54 BMWcar
TECH TALK
A tyre’s tread pattern has to be able to do a lot of diff erent things, such as
dispersing water, reducing noise, improving turn-in, minimising stopping
distances, providing optimum grip and traction and so on. It has to be as
good as possible at all of these aspects, which is no mean feat. There are a
number of diff erent tread patterns that you’ll see.
A symmetrical pattern is probably the most common and, generally
speaking, the cheapest to make. Tyres with this design don’t have an inner
or outer sidewall, meaning they can be used on either side of the car, and
are designed to perform equally well when operating in either direction. The
upside of symmetrical tyres is that they can easily be swapped from front
to back and from side to side, and you’ll usually fi nd them fi tted on non-
performance models.
Tyres with a directional tread pattern are, as the name implies, designed
to be used with the tread facing in a specifi c direction. As such, they’re
always marked with an arrow on the sidewall, indicating the correct direction
of rotation. Directional tyres will, by and large, be very good at dispersing
water, and also tend to off er very good directional stability, because the tread
pattern is focused in one direction. The downside of directional tyres is that
the tread pattern is always going to be a little compromised as it’s designed
to do just one or two things very well.TREAD PATTERNS
ASYMMETRICAL
An asymmetrical tread pattern off ers the best solution for tyre engineers when
attempting to create a tyre that can do everything well, as each section of the
tread pattern can be tailored to a specifi c purpose and then all work together.
You’ll often see asymmetrical tyres with central grooves to help avoid
aquaplaning, and sipes on the shoulder blocks to help disperse water. A
central rib will aid with straight-line stability, while the outer edge of the tyre
will often feature larger, stiff er tread blocks for improved lateral stability when
cornering, as the car will naturally lean over on to the outer portion of the tyre.
Tyre designers make use of diff erently-sized tread blocks around the
circumference of tyres to alter the harmonics and help with minimising
road noise. In recent years, the manufacturers have taken the concept
of asymmetrical tyres to the next level, and are now creating tyres with
compounds that vary across the width of a tyre’s tread. So, for example, a
tyre can be made to perform even better under cornering by using a different
c p p.tyre can be made to perform even better under cornering by using a diff erent tyre can be made to perform even better under cornering by using a diff erent
compound on the outer portion of the tread.