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Permalink Reply by Mike Schwab on March 14, 2013 at 9:10pm

http://sheldonbrown.com/singlespeed.html

Suggestion is to change axles to match the width of the frame.

 

http://sheldonbrown.com/frame-spacing.html#frameadjustment

If you really want to bend the steel frame to match the wheel.

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Permalink Reply by Kevin Mulcky on March 15, 2013 at 12:44am

There are plenty of 130 & 135mm SS hubs on the market. You should be able to dial in the chain line by choosing the correct BB length.

I'd buy the SS cassette adapter kit if the frame has dropouts with a derailleur hanger, just in case you'd ever run gears in the future.

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Permalink Reply by Kevin K on March 15, 2013 at 12:23pm

Thanks guys.  Should have mentioned that the frame is aluminum, so bending isn't really an option.

Kelvin, good point on the SS adapter kit leaving the option to put gears/shifter on later, if desired.

Picking the right BB length sounds tricky.  The adapter will make it easier to get a straight chain line.

Danke!

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Permalink Reply by Far'arned Retrogrumpalunkus #63 on March 15, 2013 at 6:33pm

It's easy to dial in the chainline and calculate the BB size you need if you have a spare BB laying around.  Install it and measure your chainline.  Your chainline will move 1mm for every 2mm you change the BB.  Of course standard BB sizes aren't in 2mm increments -but the math still works out.  Just make sure you are comparing apples to apples with spindle type.  If you try and measure off of a JIS and order an ISO bottom bracket you are in voodoo territory.  But most newer stuff is ISO these days anyhow. 

But using a spacer conversion kit for a single speed is still the easiest. 

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Permalink Reply by John C. Wilson on March 16, 2013 at 6:33am

If you run a cassette hub with a stack of spacers you could get perfect chainline without touching the BB and you could even have perfect chainline with either ring on a double crank. Or any ring on a triple.

Most any threaded hub whether flip/flop or made for a freewheel will have a few extra mm of thread to allow for spacers. You can also use any old 120 or 126  freewheel hub and space out the axle. There are limits but you have an excellent chance of having no problems.

Chainring bolts are normally an understressed piece of hardware that just work and don't ever have to be fussed with.  Adding spacers to chainring bolts is not a good idea. Do it all at the rear.

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Permalink Reply by mark stetson on March 16, 2013 at 6:56am

I'm with John.  I have a similar build coming up that I plan to do with a double crank.  It will have 2 cogs in the rear on a cassette hub, with the same tooth differential as the chainrings.  That way I can ride on the road with a higher gear and move the chain to the other ring/cog combination for trails.  Could be done with a triple crank too, just adds a bit more weight.   A cassette hub is perfect for this: lots of cog sizes available, and chainline can be made perfect for both rings by spacing the cogs where they need to be to match the rings.  I'll probably measure mine up and slice some spacers off to the correct widths on the lathe, but you should be able to get pretty close with old cassette spacers or possibley some additional off the shelf spacers.  I'd be happy to make you some if you go this route and can provide the dimensions needed.

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Permalink Reply by Kevin K on March 16, 2013 at 8:22am

Thanks y'all.  If I had a boxful of BB's it would be easier to get the right chainline on a threaded freewheel, because I could just put on the rear wheel and switch out the BB's until I got the one that fit. That would be the 'ideal' way to do it.  I know the chainline can be measured, but I'm a little fuzzy on exactly how to do that.  I'm ordering the parts online, so don't want to end up buying one BB, returning it, buying another BB, returning it, etc until I find the right one.

Mark, that setup sounds sweet, thanks for the offer on the spacers, might take you up on that.  Much appreciated.  My one-bedroom apt isn't really set up for metal lathing ;)

Out of curiousity, why are you going w/ a double chainring up front and two sprokets in the rear, vs. a single ring on the crank?  Is that so you can use a straight/SS chain, vs. a multispeed chain?

Here's another question for everyone: what advantages do you think a SS/Straight chain has over a multi-speed chain?  With multi-speed drive trains the chain is often at quite an angle, which isn't a problem. If you've got a multi-speed chain on a SS bike, does the chain line really have to be perfectly straight?

(aside: yes, I realize I could take the frame into a LBS to get this done, but 1) I like to save $$ and 2) I default to DIY, time-inefficiency be dammed)

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Permalink Reply by Far'arned Retrogrumpalunkus #63 on March 16, 2013 at 10:35am

The only time spacers should be used on chainrings is if there is an issue with the chain rubbing on the next-up ring when using an 8 or 9 speed chain on a modern 10-speed (or 11-speed) crankset. 

But even then we are talking 0.5mm "spacers" which are just really thin, precision-machined washers. 1mm might be OK, more than that and  you are just pushing your luck IMHO. You could always put a 0.5mm spacer shim on both sides of the spider and move two chainrings apart 1mm.  That should be more than enough unless you are running a crank and BB meant for a 130mm hub with a 135mm.  To fix that you can always use a BB shim too.  Those come in a bunch of different sized up to about 2.5mm (which would fix that problem moving a road crank and BB set to a bike with a 135mm hub. 

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Permalink Reply by mark stetson on March 16, 2013 at 2:03pm

Front chainline is pretty easy to measure.  Measure from the edge of the seat tube to the center of the ring, then add 1/2 the diameter of the seat tube.  For the rear, measure from the inside surface of the RH dropout to the center of the single cog, then subtract that from 1/2 the over locknut width of the hub, which is most likely 120 if SS,  130 if road or 135 if MTB. 

 

The factory stock SS I have here has a 32.2 seat tube and the ring CL is 28.4 mm from the edge of it, so 16.1 + 28.4 = 44.5 mm front chainline.  The rear spacing is 120, and the cog CL is 19 mm from the inside of the dropout.  The rear chainline is 60 - 19 = 41 mm.  Apparently whoever specified components for this bike assumes 3.5 mm off front to rear is OK for 1/8" SS chain.  So to address your chain questions, you can presumably have quite a bit of differential in front/rear chainlines and not worry about the chain coming off, but the chain and cogs are surely going to wear more than if the chainline were perfect.  The main advantages of SS chain are strength and cost as far as I can tell (disadvantage would be weight).  I'll probably just use 3/32" road chain on my bike, since that's what the cogs and rings I'm going to use are designed for.

 

I'm curious about the chainline on my other SS now, will have to go measure it. 

 

The idea behind two rings and two sprockets on my upcoming build is to have a 2 speed bike that doesn't have a derailleur or geared hub.  It's essentially a "2 speed single speed".  Since I don't usually haul my bike to the trails, its nice to have a road gear and an off-road gear.  Without a road gear, it would be a very slow 10 mile ride to the trails.   

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