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What is an overdrive pulley?

Does using a big pulley connected by belt to a smaller pulley cause a decrease in power (PLEASE READ DETAILS).?

  • Does using a big pulley connected by belt to a smaller pulley cause a decrease in power (PLEASE READ DETAILS).? i know about gear and pulley ratios...example a 10 inch pulley connected to a 2 inch pulley has a 5:1 ratio..i also know there is either a loss or gain in power, but don't know how much. Assuming i use a 5hp engine with a 10 inch pulley to turn a 2 inch pulley i will lose some of the power but need to know how much..is there a formula..an easy one i hope..lol..i hope someone can help me with this as i cant seem to find what i need online

  • Answer:

    there is one its hard to explain but i can try for you. ill give u an example for a idea and u can go from there ok But ima do it with gears which is the same idea (gears=teeth pulleys=inches) 0 = gear -- = shaft connecting them 00---00 (math i think you said you know it like 20 is half of 40 so 20 goes 2 times faster to keep up with 40) First gear has 24 teeth the RPM is 75(low i kno example member) the second is 40 teeth it is bigger then the 24 so it doesnt have to turn as fast to go to 75 rpms So the 40T is going 45 rpm that is enough to keep up with gear 1(24T) doing 75 rpms. So now at gear 2 ,40 Teeth we are already at 45 rpms say gear 3 is 12 teeth Big Change i know. well it is connected to the shaft that is on gear 2 going 45 rpms, so gear 3 has to go 45 rpms no matter what. gear 3 is connected to gear 4, it has say 24 teeth, well we kno that 12 is half of 24. So 24 is going half the speed of gear 3. meaning gear 3 is 45 rpms gear 4 is half of 45 equaling 22.5 rpms. You started with 75 rpms now your down to 22.5 rpms which is the real speed simply because of the gear reduction term. this example is lost speed got more torque how ever if you started with a bigger gear and went to smaller, the smaller has to keep up with the bigger gear so short exmaple is.. gear 1 is 40T connected to gear 2 which is 20 teeth well gear one is going 2000 rpms meaning gear 2 has to go 4000 rpms just to keep up with the bigger gear get it? simply put for One turn of 40, 20 has to do Two turns. thats how it works, big to small = speed. small to big = torque. I hope this gave you the idea you need or answer. just put it to inches. If a 2 inch is turning at 2000 rpms that is connected to a 1 inch, it will rotate at 4000 rpms, same idea as a gears.

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the 2" pulley will turn 5 times faster that the 10"

All drive trains lose efficiency the longer they become and this changes with the type of drive. A gear drive is better than a toothed belt, a toothed belt is better than a V belt. A mechanical joint is better. If you change drive plane you lose some more. All of this is academic in your case as power loss will be minimal. You say you understand ratio's, fine, but you need to take in to consideration the speed of your driven shaft. Your example would mean 5 times the speed of your input shaft. You need to check the speed ratings of any parts you have on that shaft.

In your example,a 5:1pulley configuration will produce 1/5 the torque on the driven shaft with an increase of 5 times the rotational speed of the drive pulley.

you won't lose power, but you won't get speed out of this configuration.also, i think you ratio of 5:1 isn't right. you need to count the number of teeth per inch to come up with this. the bigger wheel will turn more slowly. depending on how many teeth are each wheel, one revolution of the larger gear .will multiply the times the small one turns and will turn it much faster. 10 teeth per inch on a ten inch wheel, with a two inch wheel with7 teeth per inch should be about a 7:1 ratio

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