I had a total hip replacement back in 2003. I went through 2 months of physical therapy plus several more months of range of motion exercises to get back to "normal". Knees are far more complicated and recovery can take longer.
I used to ride 170mm cranks on my road bikes and 180mm on my off road bike. My road cadence was 90, off road it was mostly mashing.
Some folks claim to have the "Princess and the Pea" gift and can tell the difference between 170mm and 172.5mm cranks. Right now most of my bikes have 170mm cranks but a few have 175mm - I can't tell the difference.
After the hip surgery, my right leg is 3/4" shorter than my left plus my right foot is canted out about 10° more than before. I've also had chronic tendinitis in my knees and bone spurs under my knee caps which have worn grooves in the cartilage.
I use a pedal extender on my right pedal plus I ride with toe clips and straps but no cleats. This allows me to move my feet around at will much more than I could do with clipless pedals.
The angle of my feet in the pedals has a major effect on knee comfort. My feet are wide, 10 1/2 EEE so I use wide MTB pedals. The toeclips are mounted all the way to the outside of the pedals. I ride with my toes pointed outward and that's had a positive effect on the tendinitis.
You mentioned range of motion issues. I don't know that a 5mm (less than a 1/4") change is going to make that much difference for you.
You might want to try riding with just a toe clip on the affected side and let your foot "float". You may even need a pedal extender for that side.
It can take months of exercising to get your range of motion back.
Chas. Colerich Oakland, CA USA
RICHARD HOWARD wrote:
> I am 65 years old and have been using 175 mm cranks since my first real bike in
> 1967. I have had a total knee replacement and lost enough range of motion in
> the affected knee that it impacts on my ability to ride smoothly. The problem
> is mostly at the 12 o'clock position of the affected crank arm. It is a struggle
> to power over the top. I am thinking about switching to 170 mm cranks or even
> 165mm. Considering the skeletal shrinkage that also automatically comes with old
> age, I am thinking that 165 may be optimal. Has anyone else had a problem
> similar to this? Did you create any new problems for yourself while solving the
> targeted problem?
> Dick Howard
> Roanoke, Virginia