Originally Posted by MICHAELABICK

I prefer the gates calculator as ti gives you more precision and is actually made by gates: http://first.gatesprograms.com/resources

For drive systems there are two ways of going: c-c and tensioning. Tensioning will give you perfect tension. On the other hand c-c can be a lot easier, as you don't have to make bearing blocks etc. If you do c-c you want to add a couple thou to the c-c to artificially tension the belts. Based on the length of the run somewhere between .003 and .008 thou extra seem adequate.