I'm looking to buy a 4wd mower on a local auction with the idea of using the steer axle for a 4wd conversion on one of my tractors... I was looking up information on setting up a hydrostatic system and came across this link.
It has a lot of helpful calculators in it, such as:
How to determine belt length with different diameter pulleys
How to determine road speed based on tire diameter and hydraulic motor speeds
How to determine ratios based on sprocket teeth
How to determine cylinder force based on diameter, pump pressure and angle of cylinder (great for designing front end loaders!!)
And several others...
Anyway, here's the link. Hope it's helpful.