Phil Burt, the legendary physio who's worked with Bradley Wiggins and Team Sky, breaks down why shorter cranks are transforming cycling—and why most people are making critical mistakes when they switch. We dig into the three adjustments you must make to your bike when dropping crank length, plus how to fix the three most common cycling complaints: numb hands, knee pain, and lower back pain.
Key Takeaways
- Dropping crank length from 172.5mm to 165mm requires raising your saddle height by the same amount (7.5mm) and moving it forward to maintain knee extension and capitalize on the aerodynamic gains—skipping this step wastes the benefit entirely.
- Shorter cranks open up your hip angle by about 3 degrees, reduce lateral hip movement, and allow you to sit further forward over the bottom bracket, which increases power output for most riders by 20-30 watts.
- Numb hands usually come from handlebar width being too wide (forcing your wrists into a compressed position where nerves are squeezed) rather than saddle height—aim for 38mm bars as the new standard instead of the old 42-44mm.
- Knee pain in cycling is rarely a core stability issue; it's almost always a positioning problem—ensure your saddle isn't too low or too far forward, and consider adjusting cleat position or pedal stance width if pain persists.
- Lower back pain responds better to position changes (especially longer cranks and proper saddle tilt) than endless core exercises—a time trial position with a higher, more forward saddle takes massive pressure off the lower back.
- Handlebar width should match your shoulder width and anatomy: most people solve problems at 38mm, broad-shouldered riders may need 40mm, but the days of 42-44mm being the default are numbered.
Expert Quotes
"Crank length is part of your gearing system...the benefit is you have more clearance, but it's mainly an aerodynamic benefit. If you've got a good bike fit, when you drop the crank length you move higher in the saddle because you want to maintain the good side of forward—and you get the hips more over the bottom bracket, which nearly always increases power."
"Core stability is bollocks...for the effort that you're going to have to put in off the bike to make your core better, you're going to have to do an awful lot of exercises that you probably won't do. I would far rather look at positioning. No amount of good core is going to get over a bad position."
"If you're getting numbness that is continuing permanently, you might want to hold on a minute—this could cause some medium-term damage. The nerves aren't like muscle; they get really pissed off when they get irritated and they take a lot longer to recover."