[Closed] How long are your cranks?

Ran 175s on everything for years, recently swapped the FS bike over to 165mm for extra pedal clearance, my HT was still on 175, the difference when swapping between them was just about noticeable but not enough to bother me. Have sold the HT now and bought a CX bike which came with 172.5mm cranks, feels fine to me.

What's your femur length?

(170mm here btw, 5'7" small).

I've got 175's on the road bike (i think), 170's on the HT and 165's on the FS.

5'9" with 31" inside leg.

165 on all bikes but I'm a short arse

172.5 works for me.

I read somewhere that a 170mm crank is the same length as a 175mm crank, it's just the hole that is moved 5mm. Not sure, can anyone confirm this?

andy4d - Member
I read somewhere that a 170mm crank is the same length as a 175mm crank, it's just the hole that is moved 5mm. Not sure, can anyone confirm this?

Depends on the brand.

I bought some 170s cos they were cheap years ago and now all my bikes are on 170. There's just something about them that feels like it spins a bit better/more evenly and the extra ground clearance, though it might seem tiny, makes a difference.

edit: I'm 5'9" with 32" inseam if that makes any kind of difference.

170mm on my road bike, 172.5mm on my cross bike and 175mm on my mtb, it's what they came with.

FWIW Wiggo rides with 170mm cranks and he's certainly not a short arse with short femurs

170's on the MTB. Road bike - no idea.

170 on the Spitfire (fairly low BB), 165 on the Zero AM (low BB). Legs are somewhere around 33-34".

I think most riders are using longer cranks than ideal, especially those under 5'9" with average proportions.

170 for me. TBH I don't feel the difference when riding but it's more ground clearance which can only be good. (I'm a pretty average shaped 5'10). (I used to have a 175 and 170 version of the same crank on 2 different bikes, I couldn't tell you which version which was on which bike)

Did have some 165s on the dh bike and that actually felt weirdly short- not on pedalling or anything but my stance on the pedals was different. Felt like much more of a difference than 5mm ought to really.

andy4d - Member

I read somewhere that a 170mm crank is the same length as a 175mm crank, it's just the hole that is moved 5mm. Not sure, can anyone confirm this?

Sometimes. Usually on cheaper models- it's like that on my Aeffects frinstance but not on the Nexts I had. I [i]think[/i] all the named Shimanos do it with different length arms. Not ideal really but it's usually pedals you hit rather than crank arms ime

170 and 165mm on my dartmoor hornet and transition suppressor respectively

I went for 170 yesterday on an order as my PRocess 153 comes with 170mm due to lower BB. So thought it made sense when i ordered a set for the Parkwood that i'd order the same length so i've got the same on both bikes.

the difference between 175 and 165 and less than 5%, or, to put it another way, it's a bit less than the difference between a 19" frame, and an 18" frame.

ie. it's not really as big a range as we're led to believe.

i've got a selection of 175/172.5/170/165, my 5foot(1) wife has 140's.

I had this at the w/end, I borrowed a whuye901 demo bike from my lbs to try it out. I thought it felt a bit odd when riding it back from the shop. Got home and measured the cranks to find it had 170mm fitted. Jumped on one of my other bikes with 175mm and noticed the difference straight away, a much better pedaling stroke. people say you can barely tell the difference but I didn't like 170mm at all. I'm 5'4" with 30in leg btw.

If you like to spin at high RPM (I do as ride either fixed or singlespeed) a shorter crank makes that easier.

How much is debatable as the difference is small (in available crank options) but I would imagine comparing a 150mm crank to a 200mm crank would demonstrate it well.
You also have to use lower gears when using shorter arms as will be spinning more for same speed.

Keva - Member
I had this at the w/end, I borrowed a whuye901 demo bike from my lbs to try it out. I thought it felt a bit odd when riding it back from the shop. Got home and measured the cranks to find it had 170mm fitted. Jumped on one of my other bikes with 175mm and noticed the difference straight away, a much better pedaling stroke. people say you can barely tell the difference but I didn't like 170mm at all. I'm 5'4" with 30in leg btw.

You are comparing 2 different bikes..
Which probably have different geometry, reach, bb height etc..

I bought the 165's purely for a bit of extra clearance. I bought the bike off a mate and it he had 175's on it. When I first started riding it, although the shock was not set up properly for me, i had a few pedal strikes, I wanted new cranks anyway so bought some shorter ones. I think it pedals better now but i have stiffened up the shock now as well so it's probably more to do with that.....

165mm on the road bikes <- anything longer and it aggravates my dodgy knee on longer spins, I can also spin better on the short cranks, gear down by a couple of teeth and it all evens out to the same speed.

170mm on geared MTBs <- enough moving around on the bike that I avoid those issues ^

175mm on SS MTBs <- spent mostly standing pedalling or coasting so dont get the knee issues of sat down spinning unless on a longer ride, and the extra leverage is nice 🙂

5'7, 29in inside leg FWIW

the difference between 175 and 165 and less than 5%, or, to put it another way, it's a bit less than the difference between a 19" frame, and an 18" frame.

ie. it's not really as big a range as we're led to believe.

While that is mathematically true, the difference it can have on the dynamic system which is your legs spinning in circles, with all the complex muscle and joint interactions that entails can be noticeable.

Also, don't forget 10mm off the crank length is 20mm off the diameter of the circle you have to push the pedals around. On the road that can have a big impact on your position. Cranks 10mm shorter > saddle 10mm higher gains you 20mm of clearance for the pedal at the top of the stroke, which means you can either get lower or put your hips/knees through less extreme range of motion.

For some people a few mm here and there can be the difference between crippling pain after 30mins and a 7hr pain free ride, especially when looked at as a whole system with other adjustments rather than in isolation, although for some people it will have an effect even in isolation!

Different people are sensitive to it in different ways, and even though it may only be 5% in actual numbers it can be much more significant in real life. Human bodies are funny things and they all respond in different ways.

It can also be magnified or minimised by the geometry of the bike and your riding position on it, on some bikes/positions its more noticeable than others.

Different people are sensitive to it in different ways, and even though it may only be 5% in actual numbers it can be much more significant in real life.

oh absolutely. I couldn't agree more.

it's just that we're presented with a 'choice' of 165-175*, as if that's a full range to suit the buying public.

we can easily buy bikes in sizes from 13", upto 22"; to suit riders less than 5foot, to those well on the way to 7foot. More or less all of these bikes will be fitted with 175mm cranks. which is clearly daft.

(*some choice exists outside this range, but not much, and not by much)

I like 165's im 5 11 in height - dropping from 175's cleared up a hotspot I'd developed on my knee ..

oh absolutely. I couldn't agree more.

it's just that we're presented with a 'choice' of 165-175*, as if that's a full range to suit the buying public. when it clearly isn't.

(*some choice exists outside this range, but not much, and not by much)

gotcha, in my haste I misread your post and thought you were in the "it's only 5% so it's irrelevant" camp, sorry!

Indeed, a common moan, the main players are very poor at offering cranks outside that narrow range.

As you say there are other options but they are more limited, although if you're willing to look at un-tredny square taper it's not difficult to find options from 145mm to 180mm at least, and a lot of them are quite cheap.

It's one of those 'good for the average' cases isn't it. Not worth putting money into the fringe cases so they dont bother, not to mention that historically, especially in MTB crank lenght has been pretty much ignored and not really discussed, definitely not in mainstream media so a lot of people don't even think about it, they'll quite happily deliberate over the massive difference between 740mm bars or 760s, 10mm on a stem, or .5deg on a head angle, but never give their cranks a second thought...

Thanks guys! I've just got that idea which will make me a millionaire soon!!!

Expect a NEXT BIG THING that will revolutionise cycling: be it MTB or road.

Reverb-like cranks... You can reduce the lengths down to 40mm - this allows you to ride in the middle of the ruts that were previously rideable only in a "balance-bike style", or extend it to 250mm to ride up the vertical walls!!!

Kickstarter link to follow! 😀

One thing that may confuse many riders switching to shorter cranks, is that you have to raise your saddle at the same time. If you don't you won't be able to use your leg strength fully. Get your hips in the right place vs the cranks and you'll generate just as much power, and often more through increased cadence.

What may seem like the right height with 165 cranks will actually be too low if you've been riding 175 for years - it takes time to adapt.

@medoramas ^ Check out Geoff App's/Haworth swing pedals.

eccentric/offset platform, so you get the effects of a longer lever in the powery bit, and then a shorter lever as it comes back round. There are other reasons for the design too but the effective leverage bit is what I noticed most when riding a Cleland.

150 usually, though I also have 125 and 140

150 usually, though I also have 125 and 140

'bent?

It seems to me that the shorter lever arm of a 170mm crank either means you need to more grunt to push the pedals, or you need to run to shift into a larger cog at the rear

I'm convinced of this. It's got to be harder to push a shorter crank. Science innit.

I've always used 175's on everything but the dh bike. Any bike I've tried with shorter seems harder to pedal I reckon.

Pedal strikes can be an issue, not sure if 5-10mm makes too much real world difference, but I think you adjust technique to lessen the chances of that happening.

[quote=amedias ]'bent?

How dare you bring my sexuality into it!

The riding position is in fact far more upright than what most people are riding...

I'm convinced of this. It's got to be harder to push a shorter crank. Science innit.

Read more, get unconvinced (kind of), yes it IS harder top push a shorter lever [i]in the same gear[/i], but that's why we have gears!

With shorter cranks you adjust the gear appropriately, but spin a higher cadence* to compensate and it all comes out in the wash.

All longer cranks are doing is allowing you to push a bigger gear, but you can't push it as quickly, there's no point in having a massive gear if you don't have time to get on top of it. swings and roundabouts and all that...

What works for you and your riding is what matters though, some people are natural grinders and may appreciate the longer lever and harder gear, others are spinners and will prefer the shorter cranks, and it changes between discipline too. Seated accelerations I find much easier and I'm much quicker on shorter cranks, for standy-uppy sprints to get going the longer ones might work better, but then you get the trade off once you're up to speed of having to keep it spinning, so it is all very personal and situation dependant!

Have a look at how it works on the track, how they gear their bikes and the subtle difference between gearing for top speed, early acceleration, and mid-range acceleration.

You don't really lose/gain power with different length cranks, there's a lot of studies out there on this, some of them even suggest shorter ones can be better in some cases.

* cadence =/= foot speed

1 RPM of small circle means your foot is travelling less distance and [i]slower [/i]than 1RPM on the bigger circle.

So either cadence goes up if you keep foot speed roughly the same on an easier gear, you're not really pedalling faster as such, you're just doing more RPM in a lower gear but going the same overall distance at the same power.

185mm on all my bikes. Not sure what I'll do if/when they wear out or break. All other sports have always emphasised using a full range of movement, don't see why cycling should be so different.

Mine was a silly comment, but in a way my use of those crank lengths on a gearing limited device does illustrate how crank length makes a difference to your effective gearing. Not that I'm convinced that there is a significant, or possibly even a noticeable difference between 170 and 175 (I'm all fancy pants and have 172.5 on my road bikes!) - that is less than a 3% difference, which is below the standard threshold for human perception, and certainly less than any advantage being attributed to them. However I can certainly tell the difference between 150 and 125 and it makes a real difference to how fast I can spin, and hence to my speed.

[quote=thecaptain ]All other sports have always emphasised using a full range of movement, don't see why cycling should be so different.

Name me one? All of those I can think of use a similarly limited range.

I've just changed from 175mm to 165mm on my mk2 Dialled Alpine due to suffering from quite a few pedal strikes. Just got back from Bike Park Wales and Forest of Dean and can't feel any difference in pedalling but I definitely had less pedal strikes. I'm 6'2 with a 32" inside leg and the frame is 18".

i'm 5'8" and all my cranks have always been 175mm
but more recently i've been considering switching to 170mm to see if it would make any difference for me...but for the time being im sticking to 175mm until i can find the right crank at 170mm

All other sports have always emphasised using a full range of movement, don't see why cycling should be so different.

Because your limbs/joints/levers are not equally effective in all parts of that range.

It makes sense to use the [i]most effective [/i]range of motion, if that happens to be [i]all [/i]of it then fair enough, but legs certainly don't work like that, they are decidedly more crap at pushing in certain configurations than others and the loads on some joints can be excessive too.

It's also very personal and one of those cases where someone doing it differently doesn't mean they're necessarily doing it wrong.

Do we need to have a 'Pick a crank size and be a dick about it' thing like we do for wheels? 😉

All other sports have always emphasised using a full range of movement, don't see why cycling should be so different.

in that case, you'd be happy if the steps in your house were each half a metre high...?

after all, you'd be climbing the stairs with more joint movement...

Wazoo has 175 mm, all my previous had 172.

But given I have tiny legs for someone 5'10" (30" legs), my ideal size is probably closer to 160.

I'm convinced of this. It's got to be harder to push a shorter crank. Science innit.

Yep. But your legs can spin smaller circles more quickly. Go down 10mm on crank length, go down two teeth on your chainring, comfortable cadence range will increase by at least 5%. I just measured and I'm a 34" inside leg, riding 165 and 170mm cranks on my main MTBs, 170mm on my toddler XC bike and 170mm on my Brompton.

Science! 😉

aracer, I spent a few years rowing before doing any serious cyclng. But I don't see many athletes in any fields trying to restrict their range of movement when developing power. Tennis, football (when trying to hit the ball hard), swimming, javelin throwing, sprinting, you name it, a good range of movement is pretty fundamental in just about everything. Obviously short cranks works well for many people, I'm puzzled why this is though.

One downside of shorter cranks is your seat will be higher - so not ideal on bikes with slack seat angles or if your dropper post doesn't have as much drop as you'd like.

aracer, I spent a few years rowing before doing any serious cyclng. But I don't see many athletes in any fields trying to restrict their range of movement when developing power. Tennis, football (when trying to hit the ball hard), swimming, javelin throwing, sprinting, you name it, a good range of movement is pretty fundamental in just about everything. Obviously short cranks works well for many people, I'm puzzled why this is though.

It isn't about restricting range of movement, it's about optimising range of movement:

thecaptain - Member
Obviously short cranks works well for many people, I'm puzzled why this is though.

reason 1 (of many): people are available in different sizes.

awhiles, if my aim was to get up a flight of stairs as quickly as possible, I wouldn't take them one at a time (unless they were gigantic). Would you?

Look, I'm not arguing against people using short cranks if they feel it suits them. But I'm puzzled as to how this can be a good choice biomechanically.

people are available in different sizes.

Yeah, and cranks aren't! At least, not to anything like the same degree.

awhiles, if my aim was to get up a flight of stairs as quickly as possible, I wouldn't take them one at a time (unless they were gigantic). Would you?

No. But I don't generally take them three at a time either - and I notice less long legged friends more often take one step at a time whilst I usually do two.

I used 170mm for years, then moved to 175mm for at least 12 years. Now on 165mm and I cannot tell the difference!

thecaptain - Member
...I wouldn't...Would you?..

surely it depends how big the steps are?

But I'm puzzled as to how this can be a good choice biomechanically.

we're a walking/running biped, we walk / run or more or less straight legs.

this:

[img] [/img]

not this:
[img] [/img]

(would form the basis of my literature review)

[quote=thecaptain ]aracer, I spent a few years rowing before doing any serious cyclng. But I don't see many athletes in any fields trying to restrict their range of movement when developing power. Tennis, football (when trying to hit the ball hard), swimming, javelin throwing, sprinting, you name it, a good range of movement is pretty fundamental in just about everything. Obviously short cranks works well for many people, I'm puzzled why this is though.

Good range != full range. Cycling with normal length cranks utilises a good range. Sure rowing uses a fuller range than most sports, but what would your coaches say if your bum was touching your feet at the catch, or you leaned right back and pulled the handle up to your chin? None of the other sports you mention uses anywhere near a full range of motion. I was curious whether you'd come up with gymnastics - compare the range of motion they demonstrate to that of any of those other sports.

[quote=ahwiles ]we're a walking/running biped, we walk / run or more or less straight legs.

Quite - I thought of running when the "full range" comment was first made. The range of motion when running isn't markedly different to that used for cycling, even though it involves a lot more knee bend than walking. I'm thinking that rowing gets away with such a deep knee bend because little force is generated at the start of the drive.

I went down from 175 to 165 and my knee pain dissapeared completely when out on tje bike and i am 5'10 31 leg

One downside of shorter cranks is your seat will be higher - so not ideal on bikes with slack seat angles or if your dropper post doesn't have as much drop as you'd like.

Yeah, but that really is one of the cases where the difference is too small to matter, my BB-saddle height is in the region of 660mm (depending on crank length 😉 ), changing crank length even 10mm is not going to cause a significant enough change in either height or setback that it wont work within the range of adjustment*, heck, 10mm is nearly the difference in thickness between my padded shorts and not padded shorts!

* unless you're right on the borderdline of seatpost adjustment etc. in which case you're more likely on the wrong size bike/length post

But I'm puzzled as to how this can be a good choice biomechanically.

There's lots and lots of literature out there about how legs and knees work, and a lot of it specifically about how they work on bikes. To summarise, they only work efficiently and effectively within certain ranges, outside this range (but still within total range) they are significantly less effective at doing work, and with the added downside of putting undue loads on some of the joints.

Result -> optimum usable range =/= total range

175mm for me...

short little weak leggies need all the leverage I can get 😳

Height (and of course leg length) varies substantially between people. I'm exactly 20% taller than my wife, we are somewhat outlying but not all that extreme. Does it not seem reasonable that whatever the optimal value is in absolute terms, I should probably be using cranks roughly 20% longer than her? She actually rides with a more extreme knee bend (at crank top) than I do. And all frame sizes of any particular bike model are commonly sold with the same crank length. How can this make sense?

175mm for me...

short little weak leggies need all the leverage I can get

that's why we have gears, and as a a short legged comrade you're exactly the kind of person who might benefit from shorter cranks!

Does it not seem reasonable that whatever the optimal value is in absolute terms, I should probably be using cranks roughly 20% longer than her?

not necessarily no.

My Wife is 1 inch shorter than me, her legs are 3 inches longer*, she uses longer cranks than I do.

And all frame sizes of any particular bike model are commonly sold with the same crank length.

Not so, most big manufacturers, especially on road bikes, will spec shorter cranks on smaller bikes, and longer ones on bigger ones, the problem is that the range between short and long is not big enough (~10mm), and that this is also based on the false premise that big bike = longer legs, while it may hold true [i]in general [/i]it doesn't always.

How can this make sense?

It doesn't that's part of the argument, bikes are sold with a disappointingly small range of different crank sizes, and most retailers wouldn't consider a crank swap when fitting a customer. Consequently we are left with a small range of sizes that 'work' for the most people, but not necessarily working optimally. You'd tweak a stem or saddle here and there to get the perfect fit, but apparently not a crank, despite it being the one place where we subject our body to repetitive motion under significant load when riding, yet it is often overlooked, partly because for most people it's 'good enough' and partly because of the added complexity of swapping cranks to fit, and the lack of available options off the peg.

* her TT requirement is consequently shorter, and doubly so as she is less flexible at the hips/back than me, so I end up on long TT, low saddled, short cranked bikes, she ends up on short TT, higher stem, higher saddled, longer cranked bikes, despite there only being ~25mm difference in our hight.

I don't see many athletes in any fields trying to restrict their range of movement when developing power. Tennis, football (when trying to hit the ball hard),

here's some pretty dynamic football:

[img] [/img]

knees bent to something around 90degrees.
.
.
.
here's some pretty powerful tennis:

[img] [/img]

knees bent to something around 90degrees.
.
.
.
here's a fairly efficient cyclist:

[img] [/img]

knees bent to something around 90dgrees.

they all have the option of using more knee movement, but it seems approx 90degrees represents some kind of efficiency boundary, or something like that...

yunki - Member

175mm for me...

short little weak leggies need all the leverage I can get

gears for leverage, crank length for 'fit'.

Love a good crank thread. I heard wiggo uses different crank legth for climb stages (long) to time trial (shorter)?
Agree with Ahwiles and other: "gears for leverage, crank length for 'fit'."
Don't forget another property of crank length - saddle-arse clearance when descending a trail. I've moved from 170/175 to 180 on all my bikes, perception of benefits in order:
1) Lower saddle height / less drop to bars / more comfortable
2) Saddle clearance (ride a xc hardtail with 27.2 sp...but a dropper negates this)
3) Efficiency of stroke / range of motion as crank closer to 20% of leg length.
6'2" with 35" inside leg

perception of benefits in order:
1) Lower saddle height / less drop to bars / more comfortable
2) Saddle clearance (ride a xc hardtail with 27.2 sp...but a dropper negates this)

I'd take a poke at those 2 (or at least some of it)...

Yes your saddle is lower in relation to the BB. But the only reason it affected your bar drop is that you didn't move the bars as well. The same change in bar drop/comfort could have been achieved by placing the bars higher in the first place.

What you're saying here is that when you dropped your saddle height, you [i]noticed you prefer having the bars higher*[/i] in relation to where your bum is sat, as the two are independently adjustable.

Saddle clearance, do you mean in relation to not smacking you undercrackers? cos that doesn't make sense either, the saddle is in the same position relative to your (lower) pedal, so no clearance gained really when pedalling standing up, the only gain in clearance here is when the cranks are exactly level** and you're not pedalling, so there is some truth in it, but as you say, mostly negated by dropper anyway if you have one.

* and **
case **, nullifies case * as when the cranks are level, your bar is at exactly the same height as when you had shorter cranks, so that comfort increase can only applly when seated.

Having said all that, it's good that you've experimented, so many people don't bother and could be missing out on increased comfort, performance, endurance or reduced injury. And even if they see no benefits at all they will get a better understanding of how they and their bike work and interact. At your height/leg length I wouldn't be at all surprised if you might like even longer than 180mm if you could find them.

Interesting comment about shorter crank, means smaller perimeter, so even if your cadence needs to increase to maintain travelling speed, your actual foot speed probably stays the same. I can now get my head around how shorter cranks are not necessarily 'harder' work for mtb.

I just need to remember how hard that killer climb was, and do I really need a smaller ring up front, or a larger cog on at the rear, to make up for the change in crank.

I just need to remember how hard that killer climb was, and do I really need a smaller ring up front, or a larger cog on at the rear, to make up for the change in crank.

It's entirely personal of course, but when I swapped from 170-165mm on the road I dropped 2 teeth off the front chainrings to compensate, felt about right and my average speed actually went [i]up[/i] but I did notice a preference change to sitting and spinning more rather than standing to honk, so not all variables remained the same!

On MTB my SS (on 26er) ratio with 175mm was always 32/15 or 34/16. I did dabble with 170mm for MTB SS for a while and had to re-gear to 32/16 or 34/17. When I went back to using 175s for SS it also coincided with an increase in tyres size form 1.9/2.0 to 2.4 so I stuck with the easier gearing and it all kinda felt 'right'

So if you're talkign MTB, don't forget to include tyres, cranks and gears in your calculations, but ultimately, fiddle until you're happy and comfortable 🙂

170's on everything here... Road, Full sus, hardtail, CX etc.

I'm 5ft10 with 33" inside leg, but a history of knee pain. Moving to 170's a decade ago solved that! I've ridden 172.5 on road bikes, but it's just not as comfortable to ride for distance though doesn't aggravate like 175's do.

Both my current MTB's have very low BB heights (which I like) so tempted to give 165's a go off-road! But then it'd be a fair expense given is be replacing Carbon Raceface cranks on both bikes...

It's entirely personal of course, but when I swapped from 170-165mm on the road I dropped 2 teeth off the front chainrings to compensate, felt about right and my average speed actually went up but I did notice a preference change to sitting and spinning more rather than standing to honk, so not all variables remained the same!

Nice to hear that somebody actually understands the theory behind it! We have a range of different gear ratios available to us for a reason. Most people just swap crank lengths, then moan that their gearing feels harder, without of course compensating by either riding in easier gears or dropping a couple of teeth off their chainrings!

Without knowing all the science behind crank length, I do find it odd that most bikes come with set cranks lengths according to bike frame size. Shouldn't shops be supplying bikes with cranks that suit our own bodies?

I'm a [s]bit[/s] weird, I have the legs of a "normal" ~5'5" person and the torso of a normal ~6'2", all meeting up to produce a 5'10" weirdo these days (5'11" in my prime).

So I often need a larger frame, which then usually gives me cranks that are at least 172mm.... Noooooooo! 😆

as a short legged comrade you're exactly the kind of person who might benefit from shorter cranks!

I may well give it a try if that crankset you donated to my town bike ever wears out!!
My MTB is SS so I'm never sat down long enough for it to make a difference 🙂

n0b0dy0ftheg0at - Member
...I do find it odd that most bikes come with set cranks lengths according to bike frame size.

thing is, usually they don't even do that.

Shouldn't shops be supplying bikes with cranks that suit our own bodies?

at least providing the option to [i]buy[/i] different cranks would be a bloody good start.

My MTB is SS so I'm never sat down long enough for it to make a difference

😉 Same here, 175s will give me knee pain on a geared bike within and hour, SS though I'm just fine with them.

thing is, usually they don't even do that.

The big boys are actually not [i]that [/i]bad at this, Spesh/Giant/Trek/Cannondale/Canyon all do, and I think some others as well, granted it;s only 10mm between extremes but at least it's something!

at least providing the option to buy different cranks would be a bloody good start.

I think it's a budgetary catch-22 situation, there aren't many options off-the-peg, primarily because people don't tailor their crank sizes, which in part is because there aren't many options off-the-peg, because there's not enough demand, because people don't tailor their crank sizes.... repeat till implosion

...repeat till implosion...

agreed.

yes, specialized (and others) sometimes fit 165's to their XS bikes, which possibly helps strengthen the myth that 165 is 'extra small', so people happy to experiment with an alternative to their 175's only go as far as 170 (as they themselves aren't extra small), then don't notice much difference, and forget about it, so further weakening demand for alternatives...

Force X distance = work done.
Force is the grunt that can give.
Distance is the circumference of pedal spindle.
I went from 170mm. to 160mm cranks (road). I therefore have to pedal an extra 63mm now to achieve the same work done.

I am 5'4" tall with an instep of 29", and run a 48 36 26 triple with a 13 26 cassette. I climb better and feels a lot more spinny on the flats. Feels more Ferrari than Bolinder semi diesel!

Its just personal preference. This may be different on different bikes (different activities).

The crank arm is part of a SYSTEM of levers (gearing, wheel size, position of seat and handlebars, limb length etc), so cannot be separated alone as lots of people are doing in the comments above with their pseudo-science.

Various people have tried to calculate an optimum but failed. Even statistical evaluation of Pro riders choices revealed nothing.

The range is usually 160-180mm this was historically found by trlal and error and the best way to choose is those that feel most comfortable.

I'm 6ft 34" inside leg and ride 175 as thats what i'm used to and so it is my preference. I don't have extended time on any other length.

188cm tall 170mm cranks, I found going a bit shorter most noticeable on the turbo trainer.

wzzzz - Member

Its just personal preference ... the best way to choose is those that feel most comfortable.

i think we're closer to agreement than your post suggests 😉

... Various people have tried to calculate an optimum but failed.

a bit like saddle height then, lots of formulae around for calculating your saddle height, based on this, that, the other, but the best results are likely to come from personal preference. That doesn't mean saddle height isn't important, just that it's difficult to predict.

which brings me to my central moan: there isn't enough choice for people to try out a decent range, and say 'A is too short, C is too long, i prefer B'

or, to drag out a goldilocks analogy, we've only been offered one bowl of porridge, and we're poking around the edges looking for the hot/cold/sweet/salty bits that suit us best.

I ride 170 on my road and TT bike. Do you translate this directly to the mountain bike? I would assume so as the saddle height for optimal peddling I the same?

Maybe we all should have a set of these fitted for the first few rides of a new bike:

[img] [/img]

I ride 170 on my road and TT bike. Do you translate this directly to the mountain bike? I would assume so as the saddle height for optimal peddling I the same?

no the gearing is different. the bike is different, the activity is different, in fact all the levers are different.

Might make a good starting point though 😉 if you feel comfortable, carry on.

If you are chasing 10ths then experiment with longer and shorter arms.

175 gives me knee pain, 170 is marginal, but 165 gives no problem at all. I've chopped and changed between bikes for weeks at a time to prove this to myself before changing to 165 on everything (hardtail MTB, fat bike & road). I'm 5'6".

Took some doing on the fat bike:

[IMG] [/IMG]

I am 6'2" with 36" inside legs but my lower legs (below the knee) are quite stubby and upper legs (above the knee) really long - what do you think that does to my ability to run long or short cranks?