Ride, Wrench, Swap, Race
Join Date: Jan 2010
Location: Northern California
Posts: 9,196
Bikes: Cheltenham-Pedersen 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.
Mentioned: 132 Post(s)
Tagged: 0 Thread(s)
Quoted: 1566 Post(s)
Quoting their site, "It does not compromise the shifting in the smaller cogs of the cassette but yet it enables the derailleur to work with as large as a 40T cassette".
I can't see how this would be true, since the chain gap tends to be a determinant of how quickly that a shift can be completed and how well that indexing works.
Some indexed systems are reported to still shift acceptably with one of these devices, and you may be able to compensate to a great degree by adjusting the derailer's B-tension screw (since you aren't going to be using a 40t cog), but these things aren't magic and the chain gap can always be a big deal on a derailer bike using modern chain.