Describing Handling

This article was first published in 2008.

Here we cover the definitions of some of the words used to describe car handling and suspension. If you don't know how to describe it, it's a lot harder to get someone to help you fix it.

Understeer

• Understeer is when the cornering car does not turn as sharply as the amount of steering lock indicates it should. In other words, the front of the car is sliding. A car that understeers off the road does so with the front still facing the original direction. Understeer is safer than oversteer (see below) and so all car manufacturers set their cars up to understeer when grip levels are exceeded.

• A car with plough understeer has completely stopped responding to steering inputs – turning the wheel further makes no difference to the direction the car is headed. Plough understeer is dangerous because steering control has been lost.

• Power understeer means that the understeer increases when more power is applied. This normally applies to front-wheel drive cars. Power understeer can be remedied by reducing power, so transferring weight forwards and also reducing the work the front tyres need to do.

• Turn-in understeer is when the car is slow to respond to the steering when it is first applied. High speed turn-in understeer can be very disconcerting because it feels as though you will not make the corner – and it doesn’t feel like there is much you can do about it!

Oversteer

• Oversteer is where the car turns to a greater degree than the steering indicates it should. In other words, the rear of the car is sliding. A car that oversteers off the road is spinning, so it may hit sideways or tail-first (or even do a 360 degree spin, hitting nose first!). An oversteering car can be felt to be rotating around you.

• A car with power oversteer has increasing oversteer with the application of more power. This normally applies to rear wheel drive cars. Power oversteer can be remedied by gently reducing power.

• Lift-off oversteer occurs when the throttle is abruptly raised mid-corner. This normally applies to front-wheel drive cars but will occur in any car with high rear roll stiffness. A car that lift-off oversteers will normally tuck-in if the throttle lift isn’t so great – that is, the front will stop understeering.

• Turn-in oversteer is when the car initially turns-in more than the steering angle requested. This is very disconcerting because, as with turn-in understeer, it’s not immediately apparent what can be done to stop it.

Bump Steer

Bump steer occurs when the wheels change their toe angles (the direction they’re pointed in) as the suspension moves up and down. It’s generally most easily felt on turn-in, when a suspension with toe-in on bump will have turn-in oversteer (it will twitchily turn-in more than expected) and a suspension with toe-out on bump will have turn-in understeer.

Roll Linearity

A car with linear roll is progressive in its roll, with the angle of roll being directly related to how hard the car is cornering. A car with non-linear roll may rapidly lean on turn-in but then not lean any further as the cornering load increases. Roll linearity is seldom mentioned but it is very important in giving the driver the correct signals as to what is occurring.

Steady State Understeer/Oversteer Balance

When corning at a steady (or near steady) speed, can the car be edged into oversteer (or understeer) and then easily brought back to a neutral state? If it can, it has a good steady state understeer/oversteer balance.

A skidpan is an ideal test environment for assessing this trait. For example, a car might be moved into a just understeering state by going a little faster and then applying more steering lock, or it might be edged into a just oversteering state by applying a little more power (in a rear wheel drive car) and then unwinding a little steering lock.

Twitchiness

This describes how rapidly the car responds to driver inputs. A twitchy car will respond very rapidly to steering and power inputs. In a road car this tends to be tiring and at times disconcerting. However, a car that is the extreme opposite to ‘twitchy’ will feel dull and unresponsive. Stiff bump damping and stiff sway bars are two characteristics that will make a car twitchy.

Throttle Steer

A car that is on the edge of sliding (either understeer or oversteer) and can then be moved into a slightly sliding state by a variation in power is said to be being throttle-steered. Throttle steering requires a very well balanced car with an engine that has a linear torque response (so not a little engine with a big turbo!).

Overall Handling

While individual preferences vary, a car with good overall handling is one that is controllable, predictable and progressive... and has high grip levels. And, note, in that order of priority!

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