I think the effect of short chainstays is when the chain is tight on a big-big setting. The cage rotates to near-horizontal and the idler wheel moves forward by perhaps an inch, half the length of the cage. This enhances chain angularity, putting added side tension on the chain/idler wheel interface as the chain enters the cage, and pulls sideways on the big chainwheel. Not damaging, but noisy, and I think it has resulted in a few thrown chains on my bike. I adjusted it better by moving the wheel forward in the dropout, allowing the cage to rotate to a less-extended position.
With a longer chainstay tube the effect of this shortened chain run would be less than on a tighter frame. Again it probably doesn't affect how the chain clears the cog and then climbs on, but the angle itself could cause noise that is at least irritating.
Ken Freeman Ann Arbor, MI USA
-----Original Message----- From: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of Mark Bulgier Sent: Monday, February 19, 2007 7:48 PM To: Fred Rafael Rednor; classicrendezvous@bikelist.org Subject: RE: [CR]28 teeth with Campagnolo Nuovo Record?
Fred Rednor wrote:
>
> > I've been struggling with 26-13 standard-6
> > speed on my Masi for a while, and I think
> > I got it. This is a really short chainstay.
>
> So perhaps the crucial factor for those of us who have had success
> setting up the Nuvo Record with a 14-28 (or even a
> 13-28) freewheels was the chainstay length? I've never had problems
> with this setup but I've never done in on anything but 1960s (or early
> '70s) frames which had - by latter standards - long chainstays.
No, the rear derailleur capacity doesn't really depend on how long the chainstays are. Chainstay length does affect how many gear combinations are useful, before the chain deflection angle gets too annoying and/or the chain rubs on the larger chainring -- but that's not the question we're looking at here.
As several people have pointed out, to get the max range you do need to be able to move the wheel in the dropout (thus, forget vertical dropouts), but that's to change the distance between the freewheel and the derailleur, and to fine-tune the chain wrap. It's not because you're adjusting the chainstay length.
Now there might be chainstay lengths that are better and others worse. That's because we can adjust the chain length only 1" at a time. But it's not so simple as long=good. It'll be something more like 16, 16.5, 17, 17.5 and 18 all good, but 16.25, 16.75, 17.25, 17.75 and 18.25 all bad. (Exact good & bad lengths varying from bike to bike)
The idea there might be good and bad lengths is somewhat doubtful, but it's based on the fact that when you move the axle in the dropouts you're adjusting two things at once: the distance from the freewheel to the derailleur, and chain wrap angle of the cage. Maybe there could be a setup that requires a certain specific position in the dropout to get the freewheel/derailleur distance just right, but then the chain wrap isn't just right? Then adjusting the chainstay length a little (if that were possible) would provide the independent adjustment of chain wrap.
Each half-inch longer in the chainstay requires about 1" more chain. (Not exactly 1" because the upper & lower chain runs aren't parallel, but pretty close.) So the good & bad lengths will repeat for each half-inch of chainstay length (roughly).
I think, in practice, that any chainstay length can probably be made to work with a 28 as long as you have long horizontal-slot dropouts. Maybe at the very extreme of what a NR can be made to shift, then the exact chainstay length may matter a bit. I doubt anyone knows what that limit really is, but we know it is at least 31t.
Mark Bulgier
Seattle WA USA