What is Caster? (Negative vs positive roulette effects)

Vehicle suspension geometry has three common measurements, which can often be adjusted, called caster, camber, and toe. Caster is measured at the steering wheels (i.e. front wheels) as an angle that measures the forward or rearward tilt of the steering axis when looking at the car next to it.

This axis connects the lower pivot point (often the lower kneecap) to the upper pivot point (often the upper kneecap) and makes an angle with the vertical line passing through the lower pivot point.

Positive caster occurs when the vehicle’s wheel (and lower pivot point) is in front of the upper pivot point. A negative caster has a lower pivot point behind the upper pivot point, while a zero caster means the steering axis is perpendicular to the ground.

Caster affects the ease of steering and the stability of the vehicle in a straight line. Modern automobiles use positive solutions to resist unexpected vehicle turns drifting or deviating from course when traveling in a straight line at high speeds.

A car may have a negative caster angle that pulls to one side when driving in a straight line. Cars with power steering should have positive caster, so a mechanic should check and realign the suspension.

See also:

Roulette vs Camber

Camber is another angular measurement of suspension, measuring a different axis of camber than forward. Camber refers to how much the wheels “lean” toward the car or away from the car when looking directly toward the front of the car, toward the grille. This affects the area of ​​the tires in contact with the ground during various driving maneuvers.

You may have heard of cars that “bang” or “sit.” This slang terminology refers to a significant negative camber, where the tops of the wheels point toward the body of the car and the bottoms of the wheels are away from the body of the car relative to the vertical line passing through the wheels. central without inclination.

The negative cam increases grip when cornering but reduces grip when accelerating or braking in a straight line and too much can wear out your tires quickly.

Positive effects of roulette

Positive caster is when the lower pivot point is located ahead of the upper pivot point when the vehicle is facing sideways. This causes heavier steering or more difficulty turning the steering wheel (seen only in vehicles without power steering).

Modern cars can easily maximize the benefits of positive caster because they have power steering and are not affected by heavier steering. Positive caster is ideal for stability when driving straight thanks to the automatic tire alignment torque.

Self-aligning torque occurs when the lower pivot point is further forward than the upper pivot point, and then a force is applied to the front wheels to return the wheels to their neutral position in succession. Self-aligning torques are created when some of the vehicle’s weight is behind the tire, helping to position the tire in a straight line.

Vehicles with too much positive caster can understeer, which is why most modern vehicles have no more than 3 to 5 degrees of caster. This is the ideal range to maximize straight-line stability and allow for comfortable turns.

Positive caster increases negative camber when the wheels rotate due to the geometry of the suspension components. This is good for cornering, as it maximizes the surface area of ​​the tire in contact with the ground on the outside front wheel, which is heavily loaded during cornering.

The bicycles have positive caster, as the steering axis of the front wheel is tilted forward to give the rider more stability in a straight line.

Related: Signs of Poor Wheel Alignment

Negative effects of roulette

Negative caster is only found on older vehicles because it is a limitation of older technology, such as outdated chassis dynamics and tire specifications. Negative caster results in lighter, easier steering, but reduces stability when driving in a straight line. Vehicles with negative casters do not perform as well.

A negative roulette sign is a sloppy or loose wheel, ( which is much less common than a hard-to-turn wheel ). It can also be dangerous because the vehicle must turn as expected when the steering wheel is turned.

A significant discrepancy between the driver’s steering wheel movement and the vehicle’s response when cornering can lead to a collision, especially if the driver is not paying attention. Negative caster is unusual in modern cars, so if you suspect it is present in your vehicle, it should be checked by an alignment shop or professional mechanic.

The car’s asymmetrical caster also needs to be corrected for safety reasons, as the car will move sideways with less caster. This situation increases wear on tires and suspension components.

See also: 4 reasons for an off-center steering wheel

How to adjust the spinner

To adjust the caster, you must first measure the ride height, caster, camber, and toe, as each affects the others. There are special tools available to do this, such as the bubble gauge and turntables. Better equipment provides more accurate measurements, so the best place to do this is at an auto-alignment shop.

Related: Average Wheel Alignment Cost

As the front wheels lift off the ground, the wheels turn in and out 20 degrees. In this test, a bubble gauge measures the hub of the spinning wheel. For adjustment, shims can be added or removed from the front or rear upper control arms.

Once the wheel is adjusted to your liking, check the camber, toe, and ride height again and make any necessary adjustments to ensure all measurements are within vehicle specifications.