Automobile handling

Automobiles driven on public roads whose engineering requirements emphasize handling over comfort and passenger space are called sports cars.

A lower centre of mass is a principal performance advantage of sports cars, compared to sedans and (especially) SUVs.

The rearward weight bias preferred by sports and racing cars results from handling effects during the transition from straight-ahead to cornering.

However, the lateral force being generated by the rear tires is acting in the opposite torsional sense, trying to rotate the car out of the turn.

Using wheels and tires of different sizes (proportional to the weight carried by each end) is a lever automakers can use to fine tune the resulting over/understeer characteristics.

Some high performance cars have light materials in their fenders and roofs partly for this reason Unless the vehicle is very short, compared to its height or width, these are about equal.

The pitch angular inertia detracts from the ability of the suspension to keep front and back tire loadings constant on uneven surfaces and therefore contributes to bump steer.

Angular inertia is an integral over the square of the distance from the center of gravity, so it favors small cars even though the lever arms (wheelbase and track) also increase with scale.

Mass near the ends of a car can be avoided, without re-designing it to be shorter, by the use of light materials for bumpers and fenders or by deleting them entirely.

[8] The severe handling vice of the TR3B and related cars[citation needed] was caused by running out of suspension travel.

The depth of tread remaining greatly affects aquaplaning (riding over deep water without reaching the road surface).

Increasing tire pressures reduces their slip angle, but lessening the contact area is detrimental in usual surface conditions and should be used with caution.

Ideally a tire should be soft enough to conform to the road surface (thus having good grip), but be hard enough to last for enough duration (distance) to be economically feasible.

If the force of the push is sufficiently large, the inertia of the wheel will cause the tire to completely lift off the road surface resulting in a loss of traction and control.

The main factors that improve unsprung weight are a sprung differential (as opposed to live axle) and inboard brakes.

(The De Dion tube suspension operates much as a live axle does, but represents an improvement because the differential is mounted to the body, thereby reducing the unsprung weight.)

Advanced tools such as wind tunnels and computational fluid dynamics (CFD) have allowed engineers to optimize the handling characteristics of vehicles.

The coefficient of friction of rubber on the road limits the magnitude of the vector sum of the transverse and longitudinal force.

One reason that sports cars are usually rear wheel drive is that power induced oversteer is useful to a skilled driver for tight curves.

The effect of braking on handling is complicated by load transfer, which is proportional to the (negative) acceleration times the ratio of the center of gravity height to the wheelbase.

Precision of the steering is particularly important on ice or hard packed snow where the slip angle at the limit of adhesion is smaller than on dry roads.

Ideally, a car should carry passengers and baggage near its center of gravity and have similar tire loading, camber angle and roll stiffness in front and back to minimise the variation in handling characteristics.

A driver can learn to deal with excessive oversteer or understeer, but not if it varies greatly in a short period of time.

For ordinary production cars, manufactures err towards deliberate understeer as this is safer for inexperienced or inattentive drivers than is oversteer.

A-arm or wishbone front suspension tends to give better handling, because it provides the engineers more freedom to choose the geometry, and more road holding, because the camber is better suited to radial tires, than MacPherson strut, but it takes more space.

The older Live axle rear suspension technology, familiar from the Ford Model T, is still widely used in most sport utility vehicles and trucks, often for the purposes of durability (and cost).

This can be done to some extent by using plastic windows (or none) and light roof, hood (bonnet) and trunk (boot) lid materials, by reducing the ground clearance, etc.

Increasing the track with "reversed" wheels will have a similar effect, but the wider the car the less spare room it has on the road and the farther it may have to swerve to miss an obstacle.

Lighter (mostly aluminum or magnesium alloy) wheels improve handling as well as ride comfort, by lessening unsprung weight.

Fixing understeer or oversteer conditions is achieved by either an increase or decrease in grip on the front or rear axles.