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Problem with stamped dropouts on singlespeed. There were dents from the nuts. It became inconvenient to operate the bike (the wheel is poorly fixed and constantly moves out). It is impossible to tighten the nut further, this leads to further deformation.

Dropout has a pair of "constructive bulge - bulge" on both sides. I planned to make a couple of sufficiently powerful plates and install them. But I'm afraid that the plates are deformed, and the reliable fixation of the wheel will not work again.

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I tried:

  1. nuts with a different tooth shape
  2. spacers
  3. tensioners

Each option has its drawbacks:

  1. A different shape of the teeth did not affect fixation at all
  2. Washers bend and bulge into the dent cavity
  3. Tensioners have shown themselves well, because the number of violations of wheel fixation has greatly decreased, but for the time being, since they combine the shortcomings of the two previous methods. Plus, they are outrageously expensive.

I also wanted to increase the number of links from the chain, which would move the location of the nut a little further. But I'm not 100% sure about this method...

Is there any way to solve the problem with these dents? Or will I have to buy a new frame, or weld the metal with automatic welding and grind it with something like a grinder?

I would be very happy and grateful for any hint and advice.

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    If it's single speed freewheel rather than fixed, would you be open to adding a chain tensioner, and putting the wheel where it wants to sit in the dents? Or using a slightly larger chainring if that gives suitable tension where it wants to sit? Both have their downsides of course
    – Chris H
    Apr 16 at 11:04
  • @ChrisH Yes, those are good ideas, especially if we combine wheel offset by adding chain links and using a "tensioner body" as additional dropout protection.
    – dtn
    Apr 17 at 5:31

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The frame has been cold-deformed because someone's used too much torque to tighten wheel nuts which has squished the metal over time. Either the dropouts are too soft/thin or someone's used an impact driver or a cheater bar on the bolts.

Washer

You're not going to get a thick anything on the outside of the axle's bushings AND inside the dropouts - this is the Over Locknut Dimension (OLD) and will be fixed at 130mm or 135mm or maybe 126mm. If you shove the equivalent of a 2mm plate on the inside with a washer, then the rear dropouts will be forced apart, and will no longer be parallel. This makes your rear wheel get loose even faster. Not recommended. Also probable not needed because the axle's bushings are the right size to fill that curved-out area of the dropout.

A washer on the outside of the dropout is a reasonable idea and should work well. You want something that presents a flat surface under the axle nut, but is profiled to match the frame. Hopefully your axle has another 2-4mm of spare thread exposed.

  Existing axlenut  
  V _ +---+    
  _|| |  /
 |  | | /
 |OO| |O|     <-- axle hole
 |_ | | \
   || |  \
      +---+       This side touches bike

Chain Tug

To stop your rear wheel moving in the dropouts, you might want to fit a Chain Tug on the chain side, or both sides. These are mostly built for bikes with trackends, but some do exist for dropouts like yours. One example is the "Surley Hurdy Gurdy"

enter image description here

More related info Are there tugnuts made to fit forward facing horizontal dropouts?

Positioning

You could put also the axle further forward or backward in the dropout. This lets it sit against "clean metal"

Backward/up the dropout helps with climbing angles and makes the bike longer, better for long+straight rides and improves function of front brake. Also it will support the nut on about 3/4 of the circumference. Also you get a positive stop which helps a lot every time you reinstall the wheel.
Also improves "braking" if this bike is a fixed gear and you elect to skid-stop.

Moving axle forward in dropouts means a shorter bike wheelbase, leading to snappier turning, and maybe fewer links in chain, but the wheel is poorly supported by the longer finger of the lower dropout arm. Wheel reinstalls become more fiddly to get everything aligned right.

Ultimately, these stamped-metal dropouts are a bit weak. Your more-expensive solution is to talk to a frame builder and get harder/thicker ones installed. If you're competent with a brazing torch, you might be able to do this yourself, though alignment must be perfect and not move throughout brazing.

Here's a higher quality dropout example - notice how both sides bulge outward? This is a thicker insert that has been added and brazed into place. I bet the inserts are somewhat hardened too, whereas yours are plain mild steel.

enter image description here

Last Resort

It may be more viable to simply replace the frame with a used one of better quality. Keep your eyes open for options, and you might be able to move all your parts from the current frame to a replacement.

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    I'm not sure if it's possible to tighten axle nuts hard enough that room-temperature steel will squish like this. Another explanation might be that OP forgot to put washers under the axle bolts, and the serrations did this to the dropouts. I've seen that plenty of times before.
    – MaplePanda
    Apr 18 at 0:01
  • @MaplePanda yeh I suspect a combination of cheese-grade steel and an impact driver/lots of leverage on a cheater bar. And having nuts of higher grade steel than the frame, over time has monched into the dropout. Those simplex ones are at least triple the thickness of the stamped ones.
    – Criggie ♦
    Apr 18 at 1:16

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