Firstly, I know that knee pain covers a huge range of issues. But for me the last year or so on the bike has been getting less and less enjoyable...but I may have found the solution...

I have a leg length difference (3/4"), a bit of cartilage wear and tear, early arthritis, blah blah blah. I've been feeling strain down the back of my shorter leg and increasing sharp pain on the inside of my knee joint.
Cut a lonnnng story short, I spent a HUGE amount of money with Phil Burt bike fitter. Apart from the usual saddle height and fore and aft adjustment, I have now gone from 175mm cranks to 160!!! Cleats as far back as they'll go and 20mm pedal extenders. I haven't sized down my front chainring (30t).

The results have been astounding. I'm 2 months in on this set up and I now have almost zero knee pain. I feel stronger on the bike, have less fatigue and have stopped taking pain relief. Having bailed on the BB300 and an attempt on the Lakeland 300 earlier this year, I was pretty convinced my long distance riding was over.
Yes, it's still early days, but I thought that I had knee pain that felt worse when riding, now I think that the long cranks and narrow q factor were the creating the knee pain, which was affecting my cycling, hill walking and general hobbling about life. This may help some, or it may be a load of crock!

I'm a big fan of shorter cranks for that very reason.

Just had a look at his webpage -

The realisation that the modern obsession with intimate hair removal was almost certainly exacerbating saddle problems

Well done
I would say, that it would also be worth doing a load of stretching and strength balancing to build in some knee resilience. Glutes, hamstrings quads etc.

Oh and ride singlespeed

Very interesting. But who makes affordable 160mm MTB cranks? A quick search only throws up very expensive options.

This sounds like an excellent result!

My personal experience after being recommended shorter cranks by a bike fitter was a bit different. I just simply didn't like them and found them awkward, despite only changing from 172.5mm to 165mm. I'm more of a 'masher' though and like the bigger range of motion from 'standard' length cranks.

Charliecres wrote: ↑Tue Dec 10, 2024 9:19 am Very interesting. But who makes affordable 160mm MTB cranks? A quick search only throws up very expensive options.

Yeah, Shimano and Sram go down to 165mm.
Hope and Dev5 are too spendy for me. Ended up using Unite. Reasonable price with their seemingly constant discount code AND just down the road from BB Towerz.

Very interesting!

How tall are you/whats your inseam length?

I had a couple of bikefits and none mentioned using shorter cranks (mine are 175mm).
I had knee pain in the past and found that boring physio exercises worked well....only issue is staying on top of them!

Miranda cranks pop up a lot on the eBike forums as short crank specialists. I think they do regular bike cranks as well.

Very interesting. But who makes affordable 160mm MTB cranks? A quick search only throws up very expensive options.

My takeaway was see a bike fitter first before buying cranks so you get the length best suited to you

I have one of his books, and if I could afford it, I was go and get a fit from him. Have been after a pair of 165mm cranks for ages, so will have to checkout a few of those brands I've not heard of...

Oooh I've just kneed the edge of my desk ... not sure cranks are gonna help

Bearbonesnorm wrote: ↑Tue Dec 10, 2024 8:06 pm Oooh I've just kneed the edge of my desk ... not sure cranks are gonna help

Taller desk

Bearbonesnorm wrote: ↑Tue Dec 10, 2024 8:06 pm Oooh I've just kneed the edge of my desk ... not sure cranks are gonna help

You need to raise yer desk by 15mm, like I had to with my saddle, to compensate for my child sized cranks.

Valerio wrote: ↑Tue Dec 10, 2024 11:57 am Very interesting!

How tall are you/whats your inseam length?

I had a couple of bikefits and none mentioned using shorter cranks (mine are 175mm).
I had knee pain in the past and found that boring physio exercises worked well....only issue is staying on top of them!

5' 10"
Asking about my inseam, that's a bit personal!
For what it's worth Phil Burt was head physio at Team Sky. He said Sir Bradley went from 180mm cranks to 160mm 2 weeks before he won Olympic gold. He's 6' 3".

He said Sir Bradley went from 180mm cranks to 160mm 2 weeks before he won Olympic gold. He's 6' 3".

I'm sure the team behind him went home after he had the cranks fitted as redundant and not needed

I went down from 175mm cranks to 165mm eleven years ago after a bout of knee trouble, been on 165's ever since, very happy with them.

The fashion hype for shorter crank arms has finally arrived at BB too

I used to have knee pain too. Never tried shorter cranks, just did physio and trained them damaged knees and can now ride whatever length I want. In my case the pain came from trauma and tight muscles. Also affected me when mountaineering. Once the trauma had healed I simply stretched, first under the eyes of a physio, regularly. Issue solved. In the last couple of years I've suggested this to two mates, both thinking about shorter crankarms. They still ride the same cranks and are free from knee pain. In one case the pain had been so bad he couldn't ride anymore. They just needed some stretching too it turned out. Oh, one of the two had tried to get around the pain by increasing saddle height, where usually the opposite would lead to improvements.

For all those who now are pain free on shorter cranks, be aware that the source of knee pain may not come from too long cranks (alone) but a specific disfunctionality in your body that may affect you elsewhere too (perhaps not now but in future).

For a quick overview:
https://thebodymechanic.com.au/8-reason ... knee-pain/

TL;DR
Your body should come first. Bikefitting is great, a healthy body even more.

Alpinum wrote: ↑Wed Dec 11, 2024 9:23 am just did physio and trained them damaged knees and can now ride whatever length I want.

that's good to hear, I have been having trouble with my knee/calf for a year now, and my most recent physio consultation has got me onto pilates, and supplements, I'll look into the stretching / strengthening exercises in the link above too, thanks for this--I am only 57 and want to still be on the bike in 30 years time!

cheers,

Keith

My body doesn't seem to be that fussy about crank length, so long as my saddle height is dialled. As ever with these things it's gonna be n=1 and what works for you ain't necessarily gonna do it for me. Understanding that crank length might be a contributing factor to any pain you're suffering is a good thing, mind.

I did hear a rumour that someone once went for a bikefit and were told that their legs were the same length.

Alpinum wrote: ↑Wed Dec 11, 2024 9:23 am The fashion hype for shorter crank arms has finally arrived at BB too

I used to have knee pain too. Never tried shorter cranks, just did physio and trained them damaged knees and can now ride whatever length I want. In my case the pain came from trauma and tight muscles. Also affected me when mountaineering. Once the trauma had healed I simply stretched, first under the eyes of a physio, regularly. Issue solved. In the last couple of years I've suggested this to two mates, both thinking about shorter crankarms. They still ride the same cranks and are free from knee pain. In one case the pain had been so bad he couldn't ride anymore. They just needed some stretching too it turned out. Oh, one of the two had tried to get around the pain by increasing saddle height, where usually the opposite would lead to improvements.

For all those who now are pain free on shorter cranks, be aware that the source of knee pain may not come from too long cranks (alone) but a specific disfunctionality in your body that may affect you elsewhere too (perhaps not now but in future).

For a quick overview:
https://thebodymechanic.com.au/8-reason ... knee-pain/

TL;DR
Your body should come first. Bikefitting is great, a healthy body even more.

Its not necessarily "fashion hype", although there is probably an element to that.
In my case, I also did all the stretching and strengthening exercises prescribed by my Physio as well as changing to shorter cranks which he also advised.
Could I have gone back to 175mm? Possibly, but I couldnt see any benefit in doing so as the shorter cranks are more comfortable, and its basic biomechanics that suggest that reducing the flex angle of the joint places less strain on it.
Increasing saddle height definitely unloads the patello-femoral joint to some extent although it can introduce issues elsewhere. I used to find if I raised my saddle slightly it would ease the knee pain, but if I raised it too far I would get achilles tendon issues.

Tractionman wrote: ↑Wed Dec 11, 2024 9:40 amI'll look into the stretching / strengthening exercises in the link above too, thanks for this--I am only 57 and want to still be on the bike in 30 years time.

Sorry, but the link I sent is about possible sources, not how to stretch (and towards the bottom it goes down the industry's rabbit hole - to buy new stuff). I needed to learn to stretch with a physio. I thought I was doing it correctly, but I was wrong and doing it in a way it wasn't doing much at all.

Youtube may have good vids on this, but the youtubers don't see your body's functionality, hence my recommendation. Perhaps best would be to stretch (daily) and if there's no improvement within 2 months, see a physio.

I hope I can ride anywhere remotely the way I do now with 57... good for you  

ripio wrote: ↑Wed Dec 11, 2024 12:43 pmIts not necessarily "fashion hype", although there is probably an element to that.

There was a bit of sarcasm in it.
9 years ago I went 5 mm shorter than before.
After damaging a crank arm 3 years ago I went another 5 mm shorter and did the same when I broke the cranks on the other trail bike in the same year.
But I went shorter for other reasons than ergonomy and I couldn't tell the difference (I have bikes with 135, 165, 172.5 and 175 mm and only the 135 feels indeed different).

ripio wrote: ↑Wed Dec 11, 2024 12:43 pmreducing the flex angle of the joint places less strain on it.

I guess many fitters will mention the importance of opening the hip.
On a bike there are a couple of ways to this. The one way with the single most effect is steeper seat tube angle. 

There are many sources for knee pain and there are many ways to get rid of it.

If improvements in the own body's functionality don't suffice, I suggest to get a new frame rather than just new cranks 

Another thing worth bearing in mind is that if you change something - crank length, seat height, etc - you will be wearing a different bit of your knee, so that in itself will reduce pain, but you may not have addressed a fundamental problem such as muscle imbalance etc.

Good topic.. I've only ever had knee pain after a number of very long days on a loaded bike and it was pain at night rather than while riding. That was on 175s (887mm IL). I ride 170s on all but my SS now but tbh that change was more about ground clearance, toe overlap on the audax bike, adjusting to a more rearward cleat position etc - 170s just helped a little in all those areas. I also tend to push bigger gears as a natural riding habit and I hoped a shorter crank might encourage a higher cadence. Generally I just feel a bit more natural or fluid riding 170s.
I've been quite sceptical of the majority of common bike fitting methods, also I'm not a physio or sports science professional and as I get older I realise pains crop up and they're rarely related to the actual area I feel the pains. Have adjusted and experimented more in teh last 2 years than the prior 15 or 20 probably. More open minded now but some bike fit methods can still miss things that I think are important.

Basically,

Your body should come first. Bikefitting is great, a healthy body even more.

I agree with this - we should try to adapt to our (ideal) bikes as well as fit bikes to ourselves. Everything in balance and it's difficult to say what the main driving dimension should be (I have my own thoughts on it but it gets too convoluted for me to explain hence I don't think I fully inderstand it).

Shorter cranks are worth looking at if only because most of us have been directed towards the choice of 170 or 175 for a long time. It would be good to have more options down to perhaps 150mm*, for adults. Between a tall and a short rider around 25mm of crank range can maintain knee bend angles and seat angle / saddle setback is influential, so I think crank variation from a bike fit average for your height and IL is more about the range of bend that yu're comfortable with and matching the bike layout. Like your body it's all linked and it gets complicated.

*I’ve put some options into a model of bike fit and if you use Lemond method for saddle height and a normal shoe size range, same STA and ankle flex range, the knee bend is the same at 5' on a 150mm crank as it is at 6' on a 175mm crank (about the generic male bike industry spec). You can go +/- from there, going shorter tends to bring the model more into the oft-quoted ideal knee bend range. Whether the matched knee bend between those 2 fits is optimum for a particular rider is another matter, it's within ranges quoted though and I was just looking at the relative changes.
.. fwiw when I put my own IL, saddle height and 170mm crank into the model I’m pretty much dead-centre in that recommended knee bend range, yet the 21% of IL for crank length would have me on 185s. I could slacken off my STA to make the crank fit number work with knee bend, but then my CoM is way off where it’s best placed for that bike. That sort of anomaly is why I’m inclined not to believe all bike fit dimensions are proportional relationships. Fit the rider to the bike and the bike to the rider (easier said..).