Cane Creek makes a great 31.6-to-34.9 shim. Good insertion depth and not expensive.
Scott (previously) and Kona (currently) both have bikes that used 34.9 ID seattubes with shims.
Problem Solvers makes nice 4" long shims. They don't appear to offer a 34.9 to 31.6 yet but I'd guess it's just a matter of time.
March 21, 2017, 8:38 a.m. - Andrew Major
Cane Creek makes a great 31.6-to-34.9 shim. Good insertion depth and not expensive. Scott (previously) and Kona (currently) both have bikes that used 34.9 ID seattubes with shims. Problem Solvers makes nice 4" long shims. They don't appear to offer a 34.9 to 31.6 yet but I'd guess it's just a matter of time.