Tire condition – BMW 645Ci Coupe 2004 User Manual

Page 169

167

Temperature

The temperature grades are A, the highest,
B, and C, representing the tire's resistance
to the generation of heat and its ability to
dissipate heat when tested under con-
trolled conditions on a specified indoor lab-
oratory test wheel.
Sustained high temperature can cause the
material of the tire to degenerate and
reduce tire life, and excessive temperature
can lead to sudden tire failure. The grade C
corresponds to a level of performance
which all passenger car tires must meet
under the Federal Motor Vehicle Safety
Standard No. 109. Grades B and A repre-
sent higher levels of performance on the
laboratory test wheel than the minimum
required by law.

The temperature grade for this tire is
established for a tire that is properly

inflated and not overloaded. Excessive
speed, underinflation, or excessive load-
ing, either separately or in combination,
can cause heat buildup and possible tire
failure.

RSC – run-flat tires

You will recognize run-flat tires by a circular
symbol containing the letters RSC on the
side of the tire, refer to page

168

M+S

Winter and all-season tires.
These have better winter properties than
summer tires.

Tire condition

Before driving off, inspect your tires for
tread wear, signs of damage and foreign
objects lodged in the tread, and check the
tread depth.

Minimum tread depth

The tread depth should not drop below
0.12 in/3 mm, although, for example, Euro-
pean legislation only specifies a minimum
tread depth of 0.063 in/1.6 mm. At tread
depths below 0.12 in/3 mm there is an

increased risk of high-speed hydroplaning,
even when only small amounts of water are
present on the road surface.
As winter tires display a noticeable loss in
their ability to cope with cold-weather driv-
ing conditions once the tread wears to
below 0.157 in/4 mm, to ensure continued
safety you should always have such tires
replaced.

Wear indicators at the tread-groove base,
refer to arrow, are distributed over the tire's
circumference and are marked on the side
of the tire with TWI – Tread Wear Indicator.
These indicators signal at a tread depth of
0.063 in/1.6 mm that the legal wear limit
has been reached. The tread is then no
longer visible at these points.

Tire damage

Due to low-profile tires, please note
that wheels, tires and suspension

parts are more susceptible to road hazard
and consequential damages.
Unusual vibrations encountered during
normal vehicle operation can indicate tire
failure or some other vehicle defect. This
can, for example, be caused by driving over
curbs. These kinds of problems may also
be signaled by other changes in vehicle
response, such as a strong tendency to pull
to the left or right.
In these cases, immediately reduce speed.
Drive cautiously to the nearest BMW center
or tire dealer or, if necessary, have the
vehicle towed there.
Tire damage, extending to sudden and
complete loss of pressure in extreme
cases, can pose a potentially lethal safety
hazard for the vehicle's occupants and
other road users alike.

This manual is related to the following products:

645Ci Convertible 2004