Q. Is there a formula which factors in the weight of the rider to allow you to chose the correct cassette and chain ring? My reason for asking is that I weigh about 200 lbs and 6 ft 3 inches tall. I am currently using a compact chain set 50/34 with a standard 25/12 cassette. When cycling with some (lighter) friends recently in the hills in the Dordogne there was a lot of chat about gearing etc. Because of my weight I was obviously having to use more power to maintain the same speed as my friends on the longer climbs of about 5 miles. Ironically they had 28/12 cassettes on their bikes whilst I had the advantage on the flats and gentler gradients.

It got me thinking that if I could have gone to a lower gear and used a higher cadence I could have maintained the same speed and maybe used similar power to my lighter friends? Then the conversation went to crank length (mine is 175) and the whole think started to seem overly complex with too many theories and a cafe seemed the best idea! - Bill

A. A complex question, but these comments may help to make it a bit clearer.

1. Let's assume you measured your power output at the back hub. That tells you how much work you are doing (work done by your leg muscles - generally expressed in work/minute or watts). Training is the way to increase your total power output (per minute).
2. Assume you are putting out your maximum effort and producing a certain number of watts. You can deliver this power at multiple cadences. If your cadence is higher, the work per stroke is less, but total work per minute as measured at the rear wheel is the same as if you used a lower cadence with more work per stroke. You are not going to get "more power" by spinning faster. The reason you are going slower as you go up the hill (at the same work/minute output) is that you are not only working to move the bike forward at a set speed but also doing additional work to lift yourself and your bike up the elevation of the hill.
3. The reason I encourage riders to spin at a faster cadence (90 - 100 rpm) is that there is less stress on your knee per revolution (remember, assuming a similar work output per minute, a faster cadence = less work per revolution = less stress on the knee joint, than a slower cadence while maintaining the same speed).

   An example might help. I have found the calculators at the Analytic Cycling website to very helpful in sorting out questions such as this. Assuming you use the basic assumptions suggested on this webpage, and only change the cadence, you get the following:

   • 60 revolutions/minute = 260 units of force on the pedal
   • 75 revolutions/minute = 208 units of force on the pedal
   • 100 revolutions/minute = 156 units of force on the pedal
   Thus maintaining the same speed (work output) you get a significantly decreased stress on the leg (and knees) at a higher cadence.

4. Crank length is beyond me. A longer crank arm acts as a longer lever to allow more power per stroke, but again you will get more stress on the knee per revolution and I am not sure you deliver any more overall total work per minute to the rear hub than with a shorter crank and a faster RPM.
5. Heavy guys generally do better on the flats as they have more mass (and strength) per square meter of body surface area facing into the wind (which is producing resistance) than thin guys. But when you climb, you lose the advantage as you have to pull so much extra mass up the elevation gain. Basically this means you are probably putting out more work/minute) watts than your buddies and can capitalize on this on the flats. But then on a hill, you still are putting out more work per minute than you riding group, but now have the disadvantage of needing to use more of it to move a bigger mass up the grade. (see the section on energy requirements of cycling).

I was fine on gentle to average climbs because I could maintain a cadence of 90 but on any long steep climbs this would drop to 60 and I found it hard work. Using Sheldon Brown's tables I could see that a cadence of 90 on a 29 ring gave more speed and was easier on the legs than a cadence of 60 on a 25 ring. So for the mountains I have a cassette that allows me to do this which helps get my 90 kgs up the hill! Thanks again.