For starters I do have a dodgy left knee.
My e conversion bike gives me really painful knees even after a 2 mile ride to the takeaway.
I thought this was due to the q factor but after a proper measure the left pedal is the same as a normal bike. The distance between pedals is less than my fatty which I have no problem with.
Is the problem the fact that the right pedal is 20 mm further out than the left?
Would a “problem” on the right side cause pain in the left leg?

sounds like it …it may induce a muscle imbalance perhaps? I have had terrible problems with fat bikes Q factors aggravating my right arthritic knee and spent ages trying allsorts to minimize the width with some success. If however the fatty has a greater Q factor and has no knee issues then may I suggest buying or borrowing a pedal with a longer spindle ( for the shorter side ? ) Otherwise if using flats you could try a ride where you keep your foot on the right pedal close to the crank arm or mod the left so you only use the outer part to equalize / ( this might prove the problem ) If SPD’s you could change cleat position between shoes . If no change how about saddle/pedal position etc . You should be able to identify the issue through test rides and without much initial expense. Over the years I have personally had a lot of experience fault finding/ diagnosing difficult problems without substitution of pricey parts . Got an unknown suspension noise ? squirt water on a pivot then ride ..if gone ..you know which one ! HTH

Just to check …make sure it’s not just coincidence and your left knee is irritable on other bikes as well..at the moment .

20mm?!
That’s miles out!

Why the huge misalignment? I’ve never seen it that bad on any bike.

20mm?!
That’s miles out!

Why the huge misalignment? I’ve never seen it that bad on any bike.

Posted 14 minutes ago

It’s even worse with the stock Tongsheng crank arms! Most people don’t have problem with the kits, just us sensitive types.
The bike was fine before I fitted the kit so the saddle position should be ok.

Flat pedals or clipless? If clipless, you sure the cleats are set properly?

If saddle height was fine and you’ve moved the crank over 20mm, it might not be fine anymore.

If one side is 20mm further out than the other you’ll be twisting your hips a little, that twist has to come out somewhere, left knee maybe?

These might be worth a punt, but just use the left one.

Sorry, can’t help with the original Q but I’ve got some SQLabs SPDs with +12mm axles that I no longer need, might be useful if you wanted to experiment…

Let me know if any interest.

Been experimenting and managed to get the non drive side 10mm less than drive side.This is now just slightly wider than my normal bikes.
Put a 36 t chainring on as I thought pushing a 42 was putting too much strain on my knee.
Rode 3 gentle flat miles to work with full power and the same back. I’m using flat pedals and I’m still getting a painful ITB.
Is 1 cm really going to make that much difference?
When I’m riding it feels fine.