To determine the input or output speed or the pulley and cog sizes needed in a drive you may use a simple ratio. Given any three items you can solve for the fourth. With a V-Belt drive the answer is theoretical, due to belt slippage, and with a timing belt or a chain drive not every answer provided is an available combination. You may use this basic formula for more than just a two pulley setup. The RPM of the output pulley becomes the input RPM for the next stage of the drive. Done this way you can use this formula to solve for a multi pulley drive. Just remember that idlers do not change the output of the drive system. They are used to provide tension or to route the belt. Below is the basic formula, an example, and a Pulley Speed Calculator for your use. Please remember that there are more factors in a good drive setup than just if the pulleys fit.
RPM1 = RPM of Driver - RPM2 = RPM of Driven
D1 = Diameter or tooth count of Driver - D2 = Diameter or tooth count of Driven
|1750 RPM||3.5 INCHES |
|1000 RPM ||D2 |
1750 RPM ÷ 1000 RPM × 3.5 INCHES = D2
D2 = 6.125 INCHES
Pulley and Speed Calculator:
Below is a small calculator that will solve the ratio for you. Check the circle next to the item you are solving for and enter the remain three items in the spaces provided. If you have any problems with the pulley calculator please email us.
For a more complex and or new setup, a drive program is available from most belt and pulley manufactures. It should be used to account for variables such as input HP, load, and center to center distances. One drive program we use is provided by Maska, a Canadian manufacturer. Their online program, Maska Drive Selection, should be run from within Internet Explorer to work properly. Their program can provide a printout, in PDF form, listing sizing options and their respective specifications including hub loading and suggested belt tension. If you would like you then may submit the PDF to us for a quote.
If you need to estimate a belt length you can find our belt length estimator here
If you have any questions or would like a quote on pulleys and or belts please contact us.
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