Let’s talk crank arm lengths…

[jbrown15]

Well not really, a larger frame still has the same geometry. You start raising bottom bracket heights and you’re changing the geo numbers and feel of the bike. You might as well be making a different model.

 

[Monty Dog]

Would you like to tell all the road bike manufacturers that?

 

[jbrown15]

I'm 6'3" and my dad is 6', we both have XL sized Orbea Wild FS which came with 160 cranks, after a bit of idle discussion we both decided to try 165 cranks, and we've both stuck with them.
I found the 160 were just to short, I was spinning and could easily reach a point were the Bosch motor cut the power up a climb, with the 165's I don't do this as often, I do get occasional pedal strikes but most of the time I just half pedal up rocky climbs.
I also have a hard tail Cube with the same Bosch Gen 4 motor and 175 cranks, on the flat I'm usually above the speed limit with next to no effort and last time I rode it I was shocked at how little battery I used and how fast I could go. I know hard tails are more efficient but even with the suspension fully locked on the Wild FS I can't get close to the speed of the Cube and I'm guessing the crank length helps.

Wouldn’t be hard to test out your theory and take the 175mm cranks from your hard tail Cube and bolt them onto your Wild and go for a ride?

 

[jbrown15]

Would you like to tell all the road bike manufacturers that?

Are we talking about road bikes or emtb’s?
Road bikes don’t really have any concerns about low bottom brackets and pedals strikes like mountain bikes do they?

 

[mtb-steve]

Wouldn’t be hard to test out your theory and take the 175mm cranks from your hard tail Cube and bolt them onto your Wild and go for a ride?

I don't need to, the 165 cranks made a difference, I know the 175's will but they'll also drag on the ground

 

[Monty Dog]

Are we talking about road bikes or emtb’s?
Road bikes don’t really have any concerns about low bottom brackets and pedals strikes like mountain bikes do they?

They do actually. The difference is that a pedal strike is likely to be more catastrophic on a road bike coz of the higher speeds. But they all design to have lowest possible (and safest) centre of gravity.

BUT they do also take a PROPORTIONAL approach to crank length.

 

[Monty Dog]

This problem is across the board.

Hell why did my DH bike come with 170s? Who cares about spinning your feet so much on a DH bike it’s not like you ever sit down on one other than when drinking a beer or resting your legs.

I agree if you’re not going to be doing a lot of full out hard spinning, then shorter cranks makes perfect sense.

But many E-MTBers still want to go for a max workout. The e just helps crank up the speed and endurance - not about reducing the effort. That goes for me anyway.

 

[Monty Dog]

Let’s keep it in proportion guys.

I’m not arguing for longer cranks for all; just a PROPORTIONAL approach.

Are there lots of different factors that go into selecting ideal crank length? Yes.

Does this create a complicated picture for bike manufacturers? Of course.

Has it been shown that crank length doesn’t make much difference to max power output or efficiency? Yes - over very short periods.

Do downhillers care for longer cranks if though don’t intend to pedal hard for long periods. No, and rightly so.

Does altering BB heights to accommodate longer cranks on bigger bikes affect geometry and handling? Yes of course. Exactly the same as the different stack heights and reaches of different frame sizes do. So is that a reason to ignore leg length? No.

Are 175mm cranks (my personal fave on my analogue hard tail) the best for me on an e-mtb? No, almost certainly not. But only because of pedal strikes. And pedal strikes wouldn’t be an issue if the BB height was in proportion to the rest of the frame geometry.

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.

 

[Monty Dog]

On my regular mtb I run 175 cranks. I bought a used frame from my local store because it ran a 160 mm fork, I was using 140mm and wanted to try something longer. But the bottom bracket was so low, the pedal strikes were unbearable. I switched to 165 mm cranks, but I couldn't get used to them. They didn't give a long enough stroke, I was still bashing pedals. I got rid of the bike, wasted a lot of money.
Rode an emtb for several hours at an mtb festival summer 2022. It was great. Saw a deal on a norco sight, and I'll blame it on the beers, I clicked Buy. So I get it out on the trail and sure enough I'm bashing pedals. I'm kinda bummed, you dont want to fall off in the rocks and you don't want to push a 50+ pound bike thru the rocks either. I have since bought 150 mm cranks and 170mm fork, up from 160mm, Its snowing here now so I may not get to try this setup until spring.
But I saw a guy on utube , that mentioned that the norco sight and the norco range are the same frame. The range has a longer rear shock yoke and has 180mm fork vs 160mm on the sight. Now I wish I had gone with the Range, because that bottom bracket has to be higher.
But I think an ebike is a different animal altogether as far as how you ride them. Now most of your power is from the motor not your legs. You may not need the long leg stroke. I plan to use my ebike for trail maintenance, figuring out new areas and keeping my riding instincts up to par. I'll still be using my regular mtb when I'm riding with the gang.
So my point is, look at the bottom bracket heights of as many bikes as you can, if you ride a lot of rocky terrain it could be important. Get to a big mtb festival and demo some. Or find a local shop that is willing to let you try different size cranks. I would bet larger battery capacity is around the corner for most emtb's. I got mine because I just retired and I plan on doing a lot of riding in 2023, now that I'm not working 50 hours a week.

Thanks for this discdigger. Yours was the 1st response and I should have picked up on this before now. That's an interesting read. If you started on 175 cranks, I'm guessing you're quite tall...? And now you've bought 150mm. Wow. That's a heck of a change. Will be interesting to hear how you get on with those, particularly over longer rides. (There's no way that would work for me; I'm 6'4").

The bad experience you had is exactly what I want to avoid, but being tall means this is going to be really hard to find the right bike. I had my heart set on the Canyon because of that huge 900wh battery, but I just know that long rides in the saddle with 165mm cranks will lead to fatigue and maybe cramp and a general feeling of frustration that I'm not able to fully stretch out my muscles. On the other hand the pedal strikes I'd get with longer cranks won't be much fun either. So I might try and compromise with 170mm. Haven't decided yet.

I'm becoming more tempted by the Specialized Turbo Levo. Still that annoying on-size-fits-all 160mm crank length, but they have their Flip Chip meaning you can raise this by 7mm, to an accommodate switching to a longer crank. Now if only this came with 900Wh battery....

 

[steve_sordy]

...................... It’s the one-size-fits-all approach I don’t get and don’t appreciate.

I'm sure that it's a cost thing. Minimising the number of different frames and stock items is a genuine and large cost reduction. Unless someone comes up with an innovative design mod (chips, whatever...) then you are out of luck, unless you have a big budget.

 

[steve_sordy]

............................ I mean Shimano makes 175mm cranks, but why design a bike to run that long of cranks when probably less than 2% of people would run cranks that long?

Like many riders I suppose, all my bikes had 175mm cranks. At the time I assumed it was "standard". My first bike with 170mm cranks was a YT Capra with 160mm suspension. The shorter crank was to help compensate for the longer suspension travel. But that is mtbs, not emtbs.

Now that emtbs all seem to have uniformly shorter cranks, this may be due to lower BB heights across the board and/or the larger suspension travel. Probably both in my opinion. Inserting a bulky and heavy motor and battery into the bike design raises the centre of gravity, so I can see why the designer wants to keep the motor low and hence the BB. Low CofG is a good thing, right; can we all agree on that?

PS: (added later). I am 6'1" (1.85m), which means a size Large frame has always suited me. Never once have I bought a bike because of its crank size, nor changed the cranks because of pedal strikes. In fact, until the discussions on this Forum about pedal strikes I never even realised it was a "thing". Sure, I got the occasional one when hitting a tree stump hiding in the grass, or when I wasn't paying attention, but hardly any. In four years of riding emtbs I can't remember the last pedal strike, but as I say that is because they are so infrequent, that they are not noteworthy.
Crank length on both emtbs during this time has been 165mm.

 

[Monty Dog]

Like many riders I suppose, all my bikes had 175mm cranks. At the time I assumed it was "standard". My first bike with 170mm cranks was a YT Capra with 160mm suspension. The shorter crank was to help compensate for the longer suspension travel. But that is mtbs, not emtbs.

Now that emtbs all seem to have uniformly shorter cranks, this may be due to lower BB heights across the board and/or the larger suspension travel. Probably both in my opinion. Inserting a bulky and heavy motor and battery into the bike design raises the centre of gravity, so I can see why the designer wants to keep the motor low and hence the BB. Low CofG is a good thing, right; can we all agree on that?

PS: (added later). I am 6'1" (1.85m), which means a size Large frame has always suited me. Never once have I bought a bike because of its crank size, nor changed the cranks because of pedal strikes. In fact, until the discussions on this Forum about pedal strikes I never even realised it was a "thing". Sure, I got the occasional one when hitting a tree stump hiding in the grass, or when I wasn't paying attention, but hardly any. In four years of riding emtbs I can't remember the last pedal strike, but as I say that is because they are so infrequent, that they are not noteworthy.
Crank length on both emtbs during this time has been 165mm.

I’m a wee bit taller, so XL for me. At a guess, do you reckon you’d be OK with 170mm…?

 

[steve_sordy]

I’m a wee bit taller, so XL for me. At a guess, do you reckon you’d be OK with 170mm…?

Probably, but as I'm happy with where I am, I'm not prepared to pay to find out.

 

[Monty Dog]

Probably, but as I'm happy with where I am, I'm not prepared to pay to find out.

Haha - not for you. I’m trying to figure out whether I could do this…

 

[Monty Dog]

Haha - not for you. I’m trying to figure out whether I could do this…

Or whether the pedal strikes would be too much…

 

[steve_sordy]

Or whether the pedal strikes would be too much…

To find that out, you could always add a 5mm thick shim to the bottom of the pedals. The extra weight there, as minimal as it would be, would at least ensure that the shim was always at the bottom.

It need not be expensive, a 5mm thick piece of plywood hammered on so that the pins sink in, then a few zip ties to secure it, or maybe some wire!

 

[JP-NZ]

Its a large discussion when you can pick up longer or shorter cranks for cheap. All my previous MTB's have been 170mm cranks, current EMTB has 165mm cranks and I want to move down to 160 or even 155mm. I'm 6ft and similar weight to you and I get at least 5-8 small pedal strikes every ride.

If you buy the canyon just ride it with 165mm for a few months if you never get a pedal strike perhaps look at 170mm or larger. Depending on where you ride you might find the 165's perfect anyway..

 

[irie]

I get pedal strikes particularly when riding narrow deeply rutted tracks that 4WD vehicles have dug, and especially when I'm not concentrating. I reduced them by fitting Deity Tmac pedals which are a bit narrower than the previous pedals (but also a bit longer which work better with my feet).

If I really need more clearance I won't change the cranks. I will instead increase the stroke of my ZEB A2 forks from 160mm and remove spacers from the Ohlins TTX22m.2 shock to increase rear ride height.

 

[discdigger]

Thanks for this discdigger. Yours was the 1st response and I should have picked up on this before now. That's an interesting read. If you started on 175 cranks, I'm guessing you're quite tall...? And now you've bought 150mm. Wow. That's a heck of a change. Will be interesting to hear how you get on with those, particularly over longer rides. (There's no way that would work for me; I'm 6'4").

The bad experience you had is exactly what I want to avoid, but being tall means this is going to be really hard to find the right bike. I had my heart set on the Canyon because of that huge 900wh battery, but I just know that long rides in the saddle with 165mm cranks will lead to fatigue and maybe cramp and a general feeling of frustration that I'm not able to fully stretch out my muscles. On the other hand the pedal strikes I'd get with longer cranks won't be much fun either. So I might try and compromise with 170mm. Haven't decided yet.

I'm becoming more tempted by the Specialized Turbo Levo. Still that annoying on-size-fits-all 160mm crank length, but they have their Flip Chip meaning you can raise this by 7mm, to an accommodate switching to a longer crank. Now if only this came with 900Wh battery....

Yeah, 150mm is going to be interesting. I'm guessing I will probably hate them. I live in Massachusetts usa, and it can get frigging rocky on some of the trails around here. I know about reading the trail, but reading the trail and rock gardens are two different things. My 170mm fork just arrived (rockshox domain new, $350 on ebay, nuthin but the best) winter hasn't shown up yet, so maybe I'll be able to get out there soon. I paid $5733 on Jenson, no tax . It's the most I have ever spent on a bike. $3600 being my previous high. So I'm going to find a way to make this bike rideable if it kills me.

 

[Mabman]

My revelation move to shorter cranks, Miranda 155's, occurred after a pedal strike on my new to me 150mm travel bikes second ride. I was coasting into a left hand turn with my right pedal down and it dug into the ground and sent me off the bike. I thought about it and could only come up with the suspension travel being the culprit as the trail wasn't all that undulating at the time.

Ordered the shorter cranks and installed them and never have had the problem since. For me an added benefit is that my motor rewards a high cadence for the most part and the shorter cranks feel comfortable to me doing so. There are a few times that starting off in a higher gear than I should is hampered perhaps and the extra torque the 20mm of longer cranks would provide but if I gear down before stopping it isn't an issue.

 

[rzr]

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?

So now you want to repeat all mistakes roadies did/do ?
longer crankarms don't give you any benefit, only disadvantages, even on a road bike.
Do you know what length Sir Bradley Wiggins (190cm) was using ? 170mm
roadies had a lot of misconseptions about bikes (like riding on 17-19mm tires, long crankarms etc.)

Shorter crankarms allow you to pedal when the bike is leaned and give you better clearance, also they increase cadence, which is good for ebikes i guess (however i don't like it so much, i do my climbs with 65-70rpm, when i want to work hard)
BB height doesn't change with frame size.

 

[rzr]

I think the reason for this is that the bike in question has a relatively slack seat tube angle so that the BB is further in front of my hips that on bikes with a steeper seat tube, and as a result on that bike a lot of the effort is pushing the cranks over the top of their stroke....rather than pushing down past the top of the stroke.

you could try oval chainring to minimise that feeling.

 

[johnc]

you could try oval chainring to minimise that feeling.

Oval rings don’t work with e-bikes.

 

[rzr]

Oval rings don’t work with e-bikes.

ah... right, i forgot it's emtb forum
however you have strange feeling (overcoming that dead spot) on an ebike...

 

[Mikerb]

you could try oval chainring to minimise that feeling.

what I was saying was that shorter cranks made it easier to crank..........not that is was a problem or reason for changing to shorter cranks but a nice by product I noticed when I changed the cranks to 155mm

 

[Endoguru]

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.

 

[gsum]

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.

 

[3dp]

Oh hot topic again

Highpath Engineering for Cycle Products & Services

Highpath Engineering provides specialist cycle products & services for cyclists who find the 'standard' drivetrain does not fit their needs.

highpath.co.uk

some good stuff on here

I moved to 165 ( should have tried 160) from 172 on my road bike after my dura snapped again and bought rotor cranks
For me more power/comfort/cornering etc( open hip angle) not a noticeable increase in cadence I am 6ft and 90(ish)kg

when I upgrade my TT it’ll be 160’s - oddly I make/made more power on there than road bikes
as for emtb well my old school 26’s either hard or soft have sky high bb’s no dropper - maybe that’s why they get ridden not so much but Levo gen w with 165 needs a new set of cranks and pedals this year after 2 years of pennine smashing
i’ll be going smaller 160 there too

 

[Mteam]

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.

I suspect the reason that manufacturers of MTB and emtb do not vary the BB height on different sized frames of the same model of bike is that if they did it would make the sizes with the higher bb ride very differently from the ones with the lower BB, to such an extent that they wouldnt really feel like the same model of bike any more.

MTB (and emtb) have very little in common with road bikes, and are ridden in a much more dynamic manner, IE stood up,sat down, off the back,over the front, front wheel in the air, back wheel in the air, both wheels in the air, sliding the back, sliding the front, riding down a near vertical slope, riding up a 20% grade, etc etc.

I have bikes with cranks varying from 160mm (EMtb) to 175mm (road bike), they all work fine for me, my cadence is lower on the bike with the longer cranks.

 

[timcking]

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…?

MD, I'd have to agree with all your points. Surprising as it is, I believe mtb design still has a lot of development potential, and ergonomics is one of these areas as you describe.