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I have a bicycle with a 6061 aluminum frame. I had to replace the rear wheel, and I bought a wheel with an axle length that is a few mm short for the dropout spacing.

In order to fit the axle into the frame I would have to "squeeze" the dropout about 4mm. Currently the outer dropout of the frame is 144mm, and everything seems to fit if I squeeze it down to 140mm.

I have already ordered a longer hub axle, but it will be at least 2 weeks until I get it, and I would like to ride my bike with the squeezed frame until then. I know that in general, it is not a good idea to bend or even squeeze aluminum frames, but I am not sure those measly 4mm will make that much of a difference.

So, my question is:

Considering this is an aluminum frame, will the 4mm dropout squeeze cause damage in the long-term or maybe breakage? How safe is this?

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    FYI inner spacing is what counts. Sounds like you have a 135mm frame (standard for quick-release disc brake frames) and a 130mm wheel (standard for quick-release rim brake frames)
    – Argenti Apparatus
    Commented Sep 1, 2020 at 11:35
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    With a steel frame this would not be an issue but depending on the alloy it could a problem with Al-frame. At least, keep an eye on it, remove the wheel and refrain from riding not to put further stress on the rear triangle.
    – Carel
    Commented Sep 1, 2020 at 16:27

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It will damage the frame long term, or rather shorten the life expectancy for the rear triangle. Short term… it depends how short the term is.

Wheels are typically have standardized widths, as are frame's inner distances between the dropouts made to match them. Unless the frame is already damaged and bent or has a manufacturing defect, as the comments above suggest, you are likely trying to squeeze a 130 mm road hub wheel into a 135 mm MTB-frame (or maybe a 135 mm MTB wheel into 141 mm Boost-QR? does not matter, really)

Note that you may also have problems with adjusting the rear derailleur, as the cassette will also be off its intended position. It may not be possible to shift into the biggest rear cog.

If I were stranded somewhere far from proper components with only a 130 mm wheel to have, I would rather have attempted to add some sort of spacers taking up 2.5 + 2.5 mm at either side of the wheel, rather than compressing and stressing the dropouts.

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  • The dropouts have a 130mm inner distance. The new wheel has a simple coaster brake hub which is about 120mm wide. I already have washers on the axle, but the problem is that there is not enough thread on the axle to attach the nuts which hold the wheel. That is why I need the squeeze. I will get a longer axle (171mm instead of the current 158mm), but it will take two weeks to get here, and I want to ride the bike meanwhile.
    – Ferenc
    Commented Sep 1, 2020 at 20:23
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    Also dropouts will no longer be parallel, this can negatively affect bearing - rolling resistance and longevity, and puts a bending force on the axle.
    – mattnz
    Commented Sep 2, 2020 at 0:30

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