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I just realized my seat stays are slightly bent

The frame is steel. Is this something I should be worried about?

PS: notice how also the top of the seat stay is naturally bent. Perhaps a normal design of the frame?

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EDIT just found another bike parked with exact same seat stay profile so I assume this bent/curve is by design:

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2 Answers 2

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Most likely this is normal design. Although more common in aluminum than in steel, tubes that don't run straight are common. Since both sides are a same, the only possibility this is caused by an impact with for example a car, is that a car hit with same force the bicycle twice, once from each side (besides, you seem to have a rear rack that would first be bent in an accident very severely due to the thin tubes, so the only possibility two impacts caused identical bending on both sides would be that both of those impacts were without the rear rack). Not gonna happen. If you want to be 100% sure the bike hasn't been in an accident, check if the rear tire is straight. A rear tire that is not straight is a sign of an impact, although if you happen to have horizontal dropouts then it may be possible to adjust the tire to run straight after an accident.

I'd expect to see this funky bending not in seat stays but rather chainstays, mainly because chainstays have clearance problems: they must allow the cranks with narrow Q-factor to run freely without hitting the chainstays, and have enough tire clearance for wide tires and fenders, while at the same time being very widely spaced at the rear for 135mm hub so that equipment fanatics can have the 8 speed 9 speed 10 speed 11 speed 12 speed cassette that's absolutely essential for climbing up even a small hill. So I'd fully expect any "modern" bike to have something other as a chainstay than a fully round and fully straight tube.

Why the frame manufacturer used this bent tube on seat stays is a mystery to me.

Also, you are fortunate in that the frame material is steel. Steel is unlikely to break even if bent. In fact, there is an operation called cold setting in which the rear spacing of the frame is spread out to accommodate more modern wide hubs. With aluminum I would be slightly more worried if this was caused by an impact, but would not stop riding the bike. There's plenty of redundancy in a diamond frame. If a tube breaks, it doesn't leave you stranded 100km away from civilization, it only slightly slows you down. Forks would be a different matter though: there's no redundancy in a fork, so if you have bent fork legs, especially in an aluminum fork, it's time to stop riding.

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  • Concur - there's basically zero chance that an accident/impact would bend both seat stays equally, so its very likely a design feature.
    – Criggie
    Commented Jul 29, 2021 at 9:28
  • The style also supports the installation of two common 'dutch style' accessories, the rear wheel immobilizer and dress guard/wheel guard on bikes with wider modern hub spacing. (even if not utilized that way in the pictures, the shape is characteristic of the overall style of bike.)
    – Affe
    Commented Jul 29, 2021 at 19:25
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Are you the first owner of the bike? If it had another owner, then that owner could have forced a wrong wheel with a hub with wider OLD (over the locknut distance).

Howe reputable is the shop you've bought the bicycle from? If it is a good one, you could pay them a visit and ask about your concerns, it should not cost anything.

If you are certain that the bicycle has never been modified by anyone, then I would not worry too much.

Can you measure the OLD for the rear hub? Normally, I'd expect the hub to be 130 mm wide. If it is 135 mm wide, then it might be a too wide hub.

When the wheel is out of the frame, take a look at the rear frame dropouts. Do them seem to be parallel to each other? If not, then the frame might have been unprofessionally deformed to fit a wrong wheel.

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  • This bend looks so severe that I don't think cold setting is the cause. Besides, cold setting (forcing a wide OLD hub in a narrow spacing frame) is a perfectly valid upgrade path for steel frames.
    – juhist
    Commented Jul 29, 2021 at 9:57
  • When I try to force the wheel in the rear frame I definitely have to force it a bit to open up. Commented Jul 29, 2021 at 10:12
  • @juhist The seatstays may be bent both by the original frame design, and later expanded even further by the cold-setting. Cold-setting is surely may be acceptable, but can it be fully trusted if done by an unknown person? E.g. have the dropouts been re-aligned after the spreading? Was it a 130 → 135 mm or 126 → 135 mm transformation? Is the wheel still properly centered? In other words, should the OP be worried, as the question's title asks? Commented Jul 29, 2021 at 10:26
  • Yes indeed it is possible the bends are partially from original design, partially from either cold setting (nothing wrong in it), or forcing a too wide hub in without cold setting (this should be avoided, you should cold set the frame instead).
    – juhist
    Commented Jul 29, 2021 at 14:43

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