonic offers 4130 Chro-Moly cranks in 165 mm to 185 mm lengths.

Torture Tools offers ChainSaw cranks in 160 mm to 210 mm lengths.  Unfortunately, apparently that site is only viewable in German, so you may need a translator to place an order.

Short Cranks

Some of the sources for long cranks listed above can also provide short cranks.  But the short rider has more options yet. Obviously, cranksets from children's bikes are available, but finding one of acceptable quality may be difficult. There is one other possibility, though: shortening a longer crank.  It is possible to saw the ends off of a crank and drill and tap new pedal holes, making a shorter crank.  If a good quality crank was chosen to begin with, this mod will typically leave it lighter, stronger, stiffer, and structurally sound.  Combined with the fact that the smaller riders also tend to be lighter, crankset stiffness or failures are not concerns unless you really screw up the modification.

The trick is to choose the right crank to modify.  You want one with broad arms, not arms that are necked down a lot just inward of the pedal. If they are broad enough in this area, you can drill new pedal holes without weakening the crank; if the arm is narrow where the new pedal hole is drilled, it may end up with very little metal on either side of the new pedal hole.

The crank must also be long enough. Since the new pedal holes must be far enough inward of the original pedal holes to leave enough metal to surround the new holes, a crankset cannot be shortened by less than 19 mm or so. If you start with a 170 mm crank, the longest crank you can create will be a 151 mm. For this reason, if you need something in the 155 mm area, you need to start with a 175 mm or longer. If you are trying to make a 160 mm, you will need to start with a 180 mm. Fortunately, since 165-180 mm cranksets are commonly available, this shortening process means that any length up to 180 mm is available.

The last remaining challenge is finding a 9/16" tap in left-hand thread. They are available from outfits that sell bicycle tools.

Once you have taps, cutting off the crank arms, drilling and tapping new pedal holes, and grinding and smoothing the ends of the arms is all relatively easy. You can have a machine shop do it to get the pedal holes perfectly straight and true, or you can do it by hand; if done by hand and the pedal axles don't come out perfectly parallel to the BB axle, it's possible to mount one end of an arm in a large vise and forcibly bend or twist the arm a little to align the pedals.

Highpath Engineering in Wales provides a crank shortening service and stocks most sizes available.

Ken Olstad points out that Bikesmith Design & Fabrication in Minneapolis, MN also offers a crank shortening service.


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