I want to try single speed cyclocross on the cheap this fall. I have a track bike with 120mm horizontal track dropouts. Ordered ss cog 17T, some grippy 700x25 tires, and a 34T 110 BCD chainring. BB is square JIS with 103mm spindle.

Here's the question: what cranks should I use? I want 175mm for the leverage. Want 110 BCD so I can run 34T chainring. Found Dimension for 113/118 mm spindles (too wide by 10mm) and Spinz Expert for BMX (assume they are designed for 110mm spaced BMX hubs - so they are 10mm to narrow).

Would it be acceptable to run a crank that is too wide or too narrow by 10mm and not have a perfect chainline? Are there other cranks that I should look at? Have not found track cranks with 110 BCD yet.

Thanks

update: just found origin8 ss series for 107mm spindles; maybe this is the best compromise?; it comes in 175mm length/110 BCD/square taper JIS

Despite the fact that I'm not a cyclocross racer I'd question the wisdom in running 25 mm tires on a course that will at some point have mud or sandy conditions where a narrow tire like that will cut deeply into the surface and try to toss you on your noggin. Unless you already know that these tires will work for your area?

As for the cranks if you're running that small a ring then a 104 four bolt MTB crankset would be an option as well. And you can get rings in either 34 (stock) or 36 tooth size. By mounting the ring to the inside and using a bashguard on the outside and getting the optimum length BB you should be able to reduce any offset to less than 10 mm, guard the chain and rings well and be able to swap the ring for the needs of the course fairly quickly wiht the right tools.

cx was originally done with narrow tires; ss cx involves more running; a track bike with narrow chainstay clearance is another drawback - but this about a cheap rig - not an optimal rig; i'll go optimal later....maybe

so you think staying below 10mm will be good?

I can't tell you what kind of crankset to use, but remember you can use a spacer or two as necessary behind the fixed cup for a better chainline.

..and then I found this:

Sinz Expert Arm Set Black - 110bcd - 175mm
Great crank arms for the Polo Guard! Expert Square Taper Forged AL-7050 square taper interface (use 103mm BB) 5-arm 110 BCD spider

bingo!

i was settling on the origin8 single speed product but the 175 mm option is not listed on any websites; put in some special requests but no responses yet; the Sinz Expert is widely available

also was told perfect chainline most important for fixed and less so for ss

i realize i'm talking to myself but maybe this stuff will be useful in the future

A few mm off would likely not be an issue. But I'd have to agree that bad thing will happen with a full 10mm offset. I would not want to see much more than a 3mm offset if I were setting up my own SS bike. And at 4 to 5 mm I'd be swapping stuff around to make the offset less even though likely the worst effect would be a slightly reduced chain life. But at 10mm I'd not be surprised if there were not some snapping as the chain tries to climb up and over the teeth but fails and drops back down again.

U have two ways to fix chainlines... one is to move the crankset or move the hub/cog. A 103 BB is pretty short, i didn't even know there was one in jis that short (remember dura ace 104 and 107), as long it doesnt hit the chain stay you should be ok. Now the rear wheel, the easiest to fix a problem in the rear w/o having to respace the wheel and re true the wheel is to use BB spacers. If you need to move the cog out a few mms, just go to your lbs and ask them for BB spacers, they should have tons of them. Put that between the hub and the cog and you are done.

Chainlines do not have to be 100% perfect, besides the chain gives you a slack also so you should be ok. If you bought a BB sealed unit that is too short and you need to move the crankset out a few mms.. do the same thing... put 1 bb spacer at the right side between the shell and the cup and you are all set.

Good luck.

BB spacers - cool; going with the Origin8 single speed BMX 175mm cranks first; got a response on special ordering them; will measure after installation and use the spacers to adjust; entire conversion - ss cog, tires, chainring, cranks - coming in around usd220; the 103 mm is associated with Sugino track cranks; picked up a hint today that 103s might be used with BMX rigs too; will post a follow up on how it turns out