Sorry, I now see that the Avanti is a cassette hub rather than a screw-on, so, no you'll not be able to easily change it to fixed - you could use Velosolo's spacers to make it a single-speed hub if you wanted.
48 / 18 is probably not a bad gear to be starting off with, 48 / 16 possibly a bit high.
Sorry, I now see that the Avanti is a cassette hub rather than a screw-on, so, no you'll not be able to easily change it to fixed - you could use Velosolo's spacers to make it a single-speed hub if you wanted.
48 / 18 is probably not a bad gear to be starting off with, 48 / 16 possibly a bit high.