Formula for determining belt length
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 3,082
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From: eagle mountain utah
Formula for determining belt length
Old pulley size: 4"
Old belt: 60988 (Gates of course)
New pulley size: 3.5"
Belt rap around the pulley is approximately half way around the pulley. The new systems may be a little more than half, but this formula gets you close so it still works. The circumference of a circle is measured by the equation: 2 x pi x radius. But for the sake of finding new belt length and because belt wrap is only about half of the pulley, you wont' need the whole equation. Half the circumference of the pulley is just: pi x radius. pi is approximately = 3.1416 rounded off. Start with the old pulley size:
Diameter=4" then the radius=2"
So, 2 x 3.1416=6.2832 or half the circumference of the pulley in inches.
Take the new pulley size: 3.5"
Half of 3.5" is 1.75"
So, 1.75" x 3.1416=5.4978"
Now subtract 5.4978 from 6.2832 and you get .7854 or about 3/4" of an inch. The new belt size should be about 3/4" shorter than the old belt size. Convert inches to millimeters and subtract it from the old belt length and you have a good place to start. Worked for me.
Old belt: 60988 (Gates of course)
New pulley size: 3.5"
Belt rap around the pulley is approximately half way around the pulley. The new systems may be a little more than half, but this formula gets you close so it still works. The circumference of a circle is measured by the equation: 2 x pi x radius. But for the sake of finding new belt length and because belt wrap is only about half of the pulley, you wont' need the whole equation. Half the circumference of the pulley is just: pi x radius. pi is approximately = 3.1416 rounded off. Start with the old pulley size:
Diameter=4" then the radius=2"
So, 2 x 3.1416=6.2832 or half the circumference of the pulley in inches.
Take the new pulley size: 3.5"
Half of 3.5" is 1.75"
So, 1.75" x 3.1416=5.4978"
Now subtract 5.4978 from 6.2832 and you get .7854 or about 3/4" of an inch. The new belt size should be about 3/4" shorter than the old belt size. Convert inches to millimeters and subtract it from the old belt length and you have a good place to start. Worked for me.
