All-Terrain Lawn Tractor Forum
Would you like to react to this message? Create an account in a few clicks or log in to continue.

All-Terrain Lawn Tractor Forum

Like riding lawn tractors through mud, woods, rocks, and snow? Then this is the place for you! Share your ideas, Post your projects and more!
 
PortalHomeSite RulesEventsFAQSearchRegisterLog inBuild-Off

 

 Easy Belt Length Calculation: Pulley Swap Only

Go down 
4 posters
AuthorMessage
B440
Member
B440
Member


Join date : 2014-01-22
Points : 4022
Posts : 226
Location : Thompson, CT

Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitimeSeptember 9th 2014, 3:02 pm

If you are changing pulley sizes, but keeping the belt tensioning system stock, and also not altering pulley location, then this is for you.

The easy part: for every inch you change the pulley diameter, you need to change the belt length by 1.57 inches.


Example 1- My stock belt length is 95 inches. If I measured my stock pulley at 3 inches, and replaced it with a 5 inch pulley, the difference is +2 inches.

I need 1.57 * 2 = 3.14 inches extra belt length. I would go buy a 98 inch belt.


Example 2- My stock belt length is 95 inches. If I measured my stock rear pulley at 9 inches, and replaced it with a 6 inch pulley, the difference is -3 inches.

I need 1.57 * -3 = -4.71 inches shorter belt length. I would go buy a 90 inch belt. Round up or down depending on the decimal.


Why does this work? When you add 1 inch to the diameter of a circle, it adds 3.14 inches to the circumference. BUT, we are only using half of this circle! The belt only wraps around half of the pulley (generally speaking) so you only need half of the 3.14, which is 1.57 inches.

NOTE: When measuring a stock steel pulley, check to see where the belt rides in the groove. Most stock pulleys have a large lip to help keep the belt on. The belt usually rides about 0.5 inch inside. So a pulley measuring 10 inches in diameter from the edges might actually be smaller (9 inches: 0.5" on one side and 0.5" on the other side) because the belt rides inside further. Most aftermarket aluminum pulleys have no extra lip.


One last example- My stock belt length is 95 inches. If I measured my stock pulley at 3 inches, and replaced it with a 5 inch pulley, the difference is +2 inches. My stock rear pulley is 9 inches, and I replaced it with a 6 inch pulley, so the difference is -3 inches.

I need 1.57 * 2 = 3.14 inches.
I need 1.57 * -3 = -4.71 inches.

Add those two numbers together.

3.14 + -4.71 = -1.57 inches. This is the difference of the two pulleys. I would buy a belt that is 94 or 93 inches. Not perfect, but I would have to see what the store has in stock and try both if available. In my case, the store only had a 94 inch belt and it worked perfectly.
Back to top Go down
redlinemotorsportts
Moderator
redlinemotorsportts
Moderator

2500+ Posts
2500+ Posts!
2014 Build-Off Entrant
2014 Build-Off Entrant

Age : 27
Join date : 2013-03-18
Points : 7301
Posts : 3131
Location : raleigh nc

Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Re: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitimeSeptember 9th 2014, 7:28 pm

I always wondered, there had to be a good way to do it... Me and willis923 on facebook tried once, well he tried, and just confused me.

I dont remember how he went about doing it but yours sounds pretty spot on within the inch. Nothing a adjustable idler pulley couldnt handle.

Great way to go about this, i think it should be sticky'd.
Back to top Go down
B440
Member
B440
Member


Join date : 2014-01-22
Points : 4022
Posts : 226
Location : Thompson, CT

Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Re: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitimeSeptember 9th 2014, 11:30 pm

Thanks. I recall someone mentioning a 3:1 rule when changing pulley sizes, but it never came out right when I tried it. After thinking about how the belt only covers half the pulley, I realized how to do this correctly.

I was going to add it to Doc's Belt Sticky, but it's locked.

Doc: Feel free to add/edit/move this info as you see fit.
Back to top Go down
Doc Sprocket
Site VIP
Doc Sprocket
Site VIP

2500+ Posts
2500+ Posts!
2018 Build-Off Entrant
2018 Build-Off Entrant
2021 Winner of Winners
2021 Winner of Winners
1st Place Build-Off 2016
1st Place Build-Off Winner 2016

Age : 51
Join date : 2013-04-21
Points : 7136
Posts : 2914
Location : Ontario Canada

Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Re: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitimeSeptember 10th 2014, 11:00 am

Stickied! Good work, and thanks for sharing!
Back to top Go down
HelloMoto
New Member

New Member


Join date : 2017-08-19
Points : 2483
Posts : 11

Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Re: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitimeAugust 21st 2017, 12:30 am

This calculation worked awesome for me! Thank you!
Back to top Go down
Sponsored content





Easy Belt Length Calculation: Pulley Swap Only Empty
PostSubject: Re: Easy Belt Length Calculation: Pulley Swap Only   Easy Belt Length Calculation: Pulley Swap Only Icon_minitime

Back to top Go down
 
Easy Belt Length Calculation: Pulley Swap Only
Back to top 
Page 1 of 1
 Similar topics
-
» Need belt sizing help on my Dynamark pulley swap.
» Belt twisting after pulley swap
» How to determine belt length?
» Pulley swap on mtd
» I need help with my pulley swap! :(

Permissions in this forum:You cannot reply to topics in this forum
All-Terrain Lawn Tractor Forum :: Technical Forum :: Drivetrain & Brake Tech :: Pulley, clutches, and Belts-
Jump to: