I broke the top of my fibular last year. I have approx. 95% use of my knee now. The issue is that on a normal bicycle, the upward peddle position bends my knee to the point that it is very uncomfortable. I have looked into recumbent bikes but, first they are out of my budget and second, I really want to bike sitting up straight. I was thinking a shorter crank would help as well as a "comfort" crank forward bike. Any thoughts?

I've seen a old customer of mine have a engineering company turn his cranks from 175mm to 150mm. Not a huge job if they know what they're doing and make a clean job of it. Less travel for his knees, but you do spin a bit more, so you tend to go up a gear or two to compensate.
Can clarify it works though.

After a long day of cycling, I find my knees feel better when I do things like walk up stairs, etc., if I ride my bike with 170mm cranks than with 175mm cranks. A small change might be enough?

If you expect this knee situation to be permanent, that might be a good solution. But, if you did that, you would have to decide how short, and would you use that length on both sides?

Once you get outside the normal range of 165 to 175 cranks, the prices go up.

Shipping from the UK can be expensive, but this might be an option if you have a square taper crank. VAT would not be charged if shipped to USA. But this could put your feet out in a wider stance which might not work so good if you have knee flexibility issues to start with.
https://www.sjscycles.co.uk/componen...eners/?geoc=US

I've been suspicious of those crank shorteners for exactly the reason Tourist in MSN mentions. Perhaps ok for experimenting, but I have a wide Q-factor on my cargo bike, semi-FAT, and dislike riding it.

Origin8 has several crank lengths for a reasonable price.
https://www.amazon.com/Origin8-Alloy.../dp/B00R6R3ZPM
https://www.amazon.com/Origin8-Tripl.../dp/B00R6R5PBE

Usually it is best to match the right and left cranks, but it is also possible to mix lengths in special cases.

Does your bike have the clearance for a narrower crank? For example, I should have bought a bottom bracket spindle of about 133mm for chainline purposes on my expedition bike that uses a Rohloff. (I use square taper crank and bottom bracket.) But I wanted a narrower Q factor that was closer to the same as my derailleur bikes, so I got a 122.5mm spindle. That means that my chainline is off about 5mm, but I have no problems with chain wear.

if you build up a pedal you still have the full leverage thru the power segment,

your knee will flex more at the top, but have to reach less at the bottom. so oval motion ( from round chainring)

This is a little off the OP's topic, but I put a 20x4.25 tire in the rear. I don't think a narrower bottom bracket would work as it already has troubles with clearance around the tire to get into the lowest gears. Of course a little chain/tire rub doesn't seem to be a huge problem either (no knobs).

If I was doing the bike again, it probably wouldn't get the 20x4.25 tire, but even with that, I'd add an idler pulley system to allow standard Q-Factor cranks.

Not all the cranks are the same, and I think some of the vintage cranks use straighter crank arms, and potentially a narrower Q-Factor, so I might be able to save a small amount of width.

Another issue is that I normally set my cleats to the inside to push the shoes to the outside and minimize rub. I did the opposite on one occasion for the cargo bike, but wouldn't want to change the cleat position every time I changed bikes.

Anyway, back on topic, there may be some cranks like vintage Campy/Dura Ace cranks with straight arms that could potentially work better with crank shorteners than other modern cranks, potentially reducing the extra width of the shorteners somewhat. Also moving one's cleats to the outside of one's pedals and bring the shoes closer.

Depending on the crank design, it may also be possible to double or triple drill the cranks, although many cranks have a taper and hollowed parts that would make double and triple drilling cumbersome.

However, something like this White Industries crankset could likely have multiple pedal locations drilled and tapped.

White Industries Triple MTB Crankset Old School Custom Made 42/32/22T 175mm Vtg | eBay

Jumps may be large though. 20mm? 175/155/135?

There are also several adjustable PowerCrank models, but they give you independent right and left crank arms which may or may not be as desired. Maybe a few other adjustable cranks too.

I dunno if this would help. I ride on platform pedals precisely because of knee pain and the avoidance thereof. I find that being able to change my foot position on the pedal helps a great deal. In extreme cases I'll position the pedal spline under my instep and cycle "flat footed" with minimal strain on my knees. Moving the foot forward this way also reduces the necessary bending of the knee.

Here is some great information about knee problems and crank length that I found helpful:


Skip to about the 3:45 mark to hear about knee pain and crank length. There is some interesting advice here.

Have you considered a shorter crank for that knee. Odd but if you don't tell anybody, it isn't likely that anyone will notice. You could to that and shim the other cleat up that amount. Then both legs are going to the same down knee bend with a real relief at the top for that one.

I haven't "slept on this", just throwing it out there.

Edit: bring the seat and stem up the distance of the shim to keep your overall position the same.

Ben

Recumbents can be harder on the knees than a diamond frame. The max force you can exert on a regular bike is your body weight. The recumbent bike allows you to push off a back rest. In this you are limited by your leg strength not weight. I have heard that recumbent riders can hAve more knee problems if not careful to spin and gear down for stops. I don't know why they don't put IGHs on recumbents.

Sometimes they do. I have never ridden one but I had a conversation about a year ago with a trike owner in a campground, his trike had a Rohloff.

I've got a Sachs Dual Drive on my trike. The only thing it is missing is some kind of chain guide to keep the chain from bouncing off on every bump.

It is easy enough to click down to low range if one wishes.

I think the local co-op is now putting Nuvinci hubs on their cargo trikes.