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I am considering getting a stem, which is meant for a 26mm grip area diameter. However, the handlebar I want to use it with is 24mm diameter (this diameter is uniform, so 24mm both at the grip and at the edges). Since the difference is small (~2mm), would it be reasonable to expect the stem to grip the handlebar well enough when tightened?

If not, is it possible to shim the difference without compromising safety?

If these specifics matter, the stem is Deda Murex, and the handlebar in question is a vintage bullhorn from a French company named Belleri.

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  • If you want to fabricate the shims yourself, start with a short length of pipe, so it already has the needed shape. It doesn't matter if the radius is too small, as it is easier to flatten it a little than it is to roll it tighter. Roughen up the surfaces with coarse sandpaper or a file. If the donor pipe is the right diameter, it would yield the two shims if you cut it right in half. If it is smaller, then cut two lengths of pipe, and use a bit more than half circumference of each. You can obtain it from an old steel seat post or another handlebar.
    – Jahaziel
    Nov 24, 2022 at 14:39

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The combination doesn't work without a shim.

The stem is shaped to be a tight fit around the handlebar to spread the pressure evenly. If you manage to tighten the bolts enough to clamp the thinner bar, the pressure will be at small spots and the stem can just flatten the bar. Shims to match 26mm handlebar to 28.6mm stem are much more common, but on quick search it looks like Problem Solvers manufactures the correct shim from 24.4mm to 26mm. If you manage to find one and there is still slack, a strip from a soda can should be enough to fill the 0.1mm gap.

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  • Thank you, that is what I assume, but couldn't check as I haven't purchased the stem. Is it possible to make a shim like this yourself? I don't have access to this manufacturer in my location. I am thinking to try cutting a flat metal piece of the needed thickness to the grip area width / handlebar circumference length. Something this thin would probably bend easily. It won't be perfect a circle, but maybe being pressed between the handlebar and stem would shape it well enough?
    – goose_lake
    Nov 24, 2022 at 13:20
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    As far as I know, a sheet soft metal bent close to the right shape should work. The handlebar is a hollow aluminum tube so I wouldn't try bending metal against it.
    – ojs
    Nov 24, 2022 at 13:35
  • Looking at the product instructions, they've textured the surface for more grip, which would be hard to do at home. Anyway by the time you've bought material and something to use as a former, you'll have spend more than the shim costs, for something less good
    – Chris H
    Nov 24, 2022 at 13:45
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    and @ojs depending on how vintage, the bars might be steel - but I still wouldn't use good steel bars as a former (BSO steel bars I would)
    – Chris H
    Nov 24, 2022 at 13:47
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    @goose_lake there are importers in quite a lot of countries, though my distributor in the UK is out of stock (they're good - I've used them for something else recently). I reckon the texturing is probably only in the region of 0.1mm. That's plenty for increasing grip. but the thinner stock probably deforms so much better when you do up the clamps that it's not so necessary.
    – Chris H
    Nov 24, 2022 at 15:21

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