ok if you would use this formula to figure out wheel diameter then u could use it for finding a rpm right

example

3 ft/s = diameter * pi * 100rpm

3 ft/s = diameter * pi * 1.67rps (rotations per second)

diameter = 3 ft/s / (3.14 * 1.67 rps)

diameter = 0.57 ft, or 6.89"

real

3 ft/s= 3" *pi *rpm

3 ft/s= 9.42*rpm

rpm= 3 ft/s / 9.42

rpm= 3.18 ft/s or 19.12 rpm

but if u check the math it is not right or did i do my math wrong.

checking

3 ft/s = diameter * pi * 19.12rpm

3 ft/s = diameter * pi *.318rps (rotations per second)

diameter = 3 ft/s / (3.14 * .318 rps)

diameter =3.00 ft, or 36"

admin edit: Changed the subject 'i have a ?' to something more useful.