Bump steer or roll steer is the term for the tendency of the wheel of a car to steer as it moves upwards. It is typically measured in degrees of steer per metre of upwards motion or degrees per foot.
On modern cars the front of the tire moves outwards as the suspension is raised, a process known as the front wheels "toeing out". This gives roll understeer. The rear suspension is usually set up to minimise bump steer, where possible.
Typical values are from two to ten degrees per metre, for the front wheels.
Excessive bump steer increases tire wear and makes the vehicle more difficult to handle on rough roads.
Solid axles generally have zero bump steer, but still have roll steer, in most cases. That is, if the wheels move upwards by the same amount, they tend not to steer.
Roll steer is an important part of the budget used to define a vehicle's understeer, known as a Bundorf analysis.
Read more about Bump Steer: Difference Between Bump Steer and Roll Steer, Method of Adjustment
Famous quotes containing the words bump and/or steer:
“Physics investigates the essential nature of the world, and biology describes a local bump. Psychology, human psychology, describes a bump on the bump.”
—Willard Van Orman Quine (b. 1908)
“It is true, we are such poor navigators that our thoughts, for the most part, stand off and on upon a harborless coast, are conversant only with the bights of the bays of poesy, or steer for the public ports of entry, and go into the dry docks of science, where they merely refit for this world, and no natural currents concur to individualize them.”
—Henry David Thoreau (1817–1862)