Run Flat Tyre Technology

Introduction: This technology was offered to the customer for the first
time as standard in the BMW Z8 and the MINI Cooper S. This has now been
extended to the Z4 and will also feature on the forthcoming 5 Series
(from 530i upwards), the first large-volume production car in the world
to feature this technology as standard equipment. The standard Run
Flat-tyre technology in conjunction with Tyre Pressure Monitoring (TPM)
offers the customer, among others, the following advantages: Safety -
Dynamic driving stability in the event of slow or sudden pressure loss
i.e. you still maintain control of the vehicle. - Ensure the
mobility of the driver to leave areas of risk. - No need to jack up the
vehicle on the side of the road, which could potentially be dangerous.
Convenience - Keep on travelling, even with a completely deflated tyre,
to a service station/place of safety. - No worries about having to
change a flat tyre. - Low tyre noise and maximum driving comfort.
Economy - Save weight and fuel by eliminating the need to carry a spare
or jack. It must be noted that in the new E60 an emergency spare is
included. - Increase boot size. - Save the environment as fewer
resources are needed. Run Flat Tyre (RFT) To enable the driver to
continue driving on an RFT which has developed a slow or sudden
pressure loss, the inner walls of the RFT have been reinforced by
additional inlay strips made from heat-resistant rubber. This
reinforcement prevents the damaged tyre from collapsing (in the case of
a completely flat normal tyre, the rim flanges roll onto the folded
sidewalls) and remains stable even under extreme loading in the event
of a serious blow-out - also when cornering. The special rim keeps the
tyre "Run Flat-fit"; adequate steering, braking and traction
forces can be transmitted by the tyre. (Benefiting from
specially-contoured double rim humps Run Flat tyres are not able to
"jump" off the rims even under a sudden loss of pressure.)
Caution: It is very difficult to identify a deflated self-supporting
tyre by its external appearance, for the simple reason that it doesn't
'collapse' like a normal tyre! - In the event of a sudden pressure
loss, the car can be driven at a maximum speed of 80 km/h for roughly a
further 160 km. - In the event of a slow pressure loss, the car can be
driven at a maximum speed of 80 km/h for roughly a further 2000 km. -
If an RFT is not available in the event of a serious blow-out, a
"normal" tyre can also be fitted as a makeshift solution.
Tyre Pressure Monitor / Tyre Pressure Control Not all drivers notice
the deteriorating handling of their vehicle as it gets spongier as a
result of a slow puncture (which makes up approx. 80% of all tyre
failures). This defect is even more difficult to recognize in a Run Flat
tyre because its sidewalls remain rigid. The warning system, therefore,
becomes vitally important as it's the only reliable way of alerting the
driver to such a failure. That said, it does not exempt the driver from
his obligation of checking tyre inflation pressures on a regular basis.
A gradual loss of tyre pressure always presents a very significant
accident risk, since the tyre will overheat when running on
significantly lower tyre pressure, with the risk of the tyre suddenly
bursting. The Tyre Pressure Monitor therefore monitors tyre pressure by
consistently comparing wheel speed and revolutions with the help of the
signals from the ABS anti-lock brake system: A significant loss of tyre
pressure changes the circumference of the tyre and, accordingly, the
running speed of the tyre on the road, the driver being informed by
both a warning light and an acoustic signal, regardless of the type or
make of tyre or whether the car is travelling round a bend, running at
high speed or on varying road conditions such as wet or snowbound
surfaces. Designed to warn the driver of any excessive loss of
pressure, the system provides a warning as of a road speed of 15 km/h
and with a loss in pressure of more than 30 per cent. A more complex
system dubbed Tyre Pressure Control or TPC which is used on the X5 and
7 Series (optional on the new Five from mid 2004) goes one step further
than by comparing actual tyre pressure with target tyre pressures. As
soon as tyre pressure remains at least 0.2 bar below the target level
for more than eight minutes, the system requests the driver to check
the air pressure in the tyres. If the drop in pressure is 0.4 bar or
more, the driver is warned by an acoustic signal and the message
"Tyre Defect" appears in the display. And regardless of the
deviation from the desired pressure level, the data measured is
re-transmitted and presented to the driver every eight seconds as soon
as the control unit detects inadequate pressure.
Initialization/operation Regardless of whether your car is equipped
with TPM or the TPC system, reinitialization must take place when tyre
inflation pressures are changed or when wheels/tyres are changed in
order to record the current pressure required. Initialization starts
when the Tyre Pressure Monitor/Control button is pressed until the
indicator lamp in the instrument cluster lights up yellow. After a
brief driving time, from a speed of 15 km/h, the system learns the new
reference values and the yellow indicator lamp goes out. The indicator
lamp lights up red if a pressure loss is identified by the system. The
driver is alerted to a system failure by the indicator lamp in the
instrument cluster lighting up yellow.