QUESTION: I’ve heard that it’s better for knees if you spin a lower gear on climbs rather than mash a big gear. Why is it harder on the knees to pedal at a slower rpm? What about pedaling slowly when out of the saddle? — Jim M.
RBR REPLIES: Good questions! The important element here isn’t the total time taken to climb the hill, but rather the total load on the knees during any given pedal stroke.
If you ride up the hill in three minutes at 80 rpm, you’ve divided the total work into 240 pieces (3 x 80). It takes the same amount of work to climb the hill in three minutes in a bigger gear at 60 rpm, but the work has been divided by only 180.
So, there’s more work being done on each pedal stroke when you have a lower cadence in a bigger gear. There’s more stress on the knee on each pedal revolution. Make sense?
Standing up definitely takes stress off most knee problems cyclists are likely to have. It’s a good choice when you’re climbing with someone who is slower and uses lower gears. It gives you a chance to stretch your legs and take weight off your rear end, and the pressure off your lower back.
The real driver is most bikes have too long of crank arm lengths. Shorter or right sized crank arms allow you to naturally spin faster due to the shorter angular distance travelled in each revolution.
i understand that being a fitter you will say to get a proper fit but would it be wise to just buy a shorter crank or does it need to be according to some measurement in the body?.
I find that my optimum cadence varies with the gear I’m in. The higher the gear, the higher the cadence I need to “stay on top” of it. Conversely, when climbing, if I try to maintain a high cadence, my legs lock up. I’m just not comfortable using a Chris Froome or Primoz Roglic type cadence. The lower the gear, the lower my cadence needs to be, to a point. Unless I’m out of the saddle and really struggling, my cadence is typically 60 or more when climbing.
Consider a vehicle. To high a gear and rpm’s drop causing the vehicle to bog down. To low a gear rpm’s will be to high and red line the engine. The right gear and rpm the vehicle will glide up the hill effortlessly and efficiently.