So I'm building a bike from the parts bin to ride with the family. Flatbar, roadframe, 10 speed rear with flatbar shifter, single front crankset, etc.

Plan on using a Shimano Alfine single-speed crankset with a 11-28 rear cassette with Ultegra derailleur. Now, Shimano makes two different Alfine cranksets:

-One with a single chainguard and chainline of 42.7mm
-One with a double chainguard and chainline of 49.2mm

(https://bike.shimano.com/media/techdo...9830604038.pdf)

I'm assuming the double chainguard would be best for a 1x10 setup so to keep the chain on the crank. However, would the single with the lower chainline be just as good?

I don't want a dropped chain, but I also have all the parts to make this work (outside of the front crankset) so I'd really like to make this happen with just having to spend the money for the crank (the proper one, of course).

With a 10 speed rear I'd be concerned about cross chaining and having the chain rub on the guard(s). But I admit I've only done 1 x 6 (no chainguard) so I can't speak from personal experience.

I would go with the one that gives you the best chainline in the cogs you'll be on the most.

The best chainline is the one that lines up best with the rear sprockets best. That would imply lining up a single with the middle of the cassette. OTOH, you don't use all cassettes equally, so you can sometimes do better shifting the chainring in or out slightly so it's more in line with the most used sprockets.

All my bikes have the chainline slightly outboard of center, since I spend more time on the outer half of my cassette. This makes things worse than otherwise in the inner sprockets, but I use those only about 5% of the time.

I don't know the width of your frame, so can't give you a number, but you can determine line as follows. Measure from inside the frame to the middle of the cassette, subtract that from half the dropout width to get the chainline offset. Fudge it out or in slightly if you wish to account for how you ride, then get the crank with the nearest offset.

No great precision is needed since you're measuring only to within a millimeter or two. For these purposes, eyeball measurements using a ruler is fine.

Oh boy!
current specialty.
I made a series of videos about competitive viability of 1x10- 11/36 on road bikes for another forum.
a couple were specifically about specific mods to chainrings, cassettes and how to build the ideal chainkeeper, etc.
so much fun to make.
People were appalled by the narrators demeanor though, they all eventually got banned.
ya chainline not that critical
i been working on perfecting 1x's for years.
Is just a lovely and sensible drivetrain.
good luck!

Frame is a standard (road) 68mm English BB, 130mm rear dropout. Since the Alfine crankset is offered in a 39T and 45T and I know my cassette (11-28), I suppose I should choose the crankset that'll put me in the middle of the cassette for most of my riding. Still, I'm torn on the double chainguard vs single chainguard. As for the 1x10 setup, many OEMs are doing 1x9 setups (with mountain components). Is there something inherently better about a single crank with a mountain cassette/mountain rear derailleur?

#1 and #10 will be at the extreme end of practicality.. not as bad as full cross chaining, though..

chainline is the 1 ring to the middle of the rear cluster,, like center ring of a triple..

centerline of the whole bike , is the base to start measuring from..

with a 130 hub thats 65 in from either end.

Yeah, I figured that a 1x10 wouldn't be as bad as cross chaining a double, let alone a triple. I'm fine with the 1st and last cassette sprocket being virtually useless...that still gives me 8 gears to safely work with. My only concern was getting the proper chainline and figuring out what type of chainguard I need on the front (although the double chainguard version of the Alfine crankset should take care of this).

You're over thinking this. If you can get within a few millimeters of decent chainline, with either chain guard set up, pick that one. If the roads are at all bumpy, you'll probably want to go with double guides to prevent the chain from dumping in either direction. (that's what I'd do). Otherwise you can install one of those stationary chain keepers that look like front derailleurs.

Probably the biggest difference will be the chainring. Chainrings made for single speed or 1x? don't have shift gates, and are less likely to drop a chain coming from an angle

Aiee. I knew I shouldn't have peeked in, instead just kept on walking.

it may not be in line with your exact purposes, but hopefully might be of some value.
this is one of two videos for making a mid-high end 1x road drivetrain, utilizing the 11/36.

this one covers componentry and chainkeepers.
the other, which is easily found, covers easily made modifications to alleviate the problem areas fietsbob has mentioned.

by no means are you, nor should you be, saddled with two useless gears.

am no authority here, and would never pretend to be. There are many more options than what I've detailed.
but you can be assured that the suggestions made here are accurate, and they work beautifully. They've been tested in every imaginable condition. Maybe not for everyone, but a 1x10 is a good thing. I'm using it to compete in a 208 mile 16000ft climb race this summer.

ok im outta here. Good luck bro.
https://www.youtube.com/watch?v=MnY3ZtoLa6c&sns=em

With a 1Xanything setup? I don't understand.

How can there be more than ONE "proper" chainline with anything other than a single(ok....fixed)speed, 1X1, set up. As soon as the chain is moved from one cog to another it would seem to me that one combo has to be less than "proper". Am I right.................there may not be the first problem with the cog/chainring relationship but only one pair can be perfect or "proper".

Cheryl has a 1X8 setup and I have the rear derailleur set to run on cogs 2 thru 5, big to small size, (1X4 in reality) and it is working super. Of course, she doesn't fly on flats or climb any mountains. The respiratory therapist is suppose to be by this week to set her up with a portable oxygen setup---that might change the whole game-plan!!!!

At some point it would seem that it moves from "what will work" to "what do you need or use".

Yes, obviously only one sprocket can have perfect, zero deflection, chainline. So in multiple gearing, perfect chainline is less of an issue than it would be in SS. But still wand decent cheniline to keep the deflections minimized.

You have two basic choices. Set the chainline so the maximum deflection in either direction is minimized. Or offset the chainline slightly to either side of the cassette for better chainline in the gears you use the most, accepting that the maximum deflection in the other direction is worse. This is how I set up my bikes, offsetting slightly to the outer half of the cassette where I do 90% of my riding.

BTW- 10s chainline in the extremes is no worse than 9s, since the cassette width is the same. It's also only slightly worse than what would be used in a 2x10 setup, since the middle ring is between where either of the 2x rings are, so all gears are usable.

I sometimes get laughed at for asserting that a 1x is a viable and sensible thing. But here's the bottom line: Once you ride without a front derailleur, you just don't ever want to go back.

So I was looking at all these components on the floor there, and I thought, "we are increasing the range of lateral movement only about 18-20% beyond what it was engineered to do. What would the cassette and chainring look like if this were a factory issue 1x10-specific group?"

it's fun figuring out things like that.
But doing something about it was imperative because I hate clunkiness and strain and needless friction, and using the set up on a TT frame with very short chainstays aggravated that.
There's nothing nicer than something that's been thoughtfully engineered.

the conclusions I came to- I'm not sure they are comprehensive, but I bet they are pretty close. A factory-issue 1x10 might incorporate these changes:

1) the innermost and outermost edges of the cassette would have a bit more chamfer around the circumference of the cogs, particularly the inboard edge of the large cog.

2) the chainline would be slightly biased towards the outboard side of the cassette; that big cog is naturally more mechanically efficient than the tiny one, so I'd want to be a little kinder to the latter by letting the chainline be closer to it. Originally I just did that for same reason FB sez, but it makes engineering sense as well.

3) the chainring would have a bit more chamfer on both sides as well. All this chamfering I'm talking about not only decreases noise and chain-drop but may slightly decrease the deflection as well. Since the metal removal doesn't significantly affect the load-bearing area, increased wear is not much of an issue.

4) but that chainring would be a STOUT one, though. Like, 7075 Aluminum, not the butter-soft 6061. Salsa used to make fabulous unramped, unpinned, un-dished flat chainrings from 7075. A flat single-speed type chainring used in place of a dished road chainring will probably put the chainline in darn close to ideal place.

5) A 100% fail-proof chain keeper. Personally, the biggest source of aggravation from 5 years of figuring out 1x's has been chainkeeper design. Requirements: under no condition shall the chain rub (and this sends you back to trying to improve your deflection issues); then, under no condition shall that chain drop. That's a safety issue, too. If you've ever been on someone's wheel chasing them up a hill and all a sudden his chain drops, you know what I mean. Don't want to endanger anyone riding with me.

That's ended up being the most difficult problem to work through. Naturally I presumed that a chainkeeper would basically look like and be positioned the same way as a derailleur, which was wrong, since they have entirely different jobs to do. The end product that works is a really simple one, but good lord did it take a while to get there.

I'd never recommend anyone go through all this. I think I'm just sharing my own enthusiasm and excitement at having figured out a couple of things that work. And they work despite the built in liability of short chain-stays and a carbon frame that acts like a sound-box.

OP, you'll have more fun if you just throw together what you got and start messing with it, see how good you can get it. I bet you'll get better results than you'll think.

One thing that makes a bicycle such a fabulous machine is that it is the perfect platform for engaging one's mind in problem-solving just for the fun of it. Sort of like an engineering version of playing chess. A chessboard that you can ride 50mph down a hill.

My worry was trying to get the chainline smack in the middle of the cassette. That way, I could use the entire range of gears without too much deflection either way. I would choose my crank size based on that. Still though, I've often not been paying attention (usually toward the end of a long ride when I am somewhat spent) on my "normal" 2x10 setup and I've caught myself on the small front ring on the next to last (smallest) cog on the cassette. How is that any different than a 1x10 with chainline in the middle pushed to either extreme?

Just put the darn thing together and find out!

That's what it boils down to. You won't be able to think up ALL the questions to even ask until it becomes a reality. Something will pop up that you never thought of....start your project and deal with what comes.

Cheryl loves her 1X. She didn't even ride it in the 3X6 stock configuration---she wouldn't. She doesn't care about crosschaining and all she knows about it is that knowing nothing is enough. She clicks, clicks, clicks and goes faster and then clicks, clicks and clicks with her thumb shifter to make it eaiser to pedal. She loves it. As Pierce suggested, leaving her seat stupid low is working great, she's feels safe and that's what counts.

At the grocery store she made it from the front door back to the meat dept., thru the frozen section and to the register today. She's happy......he bike is helping her recovery.

+1, at this point you should have enough info. Roll the dice, make a decision about the cranks and built it. You can fine tune the details after riding it a while, dealing with issues that actually arise.

I agree...but the crankset is the *one* thing that I actually need to purchase. I just want to make sure I get one that'll work for my needs/setup. At this point though, I may just need to take a best guess and buy one.