Did you change anything after fitting shorter cranks?

irie

irie

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Just replaced 165mm cranks with 155mm cranks (2022 Trek Rail 5)

By how much did you shorten your cranks, and did you need to also change seat height/bar height/chain ring/stem/other?

Or did you just ride it and leave everything else the same as before and quickly adapt?
 
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Seat height will be wrong. Only about 10mm or so. The short cranks will feel weird out of the car park, then you won't think about them again.....until you have a pedal strike.:oops:
 
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Tone461 said:
Seat height will be wrong. Only about 10mm or so. The short cranks will feel weird out of the car park, then you won't think about them again.....until you have a pedal strike.:oops:
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Seat to pedal distance will of course be reduced by 10mm, but obviously less chance of pedal strikes.
 
irie said:
Thinking of doing exactly that and trying out before doing anything else.
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I doubt you will notice the bars or controls to be honest being different as its such a small amount by the time the effect gets that far forward (y)
 
Yesterday decided to mess with the bikes. So to get the same pedalling leg length raised seats by 10mm. Then realised that to partially compensate for increased seat height could raise the stems by max. 5mm which will also bring bars slightly nearer to seat. Will try it out today because unusually it's not raining!

Haven't told my wife that doing the same to her bike because trying to avoid the "what have you been doing to my bike???" question of course. She's had offs due to pedal strikes which affected her confidence so if they're reduced/eliminated will be a result. (y)
 
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Raised saddle and a very slight bar rotation got things feeling normal again for me.
 
Just returned from a 12 mile ride I know very well. Only differences were that because of the shorter cranks turning the chain ring in any one gear/assistance level was slightly harder (obviously), and standing on pedals descending felt slightly more compact. But wouldn't have noticed any of this if I hadn't known about the shorter cranks.
 
it is not quite as simple as thinking 10mm less crank length= raising the seat by 10mm. At the top of the crank rotation the saddle to pedal distance is 10mm longer!! Efficient leg to pedal set up is usually done at 4 Oclock which will be about 6mm difference ( not that it really matters much on an EMTB!!)

I changed to 155mm cranks on my Whyte E180RS. Never changed the seat height. The biggest difference I found...apart from helping pedal clearance on rocky climbs.............was that accelerating the bike from zero or close to zero inertia was easier...........ie it is easier to push the crank over the 12 Oclock position.
 
Mikerb said:
Efficient leg to pedal set up is usually done at 4 Oclock which will be about 6mm difference ( not that it really matters much on an EMTB!!)
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Good to know that it doesn't matter much on an eBike. 😀
 
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irie said:
Good to know that it doesn't matter much on an eBike. 😀
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didnt say it does not matter on an ebike!! :) I said it does not matter much on an EMTB. Probably not that important for either giving the assistance provided by the motor and the more limited sit down pedal distances likely on either compared to a road bike.
I spend more time up on the pedals than on the saddle and even then the dropper is usually partly slammed.
 
To keep it like before shortening cranks:

10mm shorter cranks = raise seat 10mm.
raise seat 10mm = move seat forward a little (re-measure fore/aft)
 
Mikerb said:
didnt say it does not matter on an ebike!! :) I said it does not matter much on an EMTB.
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[pedantry correction]
Electric Mountain Bike rather than Ebike.
[/pedantry correction]

Mikerb said:
Probably not that important for either
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confused3.gif


Oh.
 
irie said:
[pedantry correction]
Electric Mountain Bike rather than Ebike.
[/pedantry correction]



confused3.gif


Oh.
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not being pedantic...just explaining my perspective and experience having fitted shorter ( 155mm) cranks.

To be a bit clearer, if you look at the reason for the recommended leg extension when the cranks are at 4 oclock it is mostly about preventing hip rotation ( saddle to high) and quad muscle extension being optimum ( saddle too low not allowing full flex of that muscle group). Both are far more critical on a road bike when the rider is in the seated position for extended periods of time and pushing a high cadence. That might still be the case on a city/commuter Ebike where again the rider is mainly seated and could still be covering quite a few miles, but the assistance from the motor would minimise any loss of absolute pedalling effectiveness........(.having the saddle too high would however still induce hip rotation so that should be avoided).
My view was that on an EMTB I spend more time up on the pedals than seated and even if seated on say a single track or gravel road, it is better keeping centre of mass lower for better balance and the dropper partly slammed allows better bike control.
Add to that the fact that whilst the 10mm shorter crank may 10mm further towards the saddle at 6 oclock, it is only c 6mm at 4 oclock which is where saddle height is determined if you follow the fit guidance for standard road bikes. At 12 oclock the pedal is in fact 10mm further away from the saddle and 1 0clock is the beginning of the power stroke......and that is motor assisted!!
So simply going for 10mm additional saddle height ignores the fact that shorter cranks mean your quads will be further extended at the beginning of the power stroke than before and so a little less powerfull. Push the saddle up 10mm and the quads will be even further extended at that point.
Hence I left my saddle where it was!!
Perfectly happy for you to disagree though!!
 
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Mikerb said:
not being pedantic...just explaining my perspective and experience having fitted shorter ( 155mm) cranks.

To be a bit clearer, if you look at the reason for the recommended leg extension when the cranks are at 4 oclock it is mostly about preventing hip rotation ( saddle to high) and quad muscle extension being optimum ( saddle too low not allowing full flex of that muscle group). Both are far more critical on a road bike when the rider is in the seated position for extended periods of time and pushing a high cadence. That might still be the case on a city/commuter Ebike where again the rider is mainly seated and could still be covering quite a few miles, but the assistance from the motor would minimise any loss of absolute pedalling effectiveness........(.having the saddle too high would however still induce hip rotation so that should be avoided).
My view was that on an EMTB I spend more time up on the pedals than seated and even if seated on say a single track or gravel road, it is better keeping centre of mass lower for better balance and the dropper partly slammed allows better bike control.
Add to that the fact that whilst the 10mm shorter crank may 10mm further towards the saddle at 6 oclock, it is only c 6mm at 4 oclock which is where saddle height is determined if you follow the fit guidance for standard road bikes. At 12 oclock the pedal is in fact 10mm further away from the saddle and 1 0clock is the beginning of the power stroke......and that is motor assisted!!
So simply going for 10mm additional saddle height ignores the fact that shorter cranks mean your quads will be further extended at the beginning of the power stroke than before and so a little less powerfull. Push the saddle up 10mm and the quads will be even further extended at that point.
Hence I left my saddle where it was!!
Perfectly happy for you to disagree though!!
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As it happens on an eMTB I spend more time seated than up on the pedals, thus I await your next lengthy word spaghetti post with some trepidation. :LOL:
 
Mikerb said:
not being pedantic...just explaining my perspective and experience having fitted shorter ( 155mm) cranks.

To be a bit clearer, if you look at the reason for the recommended leg extension when the cranks are at 4 oclock it is mostly about preventing hip rotation ( saddle to high) and quad muscle extension being optimum ( saddle too low not allowing full flex of that muscle group). Both are far more critical on a road bike when the rider is in the seated position for extended periods of time and pushing a high cadence. That might still be the case on a city/commuter Ebike where again the rider is mainly seated and could still be covering quite a few miles, but the assistance from the motor would minimise any loss of absolute pedalling effectiveness........(.having the saddle too high would however still induce hip rotation so that should be avoided).
My view was that on an EMTB I spend more time up on the pedals than seated and even if seated on say a single track or gravel road, it is better keeping centre of mass lower for better balance and the dropper partly slammed allows better bike control.
Add to that the fact that whilst the 10mm shorter crank may 10mm further towards the saddle at 6 oclock, it is only c 6mm at 4 oclock which is where saddle height is determined if you follow the fit guidance for standard road bikes. At 12 oclock the pedal is in fact 10mm further away from the saddle and 1 0clock is the beginning of the power stroke......and that is motor assisted!!
So simply going for 10mm additional saddle height ignores the fact that shorter cranks mean your quads will be further extended at the beginning of the power stroke than before and so a little less powerfull. Push the saddle up 10mm and the quads will be even further extended at that point.
Hence I left my saddle where it was!!
Perfectly happy for you to disagree though!!
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Never heard of measuring seat height at 4 o´clock. I use 6 o´clock for seat height/knee extension and 9 o´clock for seat fore/aft position. Usually shorter cranks are used to open up the hips. If at the correct seat height and knee extension the knees comes too close to the core (impinging hips) then the cure is shorter cranks to open up the hips.
 
As a general fyi for Bosch eMTB owners fitting short(er) cranks the latest Bosch update (if model appropriate) now has the option choice of one of two EMTB drive modes, one listed as a short crank version. I have no idea what it does differently to the “normal“ EMTB mode. Though my Mondi Crafty defaulted to the short crank version when the update was applied (haven’t tested it yet).
 
Does anyone know if it changes tbe data in tbe computer effecting the power to pedals? Does there need to be a change in tbe chainring and if so more or less teeth?
 
Truckee Robert said:
Does anyone know if it changes tbe data in tbe computer effecting the power to pedals? Does there need to be a change in tbe chainring and if so more or less teeth?
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Bosch updated eMTB short crank mode? It probably adds a little bit more assistance (vs normal eMTB mode) as short cranks mean less leverage ( think of a short torque wrench trying to undo a nut compared to a long one on the same nut) . With that in mind short cranks don’t change the gearing just the ”effort” needed to rotate at a given speed but the biggest impact is probably how it feels on legs/knees/hips? As they have less distance/angles to cover/make with short cranks vs longer ones & pedal strikes should be less in theory.
 
I went from 160mm cranks to PINND 145mm cranks and really like them for my type of riding. (Natural rocky narrow tech trails) Im just about 6-2”, I moved my dropper up 15mm after installing the 15mm shorter cranks but quickly found it was a bit too tall on the first ride. I’m now about 10mm above my original saddle height. This is the only change I made after installing the shorter cranks. I thought about changing the chainring from 36t to 34t, but I like the feeling of having to input a bit more leg power with the shorter cranks. I like how quickly I can ratchet over large rocks while climbing and of course having less pedal strikes. I also don’t notice the Bosch rattle/crank backlash as much while descending with shorter cranks. I don’t think 145mm cranks would be desired for flow trails, roads,…
 
AlumiPro said:
I went from 160mm cranks to PINND 145mm cranks and really like them for my type of riding. (Natural rocky narrow tech trails) Im just about 6-2”, I moved my dropper up 15mm after installing the 15mm shorter cranks but quickly found it was a bit too tall on the first ride. I’m now about 10mm above my original saddle height. This is the only change I made after installing the shorter cranks. I thought about changing the chainring from 36t to 34t, but I like the feeling of having to input a bit more leg power with the shorter cranks. I like how quickly I can ratchet over large rocks while climbing and of course having less pedal strikes. I also don’t notice the Bosch rattle/crank backlash as much while descending with shorter cranks. I don’t think 145mm cranks would be desired for flow trails, roads,…
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That's interesting because I ended up raising our seats by about 6mm (1/4") for 10mm shorter cranks.
 
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Lemond Method in the day for Roadies
But it seem now they are choosing to use shorter cranks
 
I changed from 165mm to 155mm on Levo and raised seat around same 10mm. On a emtb there`s no need to change chainring. On a acustic bikepark bike I changed from 170mm to 165mm and didn`t do any changes because there`s no sitting and pedalling on a park..and I have dh gearing…😀
Huge benefits on both bikes, felt weird first time though…
 
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