Enter the total rod length and the length of the crank stroke into the calculator to determine the rod radio.

## Rod Ratio Formula

The following formula is used to calculate the rod ratio of a crankshaft.

RR = PR / CS
• Where RR is the rod ratio
• PR is the piston rod length
• CS is the crank shaft stroke length

To calculate a rod ratio, divide the piston rod length by the crank shaft stroke length.

## Rod Ratio Definition

What is a rod ratio?

A rod ratio is a ratio of the length of a piston rod to the stroke of an engine.

Rod ratios are used to determine the performance or leverage a piston rod has with respect to the crankshaft stroke.

What is a good rod ratio?

Anything above a ratio of 1.57 is considered a good rod ratio, while high-end racing cars can have ratios of 1.75+

## How to calculate a rod ratio?

Example Problem:

The following example is a step-by-step guide on how to calculate rod ratio.

First, determine the total length of the piston rod. In this example, the piston rode measures a total of 5 inches.

Next, determine the stroke length of the crankshaft. In this case, the stroke length is measured to be 3 inches.

Finally, calculate the rod ratio using the formula above:

RR = PR / CS

RR = 5/3

RR = 1.6666