CVT Belt size calculation

[sideshow]

Hey - I've been wandering around the corners of the internet, and came across this on a golf-cart modding forum. I'd make some comment about weird hobbies, but that's a bit of pot and kettle here

But I thought I'd put it up here - it makes sense to me, but I wonder if any of our more experienced people can check and see if they agree

http://www.buggiesgonewild.com/big-bloc ... ource.html

L= ((2*a*D2+2*a*D1)*Pi+D2^2-2*D1*D2+D1^2+8*a^2)/(4*a)

a=the center to center distance (distance between the center of the bolt holding on the drive and the bolt holding on the driven.)

Pi= if you don't know what this is, where in trouble.

D1=The Diameter of the drive clutch with the belt wrapped around it. Measure with a cheap dial caliper.(the belt is important because all belts are measured by the outside circumference not the inside)

D2= The diameter of the Driven Clutch with the belt wrapped around it. An easy way to measure this is to take it off the cart lay it on the concrete and mark it's diameter (with the belt on it) with a pencil then measure the distance between the marks with a tape.

[sideshow]

Alright. I'm just going to talk to myself a bit here, because on 2nd look, there are some issues with the description I found here.

For D1 - the diameter of the drive pulley - I'm getting confused on which diameter it means.

Originally I thought it meant the outside diameter of the entire pulley - just measure the outside rim of the drive pulley itself. But I realize that since the drive pulley starts open, and then closes, it probably means that you put the correct width belt on the drive pulley, and measure the diameter of the belt as it wraps around the open drive pulley. At least after reading this equation, that's what makes sense to me. Shitty paint picture demonstrating this below:

Thoughts?

[coachgeo]

Alright. I'm just going to talk to myself a bit here, because on 2nd look, there are some issues with the description I found here.

For D1 - the diameter of the drive pulley - I'm getting confused on which diameter it means.

Originally I thought it meant the outside diameter of the entire pulley - just measure the outside rim of the drive pulley itself. But I realize that since the drive pulley starts open, and then closes, it probably means that you put the correct width belt on the drive pulley, and measure the diameter of the belt as it wraps around the open drive pulley. At least after reading this equation, that's what makes sense to me. Shitty paint picture demonstrating this below:

Measuring diameters for belt length.png

Thoughts?

Yeah it seems they did say the Diameter was WITH BELT on the pulley.

Side note: Wish more folk across the whole spectrum that deal with CVT's would adopt the labels "Primary clutch/pulley" for the one powered/driven most directly by engine and the term"Secondary Clutch/Pulley" for the one powered/driven by the belt between the two. In reality both are "driven" by something thus labeling one of them as a "driven pulley" is plain confusing.

[UAofE]

Drive pulley is the one mounted to the power source. Driven pulley is receiving energy from the drive pulley. Pretty simple.

https://www.gokartsupply.com/tcbelts.htm

[coachgeo]

Drive pulley is the one mounted to the power source. Driven pulley is receiving energy from the drive pulley. Pretty simple....

simple yes, confusing yes. Could just as easily be seen as opposite your description with the Primary pulley being "Driven" by the Engine thus called Driven Pulley and the Secondary pulley is the source that "drives" the vehicle wheels so logically it could be called the Drive Pulley. Point is both pulleys are driven by an external source or could bee seen as a Drive source thus conceptually there is no clear delineation by the labels Drive/Driven. Hence why CVTech, Polaris, Honda, Team Industries and some now have gone to Primary/Secondary as labeling for the clutches.

but don't want to further distract from your thread by my quirky pet peeve so I'll shut up on this now Your info on belt length determination is very beneficial. Thank you for diving into it and sharing with us!

[sideshow]

Yeah - no worries! I definitely agree with the terminology - always just easier to go with simpler language in the end.

This formula, coupled with this website
http://www.daycoproducts.com/online-cat ... rt_type=50
really helped me - it took a while to dredge up the combo online, so I hope this thread can help other people avoid the same rigmarole. For some reason I was fixed on Gates brand belts, but their website and customer service has been entirely unhelpful. It seems like Dayco has the same product line range, from regular CVT belts to the crazy expensive hi-torque ones, so it shouldn't really matter in the end.

Now if only the primary/secondary pulleys fit on my bike better! hahahaha