Chainring warped - Replace??

anthonyjf said:

While on the road this weekend, I looked down and saw that the large chainring was warped. I have a Cannondale with a TruVatiV Elita SL Double, 39/53. This is the crank that came with the bike. Bike is about 1.2 years old, and only 300 miles. I doubt the crank in under warranty, but I will check. Should I replace the entire crank? If so, any recommendations? Also, what would cause the chainring to warp??

If it is steel, it can be straightened. If not, it is time for a new chainring. I doubt it is covered by warranty, but it never hurts to ask. I am not familiar with that bike, but if the chainrings come off the crank, then the warped one can be replaced separately.

I had a single tooth on the middle, steel chainring on my Specialized Crossroads bend completely over to the side. I do not know how or when it happened. I know on which ride, and I did drop the chain on that ride while I was downshifting, but I did not notice the bent tooth until I was cleaning the drivetrain after the ride. The tooth was bent so far out of the way that the bike felt and shifted normally. The chain just road over the gap. I took it to my LBS, where the mechanic straightened the tooth, and I have put another 1000 miles on the bike without a problem.

My son-in-law just had one of his chainrings replaced because a single tooth broke off. He does not know when or how that happened, but recently he started to drop the chain once or twice per ride. When he checked out the drivetrain, he found the missing tooth. Total parts and labor to replace the chainring, replace the chain and adjust both derailleures was about $60 (again, we are talking about a cheap steel chainring and not Dura Ace or Record).

anthonyjf said:

While on the road this weekend, I looked down and saw that the large chainring was warped. I have a Cannondale with a TruVatiV Elita SL Double, 39/53. This is the crank that came with the bike. Bike is about 1.2 years old, and only 300 miles. I doubt the crank in under warranty, but I will check. Should I replace the entire crank? If so, any recommendations? Also, what would cause the chainring to warp??

I would guess that it's not the chainring that's warped. It would be awfully hard to do that! If you want to check, you can remove the chainring and place it on a flat surface.

I think that the more likely possibility is that the crank is not properly installed on the bottom bracket. A small misalignment would make it look like the chainring is warped, when the reality is that the crank is at a slight angle to the bottom bracket. A possible cause is that the crank bolt has come loose or the crank was not properly installed.

I would take it to your local mechanic and have them take a look at it for you. Good luck!

John Swanson
www.bikephysics.com