Touring chainrings

[creadinger]

So I currently have 51-41-29 chainrings on my weekend/touring bike and I’d like to install chainrings that can actually work for heavy touring, long climbs and climbs that come 150+ miles into a ride when I’m already tired.

In the back I have the largest cog the derailleur can handle (28) and my current gear inches (sheldonbrown.com/gears) ranges from 122-27, which is way higher than I need for touring. I did a credit card tour a couple of years ago and had to stop on steeper climbs to catch my breath because I was burning my legs out. I even had to walk one in CT. The climbs would have been impossible with 30 extra pounds on a fully loaded tour.

I’m thinking something like 46-32-22 will get me down to reasonable gearing for climbing and touring. With the same cassette, the gear inches would range from 110-21.

My question is when you get new chainrings, is it advisable to change out the cranks too? Why? I know the new rings would have to be compatible with my bottom bracket. Would this big of a drop (51-44 teeth) require a new front derailleur or just a reposition? Would smaller chainrings affect anything in the rear, if I left that all the same? Last night while I was counting teeth on my gears I noticed that my chainrings were pretty worn, so a swap out may be advisable anyway… I think I need to clean my chain better.

I’m planning on going over to Bicycle Space sometime soon to work out the details but some more in depth knowledge from some of you before I have all this done would be welcome.

Topic

[jabberwocky]

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]

Shimano won’t give you a solution for low gearing on a road front derailleur with indexed shifting. If you have bar end shifters, you can do the front in indexed mode–just swap out FD & crank and you’re good to go. If you’re using flat bars, you can probably get a mountain indexed front shifter, then swap out as above. If you’re using drop bars and brifters, stick with the existing FD and hope for the best. It will take more fiddling, and you may be more limited in what gear combinations you can get working.

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). I’d rather have a tightly spaced cassette and smaller rings. Now if Shimano wanted to allow you to have something like a 14-34, this would be a more attractive option, but they really seem sure that everyone needs an 11T or 12T sprocket.

[jabberwocky]

@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.

[creadinger]

@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.

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.

I’m almost hoping wear is an issue so that the decision is made easier. I currently have 175mm cranks and a cartridge bottom bracket. I’m pretty sure it’s 9 speeds, but I could be wrong. And I have road handlebars.

You have some good points. Mstone too. I actually don’t mind wider spaced gears because when I had an 11-23 cassette on my other bike I would always shift twice anyway. Economical is good, but ultimately I’d like to do what makes the most sense even if it’s a little more $$. For example, the 51T chainring is pretty much inappropriate for a touring bike like mstone said. On the other hand, I do not want to go down the rabbit hole of indexed shifters vs bar end shifters and all that either. If I was doing it all from scratch, I would probably do what you did with the MTB drive train. Unfortunately I can’t exactly go back, and the gears I have now served me really well for the past 5 years, with very few problems.

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

[mstone]

@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.

[mstone]

@creadinger 60702 wrote:

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

Once you’ve worn out the rings you’ve got a good shot at having worn out the bottom bracket, and it’s probably cheaper to buy all of it in one box and get newer tech anyway.

[jabberwocky]

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]

@jabberwocky 60707 wrote:

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/

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.

[jabberwocky]

@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.

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