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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 11-08-13, 05:13 AM   #1
shuffer
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How high can 105 go?

I'm about to pull the trigger on a B'Twin Cyclo X, but need some advice on ratios. I do plan to enter some cyclocross races (for fun), but this bike will also be used for local XC rides as a replacement for my MTB. The going is seldom very rough (no big drops), but there are a few very steep (20%+) muddy climbs on my regular loops. I have tackled them on my heavy tourer in dry weather, but that has a mid range triple.

The Cyclo X comes with 46-36 on the front and 11-28 on the back. I know this is already quite a wide range for Cyclo, but I do want to stay in the saddle for the hills. The groupset is 10-speed Shimano 105, with what looks like a standard short cage derailleur, for which Shimano recommend a maximum of 28 at the rear on a standard compact. In view of the narrower-than-compact front range (46-36) is it possible to run a 30, or even a 32 at the back? Even with that range I'll still be pulling a longer gear than I'm used to, but carrying around 6kg less bike (and improving fitness, I hope!). I'm 40 years old, 6'5" and unlikely to see much below 14st ever again, to further explain the need for a bigger cog.
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Old 11-08-13, 06:55 AM   #2
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A 30T cog is theoretically out of range for any Shimano road derailleur. That said, the specs are conservative; I would not hesitate to run a 30T. If you want to go bigger, shimano's 8/9 speed mountain derailleurs are compatible with road shifters, so you could go significantly larger in the rear.
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Old 11-08-13, 06:57 AM   #3
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Originally Posted by shuffer View Post
I'm about to pull the trigger on a B'Twin Cyclo X, but need some advice on ratios. I do plan to enter some cyclocross races (for fun), but this bike will also be used for local XC rides as a replacement for my MTB. The going is seldom very rough (no big drops), but there are a few very steep (20%+) muddy climbs on my regular loops. I have tackled them on my heavy tourer in dry weather, but that has a mid range triple.

The Cyclo X comes with 46-36 on the front and 11-28 on the back. I know this is already quite a wide range for Cyclo, but I do want to stay in the saddle for the hills. The groupset is 10-speed Shimano 105, with what looks like a standard short cage derailleur, for which Shimano recommend a maximum of 28 at the rear on a standard compact. In view of the narrower-than-compact front range (46-36) is it possible to run a 30, or even a 32 at the back? Even with that range I'll still be pulling a longer gear than I'm used to, but carrying around 6kg less bike (and improving fitness, I hope!). I'm 40 years old, 6'5" and unlikely to see much below 14st ever again, to further explain the need for a bigger cog.
You can run a 30T but not a 32T.
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Old 11-08-13, 07:49 AM   #4
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Thanks for the help. I take it that I could swap to a standard compact and run 30t? I know it won't make much difference but......
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Old 11-08-13, 08:49 AM   #5
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Really, the best way to solve this is to put a few bucks down on an SLX rear derailleur. You can go up to 36t.

SLX derailleur is cheap and great quality. Just remember you will need the older nine speed version to work with your ten speed road shifters. The ratio changes for ten speed mtb shifters.
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Old 11-08-13, 10:38 AM   #6
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Or you can drop your chainring down to 34.
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Old 11-08-13, 10:59 AM   #7
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Originally Posted by fotooutdoors View Post
A 30T cog is theoretically out of range for any Shimano road derailleur. That said, the specs are conservative; I would not hesitate to run a 30T. If you want to go bigger, shimano's 8/9 speed mountain derailleurs are compatible with road shifters, so you could go significantly larger in the rear.
The Ultegra 6800 GS rear derailleur supports 32T.
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Old 11-08-13, 12:19 PM   #8
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Remember Cross Racing, the way to go off the back and be lapped by the leaders very quickly,

is ride up a hill that can be climbed faster running, carrying the Bike.

Thats why the gearing is what it is ..

you might be better served with a bike equipped with a triple crank

Tourist gearing .. little 3rd chainring, big cog cassettes, long cage RD.

Some Touring builds use MTB cranks , and parts swaps are possible.

Talk to your dealer , about making these changes,

component parts fitted, can be changed.

Last edited by fietsbob; 11-08-13 at 12:24 PM.
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Old 11-10-13, 06:10 PM   #9
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My wife's bike has a 105 compact crank and short cage rear derailleur. I replaced her 11-28 with a 12-30 cassette. No problem - I just wouldn't recommend cross chaining.

My cross bike has Campy Centaur 50-34 with a 12-30 cassette. I like the gearing as an all round bike.
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Old 11-11-13, 06:57 PM   #10
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Quote:
Originally Posted by fietsbob View Post
you might be better served with a bike equipped with a triple crank

Tourist gearing .. little 3rd chainring, big cog cassettes, long cage RD.

Some Touring builds use MTB cranks , and parts swaps are possible.

Talk to your dealer , about making these changes,

component parts fitted, can be changed.
+1

The 39t chainring on a triple is ideal for a Cyclocross race. The 30t inner ring can help you with those technical climbs away from the race course.
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Old 11-12-13, 07:23 AM   #11
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Originally Posted by john.b View Post
The Ultegra 6800 GS rear derailleur supports 32T.
I stand corrected. Regardless, current 105 (and I am pretty sure the previous generation) technically have a limit of 28t.
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Old 11-12-13, 10:31 AM   #12
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I stand corrected. Regardless, current 105 (and I am pretty sure the previous generation) technically have a limit of 28t.
The 6800 11-32T is a new development. My guess is that they don't want to have to stock Ultegra triples anymore (34-32 ≈ 30-28).

FWIW, I was surprised the mech at my LBS was hesitant to pair up a 105 5700 GS derailleur with a 11-32T PG-1070, even though lots of guys have had success adjusting the B tension screws to fit. Hmm...

Edit:

I've come across this on more than one occasion recently, where it seems to imply there is an updated 105 RD-5701 part number for 2013:

Quote:
Originally Posted by http://www.bikeradar.com/news/article/shimano-sora-and-tourney-2013-first-look-33204/
Ultegra, 105 & Tiagra

There are no major changes to Shimano's second-tier groupset for 2012/13. However, Ultegra 6770 Di2 gets a new top-mounted satellite shifter option and the mechanical version gets optional wide-ratio rear gearing. While the standard 6700 rear mech can only be used with up to 28-tooth sprockets, the new 6700-A can handle 30. It'll work with close-ratio gearing too, down to 11-23t, and is available in SS (short cage) and GS (medium cage) versions, in silver or black.

The mid-range 105 and Tiagra groups also both get new wide-ratio rear derailleurs. The 5701 (black or silver) and 4601 (silver only) rear mechs can both be used with cassettes between 11-25t and 11-32t, and come in SS and GS variants.
The thing is, I can't find a 105 Techdoc on the Shimano website that says any 105 RD supports 32T, I can only find the RD-5701 exploded parts diagram.

Anyone know for certain?

Last edited by john.b; 11-12-13 at 01:42 PM.
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