Crank Shorteners

[W3RN3R]

Hubbers

I would like to bounce a question of the experts.

Is there anybody out there who successfully shortened the stoker cranks on a tandem. The reason: My daughter wants to join me on rides. Unfortunately the cracks are to long for her. Keeping in mind that larger persons would also ride from time to time. There are a few ideas on the www. One to re-drill and tap new holes and cut the bottom section of the crank. Or leave the hole for later use. Bearing in mind to fit a plug when the bottom holes are used. Not to influence the structural integrity of the crank arm.

Secondly to manufacture an adaptor fitting onto the cranks. See attached artist impression sketch.

Any mechanical workshops out there to ponder on the option.

[rattlesnake]

My wife is 1.63m and rides tandem with me, bought her 170mm crankarms. - that still too long?

[nolipoli]

I would be careful using that configuration, as it will make the pedals sit far out, which is going to be very uncomfortable for a little one.

 

Instead of putting the new pedal holes on the outside of the crank, try placing them next to the crank (if viewed face-on)

Have a look at the attached pic. I have thrown together a quick sketch.

crank shortener.pdf

[Tumbleweed]

I would be careful using that configuration, as it will make the pedals sit far out, which is going to be very uncomfortable for a little one.

 

Instead of putting the new pedal holes on the outside of the crank, try placing them next to the crank (if viewed face-on)

Have a look at the attached pic. I have thrown together a quick sketch.

 

That's inspired. Nice one.

[W3RN3R]

I would be careful using that configuration, as it will make the pedals sit far out, which is going to be very uncomfortable for a little one. Instead of putting the new pedal holes on the outside of the crank, try placing them next to the crank (if viewed face-on) Have a look at the attached pic. I have thrown together a quick sketch.

 

Great Idea.

By how much will the power strock angle be out? Will it have a power delivery effect?

But if you are only going to use the tandem for social rides it should not be a problem.

[Minion]

By how much will the power strock angle be out? Will it have a power delivery effect?

Unless you are using oval chainrings, it will have now effect at all. It's a pretty rigid, low force system. Mechanically, it will behave as if there were a crank arm runny directly from the pedal axle to the BB axis.

[Vinnydabutcher]

Nice one Nolipoli,

 

I think you might just have to set the crank 1 or two chain links back or forward so that both canks have the same Top of dead centre to optimise power - I recommend putting a quick link in the chain that sincronizes the two cranks for easy adjustment.

 

Should work fine - send us a pic once your done!

[Minion]

Nice one Nolipoli,

 

I think you might just have to set the crank 1 or two chain links back or forward so that both canks have the same Top of dead centre to optimise power - I recommend putting a quick link in the chain that sincronizes the two cranks for easy adjustment.

 

Should work fine - send us a pic once your done!

I forgot it was a tandem. If you're clever about where you put the the pedal hole, you could ensure that you can offset the crank by a fixed number of teeth and still have perfect synchronisation.

[Big H*]

Go and have a look here…..

 

sheldonbrown.com/tandkids.html

[Big H*]

Go and look here.....

 

http://www.sjscycles.co.uk/thorn-double-drilled-crank-arms-115-mm-140-mm-through-drive-for-raven-tandems-110-prod11106/

[Big H*]

Go and look here.....

 

http://www.sjscycles.co.uk/thorn-crank-shorteners-prod239/

[Big H*]

And here.....

 

http://www.tandemseast.com/parts/cranks.html

[Big H*]

I forgot it was a tandem. If you're clever about where you put the the pedal hole, you could ensure that you can offset the crank by a fixed number of teeth and still have perfect synchronisation.

 

Is synchronisation not dependant on the identical sized chainblades and the placement of the chain on it?

[Minion]

Is synchronisation not dependant on the identical sized chainblades and the placement of the chain on it?

It is, but if the device offsets the pedal forward or back by a certain amount, then the two riders will not reach the top at the same time. There will be a few degrees (constant) lead or lag. You'd correct it by removing the timing chain (is that the right term?), rotating one of the cranks by a few degrees and reconnecting the chain.

[Big H*]

It is, but if the device offsets the pedal forward or back by a certain amount, then the two riders will not reach the top at the same time. There will be a few degrees (constant) lead or lag. You'd correct it by removing the timing chain (is that the right term?), rotating one of the cranks by a few degrees and reconnecting the chain.

 

A timing chain is found on an old Datsun SSS.

 

Normally left hand side drive chain but I do understand what you mean. Also you have a child riding here that is not really going to contribute yet to the pedalling. ButI do agree with your explanation.

 

Is it a Lada or have you started drinking Vodka????

[W3RN3R]

Thx for the intel. Will take all into consideration.