What is steering ratio? I always see 4:13:2 or something of the sort.?

Question

What does it represent or mean?

Answer 1

It's the reduction ratio of the steering mechanism (similar to that of a gear pair) - you divide the input rotation (either revs or degrees) by the output one.

In this case, it is the result of the math division of the 360 degrees (1 full turn of the steering wheel) and the resulting steering angle of the wheels.

To measure it more accurately, count the wheel turns end-to-end, convert them in degrees and divide by the angle (in degrees) measured on one front wheel, e.g.:

whell turns, end-to-end: 3.5

max. wheel steering angles from the center position: 30 deg. to the left, 25 deg. to the right (same wheel), total: 55 deg.

The steering ratio is

i = 3.5 * 360 /55 = 22.91 (or 22.91 : 1), in other words:

it takes a 23 deg. turn of the wheel for each degree of the steering effect on the wheel.

As in gears, the greater the ratio, the less effort, but it takes more (and faster!) steering wheel turning for the same steering effect.

This method works with any constant-ratio (traditional) steering mechanism (rack-and-pinion, s***w-and-segment, s***w-and-nut) and is independent of the length units (inch or metric).

Modern cars tend to have smaller ratios for more responsive steering. The power steering device (aka servo assistance) helps reduce the required muscle effort and steering wheel diameter, leaving more room to the driver.