Belt Length Measuring Technique For a Successful Replacement

A belt is a crucial component for ensuring a mechanical system works seamlessly in transferring power and movement from one pulley or sprocket to another. This typically occurs in the case of one pulley being attached to a power or motor source and the other being attached to other processes in the conveyor belt chain that continue output and workflow in an industrial sense.

However, drive belts, whether they’re V-shaped belts, round belts, toothed belts or flat belts will wear over time. Some may also incur unexpected damage requiring swift replacement. Yet, knowing which size belt to order from the ribbed belt manufacturer is another issue.

Here’s a guide to understanding the mechanics of a belt’s wear as well as the six different belt length measuring techniques.


How to Know You Have a Worn Belt and Need to Go to a Ribbed Belt Manufacturer

Performing regular checks on the drive belt of any mechanical component or machine is vital for preventing breaks, errors, downtime and high repair costs in the surrounding equipment. Therefore, it is advised to consider a preventive or predictive maintenance program that investigates the belt for the following signs of wear:

  • Squeaking noises
  • Cracks in the belt
  • Grazes on the belt or surrounding equipment
  • Sign of wear
  • Stretched or loose belt
  • Tears in the belt
  • A dried-out belt
  • Growling from water infiltration

Alternatively, belts have a recommended lifespan which is detailed by the manufacturer. For example, a car’s serpentine belt will typically need replacing every 8 years or every 100,000 miles. So, always check the manufacturer’s guidelines for a belt’s projected lifespan.

Read more: 3 Warning Signs of V-Belt Premature Failure


The 6 Belt Length Measuring Techniques for a Successful Replacement

There are six belt length measuring techniques you can use to source the correct belt from your ribbed belt manufacturer.

While all are effective at interpreting the correct belt size, making use of as many as possible and providing that information to the manufacturer as well as the type of belt, you’re more likely to find an accurate-fit belt.

Before you start learning about the belt length measuring techniques, we also encourage you to check out our guide on how to read V-belt numbers.

1. The Pulley Method

This is the most scientific method for determining which length to buy from your ribbed belt manufacturer. However, it does involve a mathematic equation, so be prepared with a pen, paper and measuring tools.

There are often times when you’ve only got the pulley system with the sprockets but no belt, such as in the first instance. With this, you need to follow this formula:

1.57 x (pulley A diameter + pulley B diameter) = C

C + (2 x the length between the centre of pulley A and pulley B) = Belt Length


Not all the below methods require mathematical skills, so if you don’t have a calculator to hand, there are other options for finding the right belt.



2. The Snapped Belt Method

When a belt has snapped, it is an indication that there was no elastic wear, stretching or give in the belt. However, it does pave way for the easiest method of belt length measuring for your ribbed belt manufacturer. Simply elongate the snapped belt and press against a hard surface. Then, measure along this belt using a measuring tape.

If the snapped belt in question is a V-shaped belt or a toothed belt, you’ll need to make two measurements. When inspecting the snapped belt, you’ll notice the ends are tapered which provides both an ‘inside’ and ‘outside’ measurement. Both of these are useful in determining the correct belt length needed.



3. The Tape Method

If you are buying a second belt to prepare with preventative and predictive maintenance, you’ll need to measure the current belt in use.

If you can remove this belt, simply make a small mark with a white pen on the drive belt. Then, take some electricity tape and begin taping the belt on the outside measurement from the mark. Cut the tape when it makes a full rotation, remove from the belt, stick to a flat surface and measure with a ruler or measuring tape.

Again, with a V-shaped or tootled drive belt, it is useful to take the measurement of both the inside length and the outside length.

Read more: A Predictive Maintenance Program to Prolong Electric Motor Lifespan and Prevent Failure


4. The Tooth Method (for Toothed Drive Belts Only)

With a toothed belt, there is a pre-meditated function to quantify a belt size for the ribbed belt manufacturer.

Simply take a white pen and make a mark on a tooth. Then, count the total number of teeth the belt has, using the marked tooth as a reminder for the start and end.

This is especially do-able in the case of short-length pulley system drive belts such as for bikes.

Providing this information, alongside any other obtainable information is enough for a ribbed belt manufacturer to source the right belt for your mechanical system.


5. The Diameter Method

Also known as accessing the Li measurement, this method relies on the belt being off the pulleys, in-tact and relatively small. This is because you’ll need to set the belt down and measure the diameter of the inside edges.

Laying it down on a markable surface allows you to take note of the edges and center so the accurate diameter recording is found. Once you have the diameter measurement, you need to multiply the number by 3.142 to gain the Li measurement.

With this, you can head to your ribbed belt manufacturer who will be able to aid in sourcing a replacement.


6. The Code Method

If you still have your old and worn drive belt available, you can check to see if the original code remains printed. However, if the belt is very worn, it’s likely you won’t be able to see it.

The inside code will attain the type of belt as well as the length. However, depending on the type of belt, the length noted may refer to the inside or outside circumference. For example: a classic V-shaped belt will be lettered A-E depending on the cross-sectional size of the belt. This belt code refers to the inside circumference (but you really need the outside circumference) so you should add the number on the belt code to the width of the cross-section for an accurate measurement.

V-Belt e-shop banner

Now that you know the six different belt length measuring techniques, it’s important to acknowledge the natural stretch of a belt’s material. Therefore, when you go to the right ribbed belt manufacturer, always err on the side of a smaller belt. 


Here For Your Belt Needs

From ribbed belts, flat belts, V-shaped belts, toothed belts and round belts all the way to their corresponding pulleys, SLS Bearings has a team of belt experts who works with valued industry partners to source high-quality and recognized belts suitable for your mechanical needs.

If you would like to find out more about sourcing your next belt, contact us below: Belt more info


**Some images were derived from Optibelt 


by SLS on May 28, 2021

categories: Product- Non-Bearings

Written by SLS

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