On the road bike I have Shimano roadie shoes with R550 SPD-SL pedals using the yellow cleat.
I find I get knee pain kicking in quite early (20 miles) that gets worse – not horrendous but noticeable.
I partially tore my Achilles in June 14 which know has a knock-on effect on my knee.
If I use my MTB 540 pedals with Northwave Celsius boots it’s much more comfy. There’s lots of float on the 540s but there’s a fair bit on the R550s too…just a case of tweaking cleat position on the left?
As far as road pedal/interfaces go, what are best for knees – Shimano, Time or Look?

just a case of tweaking cleat position on the left?

It’s got to be worth a try.

tweaking the cleat position should help. also check that your saddle position is correct too i.e. you’re not too far back or forward as that will put extra stress on your knees

you might want to look at the crank brother egg beaters too

Saddle height and setback are important. Cleat position (Fore/aft) is also often overlooked.

Best pedal system i’ve found over the years for knees/joints is time. Started off on TBT in about 1986 or 7. Tried a few others (even been forced onto alternatives!) always gone back to times.

Some others offer most or all of the system/mechanical advantages of the times, but usually come with some major flaw. Like randomly exploding, or cleats that last weeks, or cleats that cost almost as much as a normal pair of pedals……..

Oh, doing some exercises to stabilise the knee joint(s) might help if you have a funky Achilles.

General consensus for roadies with knee problems is to look at Speedplay, they have lots of float. However, before doing that, make sure you cleat position (fore/aft, left/right/ angle) and seat position (height, fore/aft) is right. I’ve found a low seat messes with my knee’s as does having the saddle too far back.

As mentioned by lunge, if you can not get the position correct, have a look at Speedplays.
I started getting knee problems when I moved to R550s. I tried a lot of moving things around but nothing helped.
I moved to Speedplays at the start of this year and the problem has gone away. I don’t think that it is that they have more float, it is more down to the fact that they don’t try to centre your foot. Unlike MTB pedals, most road pedals seem to have a gentle force moving your foot into the middle position. Speedplays dont do this at all.

If you unclip one foot and then try to pedal smooth circls with the other whilst messing around with saddle position/height and even cleat position it becomes fairly obvious which are the most efficient positions

+1 for the Speedplay pedals.

A bit expensive at first but I very rarely get knee problems since I started using them. You’ll need to persevere with them for about a month as they take a bit of getting used to, but once you have then you’ll stick with them.

I’d suggest a bike fit with a reputed bike-specialist physio.

Knees can be SO sensitive to the smallest mis-alignment. I fitted new Keo cleats to my shoes last year and got the left one slightly out, putting a sideways limit on my knee, which rewarded me with a couple of months of pain. It really was only a matter of a degree or two of missing float and the knee operating against the limit of the rotation. I’ve leanred now that I should be able to angle my heels in to scuff the cranks if I try, if my knees are to be comfortable.