Originally Posted by
TransitBiker
I am not worried about dirt or grease, i'm worried about the chain stretching vs belt.
How long do you expect the belt to run? The single-speed chain we use for the timing side on our tandem has run fine for 40,000 miles and over 30 years - and that's without any enclosure to keep rain and grit off of it. Sure can't say the same for the drive-side chain - but then that's a narrower derailleur-compatible chain.
Of course with a belt drive you may need to have it last for the life of the bike. Unlike chains, I wouldn't want to place a bet on compatible belts of the right design still being made 30 years later.