When
changing pulleys, this also changes the belt size.
Here is a formula that
takes the guess work out, and will save you time and money on belts.
First you need to know what size belt you are starting with. This would
be the stock size.
Then you measure the new pulley you are putting on,
across the center. This is the diameter.
Measure the old pulley.
Multiply the diameter of each by 3.14. This will give
you the circumference.
Subtract the circumference of the old from the
new.
Divide this by 2
If you are going bigger you want to add this to the old
belt size. If smaller subtract.
If the belt size isn't a whole # round to the next inch
size.
For example: If going from a 3" pulley up to
a 5.5" and your belt size is 57"
3" x 3.14 is 9.42"
5.5" x 3.14 is 17.27"
17.27"  9.42" = 7.85"
7.85" divided by 2 =3.92"
original belt size was 57" +3.92" =
60.82
I would round this one up to 61". Sometimes it's
better to round down cause it's better to be too tight than too loose.
