Many years ago when I was ~15 I rode road bikes and pushed myself pretty hard. I developed knee problems and was told by sports doctors that I should be using a shorter gear and turning ~100RPM cadence. Those knee problems eventually forced me off the bike. Now 20 years later I've been slowly getting back into it over the last couple years - not really a whole hearted comeback since free time is nearly nonexistent with a young family.

With the riding I've done one knee feels perfect the other is maybe 90%. I can feel something is not exactly right but I definitely wouldn't say it's painful. The effects don't last, as in my knee doesn't hurt after the ride or the next day, just the lingering feeling that things maybe aren't 100%. I've been keeping my cadence around 95RPM but I almost feel that in itself is putting some stress on my knee. The last while with the bike on the trainer I've tried slowing down to about 75RPM and I don't feel any more stress on my knee compared to 95RPM, maybe even a little less. But the 75RPM makes for a much more enjoyable workout. I feel like I can put some power down rather than spinning like crazy like running full speed down a steep hill if that makes any sense.

So I guess the question is: is 75RPM considered too slow of a cadence? or should I be sticking with the higher cadence given my possible or pending knee problems?