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I just discovered a crack in the back rim of my mother's bike and I'd like to replace it. The trouble is that the hub is 40 spoke and I cannot find a 40 hole rim that would fit the bike and would be less expensive than buying a new bike.

However I can find plenty of 36 hole rims that are perfect (other than the fact they have 36 holes).

I was wondering if there are lacings that are safe for connecting a 40 hole gear hub to a 36 hole rim.

I would rather not replace the entire wheel because it would, due to the rather antique internal hub currently in use, likely mean adding a derailleur, replacing the gear-line and replacing the chain, which just seems a little overkill.

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  • Is the dead rim steel or aluminium? If its steel, I'd just buy a new aluminium rim for both wheels. Yes they cost more, but aluminium rims are such an upgrade over steel rims.
    – Criggie ♦
    Commented Oct 5, 2019 at 2:53
  • I don't know what kind of vintage hub your bike is using, but you can get used internal gear hubs quite cheap. Just ask your local bike shop whether they have a used 7 gear SRAM for your purposes, for instance. I payed only 25 Euros for my last hub that way. Those SRAM hubs are not built anymore, but they are quite robust and serve you excellently in the city.
    – cmaster - reinstate monica
    Commented Oct 5, 2019 at 5:42
  • So what happened in the end? Did you move the rims around and rebuild both wheels ? How did it work out for you, and is your Mum happy ?
    – Criggie ♦
    Commented Sep 23, 2020 at 2:30

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"Perverse" is what Sheldon Brown calls this sort of wheelbuilding, but it apparently can be done. There are even video tutorials for a 32-36 mismatch, which might help you. Unless you really need a sturdy rim, you could look into using a 32-hole rim as a 4:5 pattern might be simpler than 9:10. You need several sizes of spoke for such a build.

Another option worth a look is trying to get undrilled rims, though they're probably expensive.

I have heard of people building wheels ignoring the spoke hole offset from the centreline, or filing out the holes if the offset is slight. Doing that on a 20-hole rim would mean you'd have to drill every other hole - but be careful as the valve hole could easily be a problem (most but not all of my wheels have it halfway between spokes). I'd be wary of such an approach personally.

I don't suppose the front is 40h is it? Building a new front wheel and putting the old front rim on the back would be a neat solution if it is, but 40h front wheels aren't common.

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    A quick check of UK and US sites suggests that 40h rims can be had for under £/$30, though most are twice that.
    – Chris H
    Commented Oct 4, 2019 at 19:10
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    The front rim is 40 holes! That is a clever solution I had not thought of, although I don't know if I will end up using it.
    – Sriotchilism O'Zaic
    Commented Oct 4, 2019 at 19:32
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    The downside of using the front rim is that you end up building two wheels (unless you just buy a cheap 32h/36h front wheel) but they're normal builds. I'm a novice wheel builder and would much rather build two normal wheels than one tricky one
    – Chris H
    Commented Oct 4, 2019 at 20:25
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    Brilliant thought on reusing the front rim, but then OP is left with a front 40 hole hub and no suitable rim, so it means buying a complete new front wheel. Second thought is to check for brake track wear on the front rim, which may render it unsuitable.
    – Criggie ♦
    Commented Oct 5, 2019 at 2:52
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    @Criggie indeed, but a routine front wheel is cheaper than a geared hub, even new, and there's more chance of picking up a second hand wheel. Good point about brake track wear, but hopefully the front hasn't suffered too much.
    – Chris H
    Commented Oct 5, 2019 at 6:30

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