CVT Belt Length Calculation and source

garydee

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cboger

wrap a string around the drive clutches shaft then around the outside of the driven. add a couple of inches (usually 2) and you have the INSIDE diamter of the belt. add about another inch and you have the outside diameter belt you need. www.accessdayco.com has an option to search via dimensions. plug it in there, then go to your local autozone and order it. Ill be honest, Its kind of a pain to figure out.

Unforgiven

The equation for determining belt length is:

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.

Above is from someone more learnerd than this ole wiley coyote

I used the string thingie on my neighbors ride,.....

sho305

If you know the stock setup and belt, you can cheat and just measure center distance you have (and offset of course). When you do the new install do the same offset and get a new center distance, double the increase in your center distance and add it to stock belt length. You lengthen the top and bottom of the belt when you move the clutch, so double the change in distance. It should be very close. Ideally buy that belt when you get it mocked up and check it out before you weld it up/etc., also then you know you can get that size.

garydee

sho305

You said it! Chop it up, I been working on a car just about done. Sprayed paint last weekend.

Flintrock

garydee

Attached Images

belt2.jpg (127.2 KB, 0 views)

Larboc

I went through a similar process on my columbia, PITA.

Keep in mind that there are a lot of different angles of the belts too.

IIRC O'Reilly Auto's website was the best resource I had found for belt lengths/part numbers/angles.

fstg21

Give me the center to center distance bolt-bolt. and the center diameter on the drive with the belt on it and the diameter of the driven with the belt on it. I'll do the math

Below is my complete original post on the subject.

I should build an excel file calculator.

The equation for determining belt length is:

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.

So assuming I can do math(questionable)

Lets do a hypothetical:

(These aren't real numbers, so your mileage may vary.)

a= 14"

D1= 2"

D2= 9"

((2*14*9+2*14*2)*PI+9^2-2*2*9+2^2+8*14^2)/(4*14)= 46.15 (assuming no slack)

252+56*PI= 967.61

81-36+4+1568=1617

967.61+1617=2584.61

2584.61/56= 46.15"

If that makes sense.

To figure out the amount of slack you want
You use right angle triangle Theorem.
In this same example scenario:

B = the opposite leg of the triangle

a = our center to center distance still.

C = the length of the belt between the pulleys

S = the amount of slack you want

Y = is one half of the extra length needed + (C/2)

X = the extra belt length needed for the slack you want.

(D2/2)-(D1/2)=B

4.5-1=3.5

a^2+B^2=C^2

14^2 + 3.5^2= 208.25 sqrt of 208.25 is 14.43 14.43=C

Then to set slack:

(C/2)^2+S^2=Y^2

(14.43/2)^2+1^2= 53.06 sqrt53.06=7.284 Y=7.284

2Y-C=X

2(7.284)-14.43=.138

X+L=Total Belt Length Needed .138+46.15= 46.288

It only takes a .138" longer belt to add 1" of slack over a 14" center to center.

If I hadn't done the math I wouldn't have believed it.