Measuring chain line on the rear cog can be tricky, indeed. It's why I gave up years ago and bought a Park CLG-2 chain line gauge (discontinued, apparently - don't know what their substitute is, if any). BTW, they have a pretty extensive discussion about chain line measurement and shifting/noise issues on their web site at http://www.parktool.com/blog/repair-help/chain-line
One thing that puzzles, though, is this statement from Sheldon's discussion on the matter: "… Most bottom brackets made since the mid-'90s are symmetrical, they stick out the same amount on each side. If you replace your present bottom bracket with one that is, say, 4 mm shorter, it will move the chainline 2 mm to the left, because it will be 2 mm shorter on each side, and the cranks will remain equally spaced from the bicycle's centerline …" I'm sure this statement is true - I have a symmetrical BB spindle on my Ram - *why* is it the case? Something had to give someplace else in order for the spindle to be symmetrical and yet have a crank that lines up properly with the rear cogs. Are newer crankset spyders "dished" in such a way that offset the crank arm from the chain rings to maintain proper chain lines? Looking at my bike with the very old (ca. 1975) Sugino 144BCD crank, everything seems straight up and down flat, which is why it's coupled to a BB with an offset spindle. So apparently the answer is, yes, they've changed over the years and dished the crankset. Does this factor simplify or further complicate chain line calculation? On Monday, February 10, 2014 2:52:23 PM UTC-6, Jay in Tel Aviv wrote: > > Thanks for all the input. > I tried the magic gear thing and couldn't make it work. Looking at the > calculator, I think I now understand why. It shows my 40/16 gear as a > perfect match with a 100 link chain and the Sam's 45.5 cm chain stays, as > long as there is zero (0) chain stretch. It's way off with just 0.05 inches > of stretch over 12 inches of chain. > > On Monday, February 10, 2014 7:18:10 PM UTC+2, Jeremy Till wrote: >> >> Measuring chainline on the rear cog can be tricky. My preferred method >> is to put a straight edge of some kind across the locknut on the driveside >> and measure the distance between the straight edge and the centerline of >> the cog. Then, chainline=(Over locknut spacing of the rear hub)/2 minus >> (distance between locknut and cog centerline) >> >> Another reason that once I made the commitment that I enjoy SS/fixed >> riding, I've vastly preferred to use dedicated fixed or SS hubs which have >> a standardized chainline (usually 42mm for track hubs, 52mm for SS MTB >> hubs). It's much easier to measure and dial in chainline at the front with >> the proper crank/chainring/BB spindle length combination than at the rear. >> >> On Monday, February 10, 2014 1:15:20 AM UTC-8, Jay in Tel Aviv wrote: >>> >>> I've got my Sam Hillborne set up as single speed at the moment, using a >>> track cog, spaced and rear derailler. >>> The setup looks straight enough to my eye, but it does rattle a bit. I'm >>> wondering if I've got the chain line a bit off or maybe the spacers are no >>> sufficiently tight. >>> How does one go about measuring chain line? I can't see a simple way to >>> get an accurate measurement with a ruler, what with all those pesky pieces >>> of metal in the way. >>> >>> If it helps, I'm running a Sugino triple up front with 40/26/bashguard, >>> 113 mm BB and a shimano 9 speed cassete hub. I use the 40T chainring pretty >>> much exclusively, as there is no FD installed. >>> >>> Thanks, >>> Jay >>> >> -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
