How to Determine Your Vehicle's Pulley Ratio

You should know how to determine the pulley ratio of your vehicle to better understand its running capacity. Pulley ratio determines how far and quick your vehicle can run on a specific time. Read on to learn how to determine this number and how you can use this information. You will need a calculator for this project.


    Step 1 – Know the Pulley Ratio

    Pulley ratio pertains to the relative diameter of approximately two or more drums in a belt-and-pulley system. The number of drums is essential in the calculation of speed, torque, mechanical advantage of the engine as well as other motor-driven systems. Comparable to levers and other forms of simple machines, pulleys agree with little quantity of force applied on a long distance, which is later converted in a big quantity of force applied on a short distance.

    Consider an electric motor, which normally generates ample power to enable a cylinder loaded with 3-kilogram to rotate with a rate of 6,000 revolutions per minute (RPM). Its cylinder is connected with a second cylinder through a looped belt. Once the pulley ratio among these cylinders is greater than one, then the next cylinder should rotate in a much greater rate than 6,000 RPM. Nevertheless, in order to uphold this higher rate, the weight on the other cylinder needs to be lesser than three kilograms.

    Step 2 – Use the Process

    To determine the pulley ratio of your vehicle, you need to use a formula:

    Ratio = Pulley Diameter of Crankshaft / Pulley Diameter of Alternator

    Simply plug in your numbers and do the division.

    Remember that the alternator output is greatly dependent on speed. And each alternator possesses a unique curve wherein it can make an immense dissimilarity in its output capability. Because of it, pulley ratios are really significant, particularly if using a high amperage alternator.

    The pulleys of your vehicle that are supplied along with the alternator are coordinated with the power curve and winding. It is essential that any overhaul pulley sets do not diverge from the ratio. Normally, a street driven vehicle should possess a minimum pulley ratio of 3:1. Once the car possesses an automatic transmission along with low idle, the vehicle then spends a great deal of time cruising, with an elevated pulley ratio of approximately 3.5:1. Alternators can obtain high speeds up to a maximum of 20,000 RPMs for shorter time, in which, over-driving the vehicle is not a difficulty.

    Step 3 – Compute the Ratio

    Since you already determine the pulley ratio, you can also determine the rotor speed of your vehicle using this formula:

    Rotor RPM = Pulley Ratio x Engine Speed.

    For instance, 2.1 (rotor RPM) x 870 (Engine Speed) = 1827 Rotor RPM.

    With these information of pulley ratio added with rotor speed, you know your vehicle’s capacity to run fast and efficiently.