Touring chainrings

You basically want an old-school MTB triple. What crank and BB do you have now? When I built my touring bike, I just went straight up MTB drivetrain; 26-36-48 crankset and 11-34 cassette, all 9-speed.

Chainrings vs new crankset depends on what you have now… there is a limit to how small chainrings can get with certain BCD (bolt circle diameters). Mountain cranks can take much smaller chainrings than compact road cranks, which can take smaller chainrings than full road cranks.

Depending on whats on there and how much needs replacing due to wear, it might be more economical to replace the cassette (and if necessary, the rear derailleur) to get a wider range of gearing. Mountain derailleurs can handle much larger cassettes than road ones.

@mstone 60694 wrote:

Swapping out just the rear derailleur and using a bigger cassette is an option, but not (IMO) a great one–you end up with very widely spaced gears, and functionally useless combinations for a touring bike (e.g., the entire 50T ring).

Is it really that different? A quick compare of an Ultegra 11-28 vs an XT 11-34 says that the first 5 gears don’t vary all that much. The XT goes from 11 to 19, while the XT goes from 11 to 15. MTB drivetrains seem pretty common on touring bikes specifically for the wide range.

My comment about it being more economical was based on the fact that not messing with front derailleurs and chainrings saves a lot of headache… Shimano, for example, 10 speed shifters (supposedly) work with 9 speed MTB rear derailleurs. So grab an LX rear derailleur (like http://www.jensonusa.com/Shimano-LX-M581-Rear-Derailleur ) and a 10 speed MTB cassette (like http://www.jensonusa.com/Bicycle-Cassettes/Shimano-SLX-CS-HG81-10-SP-MTB-Cassette ) and you’re into a much smaller gear range for under a hundred bucks. That would keep the top end the same, but the lower end would go to 22.5 gear inches using the same 29t granny. Obviously gearing is wider.

All kinda depends on what needs replacing due to wear though.

@jabberwocky 60695 wrote:

Is it really that different? A quick compare of an Ultegra 11-28 vs an XT 11-34 says that the first 5 gears don’t vary all that much. The XT goes from 11 to 19, while the XT goes from 11 to 15. MTB drivetrains seem pretty common on touring bikes specifically for the wide range.[/quote]

Right, the first 5 gears don’t vary all that much, but on a road crank and a loaded bike you’re mostly in the top half and ignoring the bottom half. If you were on an MTB crank you’d be much more likely to actually get some use out of the entire range, rather than using half the range and cursing 15% gaps.

Quote:

My comment about it being more economical was based on the fact that not messing with front derailleurs and chainrings saves a lot of headache… Shimano, for example, 10 speed shifters (supposedly) work with 9 speed MTB rear derailleurs. So grab an LX rear derailleur (like http://www.jensonusa.com/Shimano-LX-M581-Rear-Derailleur ) and a 10 speed MTB cassette (like http://www.jensonusa.com/Bicycle-Cassettes/Shimano-SLX-CS-HG81-10-SP-MTB-Cassette ) and you’re into a much smaller gear range for under a hundred bucks. That would keep the top end the same, but the lower end would go to 22.5 gear inches using the same 29t granny. Obviously gearing is wider.

All kinda depends on what needs replacing due to wear though.

Yes, an older 9 speed MTB RD should work (not the newest generation or the 10 speed stuff).

Note, though, that a cheap crank is in the same range as the RD + cassette (within %20, depends on what’s on sale that day). I think the $$$ is less a factor than what your FD options are or how fiddly you want to be.

If you’re 9 speed, that actually opens up more possibilities… 9 speed mountain and road stuff was much more compatible with each other than the 10 speed seems to be. You could swap to a mountain crankset and a mountain front derailleur and keep your brifters if you wanted. The M771 is the XT trekking crankset (48-36-26; identical to the standard mountain crankset but with slightly larger chainrings). Not easy to find in the US, but the british shops still carry it. See: http://www.wiggle.com/shimano-xt-m771-triple-9-speed-chainset/

@creadinger 60702 wrote:

Any idea why people replace cranks at the same time as chainrings, even if they are compatible?

Probably because a full set of chainrings can be so expensive… often, if you find a crankset on sale, it can be cheaper than new chainrings. 😮

@mstone 60709 wrote:

The front shifters aren’t compatible between road and mountain. You can use a 9 speed mountain RD with 8, 9, or 10 speed indexed road rear shifters, but nada with the FD. They’ve broken RD compatibility with the latest generation (dyna sys), but they also seem to be making road RDs with a wider range so the need isn’t as great as it was. I still hold out hope that they’ll introduce a “trekking” FD with road shifter compatibility and a lower range (it would be a simple and logical step now that they’re finally making road RDs that take larger sprockets again), but they’re nuts for market segmentation and who knows what they’ll do. We’ll only be able to buy it from europe even if it does happen.

Right, I forgot those don’t work together. My recollection is that most people use cheap road derailleurs with mountain cranks. Most low-mid range FDs work fine with mountain cranks (they are usually designed around the smaller triple ring setups that entry level road/cruiser bikes come with). The curvature of the derailleur doesn’t always match smaller MTB rings, but what I’ve seen on the interwebs says it works fine. And lower level front derailleurs are really cheap.

Thats probably the reason so many touring bikes use bar end shifters. They work with frankenstein drivetrains much easier.