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EDIT: Answer at the bottom


Hi, all

I have an issue with the shifting for my bike, a Giant TCR C1. It seems like the shifters for the Giant TCR work only with one 10s wheelset but not with another 10s wheelset.

I have 2 bikes: a Giant TCR C1 & a Cannondale


Giant TCR C1:

Dura-Ace 10s Shifters

Ultegra 11s Crankset

Ultegra 10s Chain

Dura-Ace 7800 Rear Derailleur


Cannondale CAAD9 R5:

Shimano 105 10s Shifters

Shimano 105 10s Crankset

Shimano 105 Chain

Ultegra 10s Rear Derailleur


I have 2 wheelsets: an Ultegra wheelset for my Giant TCR and a Shimano wheelset for my Cannondale. I'll be referring to the latter wheelset as my Cannondale wheelset.

When I put the Cannondale wheelset on my Cannondale, the shifting works fine. Same for when I put in the Ultegra wheelset. I don't have to adjust the barrel adjuster to adjust the position of the chain.

When I put the Cannondale wheelset on my Giant TCR, the shifting works fine also, albeit a bit more slowly on the descent from the biggest cog down to the small cog. However, when I put the Ultegra wheelset in, the shifting doesn't work properly. I have to adjust the barrel adjuster to align the chain with the cassette, and even then the shifting isn't smooth. It goes up fine but doesn't come down smoothly. It gets stuck in the biggest cog until I shift twice; then, it jumps the second-biggest cog and lands on the third-biggest. I adjust the barrel adjuster so that it descends properly, but then it has problems with shifting upwards, getting stuck on the smallest cog until I shift twice and then it goes up to the second cog.

I had initially thought it was an issue with the shifters, 11s crankset, rear derailleur, or possibly the rear derailleur cable, on my Giant TCR. However, the shifting works fine when I have the 10s Cannondale wheelset on the Giant TCR, so those are not it.

The Ultegra wheelset had originally had on it an 11-speed cassette, which I've swapped out for a 10-speed cassette. I had also initially thought it was an issue with the cassette, but the shifting works fine on my Cannondale when I put on the Ultegra wheelset with the 10-speed cassette, so I don't think it's an issue with the cassette.


Does anybody have an idea on why this is happening?


Solution

It turns out that the issues were with the rear derailleur cable and the rear derailleur. The cable was bent in two places and the derailleur was either incompatible with the brifters or not fully functional. I've replaced the rear derailleur cable and swapped the Dura-Ace 7800 derailleur out for a Dura-Ace 7900 derailleur and the shifting has started working smoothly.

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    Do the cassettes have different teeth numbers? Try playing around with the B screw.
    – Michael
    May 18 '20 at 7:05
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It's very likely that an 11 to 10 speed cassette spacer was used on the 11spd wheel that's not exactly the Shimano-specified 1.85mm thickness.

There's some range in what thickness of spacer will physically do the job. For example, people are always using 1.8mm Mavic cassette spacers for Shimano for the purpose, which works fine as long as you're not swapping wheels. But the 11 speed Shimano freehub was designed to have a 1.85mm be the size to create interchangeability with 10 speed native hubs.

If for some reason the hubs locate the cassettes differently even with the correct spacer, that would be surprising between two Shimano road hubs, but by the same token you could potentially use spacer tricks to compensate.

Once the cassettes are located right, chain/cassette wear and is worth looking at next. Wear can have enough of an influence on shifting ability to cause these problems. It's possible but not likely for it to be the decisive factor.

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everybody

Thanks for the responses. It turns out that the issues were with the rear derailleur cable and the rear derailleur. The cable was bent in two places and the derailleur was either incompatible with the brifters or not fully functional.

I've replaced the rear derailleur cable and swapped the Dura-Ace 7800 derailleur out for a Dura-Ace 7900 derailleur and the shifting has started working smoothly.

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  • Dura-Ace 7800 should be good up to 28 teeth on the largest rear cog (Shimano declares up to 27), while Dura-Ace 9100 should be good up to 32 teeth (Shimano declares up to 30, if I am not wrong). Replacing the cable was not main reason of the issue you had, but still a good idea if you changed the derailleur. Can you count how many teeth you have in the largest cog in the rear cassette?
    – EarlGrey
    May 19 '20 at 22:48
  • Hey. I had meant to put 7900 but I had put 9100 by accident instead. I believe the cassette is an Ultegra 11-28.
    – Alykin
    May 19 '20 at 23:18
  • I double checked and 7800 was guaranteed by Shimano to work up to 27t on the largest rear sprocket. Of course it may be that sometimes it worked up to 28t or even 30t, but Shimano did not design it to work with these cogs. With the 7900 Shimano started stating it works up to 28t. See largest sprocket numbers in Shimano manuals 7900 si.shimano.com/pdfs/si/SI-5X00A-003-ENG.PDF or 7800 manualslib.com/manual/364250/Shimano-Rd-7800-Technical.html
    – EarlGrey
    May 19 '20 at 23:42
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Since it works smooth one way (Giant wheel ---> Cannondale) but not the reverse, I think the culprit is the Giant Dura-Ace 7800 Rear Derailleur.

Both wheels have 10 cogs, but it looks like the Cannondale cogs are larger and that the Giant derailleur is not capable of provide enough tension to shift properly or that the spring is overstretched and therefore got stuck in the largest cog.

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    You were right. The issue was with the Giant rear derailleur not functioning properly.
    – Alykin
    Jul 6 '20 at 2:33
  • @Alykin you can then mark the answer as accepted solution.
    – EarlGrey
    Jul 6 '20 at 20:20
  • The issue wasn't that the derailleur couldn't take the same number of cogs. The derailleur was just not functioning properly, possibly because a spring had broken somewhere. I was agreeing that the issue was with the derailleur, but not with the reason given. However, you did make a good point in regards to the possibility of it being the number of teeth.
    – Alykin
    Jul 16 '20 at 3:25

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