# pulley ratio formula

digginlight(z5 va)June 14, 2008

I remember only that it's not rocket science - but I can't remember exactly what the proceedure is - "senior moment", I guess.

How _do_ I figure speed reduction offered by different sized pulleys..?

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lonewoof(z7 SC)

Drive pulley diameter / driven pulley diameter * input RPM = OUTPUT RPM

June 14, 2008 at 12:01PM
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digginlight(z5 va)

Just the diameters, eh.? - not the circumferences. Well that makes the figuring lots easier.

ThanX

June 14, 2008 at 12:40PM
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bill_kapaun

Circumference is a direct ratio to diameter, so either will work. C=D*PI.

June 14, 2008 at 1:59PM
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digginlight(z5 va)

Does lonewoof's short little formula above imply the diameter at the outside of the belt.? the inside..? the middle of the belt..?

Or does it make no difference..?

ThanX again.

June 14, 2008 at 3:45PM
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weed_cutter

As long as your measurments of the pulleys are consistent it makes no difference (measure both outside diameters).

June 14, 2008 at 5:16PM
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hillbilly_2009

how do i find the ratios of multipule pulleys for example a 24in pulley driving a 12in pulley that is driving a 2in pulley

February 3, 2009 at 10:44PM
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rdaystrom

Look up rpm calculators online such as the one on the link below and plug in the values and hit calculate.

Here is a link that might be useful: rpm calculator

February 4, 2009 at 12:00AM
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Pooh Bear

Does lonewoof's short little formula above imply the diameter at the outside of the belt.? the inside..? the middle of the belt..? Or does it make no difference..?

Actually it refers to the diametrical pitch of the pulleys.
Diametrical pitch is usually a term used in gear measurements. But the same principles are also applied to pulleys. The measurement is where the center of the belt contacts both sides of the V on the pulley. Also known as the pitch diameter of the pulley.

Pooh Bear

Here is a link that might be useful: Diametrical Pitch - Wikipedia

February 4, 2009 at 12:39AM
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mgfranz

I have packaged the RPM/Pulley Calculator into a desktop application if anyone is interested.

November 12, 2010 at 2:32PM
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stone_mike64_yahoo_com

A little off subject, but I was raised in a self sufficient heavy equipment shop, then went on to 35-40 years of welding and pipefitting and there are very few mathematical calculations I can't make! I hope to make your posters aware of the non-education your kids are getting in American schools that are dominated by the 'progressive' Department of Education, get informed ,the only thing your kids are being taught is 'progressive ideology', get involved to stop the ideologically 'dumbing down' of our kids!

Here is a link that might be useful: http://www.bing.com

April 24, 2011 at 11:11AM
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BillSPhD

I've been teaching math, physics, and computer science at the University for 20+years. The percentage of students earning Top grades vs failing grades has not changed since our current methods of teaching has come into being. Don't listen to those who say we're loosing our younger generation: they are just as sharp and driven as we were at their age.

July 2, 2011 at 11:26PM
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bill_kapaun

% of students earning top grades is the same.

July 3, 2011 at 5:18PM
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