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With my bike, in the front I just push the axle all the way onto the front fork, then tighten it, perfectly centered and straight.

With my rear wheel, it seems to be more complicated: there is some spacer on the rear dropouts on the drive side (small metal piece which holds the rear derailleur) but not on the left side dropout (see image).

I am unsure how to find the optimal position for the left side to have the wheel run as straight as possible in the frame. Is the left side missing a spacer? I managed to get the wheel somewhat centered in the frame but it's not perfect. Left side looks like this:

image of rear left side axle in rear dropout

2 Answers 2

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Back in the 80s, tolerances weren't quite as good as modern bikes. Sure, high end bikes were generally good, but mass-market bikes could be a little off.

As the machinist says, if you can't make it perfect, make it adjustable.

Technique So on the drive side, the axle goes hard against the stop and is tightened first. The non-drive side will float part-way down the dropout as per your image. To get the wheel straight, stand on the left side of the bike and hold the rear brake on hard with your left hand. Use your left foot to push the rim below the chainstay so its centered there, and then use your right hand to tighten the NDS axle nut. This provides a triangle of reference to make the rear wheel straight in the frame.

As for spacers, yes they definitely exist, but in no way are they required. Some bikes use a small bolt through the rear of the dropout, but that's a weak point.

enter image description here
Source: https://www.bikeforums.net/classic-vintage/896685-rear-wheel-spacer-dropouts-without-adjuster-screw.html

Surly have "Monkey Nuts" which are designed to sit on the axle like a washer, and fill the space. However you'd need to have exactly the right size. https://surlybikes.com/parts/monkey_nuts

Personally I find installation technique enough to hold the rear wheel. A QR wheel takes a lot more clamping force in this situation, but nutted axles like yours will be fine.

Consider that the leverage comes through the chain, so on the NDS there's over 100mm of leverage/multiplier that the drive side doesn't have.

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    Another technique that works without stretching is to simply use your left hand to centre the wheel between the chainstays, pushing or pulling against one of them. Then tighten the nut
    – Chris H
    Oct 15, 2023 at 19:16
  • @ChrisH I find a distinct lack of hands for that. If you're at home a simple clamp on the brake lever helps but I don't ride with one. I do carry velcro which would work but that's more faff. It is more convenient when the rear brake lever is on the left hand side of the bike.
    – Criggie
    Oct 15, 2023 at 20:49
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    I'm used to the rear brake lever on the left, but my method doesn't need the brake held on at all (V brakes). I'm used to swapping wheels on a bike like that because that's the kind of thing I keep at the other end of my train commute
    – Chris H
    Oct 15, 2023 at 21:26
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The process doesn't have to be complicated.

Take your shoe off. Jam it between the wheel and seat tube. It'll keep tension on the wheel and will stay put enough to keep it centered while you tighten the QR or axle nuts.

When done, put your shoe back on and off you go.

Works on geared and single speed/fixies. Battle tested in the real world.

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