Originally Posted by
PebbledChin
Amazing! That saves loads of trig for 5-bolt rings.
I decided to ride it around for a while in its original configuration,
but I've now had quite a few chain drops from the front ring.
I haven't had a single chain drop on my Xootr Swift.
I run an 8-speed (11t-34t) Shimano cassette, but I have detuned the
SRAM X.7 rear derailer H-Limit screw, to avoid the 11t cog entirely.
This makes the bike a 7-speed, if taken alone. However ...
Using only my behavior, I also avoid the 13t cog, when riding on
the inner chainring. Taken together, this gives 6 speeds, and a
more narrow chainline variance (less of a steep angle from
chainring to cog).
To pick up groundspeed, I have a 48t outer, in addition to the 40t
inner chainring. There is, however, no front derailer. I dismount,
to change gear ranges. If I don't miss, I'm back on the bike, and
riding the other chainring, about ten seconds after I'd dismounted.
. . .
The matching SRAM X.4 trigger shifter is an 8-speed shifter. Since
8th gear isn't reachable, the shift cable simply goes a bit slack if I
make the attempt -- and the bike remains in 7th gear.
The SRAM unit is a short-cage derailer, X.7, which I find reliable
and precise. I had the notion it would not take as many road dings
as a medium-cage derailer would have. Time will tell. Perhaps
it contributes to chain retention, somewhat.
The derailer cage tensioning spring of the X.7 is impressive, and
provides some needed chain discipline.
Capacity is limited! I think there's around 30t of capacity in this
derailer; I don't recall at the moment. Part of the reasoning behind
obstruction of 8th gear (11t cog) access was to narrow the capacity
a bit.
The chain is short enough that the derailer cage (and chain) does
not double back on itself (to excess) when in a slack combination
(small-small -- 40t, 13t) and long enough not to rip apart the derailer,
when accessing the large-large combination (48t, 34t).
Code:
Derailer Capacity
48t - 40t = 08t
34t - 13t = 21t
08t + 21t = 29t on a 30t capacity short-cage derailer
The driving factor, in selecting transmission components, was
the short-cage derailer, for its height above the pavement
(relatively higher than a long-cage derailer) when installed.
> On another topic, where is a rear battery-powered light
> best positioned?
I'm running a rear, bolt-on rack, and the light goes at the
back of it, as usual. That keeps it clear of any luggage
mounted on it.
Makes it a lot easier to lift the bike (as an alternative
to lifting the bike from the seatstay) while doing light
maintenance. Heel strike is a problem with any luggage
(even the rack-top bag I have offers some heel strike,
I think).