Here's my "long distance" ride, which is an old steel MTB without suspension.

I picked it up by the saddle to move it and felt some play, I thought the saddle rails might have been loose, but as per picture, there's a crack 90% of the way around the frame.

I have bent it open a bit more with medium finger pressure.

The crack shows evidence of rust, so its been a slow break rather than a sudden one.

Crack in seat post receiver

I weigh 100 kilos (220 pounds) and have long legs, with a standover height of 91 cm (3 feet). The frame is too small for me, at 20" (51 cm).

The seat post was reinforced internally with extra pipe (I have bent seat posts before). The post extended 10 cm (4 inches) into the frame — i.e., well past the crack — and then 29 cm (11 inches) up to the seat.

Strava says I've done 2,949 km (1,832 miles) on this bike in the last 15 months.

So my main question: is this an old-age fatigue failure of the frame, or did I break it by being too tall, or too heavy?

Second – is the frame repairable or is it now scrap?

  • All of the above. Probably time for another bike.
    – paparazzo
    Commented Sep 12, 2015 at 10:44
  • 2
    The failure was no doubt hastened by having a relatively short extension into the seat tube and having the seat extend so high. But rust no doubt also figured in. If you attempt to have it brazed, a patch should be brazed across the crack, after the crack itself has been brazed. (But I suspect that the bike is not really enough to merit the effort.) Commented Sep 12, 2015 at 12:04
  • show me the slit for the clamp from the back of the bike please. I have an idea why this happened
    – Noise
    Commented Oct 1, 2022 at 9:11
  • @Noise can't sorry - this bike went to the great scrapheap at least 7 years ago.
    – Criggie
    Commented Oct 1, 2022 at 21:02

1 Answer 1


It looks like plain old metal fatigue. Most probably there was a hairline crack, then water got into it and rusted it out.

Note that when you extend the seat height, you increase the lever arm of the seat post and put a considerable amount of stress on the frame precisely at that location. It doesn't help that the design of that seat clamp has no reinforcing material and is high-up, further increasing the leverage on it. Poor design.

The good news is that it's a steel frame. You could take it to an auto body welder and they could easily fix it for less than an hour of labor. Since they can't weld from both sides (the seat tube wouldn't go in), it'd still be weak and susceptible to damage. Or you could try rebrazing it yourself.

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