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| Tyre
Tips - Are you getting the most from your tyres? |
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Choosing new tyres for your car can be a complete
minefield if you've never done it before. When
you're considering which tyres you need to get,
you need to consider factors such as performance,
price, brand, comfort, appearance and safety.
But how do you know which tyres are the 'right'
ones for your car?
Legal
Requirements
- Cars, light vans and
light trailers must have a minimum legal tread
depth of at least 1.6mm across the central three-quarters
of the tyre width and around the entire outer
circumference.
- Tyre sizes must be identical
across an axle
- No tyre should have
a cut longer than 25mm or 10% of the tyres section
width, whichever is the greater
- Tyres of different types
must not be fitted to the same axle (i.e radial-ply
tyres and cross-ply tyres)
- There must be
no lump, bulge or tear caused by separation
or partial fracture of its structure, neither
must any portion of the ply or cord structure
be exposed
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Tyre
Types
- Directional tyres
- It is imperative that directional tyres are mounted so that the direction of rotation shown by the arrows on the sidewall are in the direction of the wheels rotation
- Asymmetric tyres
- Asymmetric tyres must be mounted with the correct sidewall to the inside of the vehicle, this can be identified by the wording “inside” and “outside” printed on the tyre sidewall
- Composite tyres
- Composite tyres are both directional and asymmetric. These tyres specifically indicate the wheel position to which they must be fitted and how they must be mounted on the rim i.e. “inner side right”
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Speed
rating and Load index
- The speed rating and
load index of replacement tyres should be equal
to or greater than the speed rating and load
index of the vehicle manufacturers approved
tyre for the vehicle.
- It is recommended that
for optimum performance, cars and light vans
should be fitted with matching sets of tyres,
however in general terms the effects of mixing
tyres can be divided into two categories -
those vehicles originally fitted with T rated
tyres or lower and those with H and above
- Vehicles originally
fitted with T speed rated tyres or lower are
less likely to undergo changes in handling characteristics
as a result of mixing of patterns or tyre brands.
It is a sensible precaution to confine mixing
to a minimum of matched axle sets. With reference
to 4x4 vehicles it is recommended tyres are
changed as a complete set of 4
- Cars requiring H,V,W,Y
or ZR rated tyres tend to be less tolerant to
tyre mixing as the vehicle performance increases.
Generally in these cases it is unlikely that
changes in handling characteristics would result
from the mixing of patterns or brands between
axles (matched axle sets) However it is preferable
to avoid mixing and if possible and to use complete
matching sets.
- For certain high performance
cars, matching sets of vehicle manufacturer
approved tyres are recommended to maintain the
handling characteristics of the car
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Tread
depths
- Sufficient tread depth is
vital in all driving conditions. Braking distances
can be significantly increased, particularly in the
wet, as a tyre becomes more worn
- It is not recommended that
a new tyre (even of the same type) is fitted on the
same axle as a well worn tyre. The tread depths
of the two tyres should be as closely matched as possible.
A brand new tyre will be of a larger overall diameter
than that of a worn tyre.
- For their own safety customers
should not leave their tyre change until it has reached
the legal limit of 1.6mm. Ideally they should change
at a remaining tread depth of 2 to 3mm
Tyre
Pressures
- Tyre pressures should always
be checked when cold, ideally every two weeks (including
the spare wheel)
- Vehicle tyre pressures and
tyre sizes can be found in the owners handbook or
are indicated on the drivers door, or fuel cap
- Car manufacturer's tyre
pressure recommendations should always be followed
and can de found in the car manual.
- Always measure and adjust
pressure when the tyre is cool.
- For continuous high-speed
motorway driving, increase tyre pressure by 3 to 5
psi
- Incorrectly inflated tyres
can cause;
- Increased fuel consumption
- Adverse handling effects
- Increased braking distances
- Increased risk of blow outs
- Reduced tyre life
Tyre
Size Designations
Run
Flat Tyres
Today's car manufacturers are
introducing more and more vehicles which are equipped
with RFT tyres. RFT tyres are capable of continuing
to support the vehicles weight even at zero pressure.
This enables the customer, in the case of a total air
loss, to drive at reduced speed to the next service
station. The driver no longer has to stop at dangerous
areas (motorways / Bridges / Tunnels, etc.) to jack
up the vehicle and change the flat tyre.
As the driver might not recognize
that one tyre is operating at zero pressure, a pressure
monitor system has to be installed warning the driver
immediately if air loss occurs. The sensors of such
warning systems are mostly mounted inside the wheel.
Therefore extra care has to be applied during dismounting
and mounting of the tyre. Check with the vehicles
manufacturers manual and investigate which kind of sensors
are used in the vehicle to prevent any possible damage
during handling.
As RFT (Self Supporting) tyres
sidewall stiffness is approximately six times thicker
than a standard tyre, advanced tyre changing equipment
should be used. As a reference, machinery which is
able to handle 45 series (and lower) aspect ratio tyres.
Best
tyres to the rear
Experience has shown that tyres often wear at a different
rate, so we advise that new tyres should be fitted at
the rear and the more worn tyres fitted at the front.
Practical driving experiments have proven that the grip
of the rear tyres is crucial to directional stability.
If a tyre bursts at the rear, this usually leads to
an uncontrolled slide. Losing grip at the front on the
other hand means the vehicle continues to skid in a
straight line. This is not very pleasant, but comparatively
less harmful.
Uneven tyre wear is mainly a
problem of vehicles with front wheel drive because in
this case the steering, braking and driving forces all
have an effect on the tyres together. To counteract
this, we recommend that the front and rear wheels are
swapped about every 6,000 miles. This means that all
four tyres wear evenly and can subsequently all be replaced
at the same time.
New
Tyres
All new tyres should be run in
for the first 150 - 200 miles at medium speed on dry
roads, in order to abrade the tread surface.
There are several reasons for doing this:
- Tyres are vulcanised in heating
moulds, which will have been manufactured extremely
precisely and all of their surfaces are correspondingly
smooth
- The moulds not only contain
all of the details of the tread pattern with countless
sipes, but also all of the markings and a large number
of vent holes. All of this retains the tyre when it
is being removed from the mould. Therefore the tyre
can only be taken out of the heating mould easily
with the use of a silicone-like release agent.
- It is usual to remove these
from the tread by running in on dry roads and at the
same time abrading the tread, taking care to avoid
sharp cornering and extreme braking manoeuvres. Only
after undergoing this type of running-in procedure
does a new tyre attain its intended level of performance
and its full gripping power.
Tyre age
This applies to every tyre: it has reached the end of
its life after 8-10 years, even if it still looks perfect
and has not been used very often. The rubber compound
ages with time, losing some of its properties, which
often results in a progressive breakdown of the belt
and carcass. High temperatures and direct sunlight
accelerate the ageing process. You should protect
tyres on cars and caravans parked for long periods by
covering them. You should replace tyres that are not
in continuous use after 5-7 years. You should only
use spare tyres that are more than 6 years old in an
extreme emergency.
Choosing
the correct type of tyre
When changing tyres it is vital
you decide what is important to you in a tyre. The
below chart demonstrates that when certain areas of
a tyres performance are improved, other areas of performance
may be reduced. When you have decided what your priorities
are in a tyre you can then choose between a touring,
sport or general use tyre.
Balancing
Proper balancing of wheels and tyres is vital to provide
optimum performance. Correctly balanced wheels and
tyres can be the difference between a good or bad driving
experience. Some cars are more sensitive to an out of
balance tyre than others. An out of balance tyre can
negatively affect ride quality, shorten the life of
your tyres, bearings, shock absorbers and other suspension
components. If you have a vibration that is speed dependant
and becomes noticeable around 40-45 mph and increases
as your speed increases, it is probably caused by a
wheel and tyre imbalance.
Have
your tyres checked
Above all, have your tyres inspected
on a regular basis by your local First Stop tyre centre.
Click here to find your nearest centre. |
