Bent frame
 

Hi all,

My bike mechanic has said that my frame appears to be bent. He did a quick set of measurements (he was running out of time because I had to leave for an appointment) and said that the frame seemed to be out by at least 5 mm. He said he may be able to bend it back into shape (it's a 631 steel framed Jamis Aurora Elite), but he isn't certain that it'll work or it'll take. I was hoping someone here might be able to give me some insight about the likelihood of this repair working and whether the repair is likely to revert again after use.

Thanks,
Brad

I'd have to watch the job being done. explain the technique and equipment.. that 5mm is measured where?

It'll probably work. I'd go for it.

if he or she isn't "certain", then i'd go elsewhere.
5mm is less than 1/4"... steel either bends, or it doesn't... 5mm is a minor tweak, and it won't mysteriously "revert".

go elsewhere.

Or ask for more clarification. It's very possible the mechanic didn't have the time to fully describe what he found. If he does fill in the info and dose so in a educational manor then he's likely a good guy, just in a hurry at that moment. I will agree with maddog34 otherwise. Andy

I think he is a good guy. I was in a rush to get my bike by 3pm because I had to leave for an appointment and my bike is my source of transportation. He said he hadn't measured things super carefully but he thought that the frame was bent by at least 5mm, which at the time I took to mean the rear triangle was bent laterally by either 5 mm to the left or right of the position it's supposed to be in.

The bike is shifting very poorly, even after replacing the inner cable and outer housing, new chain, cassette, derailleur (he put on a NIB derailleur to check to see if that was the problem). He said he was going to get the shifters next (next week when he's going to come back to try to sort things out), but that a visual inspection and watching them actuate the cable made him think it was fine. That's why he decided to measure the frame (quickly because I had to leave) and he said that he was thought that the frame was out of alignment by 5 mm.

also to clarify, he didn't indicate that the steel might bend back, that was my question. I was worried that if the steel bent once, and now we bend it back again that it's now been weakened and more likely to bend another time.

+1 Get more detail. 5mm at the seat tube using the "string method" is actually significant, as it translates to close to double that at the rear dropouts.

...cold bending of steel framed bikes like yours is a pretty standard repair for them, and used to be done routinely.

There are a lot of places that refuse to do anything that involves bending the frame now, and quote liability as the rationale. Regardless of liability issues, the steel in a bike frame is not going to spontaneously return to where it was in the out of alignment state........if that were possible, then a frame that got a little bent, like yours, would be self correcting.


It's not rocketry or nuclear physics, but such a straightening and realignment technique does require a modicum of sophistication in terms of technique. I guess the guy you're using as a mechanic has more of that than you do, so my inclination is to say you should go for it. Like I said, there are places now that will simply refuse to perform such a repair........and for no good reason I can discern.

Thanks for the information. I didn't think that the frame would be more likely to spontaneously bend in exactly the same way, more that the more you bend metal, the weaker it gets and the more likely it is to bend again. Like with a pop-can top. I realize that one is steel and one is aluminum - but it's just where my concern stems from.

Actually the place the frame bent is stronger than before it was bent. It's known as "cold working". It will be less ductile and, if bent repetitively in the same place, will eventually crack. However, unless you insist on bending that frame many, many more times, once it's realigned it should last for a long time.

No, a pull tab is very thin and the bend is typically over a very small area, and a bike frame tube is relatively thick and the bend is more spread out. In addition the frame is being moved sideways, and the stress on a rear triangle or fork is far more vertical than lateral. Don't worry about it.

:foo:

But this flies in the face of what many want to think, bending and bad have the same first letter so must be the same:) Andy

+10 Too little information to go on.

Google frame string test, do it yourself. I used a "foot wedge" to bend back a bent stay on my 1982 Trek 710 (Reynolds 531).

I agree with other posters who said that there's too little information to go on.

I'm a little gun-shy about mechanics looking for alignment problems in frames. Most frames these days come from the factory accurately aligned, and accidents that are severe enough to bend the frame but not severe enough for the bending to be obvious without measurement are somewhat rare. The average mechanic doesn't see many such frames and thus might be prone to performing or interpreting the measurements incorrectly.

In short, I'd be happy to trust a framebuilder's judgment about a possibly bent frame; I'd be less trusting of the average mechanic. (I've had mechanics working in shops that I ran who learned the rudiments of frame alignment measurement techniques and then started claiming that every other frame in the shop was misaligned by their measurement. They weren't.)

Was the shifting good earlier in your ownership of the bike? If so, have you recently had an accident with the bike that was extreme enough to bend the frame? If not, I'd be reluctant to use that particular bigger-hammer route before the list of simpler fixes has been exhausted.

Did the mechanic check the dropout alignment to confirm whether or not the derailleur mounting tab is square with the rest of the frame? If not, get it checked.

Also, if your mechanic didn't try squirting WD-40 into the shifters to free up the gunk that develops in the inner mechanism, I'd try that. It's a quick fix if it helps, and it can't hurt.

if shifting is issue, first thing to check for alignment and bending if needed would be the derailler hanger

Check the hanger. If that fixes it, maybe leave the frame alone.

If you can't tell the frame is bent by riding it, is it really bent? Downhill, corner left, corner right, can you tell? I've had steel bikes that were off a bit, but riding with no hands I couldn't tell anything was off. My repair method was to wait a while and forget about it. Bent and cracked is a whole 'nuther kettle of fish.

I can't remember how well the bike shifted when I first got it. It was my first good bike and it was quite a while ago. But I don't recall it being a problem.
About five years ago my bike fell over in the garage and got a large ish ding in the top tube. It's about an inch long and maybe 3/16" deep. Other then that no dramatic crashes, just an occasional knocking over.

The hanger has been checked. The inner cable and outer housing have been replaced. The shifters are pretty new, maybe 18 months old, and they are NOS ultegra 6600. The derailleur is the same age, ultegra 6700. The chain is new. The cassette is new.

At some point I noticed the shifting wasn't great, but that's also aeohnd the time I started riding much more - 300 km per week up from maybe 120. Another big difference is it used to be the riding was a lot of stop and go because of my route to work, but now I work somewhere else and the majority of the ride has no stops at all. So there is greater opportunity to notice it. I noticed how annoying the shifting was at about the same time.

Initially I thought it was in need of a tune up. That didn't help. They checked the hanger. It was fine. Tried new cassette and chain. No difference. Said mechanic loaned me a new ultegra 6700 derailleur to see if it helped. It did not. The only thing he hadn't done yet is trying to swap out the shifters themselves to see if that helps.

The thing is, where it shifts poorly is right in the middle of the shifting range. It never perfectly aligns. You can get it to shift well either in he middle or on the outer edges (one or the other). You can't get it to shift well everywhere. Which is why I thought it might be the hanger. But it isn't.

I didn't suggest the frame could be bent. He did after he said he did a quick measurement. He said he will come back and do it properly this week and bring replacement set of shifters to see if that works.

To be honest, I don't ever recall the shifting being as good as it is on my giant tcr advanced with 5700 all around. I didn't think about it a lot until I started putting a lot of kilometres on it.

More Info Please
 

Your post above came in while I was typing. After reading you above post I can't offer much.

Your input is very good. Sorry you are having this issue.

A few videos to compliment the great advice given here on Bike Forums..


https://www.youtube.com/results?sear...g+a+bike+frame

...in all honesty I'm at a loss to explain how a small frame misalignment could be causing a problem like the one you describe. That's usually either a bent derailleur hanger (which would jibe with your fall over accident) or some problem either with the shifters or the cables to which they connect. Sometimes you can run into it when trying to use an 8 speed shifter with a 7 speed cogset, or vice versa.

So I guess I have no useful advice. :( Not that unusual.:)

I appreciate your thoughts, I really do. I appreciate the time everyone has put into this thread for me. I don't understand how the frame alignment issue could be so problematic either, but we've ruled out almost everything else except for the shifters - so the mechanic dude is going to try that on Wednesday.

I should start a whole other thread, because I've also noticed that when I ride occasionally I feel this horrible grinding sensation through the pedals. But apparently the bottom bracket is fine. I don't get it. It'll feel like I'm riding over asphalt that is in poor shape, but I'll only feel it through my pedals, and only when I'm pedalling which is why I thought it was the bottom bracket. But then when the alignment issue came up I wondered if perhaps it's all related. I don't know. I'm getting a bit frustrated.

Post some pictures of your bike and drivetrain

The symptoms you describe still point to hanger, but the new symptom, the grinding felt in the pedals, indicates something else, which could be a bent frame, but without knowing more about your BB, it's just another mystery. I'm looking forward to the next report from the mech.

The mechanic is coming to work tomorrow to take a look at the bike. I am curious/excited to hear what he has to say about it. I just want to get this damn thing to shift properly. I agree that the symptoms seem like a hanger, but I've had two people look at the hanger and they both agreed it was fine. The thing is, if the rear triangle is bent somewhat, wouldn't that cause similar symptoms to a bent hanger, since the rear end of the bike wouldn't be aligned with the middle.

And on that note, today I tried to ride my bike without my hands --- and i couldn't. It kept pulling to the drive train side. So maybe that reinforces a bent frame?

I'll take some photos of my bike and frame tomorrow and post them.