Belts 9mm or 15mm?

[s_forbes]

We have been using 15mm belts in our drivetrains recently, and everybody likes the belts over the chains. I'd really prefer to go to 9mm belts on whatever we build next though to save space. 987 has been using them for years and they seem to do just dandy, even with big wheels and small pulleys. Seems like if you get the belt tension correct they will survive easily on a 6wd setup with the center wheel direct driven by the transmission. Other configurations might be different.