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Thread: Dropout Width

  1. #1
    Senior Member Smallwheels's Avatar
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    Dropout Width

    I'm planning to build a cruiser this summer. Right now I'm considering trying a three speed internal gear hub by SRAM. The specifications say it is a 130 mm unit. While looking at different bicycles to buy I'm seeing that manufacturers don't give out the width of the rear dropouts. I don't even know if that measurement is of the inside or the outside of the frame.

    So far I've learned that frames have 110, 120, 135, and 150 mm dropout widths. I've sent messages to a few retailers. So far only one responded and his frame was too skinny for the i-motion 3 speed.

    I don't want to purchase a seven speed derailleur bicycle and convert it to a three speed. That would be silly. I want to buy a single speed and convert it to a three speed.

    What are the ramifications of turning a 120 mm wide dropout to a 130 mm wide dropout? Since I want 2.125 inch wide tires with fenders I don't know if 120 mm wide dropouts even affect the maximum size of tires that fit into the frame. I'm only considering aluminum frames. I know that the i-motion 3 speed hub comes with two 2.5 mm washers so it will fit into 135 mm wide dropouts.

    Why not just buy a three speed? I see several available with Nexus hubs. I want a SRAM hub because many people who have tried several three speed hubs say the SRAM is the best of the models manufactured today. It also seems less expensive to start with a single speed and add the i-motion 3.

    There aren't many used bicycles in my small town listed on Craigslist.org. That isn't a great place to find cruisers on a regular basis. Therefore I must buy a new bicycle.

    Is there a consistent size for dropouts on single speed cruiser frames with fat tires?

    These are questions for people who sell or regularly work on bicycles. There are only two dedicated bicycle shops in town. The others that sell bicycles are large retail outfits that have some bicycles in stock during the summer months. I don't want to be limited to just Giant or Trek which are the brands carried by the two shops.
    Smallwheels

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  2. #2
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by Smallwheels View Post
    Is there a consistent size for dropouts on single speed cruiser frames with fat tires?

    These are questions for people who sell or regularly work on bicycles. There are only two dedicated bicycle shops in town. The others that sell bicycles are large retail outfits that have some bicycles in stock during the summer months. I don't want to be limited to just Giant or Trek which are the brands carried by the two shops.
    One-speed cruisers are usually 110mm between the dropouts. Since you're only considering aluminum frames, I think it's pretty chancy to cold-set one to 130mm for the I-Motion hub. Read up: http://sheldonbrown.com/frame-spacing.html

    The dropout spacing doesn't really affect what width tire will fit in the frame.
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  3. #3
    bike whisperer Kimmo's Avatar
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    It may be possible to remove some spacers from the SRAM hub's spindle.

  4. #4
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    If you put the wrong sized spindle in a dropout, it will mean the drop outs would be at an angle against the spindle. This would put high stress on one side or the other. Not good.

  5. #5
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    Most new road and mountain bikes have 130 and 135mm dropouts. The measurement is across the axle nuts.
    If you find a steel frame with lower spacing you will need to bend the rear triangle and straighten the dropouts.

  6. #6
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    Since you haven't bought either, try to select the frame you want and buy the hub to match. 110mm is standard for SS and internal gear hubs and 130 or 135 for derailleur bikes. As others have said, you can bend (cold set) the frame to change width and re-parallel the dropouts, but why do it the hard way.

    It isn't only a matter of width. Derailleur bikes today have mostly vertical dropouts which are useless for non-derailleur bikes because there's no provision to tension the chain, so you'd need to add a derailleur-like chain tensioner. You need a frame with horizontal dropouts so the wheel can slide back to tension the chain.

    As I said, pick out a SS compatible frame first, then contact Sram or others about getting a hub of the correct width.
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