Chainline tolerance?
 

Is a ring/cog chainline delta of 5mm a bad idea?

I've been looking to build up a fixie and the IRO group buy has put me into the mix.

I have a Bontrager Race Lite GXP crankset (double) that I would like to use. The chainline is listed at 44.5mm and I assume this is measured between the rings. Assuming a ring spacing of 5mm this gives a chainline of 47mm / 42 mm on the inside / outside. Most fixie hub/cog combinations look to have a chainline of 42mm (with a rebranded novatec or formula hub). Assume now that I am anal and I want to mount the ring on the outside for a clean look. This gives a chainline delta of 5mm.

The IRO geom. spec gives a chainstay length of 391mm (don't know if this if BB center to dropout center or whatnot). With fancy math I get an chain angle of 0.73 degrees [ arctan(5mm/391mm) ]. With this angle it looks like i'll be losing 0.01% power [ 1 - cos(0.73 degrees) * 100% ]. This doesn't seem like such a penalty...

I see chainline mentioned a lot here.

How important is it?

when does the delta get bad?

Having an OCD moment... tom.

i'd say it "looks better" to have your ring on the inside of the spider than hear CLACK CLACK CLACK at all times because your chainline's off.

that being said you *probably* wont throw your chain, but for the love of bob keep a brake in case you do.

chainline within 5mm is good to go.

i've ridden with a worse chainline than 5mm with no problems.

but if you have the option of a good chainline, you're really thinking of losing that for "the clean look"? i think that's silly.

QP knows his ****. listen to him.

yes, i just want to know "how silly" or what's the price of form over function. I just want to be educated :)

t

as you'll probably find, 5mm gets you the discounted price of drivetrain noise. full price is broken bones (assuming a greater chainline delta and other mitigating factors) so really it's quite a deal.

there are those that would say otherwise, but aw gee thanks. :)

I don't know. It's possible that you could wear your chain or teeth unevenly due to the little bit of lateral friction that an angled chain experiences - i don't know. it's possible you could throw a chain, especially if your chainring has ramps and pins. but i don't know the probability or the likelihood. all i know is that you've got the ability to get a straight chainline; i don't see reason to introduce an element of mech inefficiency just so that you can put your chainring on the outside.

besides, a straight chainline turns me on more than a chainring on the outside of a spider. just sayin'.

What I would do is use the inside CR. I would install a chainguard that was made to be installed on the outer position of the cranks. I don't know what it's called but I did see one/read briefly about it.

Besides, the outer CR might be too big to be practical.

(sorry, that quote was a mistake)

for ss application inside/outside doesn't matter. In fact you are better off with a chainring that doesn't even have any of that inside/outside shifty nonsense.

I ****ed up and replaced my BB on my ssmtb with the wrong spindle length. My chainline is now off by about 5.4 mm. The visibly crooked chainline bothered me for a while, but really I can't tell the difference when riding.

i thought you were starting to discuss the merits/disadvantages of meth and was about to rethink my prior statement...

I've run into the same dilemma on mine. Just accept that you really need to use the inner chainring position and do it. I'm going to paint the crank spider ends to match the crank since they're silver and the crank is black - just to clean up the look - also bought black short stack chainring bolts.

Are you building the bike to look at or ride? Do it right, 5mm off is a lot.

Thanks for all the responses. I'm coming from riding multispeed bikes where the chain is rarely in perfect alignment. Is there something different about Fixie/SS chains? Do they have less side-to-side play? I've only had a multispeed chain jump when new and poorly mated to an old ring...

No, i'm not going to risk life and limb for a clean look...

SS specific chain is less tolerant of what would elsewhere be known as crossgearing, but it's not really the biggest factor, as 5mm isn't much and many of us are using PC58 and other stuff like that anyway for 3/32" drivetrains. The issues are weird parts wear, mechanical inefficiency, and the danger of throwing a chain. With no RD to take up tension, throwing a chain is easier than you'd think, especially if your chainrings aren't really, really round.

sex_appeal(straight chainline) > sex_appeal(chainring on outside)

Plus, that's a dark crankset, nobody's going to notice which side the ring is on unless they're really looking close. If they're the kind of person that's going to inspect it that closely, they're going to be more impressed with the fact that you got your chainline right.