Shorter Cranks

[witzend]

Hi after using my new Ampere Altar bike for a while now I'm looking for shorter pedal cranks for it my knees are complaning. Ampere arn't very helpful saying they are available but not from us so tried contacting their listed dealers who refered me back to Ampere. What I need is a 48T with a center taper square with around a 150 crank presently 170 anyone a idea where I might obtain this ? Thanks

 

[RogerA]

There's nothing E-Bike specific about cranks. Have a look at Spa Cycles website. They have a good range of square taper cranks in different lengths. 150mm is quite short though. You might be in the range of children's cranks at that size.

 

[Andy-Mat]

Hi after using my new Ampere Altar bike for a while now I'm looking for shorter pedal cranks for it my knees are complaning. Ampere arn't very helpful saying they are available but not from us so tried contacting their listed dealers who refered me back to Ampere. What I need is a 48T with a center taper square with around a 150 crank presently 170 anyone a idea where I might obtain this ? Thanks

I understand your thoughts, but unless you are under 5 foot tall and/or overweight (you neglected to mention your physical attributes which are needed for a proper reply!), or have some major health problems with your knees, which a sport Doctor should evaluate for you, I do feel that you may be making a mistake.
For instance, possibly the bike you are riding is the wrong size for your bodily attributes, guessing only, it is possibly far too big for you.....
There are people here on Pedelec, that can possibly help you far better than I can, provided you can give them certain physical measurements, like leg length, height for example. Also the the size/dimensions/type of your bike itself.
I wish you success in your endeavours, but it would be sad to invest in major changes to the bike (plus the inherent costs of course), just to find out that it doesn't help you, or they may even make the problems worse......
Also, do you understand that the shorter the crank, the harder you have to physically work for the same energy input from you, therefore the greater the stress on your knees.....Its simple physics, and lever technology.
I wish you well and far less stress on your knees, but if its any help, a good friend of mine had both his knees replaced about 10 years ago, and it has improved his "knee health" dramatically, and he now rides a lot, on a non e-bike!
He has always been somewhat overweight, which may have caused the problems with his knees, and he is now 69 years old, and goes walking his son's dog for him as well as biking....
regards and best wishes
Andy

 

[Sturmey]

They can be got ok but you may also have to buy chainring and screws e.g

BCD110 152mm Crank Crankset 5 Arms Aluminium made - AliExpress 18

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

155mm are a popular size on 24 inch mtb but unfortunately usual come with a triple chainring 42/34/24/ But I have also seen 140mm cranks with 48/38/28 T on girls mtb.
I have 155 cranks fitted to middrive (which I got from scrap bike) and it helps. I did raise the saddle a little to compensate, as the pedal now is a little higher at bottom of stroke.

 

[witzend]

They can be got ok but you may also have to buy chainring and screws e.g
155mm are a popular size on 24 inch mtb but unfortunately usual come with a triple chainring 42/34/24/ But I have also seen 140mm cranks with 48/38/28 T on girls mtb.

Thanks for reply and link I've contacted them to see if they can supply 48T chainring to fit cranks

 

[Gringo]

I run 155 crank arms. Tomorrow I will have a look in my parts bin to see what I have kicking around.
I have brought 155‘s in the past but because I have several bikes (and being an engineer) I find it a lot easier to shorten the cranks that came with the bike by drilling & tapping new pedal holes.
As a rule I make the new hole 20mm inboard of the original, 175’s become 155’s etc

 

[witzend]

I run 155 crank arms. Tomorrow I will have a look in my parts bin to see what I have kicking around.
I have brought 155‘s in the past but because I have several bikes (and being an engineer) I find it a lot easier to shorten the cranks that came with the bike by drilling & tapping new pedal holes.
As a rule I make the new hole 20mm inboard of the original, 175’s become 155’s etc

Thanks. I had thought of that but haven't made any enquiries as to who localy to me might be able to under take the job several angles involved in the crank. I have a 48T chainring at the moment and just can't find a 55 crank with a 48T. This is as near as I've been able to find Would the chain need adjustment

 

[Gringo]

Firstly, if you’re keeping the same number of teeth you won’t need to alter the chain length.
shortening the crank arms by 12% (170 down to 150) and Keeping the same chainring will make it 12% harder to press the pedals for any given gear I’d consider a 42t ring.
Personally, with shorter arms I find my knees are happier on a smaller ring and spinning faster, rather than being in a taller gear and pressing harder, your knees will thank you in the future

Anywho, in my shed I found some Miche Young arms 155mm long 5 bolt 116 bcd, along with a 38t steel ring and a 36t alloy ring (48t Miche rings are available)
Unfortunately one of the threads used to remove the arms was damaged
Fortunately I’m a engineer and made a bespoke crank extraction tool, this is attached to the arm with 8 m3 screws, (it works perfectly) I also made covers to hide the extra m3 holes


I have replaced these arms only because I wanted to use a 36t oval chainring the only way to do this was to change to 4 bolt crank arms.

If you can find stock, a Miche Young chainset double will meet your requirements, (you don’t have to use both rings )

Miche Young Chainset

Well I don't know why this is called the Young chainset. obviously its aimed at youth riders but adults sometimes need shorter cranks and even tall people can ride and benefit from shorter cranks. So here it is a cheap chearful square taper chainset in 155mm or 165mm length Weight: 520g W/ BB...

thecycleclinic.co.uk

I’d kept my Miche arms just in case I wanted to build another special in the future, although I could possibly let you have them for £20 but only I f your desperate

 

[matthewslack]

Google crank shorteners. Several companies have made such things, worth seeing if they still do.

 

[witzend]

There's nothing E-Bike specific about cranks. Have a look at Spa Cycles website. They have a good range of square taper cranks in different lengths. 150mm is quite short though. You might be in the range of children's cranks at that size.

Thanks I contacted them and they say they can supply what I need Just hope so when it arrives

 

[witzend]

I’d kept my Miche arms just in case I wanted to build another special in the future, although I could possibly let you have them for £20 but only I f your desperate

Thanks that a kind offer but hopefully if RogerA's post above which mentioned Spa cycles works out I should hopefully be fixed up

 

[witzend]

Google crank shorteners. Several companies have made such things, worth seeing if they still do.

Thats a idea and Looks like they are available still

Pulse Crank Shorteners from Highpath Engineering

Pulse Crank Shorteners provide 3 or 4 new positions for your pedals and are designed to adapt adult cranks for shorter riders. High grade aluminium alloy.

highpath.co.uk

 

[Bikes4two]

Some years ago I had the rear cranks on our tandem professionally shortened (to 155mm) - I can't remember who I got to do it but iirc I was put onto them by JD Tandems, so maybe give them a ring?

 

[witzend]

Thanks I contacted them and they say they can supply what I need Just hope so when it arrives

Well they arrived an I fitted them and can say after a ride today my knees are feeling a lot easier so Thanks to RogerA and Spa Cycles and to All who replied

 

[witzend]

Well they arrived an I fitted them and can say after a ride today my knees are feeling a lot easier so Thanks to RogerA and Spa Cycles and to All who replied

If anyones interested in the ones I've removed I'm open to offers there 48t an 170mm crank 12mm square