Steering ratio
Encyclopedia
Steering ratio refers to the ratio between the turn of the steering wheel
Steering wheel
A steering wheel is a type of steering control in vehicles and vessels ....

 (in degrees) or handlebars and the turn of the wheels (in degrees).

The steering ratio, is the amount of degrees you have to turn the steering wheel, for the wheels to turn an amount of degrees.
In motorcycles and bicycles, the steering ratio is always 1:1, because the steering wheel will always follow the wheel. x:y means that you have turn the steering wheel x degree(s), for the wheel(s) to turn y degree(s). In most passenger cars, the ratio is between 12:1 and 20:1. Example: If one complete turn of the steering wheel, 360 degrees, causes the wheels to turn 24 degrees, the ratio is then 360:24 = 15:1 (360/24=15).

A higher steering ratio means that you have to turn the steering wheel more, to get the wheels turning, but it will be easier to turn the steering wheel. A lower steering ratio means that you have to turn the steering wheel less, to get the wheels turning, but it will be harder to turn the steering wheel. Larger and heavier vehicles will often have a higher steering ratio, which will make the steering wheel easier to turn. If a truck had a low steering ratio, it would be very hard to turn the steering wheel. In normal and lighter cars, the wheels becomes easier to turn, so the steering ratio doesn't have to be as high. In race cars the ratio becomes really low, because you want the vehicle to respond a lot quicker than in normal cars. The steering wheel will also become a lot harder to turn.

Variable-ratio steering

A variable-ratio steering, is a system that uses different ratios on the rack, in a rack and pinion
Rack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...

 steering system. At the center of the rack, the space between the teeth are smaller and the space becomes larger as the pinion moves down the rack. In the middle of the rack you'll have a higher ratio and the ratio becomes lower as you turn the steering wheel towards lock. This makes the steering less sensitive, when the steering wheel is close to its center position and makes it harder for the driver to oversteer at high speeds. As you turn the steering wheel towards lock, the wheels begins to react more to your steering input.

Alternate definition

Another use of the term steering ratio is for the ratio between the theoretical turning radius based on ideal tire behavior and the actual turning radius based on real tire behavior. Values less than one, where the front wheel side slip
Slip angle
In vehicle dynamics, slip angle or sideslip angle is the angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing...

 is greater than the rear wheel side slip, are described as under-steering
Understeer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Simply put, oversteer is what occurs when a car turns by more than the amount commanded by the driver...

; equal to one as neutral steering; and greater than one as over-steering. Values less than zero, in which the front wheel must be turned opposite the direction of the curve due to much greater rear wheel side slip than front wheel have been described as counter-steering.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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