Chain drops under high torque

[hockeybike]

Having an issue with a friend's bike. Shifting in the stand, and on the road is fine, but when he gets out of the saddle to try to sprint his chain drops inward. It'll fall off of both the large and small ring (50/34) the moment he torques the pedals hard.

Any mechanics have any insight into this? New chain on a used, but in ok condition cassette. No play in the crank, or in the bottom bracket--retightened both. No crack in the bb cable guide, either.

[false_Aest]

obviously we need a new bb standard.

[EricEstlund]

How worn are the chain rings? Chain line? Front derailleur adjustment (is its tossing off the inside and outside this is at least one of the issues).

[merlincustom1]

Chain rings loose?

[hockeybike]

Tightened the rings. The inner ring is worn, so that could be the culprit. Might be time for a new one.

[Steve in SLO]

I'd bet the outer FD cage plate is hitting. It could be either centering or derailleur alignment (rotation).

[Black Dog]

Check the chain too, it may be worn. Worn rings can do this too.

[Andrewlcox]

By friend's bike does the same thing. Could it be the pawls in the rear hub slipping or is that even possible. His rear hub clicks loudly when he coasts so I didn't know if that was a sign of wear. I think he has Mavic hubs.

[spartanKid]

His rear hub clicks loudly when he coasts


Some people pay a lot extra for this feature in other hubs! :D

[csm]

Check the chain too, it may be worn. Worn rings can do this too.

that's my diagnosis too.

[UberBike]

By friend's bike does the same thing. Could it be the pawls in the rear hub slipping or is that even possible. His rear hub clicks loudly when he coasts so I didn't know if that was a sign of wear. I think he has Mavic hubs.

The clicking is to let you know he is tired and its time to ATTACK !

[merlincustom1]

that's my diagnosis too.

The chain, the rings, or both together? Sounds like the OP's friend has a lot of miles on it.

[Peter P.]

Another vote to replace the chainrings. If you run the same brand crank as your friend, try mounting your crank or at least the rings on your friend's bike to confirm the rings are bad.

Also check for a cracked frame. Unnecessary frame flex can cause the chain to derail.

[oldpotatoe]

Having an issue with a friend's bike. Shifting in the stand, and on the road is fine, but when he gets out of the saddle to try to sprint his chain drops inward. It'll fall off of both the large and small ring (50/34) the moment he torques the pedals hard.

Any mechanics have any insight into this? New chain on a used, but in ok condition cassette. No play in the crank, or in the bottom bracket--retightened both. No crack in the bb cable guide, either.

Chainline? Worn, broken teeth on the rings?

[Bob Loblaw]

I take it this is a new problem since replacing the chain.

Replace cassette and rings.

BL

[MattTuck]

Chainline? Worn, broken teeth on the rings?

If he's dropping the chain while out of the saddle at high torque, I'd be worried about broken teeth in his mouth too.

Sounds dangerous.

[Andrewlcox]

I suggested we hook up a GoPro camera to watch what happens at the cogs when it slips. He said no because he values his face and didn't want to eat pavement.

It's hard for me to believe that 20 plus chainring teeth are allowing the chain to slip in the front. I wonder if the RD is dropping a gear under torque.

Andy

[hockeybike]

Looks like we're going to be getting a new cassette and chainrings. Replace one and then the other, see if that solves the problem.

Here's one thing I noticed while looking at it--some of the cog teeth look warped or bent. The cassette looks like it's in fine shape, otherwise, so I figured it was just how SRAM designed their cassette. Is that me being overly optimistic?

[EricEstlund]

http://www.rohloff.de/uploads/pics/caliber2_blue_01.jpg
and
http://www.rohloff.de/typo3temp/pics/520ab58329.jpg

will save a lot of guess work.


Probably being optimistic= but getting new stuff on there should solve the problem (or at least a host of other small problems).

[hockeybike]

I may have buried it a bit, but the chain is new (well, 80 miles). No stretch, yet. Cassette was used, but looks fine. Could just be a case of a bad cassette, for sure.

In any event, getting a new one on there and seeing what happens, asap. Worst case scenario, he has a spare cassette for when it does wear out (if it is the rings and not the cassette, that is).

[EricEstlund]

You didn't bury it. You mentioned the chain was new and the cassette was good. Makes me think it's rings and front derailleur (still).

The tools I posted above will help check chain and cassette wear, and will give a god guideline for wear on the chain rings based on the findings. They are really helpful if you don't look at these things regularly/ professionally.

[hockeybike]

Alrighty--now the search is on for better rings. I kind of hate sram's rings/cassettes/chains (and shifters...but that's another issue). Any votes for something reasonably priced (ie, not praxis)? TA Specialties Zephyr seems like it hits the right price point.

[EricEstlund]

TA and FSA are both good general purpose replacement rings. We can't forget Shimano, too.

[hockeybike]

One other thought--the hubs are chris king classics and hte cassette is sram. We didn't install a spacer behind the cassette. I know that some shimano cassettes require one. Anyone know if SRAM requires one, or requires one when used on a CK Classic hub? I'm thinking this could screw up chainline a bit if a spacer is missing.

[Black Dog]

One other thought--the hubs are chris king classics and hte cassette is sram. We didn't install a spacer behind the cassette. I know that some shimano cassettes require one. Anyone know if SRAM requires one, or requires one when used on a CK Classic hub? I'm thinking this could screw up chainline a bit if a spacer is missing.

If you had to adjust the shifting after putting on a new cassette then the chain line will have changed. This should not cause the problem that you experienced if it is jumping in any gear.

[merckx]

Check the frame carefully for a Fracture. Down tube, seat tube and chainstays in the BB area.

[oldpotatoe]

Alrighty--now the search is on for better rings. I kind of hate sram's rings/cassettes/chains (and shifters...but that's another issue). Any votes for something reasonably priced (ie, not praxis)? TA Specialties Zephyr seems like it hits the right price point.

TA or shimano. FSA is a just a thin slice better than sram...soft, wear out quickly.