Wheel Size Options Suspension
This image illustrates what is called scrub radius.
Scrub radius is very important on the front wheels
because it affects handling and steering. Scrub
radius is the distance between the center of the tire
contact patch touching the ground while mounted
on the front hub at ride height and the imaginary
line passing thought the upper and lower ball joint
balls that intersect with the ground under the tire.
It is measured in positive or negative inches or
millimeters. Negative scrub radius is where the
contact patch center is outboard the virtual pivot
axis intersection with the ground. “0” is when they
coincide, and positive is when the contact patch
center is inboard the virtual pivot axis intersection. A
slight positive scrub radius is preferable for steering
feedback and reduction of tram lining and ridge
nibbling. It is required on front drive vehicles and
vehicles with ABS to prevent excessive steering pull.
A zero scrub vehicle has somewhat “numb” steering,
but braking and steering loads are equalized.
Negative scrub is common with wide front tires as it
is difﬁ cult to build a wheel and suspension that will
deliver this with a wide tire. Try to minimize scrub
as much as possible to prevent a vehicle that follows
every seam in the road and gives negative steering
feedback, in addition to braking instability and
excessive steering component wear. View Related Article