Re: Belt drive Rules of thumb??
Working from memory, I think the absolute minimum contact patch between the flat serpentine belt and the pulley is like 90º, with around 180º being optimal. The width of the belt would of course be a factor, but I think this was with a standard 5-6 rib belt. I think my belt has around 150º of contact and seems to be working fine with my 4 rib belt.
You might want to take a look at March's website as I seem to recall some info there about setting up pulley systems. This may very well be where the notion of the 90º minimum came from, but I set that stuff up so long ago that I am not 100% about it.