Originally Posted by
Carbonfiberboy
Your knees won't get creaky if you've kept active all your life. By active, I mean like hiking, backpacking, climbing, running, biking, weights, stretching, etc. I've 73, wife is 70, knees are just fine. We both ride cranks in mm = 5.5 X inseam in inches. To get inseam in inches, stand barefoot against a wall, push a clipboard up against your pubic bone, measure to the floor. It's not your pants size.
If you haven't been "active," get after it now. It's never too late.
There are millions, literally millions, of people who's knees got very creaky despite doing all the activities you mention as being preventative. I'm one of them. There is much more to it than your small sample size evaluation has determined. And, I'm not trying to be argumentative, but it just isn't practical in 2019 to try and follow prescribments for something like crank length. Cranks come in 170mm if you are lucky. I75mm if you are not. 165mm if you were a wearer of animal fur in a previous life. 172.5?? GT_OH. Changing a crank from what the manufacturer of your bike has thus decreed will be expensive if you cannot do it yourself, a hassle if you can, and as a result, it
won't be done by millions, literally millions of bike owners. Formulas just create stress for people that fall outside of the parameters and don't have any way of fixing that. Or worse it sends people on a wild chase for the perfect crank length. One that they never actually satisfy though they may try and convince themselves if only to justify all the money and/or time spent at it.