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N. Hollywood, CA
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754 Posts
Discussion Starter · #1 ·
I took it for granted that I could get a good chainline with this esoteric list of parts, but the crank is too inboard and/or the cog is too far outboard:

- Surly singlespeed hub with White Dos Eno dual-cog freewheel. Built up in a 650b 'road' rear wheel mounted in a Velo-Orange Polyvalent frame, not that it would matter(?)

- Vintage Sugino AT triple crank: Outer bashguard, middle Surly stainless chainring, inner/granny unoccupied

- 68x127mm square taper bottom bracket

So after trying two shorter bottom brackets, I finally got a 127mm version so that the crank is farther outboard from the frame's centerline. Unfortunately, the chain just barely rubs against my bashguard when set on the inner freewheel cog. I assume a 2mm BB spacer could get me just enough clearance at the bashguard, but no way I'd be able to use the outer freewheel cog without rubbing.

I read up on Surly singlespeed hubs and it seems there are two versions. One for 'road' chainline, and one for 'mountain' chainline. I don't know which one I have, but since the wheel's all built up, I'm probably stuck with it.

Is there a way to adjust the rear hub spacing to improve my chainline (by moving the freewheel closer to the frame's centerline)? I guess that (if at all possible) would require re-dishing the wheel.

Hmmm... Maybe my bashguard is too big. I've got a 38t chainring, and what I recall is probably a 44t or 46t BBG bashguard. But regardless of the bashguard size, the middle chainring on my crank is just plain too far inboard of either freewheel cog.

Thanks for any tips...
 

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Your bashguard should be the same size as your chainring. Part of the reason is, should you really use it as a bashguard, the load will be shared by the chainring AND the bashguard. If you can't find one, another solution is to buy a chainring slightly larger and mill off the teeth.

Let me recommend another alternative; add spacers to each bashguard. It may require longer chainring bolts but that's minor. A half or maybe just 1mm on one or both bashguards may be enough to solve your problem. Any good bike shop can order such spacers and longer chainring bolts if necessary.

I'm not going to go through the math, but I suggest you either get your hands on a Sutherland's Manual or have your local bike shop measure your chainline to tell you whether the rear cog/cogs are in the proper position as well as check your chainring position. It can easily be measured with a metric scale ruler and some basic addition or subtraction.
 

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N. Hollywood, CA
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754 Posts
Discussion Starter · #4 · (Edited)
Thank you. I discovered chainring spacers on a Google search last night, so I'll have my LBS order some that will push the bash guard farther out. I hear what you're saying about bash guard diameter. Thus is just a Salsa Crossing Guard to keep my pant cuffs off the chain on a single speed townie bike. I can't consider a smaller chain guard until I can get out on a few rides and gauge the level of effort associated with the gears that I chose. Hopefully the spacers will do the trick in the short term.

That said, I suppose my original concern is unanswered, and could be expressed more succinctly. On a road bike, is it typically possible to get good chain line with a single speed hub and a road crank with the chainring on the #2 (not outer) position? Because the crank in the attached picture is on a 127mm BB, the longest offered - yet still the chain takes a healthy angle to reach the freewheel.

EDIT > Darn, I can't seem to upload a jpeg image from either my ipad or desktop browser. It's under 1MB, so not sure why there's no "OK" button in the upload dialog box...?
 
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