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-   -   Bent chainring, seeking recommendations for replacement (https://www.bikeforums.net/tandem-cycling/1006783-bent-chainring-seeking-recommendations-replacement.html)

Alcanbrad 05-04-15 07:57 PM

Bent chainring, seeking recommendations for replacement
 
We spent the weekend with friends tandeming around the Newport RI area and on our last ride, we had a tough shift while dodging traffic and ended up bending the center chainring. The chain was not seating over the teeth in the bent section and then got jammed between the middle and large chainring.

I did some searching of the forum and understand the shifting cause and the need to be a little more gentle when shifting. This is easier said than done as my stoker does not have a strong tactile feedback sense.

I have never seen, or heard of this happening before. We have sheared a few teeth off of every Suntour cassette we have cycled through our Santana, but never had a chainring issue on that bike.

I guess I can anticipate more frequent issues with the lighter drive train components on this bike.

I have a couple of questions:

-Are there any recommendation for beefier aftermarket chainrings? (I currently have FSA Gossimers)

-Is the center ring the most likely to get damaged, or is the big one just as likely?

TIA

ahultin 05-04-15 09:56 PM

we took @Ritterview's advise http://www.bikeforums.net/tandem-cyc...l#post17592656 and upgraded our gossamer cranks to the ultegra 6604 rings. Bought the set new off ebay and spent less than $100. I would highly recommend the upgrade.

Paramount1973 05-04-15 10:00 PM

You could try a steel chainring, such as the ones Surly sells. You would need to determine the BCD dimension of the ring.
http://surlybikes.com/parts/steamrol...eel_chainrings

WillFam-Reno 05-07-15 11:25 PM

I believe that the small and middle chainrings are the most likely to be damaged from up-shifting. The chain will have a harder time shifting up to the next larger chainring when shifting under power if a lot of power is still being applied. I recommend the captain calling out "SHIFT" a second or so before shifting so that the stoker can relax all power to the pedals while the Captain rotates the cranks gently until the shift is complete, then call "PEDAL" to continue on your way. This reduces the chance of getting the chain stuck between chainrings. If the amount of bend is not excesive (it usually isn't) you can remove the outer chainring and carefully straighten the middle chainring with a large adjustable wrench (add a towel for protection if you can) just like some videos show for straightening a disk brake rotor.

The large chainring is not likely to be bent, as the chain being stuck between rings, will push the outer edge of the smaller ring away from the chain, and the inner metal (closer to the axle) of the larger ring is more rigid the closer to the axle that you are.

Good luck - go easy when shifting

Will-Fam

Carbonfiberboy 05-08-15 10:39 AM

I go "spin it up" (we then accelerate slightly) and then call which ring I'm shifting to: "granny" or "middle ring", wait an instant for Stoker to back it off, and then shift. It's only an issue for us when going between those two rings. +1 on the Ultegra rings, though we use a SS granny ring as we quickly wore the alu ones out.

Alcanbrad 05-08-15 02:03 PM

Thanks for the pointers and advice folks.

I always call the shifts and my stoker knows to ease off, this was a case where I called the shift and initiated it as we were entering and intersection and car came speeding around the corner and freaked the stoker and her flight reflex kicked in. Things like this will happen from time to time. I have more of an issue with the bike being stock equipped with rings that won't take it. I have a note into Co-motion.

I ordered a Shimano 6604 center ring off of ebay and will see how it performs with the stock large ring before I drop another $100. (Also waiting for Co-Mo's reply).

I looked at the Surly rings online and they say that they are thick and recommend using a 5 speed chain and that they would be "tight" with an 8 speed chain. So these rings are a no-go for our 10 speed ultegra drive train.

I did try removing the large ring in-situ but there was not enough clearance to remove it allowing access to the center ring, so I had to remove the crank and all that that entailed and was able to straighten the teeth and ring on the bench and it is performing well.


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