I have a Gazelle dutch bike which I want to upgrade with a front dynohub. It currently has a Sturmey Archer drum-brake hub dated 1988, which I believe to be a SBF model. I bought a wheel with a Shimano DHC6000 plus the accompanying roller brake. I only now noticed that it has an axle with 9 mm diameter and the currently equipped Sturmey Archer hub has a 3/8" axle. That means the old one is about 0.5 mm thicker.

Can / should I put that new wheel in? Will the extra spacing in the fork dropout mean any problems, especially safety wise?

  • FWIW with QR disc hubs this absolutely can cause the wheel to shift under braking. There's a new bike I deal with now that's plagued by the exact issue. I don't know whether a roller brake would do this, and it probably depends somewhat on the orientation of the dropout anyway. Sep 23, 2018 at 3:11
  • Edited the title because the answer here really is contingent on the brake type. Sep 24, 2018 at 7:24
  • Do you have a reaction arm or torque arm on either wheel? this would help translate the torque away from the dropout and up the fork leg. Not uncommon on front-hub ebikes.
    – Criggie
    Sep 24, 2018 at 9:04

1 Answer 1


Any free space between axle diameter and clearance width of dropout sides can exacerbate problems with maintaining the correct tension between the dropouts when the wheel is installed. The last thing you'd want is to hit a bump, pothole, etc... have the front wheel fall out of those dropouts and put you into a faceplant or worse. Bikes are subjected to immense levels of vibration on every ride and those vibrations will work to loosen any weak fasteners. BTDT

There are aftermarket spacers designed for MTB applications that will adapt a 9mm skewer to a 10mm hub/dropout (typical of rear dropout clearance) and that 10mm converted to inches is .394" (3/8"=.375")

You might also find some aluminum or steel spacers at a local hardware/home improvement store. Measure out your skewer diameter and dropout width to be sure of what you're looking for.

  • 2
    Once installed, the axle is held by the clamping force of the QR. If the wheel fell off because the axle is smaller diameter than the dropout, it was not installed properly. Because of this requirement for the clamping by the QR, any space use must be smaller than the width of the dropout. Essentially the spacer is needed only to help with locate the axle during installation.
    – mattnz
    Sep 22, 2018 at 4:49
  • Agreed Matt, the clamping force is holding tension to the hub. The risk is if there is too much free space in that opening at the dropout point. If the skewer's (or the axle) diameter is significantly smaller than the opening width of the dropout, no amount of clamping force will keep it there. I know this from racing MTB with the old cam-lock skewers before Thru-Axles were introduced. It's a bad feeling to hit a root/rock, or loft the front; only to see the wheel go one way and you go the other. Losing wheels out of dropouts is the very reason that "lawyer tabs" exist.
    – jc allen
    Sep 24, 2018 at 12:37

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