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I have a Topeak BabySeat II MTX 2.0 Rear Rack that is supposed to mount into threaded holes in the frame. However, my old road bike does not have these holes, and instead has eyelets welded to the dropout/chain stay (pic).

My bike shop said that the rack was not compatible with this set up and that I should get a seat that mounts to the seat tube. Is there something un safe about just putting a nut on the back side of the bolt? Maybe that weld isn't rated for the weight? I've used a rack with pannier bags on that connection for years without problem, but obviously I want to be more careful if I'm sticking my kid up there.

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    If you're worried about seatpost-mounted seats, you don't need to be. I used one (Hamax Siesta) until my daughter got much too big, and left a light pannier rack underneath. The rails provide a little suspension for the child, as despite being thick steel they flex a little. It's a shame you've already got a rack-mounted seat though.
    – Chris H
    Feb 21 at 6:55

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"Is X safe?" is a personal question that depends completely on your risk tolerance. For me? Using those brazed-on mounts is better than a plastic P clip around the seat stay but they're only designed to carry lightweight mudguards/fenders and not racks.

Would I trust a cargo/parcel rack to those mounts? Yes - definitely. I might even drill out the hole to take a larger diameter bolt, and/or tap it, and/or put additional nuts on the inside.

Would I trust a child to those mounts? Personally no, but then again I'd use a childseat in front of the rider, not behind, like a weeride or similar.

You have to make your own risk assessment, and I'd carry my lunch in places where I wouldn't put a kid.


Another option might be to "sandwich" the triangular-shaped hole on both sides with two custom shaped pieces of metal as covers, and add some flanges so they locate. Then bolt both covers together through the frame, and then bolt the kid-rack to that. Advantage is it gives you as thick a bolt as you can fit in the rack's stays. Downside, its a lot of work and metal forming. Would a sketch help?

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    You're tall aren't you? Because I am and had no chance of fitting a front seat. Perhaps because toptubes don't rise or grow all that much with frame size, those of us with long legs would have to ride with our knees either side of the seat. I figured out enough dimensions to mock one up out of scrap materials when I was considering seats, and it was a non-starter.
    – Chris H
    Feb 21 at 6:59
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    It doesn't really answer the question: there can be technical reasons that makes this design inherently less safe/resistant that a thread in the dropout (and that point is not subjective), and I would think that the OP is asking for that. Maybe the the problem is not threaded vs not threaded, but the fact that this eyelet looks like an addition to the dropout, instead of being totally integrated.
    – Rеnаud
    Feb 21 at 8:53
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    Unless you need to ride up steep hills with the seat on there, with or without the child - and I dropped mine off at nursery/childminder's before commuting. Plus they're much more exposed to the weather in front of you than behind, and because they're not working, they get colder than you think in the wind
    – Chris H
    Feb 21 at 9:19
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    The problem with cutting a thread is that if it's an M5 clearance hole, as is likely, it's probably 5.5mm (maybe bigger to allow for the paint). That's too big to cut a good M6 thread, and already M6 is probably bigger than the hole in the mating part on the seat, let alone going to M7 (a nasty rare size). By the time you get to M8 there's no metal left on either part. 1/4" may be an option if you want all future users of the bike to hate you, including your future self. And then it's still brazed on with a narrow neck
    – Chris H
    Feb 21 at 9:21
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    If I look at my bikes that have threaded mounting points, the thickness at the level the thread is always larger than what you have here (around 7-8mm). For one of them, the dropout itself is thinner, but there's an embossment to have enough metal for the thread.
    – Rеnаud
    Feb 21 at 9:35

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