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Old 04-13-20, 12:57 AM
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Bikes: Cheltenham-Pederson racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.

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Originally Posted by Choke View Post
The inside width of 5sp to 11sp chains should be the same (3/32) and only the outside width should vary. This is done by changing the thickness of the sideplates.

My default chain for vintage drivetrains is a KMC 9sp and I've never had any problems. I usually do put modern pulleys on the derailleur though. My thinking with the 9sp chain is that since the outside width is a bit thinner I'm less likely to have rubbing on the chainring in extreme chain angles. I know that I'm not supposed to have extreme angles but with less gears it does happen.
My take is that, with less gears, the chainline angles aren't so extreme at all.
Assuming that the chainline is a modest 44mm and the freewheel is good and close to the dropout (allowed further by virtue of modern chain's narrowness), a six or seven-speed freewheel can be cross-chained with abandon, especially given modern chain's extreme flexibility (due to independent inner link plates and smaller-radius plate overlap). That the front derailer clears modern chain throughout the range is appropriate to the "new reality" of modern chain's narrowness and flexibility allowing "full-range" use of all gears.
Vintage frames generally tolerate cross-chaining even better, yet due to their longer chainstays.

Where modern chain perhaps falls inboard of a vintage crankset's small chainring's teeth following a downshift, fine-tuning of the beveling of the teeth can bias the location of the tips of the teeth, done by means of holding a file against the rotating chainring. I do also love the way that modern 8 and 9s chains grab the big ring's teeth when upshifting.

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