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I am converting my wife's Giant aluminium frame bike to electric by fitting a rear hub motor. The problem that I have encountered is that the e hub motor axle is much bigger than the original wheel. I have succeeded seating the wheel in the forks but there's no side to side play in the wheel resulting poor alignment. I am therefore considering filing the drop out to increase the play. What do you think ? One other point. The hub motor cable passes through the centre of the axle which may explain the increase in diameter. I have now fixed the two problems

  1. Gently filing the dropout jaws. This enabled the axle to seat correctly.
  2. Wheel mis alignment. Solved by adding two spacer washers to one side of the axle. This resulted in perfect wheel alignment and made it easy selecting all 7 gears. So many thanks for everyone's helpful comments and I can now progress further with the rear hub motor installation.
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    Hi, welcome to bicycles. It might help if you could specify the model of the bike and the e-hub. That way people can check the specs on them and see if it's reasonable to make them work. You could also add pictures, showing what you've got and what the problem looks like.
    – DavidW
    Commented Mar 1, 2023 at 21:24
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    Just to clarify - the new axle is thicker, so its not fitting up the standard dropout slots? Some electric motors require a torque arm too, to not put too much pressure on the nuts. Does your motor need a torque arm or does the axle have slots in it that are supposed to be a close fit for the sides of the dropout ?
    – Criggie ♦
    Commented Mar 2, 2023 at 0:13
  • Thanks for your help
    – Tigertone
    Commented Mar 3, 2023 at 14:50

1 Answer 1

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Since you say you were able to get it into the dropouts, it appears you're talking about the over-locknut dimension (OLD) of the hub and frame, sometimes known as the frame spacing, and that you're considering making the dropouts thinner by removing material.

The over-locknut dimension of the hub should match the frame dropout-to-dropout inner spacing exactly. You don't want there to be extra gap there; there is tolerance for some but it is strictly undesirable.

Mismatches in either direction (hub too narrow or hub too wide) between the frame spacing and the hub OLD cause stress and misalignment in the dropouts and the hub. Whether the axle or the frame absorbs more is its own conversation, but neither are good.

Many motor hubs make it confusing how the various washers and spacers on the axle are meant to be configured. Make sure you have this part right by comparing to an exploded diagram of the hub. Alternatively try the different configurations until you have it matching a real frame spacing number, i.e 135mm or 130mm for nutted and 142mm or 148mm for thru-axle.

If the basic problem here is it's not just free of side-to-side gap but the hub is also a larger OLD than the frame is intended to take, you have the wrong hub and there is no good solution. Shaving thickness from the dropouts for the purpose of installing a motor hub into is not a reasonable plan; you would ideally have more overbuilt dropouts, not less.

Some motor hubs may have alternate axle and freehub hardware that allow it to adapt to different spacings.

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