Let’s talk crank arm lengths…

[discdigger]

I come from the Trek Stache, a hardtale with a very high BB height. The Stache is undoubtedly the best and easiest to ride mtb I've owned thanks to its excellent ground clearance.

Now I have an Orbea Rise and am in pedal strike hell. Some trails such as those at Mabie and Ae, which are very narrow, are completely unrideable on the Rise with its 170mm cranks. I've been looking for 160mm cranks for several months without success.

I just can't understand this fetish with low BB height. Trek should produce an eStache.

 

[discdigger]

The Stache is a popular bike around here too. Look at Miranda ( get to their website) out of Portugal. Figure out the crank that fits your motor. They make lengths that start at 150mm and go up from there. It cost me $87 total, & shipped from Portugal in 3 days. (They obviously want to impress with their service) I haven't put mine on yet, probably today. I have read that people have bent their's from hard pedal strikes, so they probably aren't as tough as a shimano or sram crank. But for $87 I'm willing to experiment.

 

[Tepi]

Ilmoitus siirtymiseni lyhyempiin kampeihin, Miranda 155:een, tapahtui polkimen iskun jälkeen minulle uudella 150 mm:n matkapyörälläni toisella ajelulla. Olin rullaamassapyörän vasemmalla käden käännöksellä oikea poljin alhaalla ja se kaivoi maahan ja lähettää minut pois stä. Ajattelin sitä ja saatoin vain keksiä, että jousituksen liike olisi syyllinen, koska polku ei ollut tuolloin niin aaltoileva.

Tilasin lyhyemmät kammet ja asensin ei, eikä ole koskaan ollut ongelmaa sen jälkeen. Minulle lisäetu on, että moottorini palkitsee suurimman osan poljin määrästa ja lyhyemmät kammet tuntuvat mukavilta tehdessäni niin. Muutaman kerran liikkeellelähtö suurempimalla vaihteella minun tulisi ehkä vaikeuttaa ja 20 mm pidempi kammien ylimääräinen vääntömomentti antaisi, mutta jos vaihdan ennenmpien pysäyttämistä, se ei ole ongelma.

Bosch gen 2 moottorilla on päivitys 155 mm,kammelle poistaa ongelman.

 

[MountainBoy]

I have a real beef about crank arm lengths on all E-MTBs. Here’s the thing; all E-MTB bike manufacturers stick to the same sized crank arm across all of their frame sizes. You don’t get this in the road biking world, so what’s going on?

It doesn’t take an Einstein to figure out that the correlation between average leg length and body height is going to be high. The road bike design engineers all know that tall riders usually equals long legs whereas short body = short legs; but this simple fact seems to have passed Canyon and other E-MTB design engineers by.

I’m tall, at 6’4” (193cm), and I’ve been riding for a long time (I’m 57). Through trial and error and a professional bike fit, I’ve found that 175mm is perfect for me on my various road bikes. When I bought my (used) Bird hardtail MTB a few years back, it came with 165mm cranks, and I did try to stick with these, because I knew the prevailing wisdom says shorter is better for off-road. But the problem for me was on really long rides, I felt like my leg muscles just weren’t being stretched out enough, and sometimes I’d get cramp.

So I changed to 175mm and never looked back. You feel a subtle difference at first, but for long rides, it’s huge. I do suffer the dreaded pedal strikes - not helped by the long low slack frame geometry - but for me there’s no real option; I just can’t go shorter.

Fast forward to now, and I’m in the market to drop £6k or more on an E-MTB. Being 105kg and less fit than I used to be but never-the-less still enjoying long rides out in the saddle - I really like the sound of the Canyon Spectral:On CF 8 or 9, because of that big 900Wh battery. But hang on - what’s this? 165mm crank arms on ALL frame sizes including XL…?? And no they won’t swap this out.

How can a one-size-fits all approach to crank arms possibly make any sense when you have a range of frame sizes to cater for anywhere between 5’4” in 6’6” in height…? Shimano, SRAM and all the others make a whole range of crank arm lengths, so why not use them?

All of the info I’ve seen out there on webland make the points that different riders have different preferences, and different crank lengths suit different terrains and style of riding, and bike companies can’t possibly predict what each rider will want. All true. To a degree. But this doesn’t change the fact that crank lengths still need to be PROPORTIONATE to leg length.

Another side note; the bottom bracket clearance distance is ALSO exactly the same for each frame size - for every E-MTB I can see out there, not just Canyon. Only makes sense if you believe that everyone - regardless of height - needs the same crank arm length.

And here’s another related point. As well as longer legs, the taller rider is also likely to be heavier. Think about it - a short rider who is (in all likelihood) of shorter leg AND lighter weight AND suited to a shorter crank arm length gets the same bottom bracket clearance as the taller, heavier, longer legged, longer cranked rider.

This is my first post here and quite a rant. I hope that’s OK on this forum. The thing is bike manufacturers need to understand that customers need to believe in their brand if they’re going to part with multiple £1,000’s. And that belief simply won’t hold if the customer sees that they can’t be bothered to properly consider something so very basic.

Question to all you lovely forum members: if I order a Spectral:On CF 8 or 9, and I retro-fit 175mm crank arms, will that be a mistake? Bear in mind I weigh 105kg. What about 172.5mm or 170mm…?

I agree. It would make a lot of sense, for the reasons you mentioned, for larger frames to have higher bottom brackets and longer cranks. but it shouldn't stop there. How about wider tires/rims to deal with higher rider weight? And smaller frame sizes could step down in tire diameter too.

I had the same issue when I wanted to buy a sporting motorcycle for road use. I'm 6-04" and all the sportbikes felt like I was on a children's motorcycle. I ended up with a Ducati ST4s Sport-touring bike and it fit me like a sport bike should! I finally had a big, gutsy streetbike that fit me like a 600cc supersport fits average height riders!

It made me wonder why motorcycle models didn't come in Small, Medium and Large!

 

[Monty Dog]

Hmmm... Thanks for your thoughtful reply, but not sure I fully agree....

MTBs / EMTBs are indeed ridden differently. I agree with that. Off-road much more technical and 'dynamic' as you say.
However, as for the different feel across the sizes, I would argue that the exact opposite applies.

The fact that BB heights + cranks are NOT proportional to height / leg length... THIS is what must surely give rise to a different feel across the different sized frames.

I guess you could argue that in a weird artificial scenario where you have just ONE specific rider trying out all the different frame sizes of one model of bike, then he / she would feel more consistency if that crank length and BB height were the same for each.

But surely, what you really want is for the short rider to have the same feel as the tall rider. And you'd only have that if stack, reach AND crank lengths are all in the same proportion.

It's interesting that you personally get on with a variety of crank lengths, and maybe that's true for many riders who not far from average height. But in my experience, as an unusually tall rider, the one-size-fits-all approach to crank lengths (and BB height) is a problem. If I'm forced to go for shorter cranks (because of that pesky BB height) I feel greater fatigue / discomfort / cramp on rides of 3-4 hours or more. (Though admittedly my legs are more forgiving on the shorter rides).

When you think about it, it just makes intuitive sense that crank lengths need to be considered alongside stack and reach...

I think the problem is that the bike designers are overly influenced by the pros and by bike reviewers and by their own in-house designers who are all not far off average height. (Probably). And those of us at the height extremes (v short and v tall) just don't make our voices loud enough....

 

[Monty Dog]

I agree. It would make a lot of sense, for the reasons you mentioned, for larger frames to have higher bottom brackets and longer cranks. but it shouldn't stop there. How about wider tires/rims to deal with higher rider weight? And smaller frame sizes could step down in tire diameter too.

I had the same issue when I wanted to buy a sporting motorcycle for road use. I'm 6-04" and all the sportbikes felt like I was on a children's motorcycle. I ended up with a Ducati ST4s Sport-touring bike and it fit me like a sport bike should! I finally had a big, gutsy streetbike that fit me like a 600cc supersport fits average height riders!

It made me wonder why motorcycle models didn't come in Small, Medium and Large!

Totally!

 

[SwampNut]

From my small group of riding partners, I’m the only one with a somewhat normal ratio. Maybe that’s true all around? Dunno. My wife is all leg, with the same inseam as me. The guy I ride with most often is taller than me but shorter inseam. If crank length varied, hers would be vastly short and his way too long. Might as well default medium.

 

[Monty Dog]

Of course. But average inseam of a 4’11” rider will be shorter than average inseam of a 6’8” rider. Right…?

 

[SwampNut]

Is there actually an average rider? I suppose I am. So, are most riders inside some average? I mean, mathematically yes, but what’s the spread? What’s the penalty for being outside of it?

 

[Pace 1234]

Run 170 ‘s , sweet spot , anything less and your running a hamster wheel , spinning cotton .

 

[emtbPhil]

Strange thing to get worked up about
Bottom brackets are same height, the bikes are designed to be abused, 165mm means less pedal strikes so that's what they go with - and they're a piece of piss to change and don't cost a lot
My bike, the bars were too narrow as I'm a big guy, but after 25 years in IT I prefer bars with a rise on them so I'm not so bent over - easy problem to solve, changed the bars.
I like grips with a bit of support for my wrists as I have wrist issues from typing, so I bought new grips.

If you have long legs then buy longer crank arms.
Also you realise that bodies aren't all the same proportions right? I'm 6ft but have a very short inside leg, long torso, short legs. I know plenty of people the other way around.

Expecting bikes to be a perfect fit based on frame size is never going to happen.

And frankly the seat, grips, pedals etc.. that come on bikes I always view as throwaway items anyway, all mine are hung in the garage on the wall of shame.

 

[emtbPhil]

Sorry if I’ve missed this, but so far on this thread, nobody has been able to give me any rationale for defending the widespread use of same BB heights and cranks for all size of riders.

Spin that around - how would you change the bottom bracket height proportionally?
The reach on the larger bikes changes but most of the rest of the frame is the same, you can't expect manufacturers to design and machine completely different frames to keep geometry right but with different BB heights? Bikes would be £15k each and people would moan.

Or are you saying short people should have 100mm travel but tall people should have 180mm travel?

 

[Pharmaboy]

Strange thing to get worked up about
Bottom brackets are same height, the bikes are designed to be abused, 165mm means less pedal strikes so that's what they go with - and they're a piece of piss to change and don't cost a lot
My bike, the bars were too narrow as I'm a big guy, but after 25 years in IT I prefer bars with a rise on them so I'm not so bent over - easy problem to solve, changed the bars.
I like grips with a bit of support for my wrists as I have wrist issues from typing, so I bought new grips.

If you have long legs then buy longer crank arms.
Also you realise that bodies aren't all the same proportions right? I'm 6ft but have a very short inside leg, long torso, short legs. I know plenty of people the other way around.

Expecting bikes to be a perfect fit based on frame size is never going to happen.

And frankly the seat, grips, pedals etc.. that come on bikes I always view as throwaway items anyway, all mine are hung in the garage on the wall of shame.

100% correct. Further BB heights are part of the frame design and handling of the bike - a Santa Cruz is going to be wildly different with a half inch higher BB.

The greatest change with higher BB’s is higher centre of gravity - this would make the XL a totally different bike to a medium if you increased BB because of some imagined difference between taller and shorter riders.

Why is this important?- because bottom brackets determine clearance and hence crank length in large part - so XC bikes are more likely to have longer cranks with high BB clearance and enduro bikes more likely to have shorter with lower COG BB heights.

The best modern solution is the flip chip for BB clearance plus the ability to buy cranks for your own preferences (just like all the other things you list in your post )

The flip chips like in the trek are an easy lesson in how much a half inch change in BB changes the way a bike rides - if there’s a complaint about Canyon, it’s that they still haven’t introduced this when manufacturers are clearly moving this way

My previous bike was a neuron and I had to shorten the cranks because of the rediculously low BB (6,1)

 

[Manc44]

OP you have a great point about taller riders needing longer cranks but MTB cranks need to clear the ground and that's why they are typically 170mm or less, with road being 175mm (or more?) To accommodate longer cranks, the whole design of the frame would need to be changed so the BB shell is higher up. They aren't going to do it.

 

[emtbPhil]

OP you have a great point about taller riders needing longer cranks but MTB cranks need to clear the ground and that's why they are typically 170mm or less, with road being 175mm (or more?) To accommodate longer cranks, the whole design of the frame would need to be changed so the BB shell is higher up. They aren't going to do it.

No people with a longer inside leg need longer cranks, there are plenty of 6ft people who would also need a longer crank arm and there are plenty of 6ft4 people who wouldn't.
This is just the same argument as why are larger waist jeans longer - not all fat people are tall, and not all short people are skinny. But when you're paying design, tooling and manufacturer costs you aim to cover "average" people whilst keeping costs low and retail price marketable.

 

[Monty Dog]

Strange thing to get worked up about
Bottom brackets are same height, the bikes are designed to be abused, 165mm means less pedal strikes so that's what they go with - and they're a piece of piss to change and don't cost a lot
My bike, the bars were too narrow as I'm a big guy, but after 25 years in IT I prefer bars with a rise on them so I'm not so bent over - easy problem to solve, changed the bars.
I like grips with a bit of support for my wrists as I have wrist issues from typing, so I bought new grips.

If you have long legs then buy longer crank arms.
Also you realise that bodies aren't all the same proportions right? I'm 6ft but have a very short inside leg, long torso, short legs. I know plenty of people the other way around.

Expecting bikes to be a perfect fit based on frame size is never going to happen.

And frankly the seat, grips, pedals etc.. that come on bikes I always view as throwaway items anyway, all mine are hung in the garage on the wall of shame.

Not strange to get worked up if you want to spend £6k+ on a bike, but you know that no thought is given by designers on leg length for tall riders. Prob same for small riders I imagine.

Most components can be swapped out without much issue. But cranks are different because of unintended consequences.

Small riders could likely go for 150mm cranks and so could ideally do with even lower BBs to get even better handling. (Tho maybe not a big issue). Whereas tall riders are stuck with pedal strikes if they want 170 or 175 cranks that give them the leverage they need. (This is defo a big issue).

Many factors determine a riders preference for cranks. But leg length is highly correlated to height. This is simple biology. One rider might be 20% taller than another. In which case their legs are almost certainly longer - maybe 15% , maybe 30%. But defo longer.

 

[Manc44]

Right but in general it's true that taller people have longer legs. It's not the "same argument" as waist size and leg length, because you're born with a set bone ratio that doesn't deviate much between all people, whereas your waist can change dramatically over the years... ask me how I know.

 

[Slymobi]

Jeeeez just ride your bikes get whatever crank you are happy with for clearance wise, set your seat post to accommodate your cranks and smile. If you're still worried about BB clearance inflate/deflate tyres to suit yeah not the best input I know but ! Life in general is indeed too short.

 

[Monty Dog]

Jeeeez just ride your bikes get whatever crank you are happy with for clearance wise, set your seat post to accommodate your cranks and smile. If you're still worried about BB clearance inflate/deflate tyres to suit yeah not the best input I know but ! Life in general is indeed too short.

Spoken like a true ‘average heighter’.
;-)

 

[Slymobi]

Spoken like a true ‘average heighter’.
;-)

Haha !! I'm 6ft 1, ride an XL HT on 155 cranks with a 170mm dropper. Love being average me

 

[emtbPhil]

These threads are pure entertainment.

Having to change out some £40 crank arms is not a big issue. Moaning that you need longer ones because you have long legs so manufacturers should design an entire new frame to raise the BB so you don’t smash the pedals off everything - like timing your pedal strokes isn’t a thing.

You said it yourself really you spent £6k on a mass produced cheap emtb. Swap the crank arms and bars and seat and wherever to get a good fit. If you don’t want that spend £15k on a custom build. But personally I’ll take the first option.

 

[Monty Dog]

These threads are pure entertainment.

Having to change out some £40 crank arms is not a big issue. Moaning that you need longer ones because you have long legs so manufacturers should design an entire new frame to raise the BB so you don’t smash the pedals off everything - like timing your pedal strokes isn’t a thing.

You said it yourself really you spent £6k on a mass produced cheap emtb. Swap the crank arms and bars and seat and wherever to get a good fit. If you don’t want that spend £15k on a custom build. But personally I’ll take the first option.

You missed the point. Nothing to do with cost of cranks.

 

[rzr]

Maybe pedal cadence has something to do with crank length. I’m 5-11 with long legs (almost 34” inseam). I’m a spinner not a pedal masher. There are no downsides for me running 155-160 cranks.

yes, shorter cranks make you spin faster.
from some researches, looks like cyclist like to keep the same linear velocity of feet. (so shorter crank arm, to keep the same linear velocity, you have to increase angular velocity).
and also to produce the same power, with lower torque, you have to increase cadence (by few percent)

 

[rzr]

Sorry if I’ve missed this, but so far on this thread, nobody has been able to give me any rationale for defending the widespread use of same BB heights and cranks for all size of riders.

coz it's not connected with bike size too much.
wheels have the same size (despite bike size), weight is roughly the same - so BB height is the same.
raising BB affects cornering and handling in negative way.

 

[rzr]

but why do you want to make the same mistake and return to this flawled theory that longer legs=longer crankarms ?
Roadies just realised (last 5 years) that there is NO correlation longer legs - longer crankarms.
crankarms can be safetly shorter, it won't affect your power and in fact it makes most people more comfortable on a bike (not everyone is yoga master)

 

[Monty Dog]

but why do you want to make the same mistake and return to this flawled theory that longer legs=longer crankarms ?
Roadies just realised (last 5 years) that there is NO correlation longer legs - longer crankarms.
crankarms can be safetly shorter, it won't affect your power and in fact it makes most people more comfortable on a bike (not everyone is yoga master)

Yeah OK rzr. If you say so. I guess my 40-odd years of cycling on and off-road, my pro bike fitter and my cycle club buddies must all be wrong then...

 

[rzr]

yep... that happens .... similar with stubborn use of 17-19mm tires (coz of course everyone KNOWS that they are the fastest)

 

[emtbPhil]

You missed the point. Nothing to do with cost of cranks.

One of us missed the point but it aint me - you're arguing for an industry wide change, with a huge increase in R&D and manufacturing costs, because you don't want to spend £40.

Yeah OK rzr. If you say so. I guess my 40-odd years of cycling on and off-road, my pro bike fitter and my cycle club buddies must all be wrong then...

What's more likely - an entire community being right or you and your "pro bike fitter" being right
As has been said but seems to be beating a dead horse - crank arm length may be related to LEG LENGTH (not height) the same as stem length, bar width, bar ride, saddle position are all related to reach. There will NEVER be a bike that fits everyone out of the box, these are all components you are expected to change to gain the correct fitment of the bike. What is important for the bike is travel appropriate for use, and geometry appropriate for use. Everything else you sort yourself unless you are the literal perfect 5ft 11 10stone 32" inside leg AVERAGE.

 

[SwampNut]

Yeah OK rzr. If you say so. I guess my 40-odd years of cycling on and off-road, my pro bike fitter and my cycle club buddies must all be wrong then...

Would not be the first time, and in fact, "old wisdom" should be looked upon as suspect. There are so many cases of old-think sticking around much longer than it should.

Discussing this with my top riding buddy yesterday, we both are thinking we may try 155mm cranks (we have 165 now).

 

[Mikerb]

I concur with a couple of points a bove. I am 6ft tall with 34 inch inside leg...meaning my torso is relatively short for my height. So height is not a good guide for bike fit because body proportions vary. The one thing that usually enables me to get a good cockpit fit is to fit higher rise bars than are typically supplied with bikes as stock...............in fact I think the 20 or 25 rise bar "standard" should be reconsidered! My bikes are size large and I use 165 cranks on one bike and 155 on another......no problems.
Lots of guys choose to ride a bike supposedly one size down from recommendations, simply because a smaller bike can feel a lot more throwabout and controllable.

I also mentioned before that unlike most road bikes, the position of the BB relative to the riders hips varies depending upon the seat tube angle.........further behind the BB with a slack seat tube angle....closer to being over the BB with a steeper seat tube angle; and that is one reason in my opinion why very often a shorter than stock crank can feel better.

As was said above, at the end of the day the bikes are designed for MTB, so how they handle at speed in terms of cornering and steep decending as well as climbing are the most important aspects for designers................not pedalling efficiency..........most especially when there is a motor. Before the advent of very low stepover frame design the guys we had to have most sympathy for were the ones with very short legs!! ( and as a result probably very bruised gonads!!)