hobkirk

ISSUE 1, CASSETTE COMPATIBILITY: Are ROAD cassettes and MTB cassettes interchangeable? I need easier gearing than my Shimano 105 triple with 11-27 cassette and an Ultegra SS RD.

Will a Shimano XT CS-M771-10 Speed Cassette fit the splines on a Shimano free hub?

NOTE: I plan on replacing my Ultegra SS RD with a GS - it increases the tooth capacity from 33 to 39. So the Compact is 16 teeth (50-34) and the cassette is 23 teeth (34-11) making 39 teeth total.

Any problems?

ISSUE 2, TRIPLE VS COMPACT DOUBLE: I like the idea of less shifting up front, a supposed advantage of a triple. But I find myself shifting into the largest ring on almost every downhill and regularly needing the small ring on hills. I think I am shifting my FD more than I do on the compact double.

Or is my thinking wrong? I've only gone out a couple of times since I switched over to the compact double, so I haven't gotten much of a feel for it yet.

ISSUE 3, REPLACE JUST 1 COG? I noticed Jenson USA sells a Shimano 11 tooth cog by itself. Why? Do racers wear out just the one gear? I realize it is the smallest cog so the geometry is bad, but I didn't think that would be significantly more of a problem than on the next cog up. Just Curious.

THANKS

Bianchigirll 

if the freehub body is 10spd then it should fit.

I think changing both the cassette and the cranks at the same time will just change the position of the gearing and not give the low gear you are lookign for. I would change the cassette and RD and see if that suites your neds

relyt

If you don't run the gears in the small/small combo you could probably get away with the derailleur you already have. Capacity specs are conservative.

fietsbob

11 would wear quickly, load over just 6 teeth ,
the Capreo freehub uses a 9 tooth with small wheels so less wear/miles yet..

so a spare 11 or so makes sense..

JiveTurkey

Helping my step-dad do something similar. He's going from 50/34 & 12-25 to 50/34 & 11-34 in 10-speed. Here's what we determined he'll need and why:

New RD: Shimano MTB, SGS (long cage), 9-speed
- MTB because road RDs are officially rated for a maximum cog size of 27T or 28T, though some people have reported making a 30T or larger cog work.
- SGS (long cage) because the MTB GS (short/medium cage) did not have enough wrap capacity.
- 9-speed because the newer Shimano 10-speed Dyna Sys system uses a different cable-pull ratio than all the road stuff (excluding pre-9-speed Dura Ace) and older MTB.

New 10-speed chain, possibly two (or leftover scraps of another) because one chain may not be long enough to do the big/big (50T chainring/34T cog) + 1" chain sizing method.

New Shimano or SRAM 11-34T cassette. Even though Shimano changed the shifter and derailleur cable-pill ratio for 10-speed MTB, the cog spacing for 10-speed MTB is the same as 10-speed road. The existing freehub will handle both.


As stated above, going to a cassette with a bigger big cog (27T --> 34T) while increasing the number of teeth on your inner chanring (30T --> 34T) will counteract each other somewhat in terms of your low gear ratio:

Old system: 30 / 27 = 1.11
New system: 34 / 34 = 1.0

If your major concern is lowering your low gear, you can consider swapping the 30T inner chainring for a 26T or 28T.

cyccommute 

Capacity ratings are conservative but not that conservative. Most people can easily make a 30 tooth low work, some can make a 32 tooth low work but I doubt that you could get a 34 tooth low to work with a Ultegra GS.

shelbyfv

I agree with Cycco, a 34 is not likely to work with a GS. If you want a 34, make it easy on yourself and get an LX or other mtn bike rd.

oldbobcat

Shimano 9-speed road and MTB are completely compatible except for chain length and derailleur cage length issues. When you go to 10-speed, though, things get a little funky. 10-speed road splines are deeper and there are 10-speed-only cassette bodies (not 9- or 10-speed with a spacer) with deeper splines that will not accept 9-speed cassettes or SRAM 10-speed cassettes.

If you're thinking about going to 10-speed, check your cassette body before buying any new equipment.

Elvo

I don't think you can do a 11-34T cassette and still be able to do all 10 cogs without switching to SRAM APEX.

JiveTurkey

Sure you can. See my post above.

Burton

Nice post - someone did their homework!

Just to emphesize a couple points - derailleurs have a couple specs: the amount of chain slack that they can take up, which is determined by the cage size and maximum cog size, which is determined by the derailleur body size. There isn`t a road derailleur on the market that I`m aware of that will handle a 34T cog - you`ll need a mtb rear derailleur.

hobkirk

The Shimano web page for the GS RD is broken, but I managed to find a PDF that listed the maximum sprocket size for the GS as 28. Previously I had only had the spec for the maximum number of teeth (which was OK in my proposed changes).

It looks like I need to inject a lot more power into my old legs or switch to a SRAM medium cage RD (32 cog capacity).

Thanks all - I was ready to order wrong parts.

JiveTurkey

To clarify, the road GS and SS both have a max cog rating of 28T. Cage length has no bearing on max cog capacity; cage length determines wrap capacity. MTB GS and SGS are both rated up to 34T (maybe even 36T now).

If you go with a SRAM RD, you need to have a SRAM rear shifter, or get something to convert the cable pull ratio.

hobkirk

Thanks, Mr. Turkey! I just got a return email from a friend who had converted to a SRAM RD and he told me he had converted the levers when he did the RD.

Is there any disadvantage to a MTB RD on a road bike?

cycle_maven

No real disadvantage to a MTB rear derailleur. My wife's bike is using a Deore RD with Ultegra shifters, and it works flawlessly on a (albeit 9-speed) 13-34 cassette.

ericm979

30t is pushing for Shimano road triple derailleurs. 32t or 34t would be too much.

The 9sp MTB derailleur will work fine with Shimano 10sp (or 9 or 8sp) shifters. They use the same cable pull.

I am not positive but I don't think the Shimano 10sp MTB cassette has the same spacing as road 10sp. You can use an Sram 10sp cassette (or IRD) instead.

Adding a large solo cog won't work unless you can find one that is dished. With 10sp the last cog is offset to the left (vs to the freehub). I have not found a dished solo cog.

digibud

It depends on your desired goal. I just bought a Roubaix triple. I could have gotten the Apex for less money. The Apex is essentially a wide range cassette with a mtn bike derailleur with a compact double chainring. The triple and the Apex double give pretty much the same bottom gear but the triple has two potential advantages. The first has to do with riding on flat ground, not hills. When the breeze kicks up just a bit...or when I start up a very gentle incline, I want to be able to shift to a gear that will allow me to keep my cadence where I like it. With a mtn bike type rear, the shifts in the larger cogs make bigger jumps and you find yourself spinning too fast or mashing too hard when you change a gear. I very much appreciate subtle gear changes. My wife brought home the point after complaining about a shift being too "much". It would have been just that much worse in terms of dropping to an even lower gear had she been riding a compact double with an Apex. Secondly, we live around mountains and have 15 mile climbs available. So far we can do all of them with our triples but I know of some that we can't do, and we are also considering a trip to my homeland, Switzerland. If we go we'll take our bikes and we'll put an even smaller inner chain ring on. With a compact double, even with Apex, there isn't too much you can do to get lower gearing. Not impossible, but not as easy as with a triple where you can change out the inner chain ring. If a compact double meets your needs, then I think it's a preferred solution for some, but for me and others with experience riding mtn bikes as well as road bike, it's all about keeping a good cadence and a triple helps a lot with that.

Chris_W

I would also recommend going with this option of putting a 26 tooth inner chainring on your current cranks. I've done it on my bike and on many friend's bikes (I live in Switzerland and we often do long rides in the Alps). You should still change the rear derailleur, but can still use a road model made for a triple chainring. Also think about adding a Chain Catcher or similar device that will prevent the chain from derailling off the inside when shifting into the small ring.

JiveTurkey

No. Use the RD you need to make the desired gearing work.

There might be a disadvantage if you used a road cassette with MTB RD because the RD sits unnecessarily far from the larger cassette cogs.

digibud

I find no chain catcher that is made to work with a Roubaix. Does anyone know of such a thing?

Chris_W

The Jtek DropStop and the K-Edge Triple Chain Catcher both work with a road triple to prevent dropping your chain and do not mount to the seat tube.

digibud

Unless I hear of reports that say otherwise, I don't believe either of these would work with a Roubaix triple. The K-Edge is totally out. Neither of our triples have braze on derailleurs. The DropStop would move the chainline 1.5mm. They would like you to think that isn't a problem. Perhaps if I shimmed the rear cassette out it wouldn't be, and maybe I'll look into that but I'm not sure it's worth bothering. If I am corrected and 1.5mm is no big deal then it sounds interesting but that will be my next question in another thread so as not to hijak this thread any further.

mihaitintea

Here's what worked for me:

- Shimano Ultegra 6800 hub
- SRAM PG 1070 10-speed casette with 11-36 teeth (yeah !)
- Shimano Deore XT RD M772 SGS 9-speed rear derailleur
- Shimano 6701 10-speed chain
- Shimano 105 10-speed shifters
- FSA 50/34 10-speed compact chainrings

Works like a charm. I scaled 24% climbs like nothing. Shifting works very well.

AnkleWork

You needed over four years?

DiabloScott

That's how far back he had to go to find the question he wanted to answer.