Hi,
I'm looking to take a mountain triple, remove the outer chainring and use it as a double on an 80's road bike. The triple I have is a Sugino RD2 600 26-36-46 which is designed for a 113mm bottom bracket. The bike has a 110 (I actually measured 111, it has french parts, so who knows) bottom bracket. I took the original double off and put the Sugino on, just to see if I could rig it up. The inner chainring does clear the chainstays, however it appears to be significantly farther out than the double it replaced. Just on a visual, the small chainring seems to line up with the 4th cog (with the 1st being the largest) of the 6 speed cogset. Looking at the two cranksets visually, the original is a double 42-52 with a single spider (and spacers between the spider and inner chainring). If you look through it, between the chainrings, the mount (where it mounts onto the spindle) is almost exactly between the chainrings, so the inner chainring sits inside the spindle mount.
When I do the same on the Sugino, the mount is pretty much even with the inside of the inner chainring. I haven't measured the actual dimensions, but it appears that the Sugino inner ring, on the same bb, sits 5-10mm farther out than the original.
So my initial thought is, and I've never worked on cranksets, could I add spacers to the inner and middle chainrings of my Sugino to decrease the chainline? Or do they make mountain triples that would have a lesser chainline? I didn't buy the Sugino for this purpose, I pulled it off another bike that I sold, so I'm not stuck on using it, in fact, it will likely go on my next commuter.
I suppose another option would be to try and get a smaller (lower tooth count) double crank, however I haven't seen any that have small ring in the low thirties, high twenties. Rivendell sells a low wide double with 29-40, but it is essentially a Sugino RD2, just like mine, but with a chainring guard in place of the outer chainring.
I suppose I could try to run it as is and see what happens, but with the shorter chainstays of a road bike, I think the performance will be marginal at best, and at the worst possible place, the low gear.
If it is possible to add spacers to the Sugino, I would want to know what to search for, I don't know how they are spec'd, etc.
Thanks!
Jon