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I have the Topeak MTX 2.0 bike rack, and hoping to install on a KHS Flite 223 road bike.

The M5 screws that come with the rack screw in as expected to the braze-ons near the rear brake caliper.

But the same M5 screws slide right through the braze-ons located near the rear hub. M6 screws will screw in (with moderate effort) but won’t fit through the eyelet on the rack.

Any suggestions on what to do? Seems odd KHS would use different sizes on the same frame. It doesn’t seem to be paint in the frame’s braze-ons, because the rear ones are too big, not too snug. Screws for the bottle cage also appear to be M5.

enter image description here

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  • Are the threads at the bottom the same (size and position) on both sides? I have had to drill out a rack once, and I've also tried running an M5 with a low head (button head) from the inside out through an M6 hole, with a nut on the outside. Mind your chain in that case
    – Chris H
    Commented Oct 17, 2023 at 6:11
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    @ChrisH they are the same on both sides. That was my thought - find a longer M5 screw and add a nut to keep it secure. Just doesn’t make sense why it’s different than the other braze-ons.
    – Matt
    Commented Oct 17, 2023 at 13:28
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    @ArtGertner or just drilled it to 5.5 as a clearance hole. But it looks painted on the inside, and unthreaded.
    – Chris H
    Commented Oct 17, 2023 at 14:51
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    I bet that resistance is due to the paint
    – Paul H
    Commented Oct 17, 2023 at 22:25
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    @Criggie with the new picture, probably not - the most likely imperial threads into which an M6 would start to screw are noticeably coarser
    – Chris H
    Commented Oct 18, 2023 at 10:40

1 Answer 1

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I think your options are as follows:

Opt 1. Modify the rack

  • Drill out the rack clearance holes to accept M6 bolts.
  • Use M6 bolts

Considerations:

  • This might void the warranty of the rack. Decide for yourself if this is a big deal
  • This might reduce rack's max weight capacity. Manufacturer would definitely not welcome that option. I would not worry too much as long as there is enough material left around the hole, overall strength should not be compromised.

Opt 2. Use bolt + nut

  • Treat a larger braze on as a clearance hole for m5 bolt
  • Pass the bolt through both braze-on and the rack
  • Use the nut to secure the bolt

Considerations:

  • Use a nyloc nut
  • I would strongly recommend using washers on both bolt head and nut sides
  • I would recommend having the bolt head on the inside and nut on the outside
  • Make sure that bolt head clears your spokes / hub flange. To further reduce the profile, use button head bolt.
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  • I think the eyelets are the same size on each side
    – Paul H
    Commented Oct 17, 2023 at 22:21
  • You are right @PaulH. Updated my post
    – Art Gertner
    Commented Oct 17, 2023 at 22:23
  • I made the same mistake mentally as the OP's "braze on near the brake caliper" made me thing of the non-drive side of a disc brake bike at first.
    – Paul H
    Commented Oct 17, 2023 at 22:24
  • You need to be very careful indeed on the drive side, that nothing contacts the chain. When I've done this, I had to use not just any bolt but one with a low head on the inside of the frame, and the nut on the outside, otherwise the chain would catch badly when changing between the 2 smallest sprockets. There was also no room for a washer there
    – Chris H
    Commented Oct 18, 2023 at 10:43
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    @matt it's still worth a try to put a button head M5 screw through from the inside. You could even get a countersunk (flat head) M5, and countersink the inside of the frame. But I'd rather drill out the rack than the bike
    – Chris H
    Commented Oct 25, 2023 at 5:31

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