Poly-V and PJ-section seems to go under very many names, but I found this site:http://www.best-drive-belt.co.uk/index.html
and ordered two three rib PJ-section poly-V belt and two 10 mm wide flat belts. Flat belts should be interesting, they should allow 12 mm small pulley and over 30000 rpm and still transmit 0,4 kW no problem. Have to consider centre distance.
I have no first hand experience on small fast flat belt drive. On my milling machine there is about 2" wide, just under 1/4" thick modern spiced belt for slow 3-5 kW motor and about metre centre distance. Crown on the wheels is very small. On grinder there are bits and bobs of ID grinder attachement and smaller wheels have a really pronounced crown. They look pratically like 1" dia miniature old whiskey barrels. I would imagine that modern low strech wheels will need a very small crown if properly lined up. Any opinion this one?
Belt calculators there were very professional lookking and easy to use. They even calculate belt tension and equivialent resonance frequency.
Now I have to find a way measuring 60-100 Hz frequency trough microphone.
Postage was whopping 29€ euros, they probably don't like to get european customers. But because they had multirib, flat nad round belt AND they had a very nice calculator I desided to give them a try.