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Slightly warped sense of reality

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Slightly warped sense of reality

Old 03-02-16, 12:49 PM
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dailycommute
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Slightly warped sense of reality

I have been riding the 1991 Miyata sportcross quite a bit lately on our rough frost heaving roads. It is a great bike, I have put hundreds of miles on it in less than a year and it is very solid and stable. Just a few days ago went down some of the steepest hills around here and it was very stable at 30-35 (yeah I am wimpy these days!) and the bike tracked straight, no shimmy, very solid.

The whole point of this is that from day one I had noticed the rear stays on this bike were not totally square. They are not bent in the traditional manner of in/out but rather slightly bow/curve down if I hold straight edge carpenters square from top of seat lug. Both sides appear about the same. The dropouts are aligned, the rear wheels mount center (have run 2 different rear set ups on it now), no shimmies, shakes, etc. All I can think is some previous clyde bunny hopped a curb and slightly bent the seat stays about evenly as have never seen vintage steel rear stays that were designed with any type of curve/bend. I have kept a regular look out for any changes to the paint or evidence of fatigue but so far nothing.

Guess that is one thing I really like about steel is is can bend and still hold integrity--at this point I doubt the bike is going to have any type of failure but just curious if others ride anything like this. May take a few pictures to show but for example in the outlink here the rear triangle looks normal, the bend is slight but most definitely there.
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Old 03-02-16, 01:15 PM
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Are you sure it wasn't spread from 126 to 130 at some point?
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Old 03-02-16, 02:22 PM
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Originally Posted by dailycommute View Post
I have been riding the 1991 Miyata sportcross quite a bit lately on our rough frost heaving roads. It is a great bike, I have put hundreds of miles on it in less than a year and it is very solid and stable. Just a few days ago went down some of the steepest hills around here and it was very stable at 30-35 (yeah I am wimpy these days!) and the bike tracked straight, no shimmy, very solid.

The whole point of this is that from day one I had noticed the rear stays on this bike were not totally square. They are not bent in the traditional manner of in/out but rather slightly bow/curve down if I hold straight edge carpenters square from top of seat lug. Both sides appear about the same. The dropouts are aligned, the rear wheels mount center (have run 2 different rear set ups on it now), no shimmies, shakes, etc. All I can think is some previous clyde bunny hopped a curb and slightly bent the seat stays about evenly as have never seen vintage steel rear stays that were designed with any type of curve/bend. I have kept a regular look out for any changes to the paint or evidence of fatigue but so far nothing.

Guess that is one thing I really like about steel is is can bend and still hold integrity--at this point I doubt the bike is going to have any type of failure but just curious if others ride anything like this. May take a few pictures to show but for example in the outlink here the rear triangle looks normal, the bend is slight but most definitely there.
Yes, post pics. If you don't have to spread the frame to get the rear wheel in, and the dropouts are aligned, I wouldn't worry if the stays aren't perfectly straight. Your fork blades were perfectly straight when they got to the factory, and were bent on a jig to make the fork. You don't worry about that much now, do you?

The people that say "steel is real" should know that they're not completing the sentence. One should say "steel is real(ly) tough".
@andr0id is suggesting the curve may have been set if/when the frame was spread. It could also be the case that they were built that way in the factory, perhaps with crank clearance in mind. Many modern tubing sets come pre-bent:


Columbus Zona 29er S-bend seatstays
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Old 03-02-16, 07:35 PM
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Yeah, I am not worried, just curious. I doubt this lower end hybrid built in Taiwan was using anything but straight stays, I could not think of how the stays could be bent during production. The dropouts are not spread best I can tell, running a 8 speed on there which I can slide in without effort. The bend is counter to where I would expect cold set bends to show. Took these drive side shots but the other side bends at almost the same angles.

edit ends up these cross bikes did ship with 130mm spread so unless it was some cutting edge "hybrid tech" on these stays will chalk it up to previous riding. Heck, could have been me I guess, did ride it on some gravel/light single track before converting it over. But still rides very nicely for bent reality.

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Old 03-02-16, 09:36 PM
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Might just be the force of those cantilevers exerting on the seat stays.
Stop less, go faster.
A rack was mounted in a previous life and got a whack from behind?
Leave it.
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Old 03-02-16, 10:29 PM
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Originally Posted by dailycommute View Post

I wouldn't worry about it, this is relatively common.

if you put a straight edge alongside the top tube of many bikes, youll see uneveness particulary around the joints/lugs.

yours looks to have a more pronounced bend, but I have a (high end hand built) Schwinn Paramount with the same issue.
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Old 03-03-16, 05:09 AM
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Originally Posted by dailycommute View Post
Yeah, I am not worried, just curious. I doubt this lower end hybrid built in Taiwan was using anything but straight stays, I could not think of how the stays could be bent during production. The dropouts are not spread best I can tell, running a 8 speed on there which I can slide in without effort. The bend is counter to where I would expect cold set bends to show. Took these drive side shots but the other side bends at almost the same angles.

edit ends up these cross bikes did ship with 130mm spread so unless it was some cutting edge "hybrid tech" on these stays will chalk it up to previous riding. Heck, could have been me I guess, did ride it on some gravel/light single track before converting it over. But still rides very nicely for bent reality.

If the seats stays are bent then you would see some kind of bending in the chainstays. You can't bend one without bending the other. The curve you're showing would result in the chainstays being bent upward. Brazing and welding heat can result in mild warping. My vote goes for it happened in the manufacturing process.
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Old 03-03-16, 06:09 AM
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I have seen thick aluminum mtb seat stays that bow outwards when the brakes are squeezed hard. Hard braking on the rear could bend the stays forward I imagine.,,,,BD
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Old 03-03-16, 07:00 AM
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They appear to be normal tapered stays to me; smaller in diameter at the bottom. But it's hard to tell from the photos.

BTW, looking at your address, is that River Road in Windham, ME?
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Old 03-03-16, 07:00 AM
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Couldn't say, but I was drawn in by the thread title.
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Old 03-03-16, 09:36 AM
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I'm with the people that say it came out of the factory that way. Certainly nothing to worry about..
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Old 03-03-16, 11:38 AM
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Hey thanks all, may update the Miyata cross thread on here to see if anybody else with this era bike can confirm these factory stays. No matter really though as it rides fine and not changing anything else on this current setup.

River road is reference to the Penobscot (or close to it) which I cycle up/down everyday during commute season-- but have lived on the Kennebec as well. No lack of water /ice in Maine, that is for sure. Hope to get out this spring or early summer on a mini 4-5 day T700 state tour to try and hit some trout water (prefer wild streams/ponds vs rivers) as the state has some fine fishing spots.

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Old 03-03-16, 02:11 PM
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I have a mixte frame with the same affliction, only worse. I'm pretty sure the previous owner carried a heavy load on the rear rack. Like another person. Common practice here, but not such a good idea on a Gazelle Champion Mondial.
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