Bicycle Mechanics - Old Mixte frame with bent seat tube
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03-28-11, 04:20 PM
Okay, so I have this roger riviere frame that a friend gave me. He got hit by a car while riding the bike, and the only semi-noticeable damage is the seat tube is BARELY bent, like you have to look very hard to even notice the bend at all. I was wondering if y'all think it is safe to ride, or is it not a good idea, and why. Your help will be greatly appreciated.
Thanks for your time,
03-28-11, 04:27 PM
What's it mades of, and pictures would be useful
03-28-11, 05:09 PM
Hmm. I guess it's a little more noticed in photo...
Also, I think it's steel.
Yes it's safe to ride if the handling is OK.
I wouldn't expect it to break without tons of warning by way of development of obvious cracks. A process that could take years, if ever, on this frame.
But a sideways bend of this type is likely coupled with deflection of the rear triangle. Either or both will cause handling issues because the wheels don't track exactly one behind the other, and/or because your center of gravity won't be directly over the track line unless the bike is tilted slightly to one side.
The end result will be a tendency for the bike to pull to one side and probably steering instability (shimmy) at higher speeds. Plus riding the bike tilted will not be comfortable for any length of time.
If you have the various parts to rebuild this without investing more than a few dollars it might make an OK town bike for shopping or errands or short loops for exercise, but I wouldn't expect it to ride decently enough for anything beyond that.
BTW- since you asked if it was safe, it is structurally, but shimmy or tracking issues (if they exist) would make it unsafe at any decent speed such as when descending hills.
03-28-11, 05:52 PM
Awesome, Thanks NY, That was very helpful, Fortunately I do have all the parts to rebuild it, and when I am back on my feet, I will rebuild it and test if there's any noticeable shimmy.
03-29-11, 01:27 PM
Those bikes are made from High Tensile steel. As such you would be prefectly safe in rigging up some form of jig and using a jack or big lever to bend the seat tube back straight. Just don't begin wailing on it with a hammer. Use pressure to bend it, not impacts. How you'll set up to bend it back will have to be up to you and some ingenuity since it'll depend on your tools and resources. I'd say it would be worth bending it back before you rebuild it. If you're going to put that much effort into it you may as well start with a straight "foundation".
A car jack or hydraulic bottle jack could supply the force. Then it's just a case of rigging up some way to hold the frame in such a way that you can apply the force to it. Some lumber screwed or nailed together along with a tie down strap or two could be used to produce a quicky frame jig suitable for doing a job of this sort.
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