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Anyone running a Claris Derailleur with 34 tooth cog?

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Anyone running a Claris Derailleur with 34 tooth cog?

Old 04-13-18, 07:43 PM
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IslandTimePE
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Anyone running a Claris Derailleur with 34 tooth cog?

Hi All: I have a Giant Revolt 3 with Shimano Claris drivetrain. 50/39/30 triple up front and 8 speed 11-32 cassette in the back with the long cage version of the Claris rear derailleur. Some of the gravel/dirt roads I ride are quite steep and I would love to lower my lowest gearing just a bit more. I believe replacing the cassette would be the most economical way to do this - would need to replace multiple chain rings on the front to lower the ratios and not exceed the capacity of the front derailleur.

The Shimano recommended max rear gear for the Claris is 32 tooth. So my question is: has anyone actually run a Claris RD with a 34 tooth max cog? If so, does it work well?

Would like to hear from someone who has done this before purchasing the new cassette.

Thanks!
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Old 04-13-18, 08:17 PM
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I can’t definitively answer your question about the viability of using a 34t rear for with your setup ......but the alternative is to swap out the 30t for a 28t front chainring.
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Old 04-13-18, 08:28 PM
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So exceeding the rear's capacity is better then the front der's?


The rear capacity id determined by both the large cog's diameter WRT the upper pulley's distance from it/the axle and the amount of chain wrap the cage can handle. The ft is more to do with the cage's sculpting/shape and where along that the chain runs.


If one knows how to shift the ft well (and this is not a light statement, many riders don't shift the front well at all) the small change to the chain's location within the ft der's cage contours is a smaller issue then potential pulley knock (up against the rear cog's underside).


There are many riders who have swapped out the 30T granny for a 28T or 26T with little/no real life issues. A 2 0r 4T change here will produce a greater reduction of your gearing then that off the rear cog set.


If you do decide to change the rear instead then make sure the upper pulley will clear the 34T cog's underside when in the granny up front. The "B" screw adjusting screw can be lengthened if needed to gain a tad more clearance.


Either way the good rider will also try to avoid their cross over combos, a good practice regardless of the cog/ring tooth counts anyways. Andy.
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Old 04-13-18, 09:06 PM
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Either change, ft or rr tooth counts, can be done. The rear will challenge the der's ability to not end up with pulley knock on the cog's underside. The ft change will locate the chain lower within the ft cage's contours then Shimano intended.


I find that a rider who knows how to shift the ft well (this is not a light statement as many riders don't seem to be able to do this, witness the move from ft shifters all together) can handle the slight decrease of ft shifting that is the result of a smaller ring. Even 26T rings can be shifted well enough with small effort change.


Moving to a 34T cog is also not that big a deal but the "B" screw adjustment sometimes isn't enough to compensate for the larger cog. Depending on the cogs' wear another chain might be prudent if the cassette is changed. This would offer one more option to discovering the best final system, chain length impacts the rear der cage's rotational attitude and thus the upper pulley's proximity to that larger then designed for cog. Sometimes these changes result in the cross over combos becoming more problematic then before. Shortening the chain (to rotate the upper pulley away from that 34T cog) can result in the chain not being long enough to handle the big/big combo. Tearing off the rr der is not trivial. Andy
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Old 04-13-18, 09:09 PM
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Wow! I will never understand how these forum posting protocols work. I thought that first post was deleted only to find after re writing and posting a second attempt that the first was "found" and did post. Oh well. Both say some of the same. Andy
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Old 04-13-18, 09:54 PM
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It is my understanding that the derailleur hanger has a lot to do with how much you can exceed the derailleur capacity so the answer may not be the same for 2 different bikes. If the "B" screw is maxed out now, it might be tough, if it is backed out now, you have a better chance. That said, I have almost always been able to push 2t regardless of the bike.

It is a good suggestion to look at going to a 28t chainring.

FWIW, you can run a 9 speed mountain bike derailleur, such as an XT 750, with the Claris shifter.

John
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Old 04-14-18, 05:29 AM
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Originally Posted by Andrew R Stewart View Post
So exceeding the rear's capacity is better then the front der's?

Simply a matter of my being more comfortable setting up/adjusting rear derailleurs. But I apperciate your point that changing the front granny to a 28 could be the better technical option.


Originally Posted by Andrew R Stewart View Post
If you do decide to change the rear instead then make sure the upper pulley will clear the 34T cog's underside when in the granny up front. The "B" screw adjusting screw can be lengthened if needed to gain a tad more clearance.
I do still have range to use the B screw to lower the derailleur wrt the large cog.
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Old 04-14-18, 05:31 AM
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Originally Posted by 70sSanO View Post
FWIW, you can run a 9 speed mountain bike derailleur, such as an XT 750, with the Claris shifter.John
Thanks. Hadn't considered the possibility of swapping the RD to a mountain model.
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