* * Chas said:I picked up a used Campy Mirage crankset with 53/39 chainrings.
I don't use front index shifting and I'm planning or running this with 7
or 8 speed cassettes. I'm not familiar with Campy's pins and ramps or
chainring spacing.
The 53 tooth chainring is a little tall for me, I've used 49/13 top gears
for years. It looks like Campy had or has 50 tooth chainring for this
crank. If I find a Campy 50 tooth chainring will it work OK with my
existing 39 tooth chainring.
My understanding is that the pins are "timed" to be positioned around the
ring, so that they line up with in the middle of a link on the smaller ring
(not a pin), and lift it onto the middle of the ramped tooth of the larger
ring.
If the rings weren't timed to be put together, it might put the roller on
top of the tooth, and it'd take a little while for the chain to snap into
the gaps properly.
Perfect timing of ramps and pins isn't essential. My triple use a
Specialites TA 28t small ring with a middle designed to lift of a 30t, and
it is only very slightly worse at shifting.
Any ring with a 135 BCD should work, by the way, it doesn't have to be
Campag, but of course the timing will be better if you get a Campag big
ring designed to carry from a 39t. Quite a few makers do rings with that
BCD.