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I have a kids' 18" bike with a fixed gear and a coaster-brake. I would like to replace the rear hub with a (preferably 3-)geared hub with a coaster brake as it is the kind of brake my kid is most comfortable with.

The problem I am facing is that it is an aluminium frame bike and it only would take a hub with 110mm OLD. Yet, all the hubs I am able to find are 116-120 (Sturmey Archer S2, SRAM T3, Shimano Nexus SG3C-41) or even 130mm (SRAM i-Motion) in width.

Is there any chance of modifying the Shimano Nexus or the Sturmey Archer hubs to fit a 110mm frame (e.g. by replacing the outer screw/lock nuts with narrower variants)?

  • Would it be possible to force the bike to take a wider hub without endangering safety? – Willeke Apr 18 '15 at 10:08
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    Nope. It is an aluminium alloy frame which is generally considered non-adjustable due to being too brittle. – the-wabbit Apr 18 '15 at 17:29
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I finally got it going using a Shimano Nexus 3 (SG-3C41). Looking at the pics, I figured that I could remove the massive outer distance nuts to make it fit a narrower fork:

SG-3C41 right SG-3C41 left

This was not quite sufficient to get it to 110mm so I had to make use of an angle grinder to cut a couple of mm off the cone-shaped nut on the right side of the axle.

The most tedious part of it all was finding an 18" bicycle rim with 36 holes. I could not get one, so I ordered a 32-hole rim ending up with three different spoke lengths (3-crossed) in the wheel. It took me some effort to figure out of how to lace the wheel and seems to bring some durability / stability issues due to the difference in spoke tensions, but this is a kid's bike after all so great strain on the rear wheel is not to be expected.

  • What's the "official" outer locknut dim on these? I'm looking for a hub for my wife's bike with 110 (112?)mm between forks. – Andrew Wolfe May 13 '17 at 3:37
  • @AndrewWolfe the 168mm axle variant is built for a 120mm fork, the one with a 175mm axle is for 127,5mm. According to the tech doc the difference in outer locknut dimensions is achieved by using wider locknuts. Note: while the bike is still in good use (by my younger son now), I am not all that sure it would be a good idea to remove the locknuts on this hub when fitting into an adult's bike. You might see the cone nut loosen under strain, making the hub prone to malfunction. – the-wabbit May 17 '17 at 18:35

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