Quote Originally Posted by sarahspins View Post
I think a slower cadence puts more stress on your joints at 20mph than it does at 12mph.

It's the force, not the speed.

Climbing is when cadence is most likely to be very low, and it's also where there's automatically a large amount of force involved. In my actual riding, there's a WHOLE lot more force on my knees driving 65 rpm up a 15% grade at 5 mph than there would be, say, descending a 1% grade at the same cadence at 25 mph.

All other things being equal (grade, wind including whether or not you're drafting, road conditions, bike), then yes, there will be more force at a higher speed than a lower one - but all things are almost never equal, on a bicycle. That's why people spend thousands for power meters.