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Old 12-21-06, 06:17 PM   #1
kmart
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Convert a Shimano Triple Crank to single ring?

Hi all, I am looking at converting an old bike to a fixed gear, but the cranks have a double chainring with the large ring and crank being a single piece. Is it possible to take a newer Shimano crank (or similar), double or triple ring (does it matter?), remove the unwanted chainrings and bolt the crank arm and spider back onto to a single chainring? In my case, I would want to use the middle ring of a triple crank or the small ring of a double crank and remove the other rings.
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Old 12-21-06, 06:56 PM   #2
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Yeah. My fixie uses just the 39t ring on an Ultegra double crankset. Your chainring bolts will probably be too long so you'll have some from a single chainring crankset. Try a BMX oriented LBS for short chainring bolts. You also have to consider which chainring position is going to give the best chainline. In my case the inner chainring position from the Ultegra double worked out perfect.
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Old 12-21-06, 08:10 PM   #3
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Since the chainline can be adjusted on the rear hub using spacers, as long as the chainring isn't too far off, it should work out right?

Thanks for the help.

EDIT: Another question. Would these cranks be OK for a fixie? Now, I am the kind of person who looks for low prices, and then later ends up upgrading to more expensive stuff, but I am just not sure if I will devote a lot of ride time to the fixed gear. Also, these other cranks cost about the same, but are they OK for a fixed gear?

Last edited by kmart; 12-21-06 at 08:19 PM.
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Old 12-21-06, 08:50 PM   #4
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Are you talking about a freewheel hub? Don't count on being able to do much chainline adjustment with spacers. There aren't enough threads on the hub. You need to respace and redish. If you're talking about a cassette hub, then you probably mean single speed unless your going to buy a $65 Surly Fixxer.

You don't have to buy short chainring bolts. I shortened the ones I had on a bench belt sander. Actually it's the nuts on the back side that need to be shortened.

That crank will work. One of my single speeds uses a converted road double. The other uses a converted mtb triple. I used the shortest BB spindle that would allow the chainring to miss the chainstay.


Last edited by Grand Bois; 12-21-06 at 09:00 PM.
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Old 12-21-06, 10:52 PM   #5
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So, is it possible to have multiple combinations of crank+BB to get the correct chainline? Could I pick a BB length, and adjust the chain ring distance from the crank spider using long chainring bolts?

All of a sudden, I am intimidated by the apparent variety of options here....
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Old 12-21-06, 11:27 PM   #6
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Sheldon Brown, as usual, has the information on chainline you are seeking. Try www.sheldonbrown.com/chainline . He details how to measure chainline at the cogs and the chainrings, and lists the likely chainlines for various sprockets and crankset types (road, triple, MTB, etc).

Don't be intimidated by it. The research will help you. It's great fun playing around with, and when you get it to work, very satisfying.

Basically you can eyeball chainline between rings and sprocket, and judge how the teeth mesh between the sideplates of the chain (centred is perfect, off to one side slightly means chainline is off. You could go to the lengths of using a piece of twine held against the front of the outside of the chainring, and see how it lines up against the outside of the sprocket. I used a straight length of thin aluminium angle the first time I did one.
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Old 12-23-06, 04:08 AM   #7
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Chainline can be a ***** for the uninitiated, but in the end you'll have learned a lot, and you'll see its not that big a deal.

Yes you can adjust chain ring distance from the spider with washers, but that's kind of a gross looking way of doing it; it's much nicer to finesse the bb spindle length.

FWIW, lots of other conversion riders (incl. me) get a nice circa 42mm chainline (this lines up with standard track hubs) with a set of 80s 600 cranks (50-70 bones on ebay/ craigslist, and way nicer than the cranks you are asking about) on the outer ring position, and a 107mm shimano square taper cartridge bb.

Also, the ssfg forum is a good place to ask about this stuff.

Last edited by mander; 12-23-06 at 04:16 AM.
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Old 12-23-06, 05:59 AM   #8
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Just out of curiosity, why do you need to take off chainrings for a fixie? Why not leave it on and just not use the front shifter?
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Old 12-23-06, 07:38 AM   #9
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Originally Posted by mike
Just out of curiosity, why do you need to take off chainrings for a fixie? Why not leave it on and just not use the front shifter?
I did that with mine, and a bike messenger pointed out that I was doing the bike geek's equivalent of "picking my nose in public"
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Old 12-23-06, 07:59 AM   #10
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Quote:
Originally Posted by Scooby Snax
I did that with mine, and a bike messenger pointed out that I was doing the bike geek's equivalent of "picking my nose in public"
Largely aesthetic- a fixie looks a lot smoother without the extra chainrings (slices off a bit of weight too)- although my friend swears by using the middle ring and leaving on the big 'un as a guard.

As for chainline- when I built mine I worked on trying to "space it out" without redishing and it was not going to work. I considered learning to redish (which would be a good skill I think- I've never done any wheel building)- but I ended up buying a low end rear wheel on ebay for about $70. It got me right on the road and has a flipflop hub (which I haven't used...)
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Old 12-23-06, 08:41 AM   #11
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Quote:
Originally Posted by kmart
EDIT: Another question. Would these cranks be OK for a fixie? Now, I am the kind of person who looks for low prices, and then later ends up upgrading to more expensive stuff, but I am just not sure if I will devote a lot of ride time to the fixed gear. Also, these other cranks cost about the same, but are they OK for a fixed gear?
The key thing to look for in a crankset is bolt-on chainrings. Be careful with lower priced cranksets because a lot of them have permanently attached chainrings.

You'd think that removing a lot of parts to convert a bike to a single speed would be simple but, as you get into it, it gets progressively more interesting. I love doing this kind of project.

Last edited by Retro Grouch; 12-23-06 at 10:52 AM.
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Old 12-23-06, 11:01 AM   #12
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Quote:
Originally Posted by Scooby Snax
I did that with mine (left the chainrings on), and a bike messenger pointed out that I was doing the bike geek's equivalent of "picking my nose in public"
That's funny. I thought the whole fixie conversion thing was to be non-conformist. But if you don't non-conform in a certain way, then it isn't cool... hmm.
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Old 12-23-06, 04:55 PM   #13
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Its got nothing to do with fixed; not wanting to ride a bike that looks ass crosses all boundaries.

Last edited by mander; 12-23-06 at 05:03 PM.
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Old 12-23-06, 06:12 PM   #14
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Quote:
Originally Posted by mike
Just out of curiosity, why do you need to take off chainrings for a fixie? Why not leave it on and just not use the front shifter?
The shifters would be removed anyway, and I think the extra rings just look stupid if they're not being used. As for using them as a chain guard, I don't see how pointy gears are going to protect your pants from getting ripped to shreds. So, off with the chainrings!

In other news, I read sheldon's page on chainline and my head exploded.
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Old 12-26-06, 01:56 PM   #15
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I think chainline discussion gets more complicated than necessary. If you buy a double road crank, you can mount your new chainring on the inside or the outside of the crank. Between that and the square taper (tightening your crankarms super tight or just tight), you should be able to line up your chain sufficiently with a SS freewheel. If you're using your old wheel, you have lots of options with spacers. Good luck!
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Old 12-27-06, 02:43 PM   #16
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FWIW, I converted my 6603 crankset to a single on my cross bike. I removed the granny, replaced the 39 middle with a Spot 42t (non-pinned or ramps) and replaced the 53t with a Spot chain guard. I didn't have to worry about chainline since I was still running 10sp on the rear.
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