Author Topic: Drivetrain HELP  (Read 13302 times)

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Offline balm426

Drivetrain HELP
« on: December 08, 2015, 11:09:14 pm »
I just bought my first touring bike. It is a Surly disc trucker. It is used and has quite a few miles on it. The drivetrain is pretty worn out. I have my first tour coming up in March and want to upgrade some of the components. I am only really looking at Shimano triple cranks.

My question is what is the optimal gearing. I live in the mountains so there are nothing but hills around here. The tour I am planning right now is the southern tier so there may not be tons of climbing but I want to be ready for it. We will be going unsupported so I will be carrying all my gear. I am also 6'4" 270 and put some abuse on cranks.

My options seem to be:
Shimano XT M770 9 Speed - 44/32/22
Shimano XT M780 10 Speed - 42/32/24
Shimano XT M782 10 Speed - 40/30/22

I am planning to buy the entire groupset but not sure what would be the best. The prices for these are all pretty close and in my budget. Is there another set I should be looking at?

Offline mbattisti

Re: Drivetrain HELP
« Reply #1 on: December 09, 2015, 07:51:37 am »
26 or 700 wheels?  If the former, I'd go with the larger choice of cranksets.

Offline Pat Lamb

Re: Drivetrain HELP
« Reply #2 on: December 09, 2015, 09:18:58 am »
I'd match the rear cluster; I think the LHT has nine speeds, so go with a nine up front.

It doesn't make much difference, but the trim may be a bit finicky if you put an 11 speed derailer around a (wider) nine speed chain.  At the other end, it's touchy to get a wider derailer (9) tuned to shift a narrower chain (11) without dumping the chain while shifting at one end or the other.

Offline balm426

Re: Drivetrain HELP
« Reply #3 on: December 09, 2015, 11:28:57 am »
The bike is set up with 700c wheels. I am planning to build a new rear rim as well.

I was leaning towards the 9 speed but didn't know if there was much difference going with the 10 speed.

I am going to replace the rear cassette no matter what since it is shot. Planning to buy the entire group to make sure everything is compatible.

Offline DaveB

Re: Drivetrain HELP
« Reply #4 on: December 09, 2015, 11:50:16 am »
If the bike has drop bars you will have to use a 9-speed MTB rear derailleur to index with road 10-speed shifters.   Shimano's 10-speed MTB groups are not compatible with road components

Offline RussSeaton

Re: Drivetrain HELP
« Reply #5 on: December 09, 2015, 01:13:03 pm »
I have 10 speed Shimano on my touring bike.  Triple crank.  I'd suggest going 10 speed cassette.  9 is slightly old, outdated, and the 10 works perfect.  So no rational reason not to have one more gear.  You are buying everything new, so get the newest, most up to date components.  As DaveB said, there are some compatibility issues between road STI shifters and MTB derailleurs and speeds.  I have some 105 STI 10 speed levers and a very cheap 9 speed Deore rear derailleur.  Might have cost all of $20 for the rear derailleur.  So its real easy and cheap to make things work right.

As for gearing choices, I like about a 4 to 1 high gear.  So 44 chainring and 11 cassette.  42x11 is also close enough.  Your 40 outer ring choice would not be my choice.  For the inner chainring, smallest possible no matter what.  For your cranks it is 22 tooth inner chainring.  64mm bolt circle diameter.  Its very easy and inexpensive to replace the inner ring on a crankset if the outer and middle are your preferred choice.  And biggest cassette cog possible, sort of, on the cassette.  Cassettes for 9 and 10 speed have either 32, 34, or 36 for the biggest cog.  32 and 34 will work with about all touring bikes no problem.  The 36 may be too big on some touring bikes.  Have to try it to find out.  The rear derailleur upper pulley will not be able to get under the 36 cog.  Likely due to the rear derailleur hanger not being long and low enough to allow the pulley to get under the cog.  Works for 32 and 34 big cogs, but not enough clearance for the bigger 36 cog.  But whether you have a 32, 34, or 36 big cog, does not matter because it amounts to about 1 gear inch difference between each.  Tiny.

Offline balm426

Re: Drivetrain HELP
« Reply #6 on: December 10, 2015, 11:57:43 am »
Thank you for the info.

RussSeaton - What would pick if you were choosing a gearing set I have listed. What it sounds like to me is 10 speed 42/32/24 but change the smallest ring to a 22. Does that sound right? I could go with 11-34 rear cassette so everything should work.

I am planning to change the bars to a trekking style handlebar so I will be able to run MTB shifters and brake levers.

Let me know what you think about that plan.

Offline RussSeaton

Re: Drivetrain HELP
« Reply #7 on: December 10, 2015, 03:13:23 pm »
What it sounds like to me is 10 speed 42/32/24 but change the smallest ring to a 22. I could go with 11-34 rear cassette so everything should work.

Sounds just about perfect gearing for a loaded touring bike.  The 42x11 high gear may limit you to only achieving 56 mph down a mountain instead of the 58 mph you could achieve with a 44x11 high gear.  You will have to learn to live with that deficiency and overcome it somehow.  The 22 inner chainring will rarely see much use.  Unless you have steep hills around home or are in the mountains, you will never shift to the inner chainring.  The 32 middle ring and the bigger cassette cogs will allow you to climb pretty steep hills.  The inner ring is just an emergency, just in case gear.

Offline RonK

Drivetrain HELP
« Reply #8 on: December 10, 2015, 05:28:21 pm »
I live in the mountains so there are nothing but hills around here.

I used Shimano XT M770 9 Speed - 44/32/22 when I owned a LHT, after struggling through a hilly tour on the stock LHT gearing which has only a 26 inner ring.

It suited me fine so I'm using the same size chainrings on my current bike.

I think a 22x32 low gear is a sensible choice in hilly terrain, and there have been a few times when I wouldn't have minded having an even lower gear.

And since I rarely use the outer chainring, so for my new build I have decided to dispense with it altogether, and use a 2x10 setup with 36x22 chain set and an 11-36 cassette.

On the 36x11 combination I could reach 25mph at 90 rpm, but such pace is unlikely when loaded unless there is a strong tailwind or steep descent.
Cycle touring blog and tour journals: whispering wheels...

Offline DaveB

Re: Drivetrain HELP
« Reply #9 on: December 11, 2015, 09:24:48 am »
And since I rarely use the outer chainring, so for my new build I have decided to dispense with it altogether, and use a 2x10 setup with 36x22 chain set and an 11-36 cassette.

On the 36x11 combination I could reach 25mph at 90 rpm, but such pace is unlikely when loaded unless there is a strong tailwind or steep descent.
This makes sense if you only use the bike for loaded touring.  If you ride it unloaded, the 88 gear-inch high gear may be a bit of a nuisance downhill or with a tail wind.  The 103 gear-inch high gear provided by the 44T chainring would be more versatile. 

Offline Pat Lamb

Re: Drivetrain HELP
« Reply #10 on: December 11, 2015, 03:25:10 pm »
And since I rarely use the outer chainring, so for my new build I have decided to dispense with it altogether, and use a 2x10 setup with 36x22 chain set and an 11-36 cassette.

On the 36x11 combination I could reach 25mph at 90 rpm, but such pace is unlikely when loaded unless there is a strong tailwind or steep descent.
This makes sense if you only use the bike for loaded touring.  If you ride it unloaded, the 88 gear-inch high gear may be a bit of a nuisance downhill or with a tail wind.  The 103 gear-inch high gear provided by the 44T chainring would be more versatile.

I'd modify Dave's statement to say the "limited" top gear might be an issue with a whopper of a tail wind or riding with a fast group.  The few days I've been loaded touring and had a decent tail wind, I was delighted to top 20 mph, which is achievable with the 36 "big" ring.

Is "more versatile" a matter of riding a loaded bike up a 12% grade or an unloaded bike up a 20% grade, or is it being able to hang on a group ride doing 25-30 mph?  Is vanilla ice cream better than a brownie?

Offline RonK

Drivetrain HELP
« Reply #11 on: December 11, 2015, 06:36:13 pm »
And since I rarely use the outer chainring, so for my new build I have decided to dispense with it altogether, and use a 2x10 setup with 36x22 chain set and an 11-36 cassette.

On the 36x11 combination I could reach 25mph at 90 rpm, but such pace is unlikely when loaded unless there is a strong tailwind or steep descent.
This makes sense if you only use the bike for loaded touring.  If you ride it unloaded, the 88 gear-inch high gear may be a bit of a nuisance downhill or with a tail wind.  The 103 gear-inch high gear provided by the 44T chainring would be more versatile.
You will have to be pretty darn fit to ride a touring bike at more than 25mph even unloaded.
However with a 36t chain ring this can be achieved at a cadence of only a fairly average 90rpm.
It it quite possible to go faster if you (or the wind) are strong enough, or the descent is steep enough. In such circumstances I have little difficulty reaching a cadence of 130rpm. 
But ultimately such opportunities are rare in the touring context.
« Last Edit: December 11, 2015, 06:41:17 pm by RonK »
Cycle touring blog and tour journals: whispering wheels...

Offline CanvasAndSteel

Re: Drivetrain HELP
« Reply #12 on: December 12, 2015, 06:02:22 pm »
Just curious, for a touring bike what's the perceived benefit for going with XT instead of mid line Shimano?

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Offline DaveB

Re: Drivetrain HELP
« Reply #13 on: December 12, 2015, 06:45:59 pm »
Just curious, for a touring bike what's the perceived benefit for going with XT instead of mid line Shimano?
I thought XT was mid-line and sort of the Ultegra of the MTB world.  XTR is the Dura Ace equivalent.

Offline RussSeaton

Re: Drivetrain HELP
« Reply #14 on: December 12, 2015, 07:32:08 pm »
for a touring bike what's the perceived benefit for going with XT instead of mid line Shimano?

Perceived benefit.  Easy.  The top groups, XTR for mountain, Dura Ace for road, are better because they are lighter, higher quality, more expensive, prettier, nicer, etc.  Maybe, maybe it lasts longer too.  Maybe.  Higher groups may use bearings instead of bushings.  Maybe the higher groups have more advanced, newer features.  Maybe.  Higher groups may use more exotic material, titanium and carbon instead of aluminum or steel.  Within the Shimano lineup, they all work very well, last a long time, cost different.  Buy whichever you want.  They all work the same.