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.
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.
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.
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.
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!).
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!