Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

Crank Length

Go back more than fifty years and road bike geometry was a bit different from what it has been in the period since. Bikes got taller with increasing sizes, but they barely got any longer – instead this seemed to be left up to the longer stem. Even with stems up to 14 (or more) centimetres long, big guys often look pretty squashed in older race images. I guess it proves you can adapt to many things.
Currently one would be shopping smartly if one looked for a new bike based on top tube length (or reach). The gap between sizes for most companies is consistent for both the frame’s height and length. That is, each size is 2 cm taller for each size up (in traditional sizing at least) and each size is a consistent X mm longer (with X being model dependent around 15 mm) for each size up.
One thing that didn’t change in the old days was crank length. Occasionally I see a non-170 mm crank on an old gear website, but that seemed to be the size that most things came in. My first good bike was a 60 cm frame with 170 mm cranks. My second bike was a 61 cm frame with 170 mm cranks.
And then one day someone decided that crank length mattered. But only for those in the middle of the size distribution. Check out the size range offered by most manufacturers. It amounts to three sizes: 170, 172.5 and 175 mm only. Move up to the current 12-spd Shimano Dura Ace and you can go both shorter and longer – but not by much (160 or 165 mm and 177.5 mm are your choices). On the Campagnolo side of things, only the basic three lengths are available regardless of price (Super Record is super expensive but has three choices). This wasn’t always the case. I have had numerous 180 mm Dura Ace cranks over the years (from 8-spd, 9-spd and 10-spd models) and I currently have two Campagnolo 11-spd cranks in 180 mm (one Record and one Super Record).
If you require short cranks, there are numerous choices for children that function fine for height challenged adults. If long is what you want, then you are in trouble. As much because off-the-shelf frame won’t work with cranks much longer than 180 mm as because of the difficulty in getting anything longer than 180. Lennard Zinn has you covered if you are really tall and want a suitable bike because he can make both for you – cranks up to 230 mm long (I think) and commensurately higher bottom brackets to avoid driving those cranks into the ground when pedalling.
I cannot understand how anyone can think “My company needs to make cranks in different lengths because legs come in different lengths” but we aren’t going to make crank lengths representative of leg lengths. Where adult leg lengths cover about a 25% range, the cranks cover around a 2.5% range. There is no explanation that makes that sensible for me. Except that the range is SO small and 3 sizes is so few that it is possible to stock 3 SKUs and fit them on any bike. The bike industry runs afraid from discussions of biomorphology and optimal crank length.
Reality suggests that a 50 cm frame should have 165 mm cranks – possibly a bit shorter. And that 62 cm frame should have 190 mm cranks (possibly a bit longer). What we get instead is each frame size up receives a slacker seat tube angle. This moves the riders pelvis backwards in relation to the pedals so that the riders legs sit behind the pedals similarly for each bike size without the desired extra crank length. Basically, it is a cheat. All sizes of riders should be on the same seat angle, but have ever-higher bottom brackets to go with ever-longer cranks as the size increments up.
When I got my Trek Checkpoint, I had a full Record group to hang on it. Only the cranks didn’t fit. The frame was designed around Shimano cranks only. The offset in Shimano cranks is all at the axle. In SRAM cranks, the offset is in the middle of the crank in a gentle curve. For Campagnolo, the offset is near the pedal after the crank runs straight out of the axle. The bulge in the offside chainstay hit the Record crank. I was able to use the Record cranks on my old Madone (the one that lives in the trainer) and bought some new-old-stock SRAM Red GXP cranks for the Checkpoint in the longest size SRAM makes – 177.5 mm. It is only a single size, a tiny difference, but I never liked the 177.5 cranks. They always felt a bit wrong.
Then they broke. I was simply going to replace them, except a year later and SRAM hasn’t been able to come up with a solution. They were going to send me some Quarq cranks in 177.5 mm length with the old GXP axle and old 3-bolt interface for the spider. But they didn’t have a matching spider. So my bike shop found a spider. When the cranks finally arrived, they were 8-bolt interface. The spider won’t fit. They sent the cranks back but got stuck with the spider. A part they don’t need and might never sell. SRAM is all about the DUB axle these days and that 29 mm axle won’t fit in a Trek BB90.
What about other options? Rotor once made 180 mm cranks, but it appears not to have done so for many years. At least one generation. I didn’t go with Shimano in the first place because there is a general sentiment that Shimano and Campagnolo do not mix. Now with the 12-spd new generation of Shimano parts, there is no 180 mm crank in the parts list. SRAM still makes 177.5 mm, but I know I don’t really like that length and non-DUB axles are harder to find. Campagnolo abandoned anything longer than 175 mm when they went to 4-bolt spiders about 2015. Miche, an Italian brand that makes a lot of bike parts, only makes the 3 lengths from 170 to 175 in their racing models (and shorter for kids).
Lightning, in Los Angeles California, makes some very fancy carbon cranks with a bolt on spider and a 30 mm axle stub on each arm. Like Campagnolo cranks, each half-axle stub bolts together inside the bottom bracket. They have a Trek BB90 solution that involves very tiny bearings. I have read many stories of premature bearing failure and constant creaking from these very expensive cranks. At least they produce cranks from 150 mm up to 190 mm, which is a vastly superior range to most brands.
In the past 5 years all my mountain bike cranks have gotten shorter for better ground clearance as bottom brackets have gotten lower for handling. I had a trail bike until 2017 that ran 180 mm cranks. They were great for pedalling up open fire roads and the like, but I got so many pedal strikes on singletrack. The Slash I got in 2018 came with 175 mm cranks, but the shop arranged for me to get 170 mm cranks. A change made by 2019 for all Slash models. Then I replaced the short travel bike in 2020 with 170 mm cranks; partly so they’d be the same as the Slash, partly to ensure better ground clearance. My personal corollary on crank length is my new hardtail, which came with 175 mm cranks. I get more pedal strikes than I would like and think that I should replace the cranks with some 170 mm variants. As is typical of DH bikes, my new DH bike came with 165 mm cranks for even more ground clearance. This is the same as my old DH bike, but because I haven’t ridden that since about 2015, it is long out of my head.
My latest thinking, then, about the Checkpoint cranks is to run with 170 mm. Maybe that is the compromise that has to happen because there just aren’t sufficient choices in 180 mm cranks. I’d be happier if I could swap all three road bikes over but maybe it won’t matter? I’m considering something inexpensive (like Shimano 105) in case I don’t like the 170 mm length on the road bike.