For those who also ride road bikes , do you use the same crank length on both your road bike and mtb based bikepacking bicycle? It seems to be that MTB's are generaly equiped with 175mm for a frame size that the equivalent road bike would have 170 or 172.5 cranks.

I have 175mm on the SS, 172.5 on my geared bikepacker MTB more by chance of having a nice crank available in that spec, and 170s on my road and gravel bikes. Basically, the longer I spend on the bike in one position or spinning a reasonably low gear the more I prefer a shorter crank. I'd generally go 170mm on all but the SS - wouldn't have a problem trying 170s there either. 34.5" inside leg.

I am 5’7 with a 29” inside length and had a bike fit a few years ago due to knee pain on long rides- he recommended 165 cranks, so I have those on my road bikes and 170 or 165 on mtb and 175 on my ss mainly because I don’t ride it long enough in the saddle for crank length to be really important. Knee pain has gone. There’s no difference in power either, if anything I just spin a bit faster, and off road pedal strikes are reduced. I think crank length is hugely related to leg length and knee/hip articulation than anything else

As another short arsed Steve I switched to 170’s several years ago, much better and I probably should ride 165’s. It does seem odd that 175 is the default crank length.

I've struggled to see much reason or sense in the tiny differences in crank length and them supposedly being suitable/unsuitable for the massive range of leg lengths of us all*.

I've never looked into what any of my crank lengths are and so far so good

[*obviously some folk have specific issues which might make crank length an issue but for the majority of us not so much]

Like Steve, I ride 165 when possible now.

165 if I can find them. Unfortunately, Shimano don't (or didn't) do XT in Boost and 165 so I had to settle for 170. Climbing is so much easier with the shorter crank, plus there's the ground clearance improvement.

gairym wrote: ↑Sun Oct 18, 2020 12:40 pm I've struggled to see much reason or sense in the tiny differences in crank length and them supposedly being suitable/unsuitable for the massive range of leg lengths of us all*.

I've never looked into what any of my crank lengths are and so far so good

[*obviously some folk have specific issues which might make crank length an issue but for the majority of us not so much]

Short version but my understanding is that a shorted crank helps those with either shorter legs or those who can’t bend their knees well. The shorter cranks help at the 12 o’clock position when the knee is bent most, a shorter crank will help the knee to bend less.

Yeah, get that but I just don't really see how 5mm here and there will make much difference when my legs might be up to 300mm longer than a tiny wee persons.

gairym wrote: ↑Sun Oct 18, 2020 3:48 pm Yeah, get that but I just don't really see how 5mm here and there will make much difference when my legs might be up to 300mm longer than a tiny wee persons.

You're lucky, like me you're a taller rider and crank designs seem biased to fit us. Shorter riders could see more need for those variations? 5mm is a fine tune for most of us that don't have knee problems but I think of pedalling as an action that's not totally natural to us (vs walking) and it's repeated so many times so small differences in length may mean a real reduction in stress. I think we can fit a wider range of bikes than we think but at the same time when it comes to bar position there can be only 5-10mm difference between one end of a fit range and a stress position.

I'm not sure what height / inside leg percentile range cranks are really designed for (historically, 170mm for road racers of average male height I guess) but I don't think the 165-175mm range is enough for the height range bikes generally cover. If I'm happy using 170mm at 6ft it's always seemed daft that the shortest crank I can fit to a mid-range women's road or city bike is 165, sometimes 170mm. Maybe 160, 167.5 and 172.5 (edit, doh, make that 175) might be better for 3 sizes, add in a 152.5 ideally.

jameso wrote: ↑Sun Oct 18, 2020 4:08 pm Maybe 160, 167.5 and 172.5 might be better for 3 sizes, add in a 152.5 ideally.

This. The variances aren't anywhere near enough. I'd happily have a 160mm crank.

Exactly what I'm getting at, the range isn't much of a range at all.

I'm 168cm and use 170 all round.

I would go to 165 if it was feasible, but it would cost too much to do in one hit and I test lots of bikes and all those are 170 or 172.5 so it's not perfect.

I used to use 180mm on my MTB SS years ago and was told a bigger arm gives more leverage and power. Ooops.

170's all round for me (185cm high with longish legs) Started on the Jones to increase its woeful ground clearance and then did all the others as it seems to favour my dodgy knees - probably more psychological than physiological tho....

Still got 175's on the Kramp SS. When I SS'd the Jones I tried to convince myself that the kramp climbed better due to the longer cranks but I suspect this was more to do with the kramps extra wide bars....

gairym wrote: ↑Sun Oct 18, 2020 3:48 pm Yeah, get that but I just don't really see how 5mm here and there will make much difference when my legs might be up to 300mm longer than a tiny wee persons.

Well it’s actually 10mm and if I fitted what would possibly be my optimal length of 165 it’s a whopping 20mm from the standard 175mm fitted to most MTB’s. Try setting your saddle to the correct height then raising it 20mm, I’m quite sure you would notice. The first thing I did after buying Dee’s inbred for my lad was to calculate the correct crank length for his height, in his case it was 155mm.
Now we’re looking at 40mm which would lead to hip rotation and side strain on the knee joints, no way in the world I’m risking my son’s health for the price of a crank set.
I’m no expert but I have spent a year of my life with my legs in plaster due to Osgood-Schlatter Disease and hence look after them. Although I had surgery on my left knee ultimately cycling was the cure as it built up the surrounding muscles without impact.
Your joints are a marvel of bio mechanical engineering which can propel you around the world if they are working or leave you unable to walk to the shops if knackered.

This made a lot of sense to me

https://ridefar.info/2020/04/recommende ... iscomfort/

I dropped to 170mm and it made a big difference, much more comfy for me

BigdummySteve wrote: ↑Sun Oct 18, 2020 9:26 pm

gairym wrote: ↑Sun Oct 18, 2020 3:48 pm Yeah, get that but I just don't really see how 5mm here and there will make much difference when my legs might be up to 300mm longer than a tiny wee persons.

Well it’s actually 10mm and if I fitted what would possibly be my optimal length of 165 it’s a whopping 20mm from the standard 175mm fitted to most MTB’s. Try setting your saddle to the correct height then raising it 20mm, I’m quite sure you would notice. The first thing I did after buying Dee’s inbred for my lad was to calculate the correct crank length for his height, in his case it was 155mm.
Now we’re looking at 40mm which would lead to hip rotation and side strain on the knee joints, no way in the world I’m risking my son’s health for the price of a crank set.
I’m no expert but I have spent a year of my life with my legs in plaster due to Osgood-Schlatter Disease and hence look after them. Although I had surgery on my left knee ultimately cycling was the cure as it built up the surrounding muscles without impact.
Your joints are a marvel of bio mechanical engineering which can propel you around the world if they are working or leave you unable to walk to the shops if knackered.

I think I wasn't clear. I'm not saying that there's no need different crank lengths for different sized folks only that the current mainstream off the shelf offerings (mostly 165-175mm) aren't sufficient to cover everyone's needs and yet those 3 options are touted as being radically different.

Nice one for taking the time and effort to make sure you got the right length for your young 'un.

I think I wasn't clear. I'm not saying that there's no need different crank lengths for different sized folks only that the current mainstream off the shelf offerings (mostly 165-175mm) aren't sufficient to cover everyone's needs and yet those 3 options are touted as being radically different.

..in hindsight I think you were clear, to be fair - I misread the '5mm makes little difference' bit in the wrong context.