Minneapolis frame builder Matt Appleman has gone deep into the subject of crank length, and he’s just not quite sure, but he thinks there’s a fair chance the cranks on your bike are not the optimal length for your legs. He discusses this in Seminar Room 123 on Sunday March 17 at 1:30PM.
The main point here is that crank length can have a big impact on your pedaling comfort, and a growing body of cyclists believe the standard industry offerings of 170, 172.5, and 175mm cranks don’t cut the mustard.
Just because it’s generally the done thing doesn’t make it the right thing. Look at what’s happened to gearing for road race bikes in the past 20 years. The pros now spin up the big climbs at a high cadence whereas for decades before they’d be heavily over-geared, painfully grinding up those long alpine climbs.
Key body issues related to crank length include how much your knees and hips flex, particularly at the top of the stroke. The idea is that more bend in the knee at the top of the stroke, means more forces across the knee joint as you push down on the pedal. Fit experts have noted that this can lead to pain at the front of the knee. It’s more or less the same story with the hip flexors.
While Appleman thinks many cyclists should be thinking about shorter cranks, switching from 175 to 170mm will be hardly noticeable. So he is now selling a range of crank lengths in his 2XR crankset project, from 175mm – 135mm in 5 or 10mm increments, then there’s a jump down to 100m.
The science is inconclusive about the optimum crank length for efficiency–how fast you’ll go for a given effort. There are a lot of variables to consider, there’s a wide range of body shapes, subjects would need a lot of time on the bike with each crank length to meaningfully compare differences, and you’d need a large sample population.
The science seems to be clearer though on the risk of injury. Less flexion is widely accepted as likely to be easier on most bodies.
Appleman reckons for this reason alone, most riders could benefit from shorter crank arms. Additional bonuses may include reduced risk of pedal strike, which is great for mountain bikers, and for the go-fast set there are aerodynamic advantages from a smaller frontal profile.
He’s still cagey about it though, and wisely so. “It’s a spectrum, a range, there’s no single ideal crank length,” he says, and suggests people should be looking for a knee bend angle around 60 degrees at the top of the stroke, and 56 degrees of hip flex.
Before you go out and buy a 145mm crank set from him, here’s something to keep in mind. Bike frames are designed around crank length, and this is why mass bike manufacturers would find it difficult to offer a wide range of crank lengths. “Once you adjust one thing then everything else changes: bottom bracket drop, seat tube angle, top tube length, seat height, and front wheel toe overlap.” You may need to make changes in a few places after changing your crank length, and for the most fortunate this is the perfect excuse to order a new custom frame!
Appleman has an article on his website with useful tips on how to determine the best crank length for your legs, and he even has a rental program so you can try out a few different options once you’ve installed the central components.
Built on a 30mm spindle, the 2XR crankset comes in five bottom bracket widths: Road, Adventure, Mountain, Mid-fat and Fat bikes. Appleman suggests this, “You can buy one and a half cranksets and outfit two bikes, and switch arms between bikes. That’s part of the design.”
Why that suggestion works is that only a 5mm allen wrench is needed to remove the crank arms. “There’s no custom lock ring or 15mm hex bolt that nobody has.”
It’s great for trailside repairs too.
