Originally Posted by
RiddleOfSteel
Ah, good ol' knees. I know this battle well. As a tall guy, it is common enough for us to run into issues, especially as we get older. I will still take being 6'5" 10 out of 10 times, though.
I think my sit bone plane+elevation point (on the saddle) to BB spindle was 34" before (add 6.8" to pedal top then) eventually working it down to just below 33.0" and now having it at just above 33.0" after having it at 33.0" exactly for a year or so. The goal is to bias against hyper-extension. From what I've understood, knee/leg pain or fatigue in the aft part of the leg (hamstrings, back of knee, etc) = saddle too high, and knee/leg pain/fatigue in the fore part (quads, knee cap, associated muscles and tendons around the cap) = saddle too low. This is, of course, a very rough method. My sit bone plane to BB spindle distance, when measured horizontally, is 11.5" or so (no more than 11.75", which it used to be).
Another thing not discussed here with regard to your knees feeling back is pedaling style and cadence. I used to be more of a masher, but the strain on the knees was no good, so I spin at 70-80 rpm and just change gears to keep me in that cadence range. I'm still not a true spinner and will never be, but I can do 120 rpm briefly and smoothly. Leg motion is always smooth, no knee flaring or kicking out. Where is the ball of your foot in comparison to the pedal spindle? Saddle fore/aft position is also critical to try and nail down (hence the above 11.5" measurement). You could always experiment with sliding things way forward or way backward and seeing how things are, keep the saddle measurement the same. Some people need a lot of set back, and that plays into bar/hood height etc, which is a whole other discussion.
I just put the balls of my feet directly over the spindle and then moved the saddle back until it felt OK, it ended up going back about as far as I took it down, 5/8”.
My body was confused as hell this morning, and had a headwind to boot. Halfway to work I stopped and slid the saddle back another 1/8” or so. It felt pretty good but I had to drop into the small ring to keep moving, which I almost never do. Watching the speed on my computer was heart breaking, 11mph uphill. My legs just wouldn’t go. Ride home was pretty nice, had a bit of a tailwind and was also able to use my 16t cog for a little while which I never use, wind or no. So 25 miles in, so far so good but man do my legs feel weird. The Raleigh was like a different bike. I felt like I was way lower to the ground even though it was only like 5/8”. I had to go a lot farther to get out of saddle. It for sure tracked a lot better through the corners and it was easier to ride hands-free, even on the some of the rougher back roads. But spin spin spin. It was weird. Riding that Fuji I had pretty much left it in 50/21 or 50/18 for the last 6 weeks or so, and I would typically spin around 85rpm give or take 5. I had to spin around 90 just to keep moving today. I don’t have a cadence meter or whatever, but Strava and a little math. I didn’t have any trouble spinning, it felt pretty good, it was just weird. I wasn’t as winded as I expected to be. It’s almost like having to learn how to ride all over again. Up and down the gears, all over the place. It felt like I was like trying to run an old steam locomotive, pulling levers and pushing buttons and turning knobs constantly.