Originally Posted by
HillRider
Actually the radial difference between 38T and 42T chainrings is about 8 mm.
Most current front derailleurs have a manufacturer recommended minimum tooth difference between chainrings and it's typically 10 teeth or more.
I haven't tried tried closely spaced chainrings in many years since the mid-80's 46/42/26 triple crank and Sun Tour ARX front derailleur system I mentioned above.
It makes sense. For inner plate to clear the middle ring, with 42-38, FD would have to be mounted very high - not a few mm from the largest, but 1 cm, or more over the largest chainring.
Though, from what I've measured: two Shimano models. 48-38-28 and 42-32-22 - difference between the
42 and 38 is about 1.2 cm the closest I got.