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bent derailleur hanger(9 posts)

bent derailleur hangermapman
Sep 19, 2001 2:08 AM
I have this continuing problem with bent derailleur hangers on my road frames, 10 yr old 58 Long cm Serotta Colorado 2 & 15+ yr old 56 cm Basso Gap. The hangers come up bent about every 3-6 weeks of riding. No bumps or crashes just good rides. Chain line seems good on both according to 2 LBSs. Any thoughts?
Hmmmm....Greg Taylor
Sep 19, 2001 5:08 AM
Unless they are incredibly metal-fatigued, hangers don't just bend by themselves. I'd suspect that you may have little gremlins bumping into your pride and joy when it is stored, or locked up. Is the bike leaning/resting on the rear derailleur when stored? Do you ever put the bike down on the ground with the crank/derailleur side down? Done any travel with the bike where it would be packed up in a box or case?
Hmmmm....mapman
Sep 19, 2001 5:27 AM
Therein lies the mystery. Everyone I've mentioned this to seems to side with your opinion. But I never lay the bike down on the derailleur side nor have I travelled with the bike in a box or crate. I do, however, lean the bike up, derailleur side to the wall, but it is out of traffic flow and doesn't appear to have been bumped between rides. How might I check for metal fatigue?
Well, that IS a mystery...Greg Taylor
Sep 19, 2001 6:01 AM
I don't know of a readily-available test to measure fatigue in a rear hanger. You could, I suppose, rig up a torque wrench to see how much oomph it takes to get the hanger to deflect and bend, and then compare it figures for a similar "healthy" bike. You might, however, wind up finally doing the deed and wrenching the thing off of the bike.

Your best bet it taking to a frame builder (or sending it back to Serotta) for them to look at.
re: bent derailleur hangergrzy
Sep 19, 2001 9:37 AM
Well the obvious source of bent der. hangers is from something contacting this area from either resting the bike with the driver train down on the ground, crashing/falls.

Another not so obvious source is having too short a chain. When this happens and you cross shift into big/big you put a huge load on the driver train and you bend the hanger or the rear der. or both.

It certianly isn't normal on the mentioned bikes (current GT's are very bad) so it's got to be something you as the rider/owner are doing.
Hey, I hadn't thought of that one...Greg Taylor
Sep 19, 2001 9:54 AM
Makes perfect sense. Thanks Grzy, I'll put that bit of wisdom in my toolbox.
except that he said that two LBS's checked the chain. Not thatbill
Sep 19, 2001 11:11 AM
14 million Frenchmen or whatever that ol' chestnut is can't be wrong, but a too-short chain is the most obvious culprit (or, it was to me, with my fine, steel-sieve-like mind!), and I would think that the length of the chain would be examined along with, as he said, the chain line.
re: bent derailleur hangermapman
Sep 20, 2001 4:26 AM
I don't often run the big/big combo but do occasionally on those short but steep climbs. My circumstance is the bend goes in, toward the wheel. My physics is rusty; is this what to expect from the big/big stress?

Thanks
Yes Indeedygrzy
Sep 20, 2001 8:57 AM
Definitely bends inward which means that you see most of your problems when on the big cog with the rear der. hitting the spokes no matter which CR you're in. If you're really "lucky" the spokes will catch the rear der. and rip it right off the bike, often taking part of the hanger with it. So, saving a buck on a link or two ends up costing on the order of one hundred, minimum. I'm just a *little* embarassed to know all the gory details about this first hand.

There are those among us who ride with chains too short, but maintain they always know not to shift into the big/big combo. I'm not one of them.

If the original poster isn't having problems with his chain length then he's obviously doing something to bend the hanger when the bike is not being riden. Maybe his dog knocks it over and his wife sets it back up, but never mentions that his pride and joy took a spill so as to not upset him. Stranger things have happened. The current crop of GT hangers practically bend just by looking at them. The hanger is replaceable, but it's made of the softest aluma-cheese imaginable and has zero heat treated properties. The bonus is that when you try to bend them back with the Park DAG-1 you just weaken them further. If I rode one of these I'd carry a spare hanger in my tool bag, like I do on my aluminum Cannodale MTB.