Rohloff 54mm chainline recommendation wrong?
I've just started using a Rohloff equipped wheel which I bought used & in setting up the bike have started out with the recommended 54mm chainline but it's waaaaaay wrong!
I could tell eyeballing it before I even mounted the chain. But as confirmation, I took a straightedge & laid it flat against the inside of the chainring & extended it to the rear cog. Did that with both sides of the straight edge to be sure that the measurement wasn't off due to the straight edge not being straight. In both instances I found the gap between the straight edge & cog to be ~8mm.
Which is huge! Even with the chain on, & sighting along the chain from the front the front inward bias is obvious where the chain passes over the cog.
Has anyone gone with a longer BB to correct the difference?
Can anyone else (whether you have the Rohloff or not) think of any negatives in doing so,
I'm currently using a tapered BB in a 113mm length but I'm considering at least a 118mm as a replacement. Figure split the difference. Sort of. Besides the next step up is a 122mm & that's just a bit too long. The bike I have has a EBB so I'll be able to fine-tune it from there.
Thanks in advance.
Rohloff recommends a 54mm chain line because the cog is 54mm from the center of the hub. If the chain is not lining up, then your chain-ring is not at a 54mm center, or your frame is out of alignment.
I'd guess your chain-ring is not at 54mm, square taper BB systems vary in chain line.
Thanks for the reply & ideas.
Originally Posted by itsdoable
I just double-checked the frame for straightness with the simple string test & it looks good. Also, double-checked chainline again to be sure that I hadn't made a mistake earlier & it's now at ~55mm. I just re-installed the drive side crank & it takes a while for it to 'settle' in. I have to re-tighten it periodically after the first few rides & then it'll be good.
Shortly after I did all that I realized my error. I'm new to SS'ing & now IGHs & have never really had to think too much about chainline. It didn't help that the bike I bought used came with a crankset with a built-in bashguard & other cranksets that I've bought off eBay also had the bashguard.
Took me awhile but I just realized that chainline for triples is measured to the middle chainring. So ... if I'd installed my chainring(s) on the outer, where the bashguard is, instead of the middle, chainline would've been near perfect since the difference between rings is ~4.75mm. Not quite the 8mm I thought I measured but it confirms that I need a longer BB. Going from 113mm to 118mm is close enough so I'll definitely be ordering the longer BB soon.
EDIT: Made a mistake in the replacement BB length. Should be 122mm. 122-113=9, 9/2=4.5 which is close enough to 4.75mm for me. There goes my Q factor :-). Truthfully, never been an issue for me. In fact, altough it's been awhile, I think I actually prefer slightly wider spacing of the crankarms.