pulley size vs belt legnth

[DUBB Motorsports]

When going down in pulley size how much does the belt size go down......
If I am running a 3.75 pulley now with a belt size of k080485 which should be 485???If I want to go with lets say 3.5, or 3.25 what size would the belt have to be?

 

[Sean124]

genrally the belt has to shrink 25% of diameter change in the pulley. Alot of times that close.

 

[cjmatt]

pi*r^2 times the percentage of the pulley that is touched by a belt for both pulley sizes. then subtract

 

[Sean124]

Nice little formula. I just wish all the belt ribs were cut the same. Ugh

pi*r^2 times the percentage of the pulley that is touched by a belt for both pulley sizes. then subtract