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A Bent Look at Self Contained Touring

So you want shorter crank arms – now what?

with 8 comments

 Shortened Cranks

Continued from Are your crank arms too long?

Ok, I have decided that I want to replace the standard 170 MM  cranks on my Slipstream with 155 MM cranks more appropriate for my Hobbit legs.

So I Googled and found almost nothing. Looks like the shortest commercial Road and MTB cranks are 165 MM. There are 155 MM and shorter cranks out there but they are BMX cranks and cranks for kid’s bikes. None of those are drilled for a Triple Chain Ring. There is no way I can give up my Triple.

However, I did read in the forums that there are companies in the UK and USA that remachine Cranks to provide shorter crank arms. They will shorten yours if possible or sell you a remachined set. With the current Euro-Dollar exchange rate I am only interested in USA suppliers.

Bike Smith Designs for short cranks

The company in the USA is Biksmith Design & Fabrications.

They have a selection of  good crank sets at a range of prices. For what they do the prices seem quite reasonable ($80 to  $160 for a set with chainrings).

You can pick road or MTB sets with arm lengths down to 145 MM and several choices at 155 MM. In general they recommend not using Kneesavers with these shortened crank arms. But they do have a set of remachined Salsa Cranks that can be used with Kneesavers.

I haven’t quite decided which set to buy yet, but I am leaning to the Salsa Cranks because my industrially sized feet rum most cranks.

Next Steps in the process are:

1. Find a Bottom Bracket to work with the new cranks

2. Do I need any other hardware for new cranks?

3. Learn how to remove my Shamino HollowTech II cranks

4. Learn how to install the new cranks

5. Learn How to Set Up Front Deraileur with new cranks

This sounds like fun, I’ll post my experiences as I work through this process.

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Written by Roland

March 5, 2008 at 9:25 am

Posted in Cranks and BBs

8 Responses

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  1. Mark Stonich is a great guy to deal with. He can answer all your questions. In fact, the process for switching to short cranks is simple. The most important question is: Do you have a large enough frame? Your seat will have to move back. As for your other concerns:

    1. Anytime you switch cranks to another model, you may run into the need for a different length BB and short cranks are no different. Not what I would call a problem though and maybe you can get cranks that use the same length BB as your current ones.

    2. No.

    3 & 4. Don’t know about Hollow Tech (only use square spindle type) but you can look here:
    http://www.parktool.com/repair/readhowto.asp?id=35
    http://www.parktool.com/repair/readhowto.asp?id=103

    5. You likely won’t need to fiddle with the front derailleur much (if at all).

    Good luck.

    PS. If you’ve been thinking about trying Q-Rings, this might be a good opportunity.

    http://bikesmithdesign.com/Short_Cranks/m440rotor.html

    PSS. If you go with round rings, I really like the Dotek crank set. Good price and looks good in silver.

    PSSS. Shorter cranks tend to have wider Q-factor so usually no need for knee savers.

    macpublish

    March 5, 2008 at 11:13 am

  2. The Q-Rings are a great suggestion. Thanks a lot, I never noticed them on Mark;s site.

    I will defeinitely be changing BBs. The HollowTech BB doesn’t match up with the new shorter cranks. I am not sure what size BB to order because it is hard to measure the size with the HolowTech’s in place. I have requested infor from Longbikes. I’ll need a few new tools to take the HollowTech’s off but it looks fairly simple with those tools.

    I don’t understand why the seat needs to move back with shorter cranks. I thought I’d be moving the seat foward to make up for the shorter cranks.

    Thanks againg for suggestiong Q-Rings. I am definitely looking into them. My only concern is that the Q-Ring story sounds so much like the Shimano Bio Pace story I bought into in days of old.

    Roland

    March 5, 2008 at 2:23 pm

  3. I also recommend following Mark Stonich’s recommendation to get smaller chainrings. The shorter crank/smaller chainring combo makes climbing easier and acceleration faster.

    mBent

    March 5, 2008 at 3:28 pm

  4. Thanks mBent these comments are making me feel a lot more comfortable about this expenditure.

    Can you explain why folks are saying that shorter cranks require you to move your seat back? That seems counterintutive to me.

    Enjoy the Ride …. Roland

    Roland

    March 5, 2008 at 3:45 pm

  5. With shorter crank arms, the distance from your seat to the farthest point of travel of the pedals will be less by the amount your have shortened the crank arms. In order to keep proper leg extension, you should move your seat back by this amount. (assuming you are happy with your current pedaling situation)
    I’ll be watching with interest to see how you get on with shorter crankarms.
    mBent’s suggestion for smaller chainrings is interesting. I might be able to survive shorter crankarms with a smaller inside chainring for climbing and keep the big ring as it doesn’t seem to be a problem. Wonder if my rear derailer can wrap a bit more chain?

    Charles

    March 5, 2008 at 4:20 pm

  6. Another way to think about the crank arm/seat length issue is to imagine a SWB with cranks in line with the main tube. Now imagine a shorter crank – the pedal is closer to the bottom bracket, but your legs are still the same length, so you have to move the seat back.

    mBent

    March 6, 2008 at 4:02 pm

  7. I’ve got it now. Seat position is based on the pedals maximum distance from the seat. Since the pedal is closer with shorter cranks then unless your legs get shorter you have to move the seat back.

    mBent, Thanks for your patience and great explination.

    Roland

    March 6, 2008 at 6:35 pm

  8. […] Continued from So you want shorter Crank Arms Now What? […]


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