Press Release
Tire treads are one area of tire design that directly influences safety and traction on
the road.
Continental treads ensure safety with variation
The wrong tread has never done anyone any good — people make a bad impression and
vehicles using tires with the wrong tread sometimes do not just have bad economic
consequences: Losing grip can also have fatal consequences when handling the high-tech
rubber structures.
In both cases, the fault lies in poor coordination of the “active partners”. For the tires, there
are also sometimes planning, servicing and care faults.
To begin with, “road adhesion” and “grip” are the two key terms that sum up the requirements
for tire treads. The tires are the only direct contact between the heavy vehicle and the road
surface so they should adhere to the ground as best possible and ensure the contact is
intensive as possible.
It is obvious that you then come up with soft round tires with an even, smooth surface and
many minute surface structures. On dry roads, this kind of slick tire takes hold of the asphalt
so firmly that it transfers propulsion and steering movements ideally. The static friction is
high, the vehicle does not slip and is easy to control and steer.
The first raindrop changes these properties dramatically, however. The slightest water film on
the road reduces the static friction between the rubber and the road, however. Once the tire
starts to “float”, i.e. cannot displace the film of water, despite the vehicle weight it is bearing,
it will act as a slippery film. The steerability, grip and safety are thus gone — the vehicle
sometimes too.
Furthermore the deformation of the soft tire, which should also be elastic as a vibration
damper, also produces resistance to rolling — the rolling resistance.
-2-
Something always gets in the way
The task for the tire engineers at Continental is therefore to design the tires so that they also
do not lose grip on wet road surfaces — or sand, snow, clay and other soft surfaces, have
minimum rolling resistance and still transfer as much propulsion as possible.
The simplest way to grip a surface through a soft medium are fingers or studs — on tires
they do not move and are called “tread segments”. Their surfaces reach through water, sand
or snow onto the ground and drive the vehicle forwards. Their invention also marked the
beginning of a complex development: The smallest tread segments have a negative shape
— pores or cylindrical microscopic holes, i.e. small recesses in the tread. These allow the
slick to grip the asphalt, they absorb water and also sand or snow that is then no longer
released that quickly. The tread segments therefore need to be larger and also active:
protruding blocks, studs or sipes can be used to lead away interfering media like water,
pebbles or sand.
There are also two disadvantages associated with this, however: Regular tires have a
smaller overall contact area than slicks when resting on all tread segments. It can thus
transfer and control fewer forces. This is also bad for the large tires on commercial vehicles.
The tread blocks should also be relatively large for this reason. However, the grooves
between them should also not be too small because they will otherwise lose their cleaning
effect.
To solve this problem, the Conti tire developers use inverse sipes: They are slightly larger
and more mobile in the surrounding material than the mainly cylindrical microcapillaries of
small pores. In the form of perfectly scaled and positioned grooves in the tread blocks, they
can increase the grip and release any material picked up. In the tread grooves between the
-3segments, standing sipes are used as small material tongues to briefly hold sand, snow or
other media and then eject it from the tire surface.
But that is not where it ends. Truck tires, being elastic interfaces between the vehicle and
ground, are flexible in themselves. During use, they deform themselves and thus also all
tread segments that the engineers have come up with so far.
For this reason, the tire engineers at Conti have added the factor of deformation resistance
to the interaction of rolling resistance-slip-traction. So that the smaller contact patches
formed from the tread segments can still have an effect, their shape may change too much
during use. This is intended sometimes, however. For example, a notched sipe opens wider
when the tread runs out of the contact patch so that deposits are released more easily.
Simply complex tasks
For this reason, the Conti development engineers run through the different possibilities to
optimize a tread for each new tire generation with different kinds of tread segments. This is
not always made easier by their colleagues from the “rubber kitchen” in Stöcken being able
to trim the raw material as they wish for hardness, softness or elasticity.
It would otherwise hardly be possible to manufacture the high-quality vehicle carriers out of
rubber in the special variety that is required by today’s logistics. To reach this aim, the test
engineers coordinate their tire series with different shapes and rubber compounds to
surfaces, climate zones, optimum handling, economic aspects and also for several product
life cycles. They want to make the movement of the tread segments as large as possible and
as small as necessary.
If we simply take a standard combination of tractor unit and trailer for road use, we already
have three different types of Continental tire, some of which are in different sizes. On the
steering axle, there are tires that are made above all with longitudinally running tread rings
that are only bladed in the center. The tire developers thus create extremely good tracking
-4with low rolling resistance and high stability against the torque occurring when the vehicle is
steered. The outer areas of the closed seat rings are made movable by means of slight
chamfering so that they cannot tear when turning. The drive tires are different: pronounced
tread blocks are mainly used here with partly strong siping that should transfer the traction to
the road as the sum of individual access areas in a complex design. They have larger
grooves that also ensure stability by bridging the tread segments without hindering the
ejection of sand, pebbles or snow. The tires for semi-trailers and trailers clearly have a
smoother pattern. Their function is mainly to support heavy loads and, depending on the
axle, extreme shearing forces. For this reason, they mainly consist of tread rings even more
than steering tires — with less marked siping — and have more and stronger shoulder
notches.
Suitably meeting tougher requirements
The climate and the ground are further modification parameters for tire treads. All in all,
winter tires need to have more defined tread segments than simple summer tires so that they
can transfer the steering, propulsion and braking forces even on snow or ice. This creates
new problems when designing the tire — in addition to the question of rubber compounds
that are compatible with the cold. The best way to get through snow is with powerful tread
blocks between which wide grooves dispose of the loose frozen water. On the cold, solid
frozen ground, you need lots of small pores with which the cold rubber can suck itself onto
the ground. The useful combination of these properties comes together in the cold-resistant
treads, whose architecture is very different in detail from the very smooth running summer
tire. On the winter tires, the tread normally consists of lots of small tread blocks each with
fewer sipes. The tread grooves and shoulder sections intended for material ejection and
elasticity of the blocks among each other are kept more open and thus allow good clearance
of any material picked up.
-5Even larger calibers are used for truck tires that are used on loose surfaces off the road. The
pure rolling properties are increasingly in the background while load bearing capacity and a
gripping tread are becoming more and more important. If you have ever driven an empty
dumper truck or an articulated loader in traffic on an asphalt road, you will be familiar with the
vibrations that arise. Coarse-stud treads on construction site tires with large blocks and
grooves and normal coarse off-road tires whose “blocks” look more like rungs on a ladder are
designed to give the vehicle traction, steering capability and safe braking even on soft
ground. For this reason, Continental makes these types of tire almost without fine sipes and
with wide open shoulder segments. Sipes would fill up while the grooves that run right into
the shoulders keep the tire tread clear and operable even in soft clay or deep sand.
Quiet performance....
Apart from all of this, today’s commercial vehicle tires also need to be quiet. This simple and
basic requirement for sensory environmental friendliness sets further complex tasks for the
tire developers in Hanover. The gripping treads above all on construction site tires and
traction tires for drive axles are designed for smooth running and relatively low vibration for
better handling and reduced running costs. However, it is above all the traction properties
that set a high threshold for dealing with the additional acoustic requirement for the highly
optimized tires. If you alter the main source of noise emissions, the well-designed open
edges of the tread blocks whose constant impact on the surface while rolling makes traction
treads louder than steering or trailer tires, you also have to change the complex tire design in
itself.
The tire engineers then have to adapt the shape of the tread segments and thus also
recalculate components like sipes, grooves, wall radii, rubber compounds, intermediate area
topography etc. This is why the tire engineers at Continental adjust their products to
increased requirements in each development cycle and then present tires again that provide
their high performance for longer than older types on a regular basis.
-6-
However, this not a matter of course — without any care, even the high-tech treads from
Conti tire engineering will wear out prematurely. It is therefore economically worthwhile to
keep the expensive rubber grooves and blocks away from hard edges and sharp or pointed
material whenever possible during use. After usage, the tires should always be checked and
objects removed from the grooves, blocks and sipes. It is also very important to observe the
minimum tread depth in addition to the tire pressure. The refined traction system of the tread
can only work correctly if it has enough reserves. The specialist “workers” on the axles can
only reliably do their job — produce turnover — if these few simple maintenance tasks are
performed.
With targeted annual sales of more than €26.4 billion for 2008, the Continental Corporation is one of
the top automotive suppliers worldwide. As a supplier of brake systems, systems and components for
the powertrain and chassis, instrumentation, infotainment solutions, vehicle electronics, tires and
technical elastomers, the corporation contributes towards enhanced driving safety and protection of
the global climate. Continental is also a competent partner in networked automobile communication.
Today, the corporation employs approximately 150,000 people at nearly 200 locations in 36 countries.
The Commercial Vehicle Tires division, which oversees the development, production and global
distribution of truck, bus and industrial tires, posted a turnover of approx. €1.5bn in 2007 with a
workforce of over 8,000 employees.
The tire divisions are an official sponsor of the FIFA World Cup 2010TM, which will be staged in South
Africa in 2010. You will find information on this at www.ContiSoccerWorld.de,
www.ContiFanWorld.com and www.continental-corporation.com