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n00bus
11-23-2011, 06:48 PM
Hi i didnt know where to put this so if its in the wrong place please feel free to chastise :P
Ive taken my sled for a couple of decent test rides (a couple kays) during the last week and ive fine tuned the gearing to get it right so it has just enough top speed with the tallest gears and the shortest gears are right on the verge of being too short to push without falling over because im not moving fast enough LOL
But then i have a bit of a hard time peddling it up a slight hill for 300m to get it home again. I feel the gearing is right and that i wouldnt go any shorter as i cant peddle any faster for the speed im doing so im thinking a bit more crank arm length would solve this by giving me more leverage to push with resulting in less effort to peddle it.
So in trialing this i removed the one piece crank i had in there with arms at 165mm and fitted a 3 piece in its place with 180mm arms and hey presto theory proven to work. But still i feel a bit more length would give me more leverage without affecting the gearing, so the question is how long do they make crank arms and can i get them to fit the BB ive got without having to chop and weld?

PeterT
11-23-2011, 08:01 PM
Using a 1-piece BB or a 3-piece BB: find some steel the identical diameter of the cranks, cut your original cranks equally in the middle, if possible with your tools, drill & tap a thread (For round rod) centrally in both ends, then cut the insert piece to size and drill and tap those ends, screw headless bolt into each section to join everything back together, and then weld it all tight. The bolted inside will increase its strength, or if you trust your welding skills, simply weld without bolting.
For non-round cranks, similar process, 2 pins are used instead of bolts for internal support.

Another idea is to cut off square taper and pedal ends from metal cranks, and make your own style cranks that suit your ride, at your custom length using the square taper & pedal ends to finish your design.

PeterT

n00bus
11-24-2011, 12:06 AM
So are you saying you cant get longer arms than 180mm? I really wouldnt like to cut up the arms i got, maybe another set that im not too fond of. Maybe i need to design an adapter of sorts to stretch these arms longer without it looking like a bashed crab, ill have a think about it some more.

n00bus
11-24-2011, 12:12 AM
I found these to shorten the arm

http://faqload.com/gfx/pubs/1285501306_r0.jpg

Maybe something similar but the opposite is in order.

PeterT
11-24-2011, 07:33 AM
Can't those things be rotated 180 degrees to extend your pedals, rather than reducing your pedals?

PeterT

n00bus
11-24-2011, 09:31 AM
You would need to lock them in somehow, from what i gather they have a locating tab either side of the crank arm to stop it twisting off while peddling it, if you mounted them hanging out it would only have the bolt stopping it from winding off.
But something to that effect but longer and canterlevered out would be easy enough to whip up

Modern man
12-27-2011, 10:53 AM
I found these to shorten the arm

Where did you find those? I would like to try shorter arms before actually hacking some up.

Cheers

socialtalker
12-27-2011, 12:49 PM
perhaps you can get some home hobbyist to cast some longer crank arms out of aluminum for you. some people on this forum do casting. i am planning on building a foundry once i have completed my welding for the winter, but havent done so.