MERCEDES-BENZ R320 2008 W251 Owner's Manual

370 Operation
Tires and wheels
Certification label
Even after careful determination of the
combined weight of all occupants, cargo
and the trailer tongue load (if applicable)
(
page 370) as to not exceed the permis-
sible load limit, you must make sure that
your vehicle never exceeds the Gross
Vehicle Weight Rating (GVWR) and the
Gross Axle Weight Rating (GAWR) for
either the front or rear axle. You can obtain
the GVWR and GAWR from the certification
label. The certification label can be found
on the driver’s door B-pillar, see “Technical
data” (
page 524).Gross Vehicle Weight Rating (GVWR): The
total weight of the vehicle, all occupants,
all cargo, and the trailer tongue load
(
page 370) must never exceed the
GVWR.
Gross Axle Weight Rating (GAWR): The to-
tal allowable weight that can be carried by
a single axle (front or rear).
To assure that your vehicle does not
exceed the maximum permissible weight
limits (GVWR and GAWR for front and rear
axle), have the loaded vehicle (including
driver, passengers and all cargo and, if
applicable, trailer fully loaded) weighed on
a suitable commercial scale.Trailer tongue load
The tongue load of any trailer is an impor-
tant weight to measure because it affects
the load you can carry in your vehicle. If a
trailer is towed, the tongue load must be
added to the weight of all occupants riding
and any cargo you are carrying in the
vehicle. The tongue load typically is
between 10% and 15% of the trailer weight
and everything loaded in it.

371 Operation
Tires and wheels
Recommended tire inflation pressure
Your vehicle is equipped with the Tire and
Loading Information placard located on
the driver’s door B-pillar (
page 366).
The tire inflation pressure should be
checked regularly and should only be ad-
justed on cold tires. The tires can be con-
sidered cold if the vehicle has been parked
for at least 3 hours or driven less than
1 mile (1.6 km).
Follow recommended cold tire inflation
pressures listed on Tire and Loading
Information placard on the driver’s door
B-pillar.
Keeping the tires properly inflated
provides the best handling, tread life and
riding comfort.
In addition to the Tire and Loading
Information placard on the driver’s door
B-pillar, also consult the tire inflation
pressure label (if available) on the fuel filler
flap (
page 352) for any additional infor-mation pertaining to special driving situa-
tions. For more information, see
“Important notes on tire inflation
pressure” (
page 372).
1Tire and Loading Information placard
with recommended cold tire inflation
pressuresWarning!G
Follow recommended tire inflation
pressures.
Do not underinflate tires. Underinflated tires
wear excessively and/or unevenly,
adversely affect handling and fuel economy,
and are more likely to fail from being over-
heated.
Do not overinflate tires. Overinflated tires
can adversely affect handling and ride
comfort, wear unevenly, increase stopping
distance, and result in sudden deflation
(blowout) because they are more likely to
become punctured or damaged by road
debris, potholes etc.
Do not overload the tires by exceeding the
specified load limit as indicated on the Tire
and Loading Information placard on the driv-
er’s door B-pillar. Overloading the tires can
overheat them, possibly causing a blowout.
Overloading the tires can also result in
handling or steering problems, or brake
failure.
iData shown on Tire and Loading Information
placard example are for illustration purposes
only. Tire data are specific to each vehicle and
may vary from data shown in the following
illustration. Refer to Tire and Loading
Information placard on vehicle for actual data
specific to your vehicle.

372 Operation
Tires and wheels
The Tire and Loading Information placard
lists the recommended cold tire inflation
pressures for maximum loaded vehicle
weight. The tire inflation pressures listed
apply to the tires installed as original
equipment.
Important notes on tire inflation
pressure
Tire temperature and tire inflation pressure
are also increased while driving, depending
on the driving speed and the tire load.If you will be driving your vehicle at high
speeds of 100 mph (160 km/h) or higher,
where it is legal and conditions allow,
consult the tire inflation pressure label on
the inside of the fuel filler flap (if available)
on how to adjust the cold tire inflation
pressure. If you do not adjust the tire infla-
tion pressure, excessive heat can build up
and result in sudden tire failure.
If your vehicle is not equipped with the tire
inflation pressure label on the inside of the
fuel filler flap, contact an authorized
Mercedes-Benz Light Truck Center for
proper tire inflation pressure.Make sure to readjust the tire inflation
pressure for normal driving speeds. You
should wait until the tires are cold before
adjusting the tire inflation pressure.
Some vehicles may have supplemental tire
inflation pressure information for vehicle
loads less than the maximum loaded vehi-
cle condition. If such information is provid-
ed, it can be found on the tire inflation
pressure label located on the inside of the
fuel filler flap (
page 352).
Tire inflation pressure changes by approxi-
mately 1.5 psi (0.1 bar) per 18°F (10°C) of
air temperature change. Keep this in mind
when checking tire inflation pressure
where the temperature is different from
the outside temperature.Warning!G
If the tire inflation pressure drops
repeatedly:

Check the tires for punctures from
foreign objects.

Check to see whether air is leaking from
the valves or from around the rim.
iDriving comfort may be reduced when the
tire inflation pressure is adjusted to the value for
speeds above 100 mph (160 km/h) as specified
on the tire inflation pressure label located on the
inside of the fuel filler flap.

373 Operation
Tires and wheels
Checking tire inflation pressure
Regularly check the tire inflation pressure
at least once a month.
Check and adjust the tire inflation
pressure when the tires are cold. The tires
can be considered cold if the vehicle has
been parked for at least 3 hours or driven
less than 1 mile (1.6 km).
If you check the tire inflation pressure
when the tires are warm (the vehicle has
been driven for several miles or sitting less
than 3 hours), the reading will be
approximately 4 psi (0.3 bar) higher than
the cold reading. This is normal. Do not let
air out to match the specified cold tire
inflation pressure. Otherwise, the tire will
be underinflated.Checking tire inflation pressure
manually
Follow the steps below to achieve correct
tire inflation pressure:
Remove the cap from the valve on one
tire.
Firmly press a tire gauge onto the
valve.
Read tire inflation pressure on tire
gauge and check against the recom-
mended tire inflation pressure on the
Tire and Loading Information placard
on the driver’s door B-pillar
(
page 366) or, if available, the tire in-
flation pressure label on the inside of
the fuel filler flap. If necessary, add air
to achieve the recommended tire
inflation pressure.
Warning!G
Follow recommended tire inflation
pressures.
Do not underinflate tires. Underinflated tires
wear excessively and/or unevenly,
adversely affect handling and fuel economy,
and are more likely to fail from being over-
heated.
Do not overinflate tires. Overinflated tires
can adversely affect handling and ride
comfort, wear unevenly, increase stopping
distance, and result in sudden deflation
(blowout) because they are more likely to
become punctured or damaged by road
debris, potholes etc.
Do not overload the tires by exceeding the
specified load limit as indicated on the Tire
and Loading Information placard on the
driver’s door B-pillar. Overloading the tires
can overheat them, possibly causing a
blowout. Overloading the tires can also
result in handling or steering problems, or
brake failure.


374 Operation
Tires and wheels
Install the valve cap.
Repeat this procedure for each tire.
Run Flat Indicator (Canada only)
While the vehicle is being driven, the Run
Flat Indicator monitors the set tire inflation
pressures by evaluating each wheel’s rota-
tional speed. This allows the system to de-
tect a significant loss of pressure in a tire.
If a wheel’s rotational speed changes due
to falling tire inflation pressure, you will
see a corresponding warning message in
the multifunction display.The Run Flat Indicator may function in a re-
stricted manner or with a delay

if snow chains are mounted to the
vehicle

in presence of ice and snow

if you are driving on a loose surface
(e.g. sand or gravel)

if you are driving in a very sporty
manner (involving rapid acceleration or
high speeds in curves)
iIf you have overfilled the tire, release tire in-
flation pressure by pushing the metal stem of the
valve with e.g. a tip of a pen. Then recheck the
tire inflation pressure with the tire gauge.Warning!G
When the multifunction display shows the
message
Tire Pressure Check Tires,
one or more of your tires is significantly un-
derinflated. You should stop and check your
tires as soon as possible, and inflate them to
the proper tire inflation pressure as in-
dicated on the vehicle’s Tire and Loading
Information placard or, if available, on the
tire inflation pressure label. Driving on a sig-
nificantly underinflated tire causes the tire
to overheat and can lead to tire failure. Un-
derinflation also reduces fuel efficiency and
tire tread life, and may affect the vehicle’s
handling and stopping ability. Each tire, in-
cluding the spare, should be checked
monthly when cold and set to the recom-
mended tire inflation pressure as specified
on the Tire and Loading Information placard
(
page 366) or on the tire inflation pres-
sure label located on the inside of the fuel
filler flap (
page 352).


375 Operation
Tires and wheels
Reactivating the Run Flat Indicator
The tire inflation pressure monitor must be
reactivated in the following situations:

if you have changed the tire inflation
pressure

if you have replaced the wheels or tires

if you have installed new wheels or
tires
Using the Tire and Loading Information
placard on the driver’s door B-pillar or,
if available, the tire inflation pressure
label on the inside of the fuel filler flap,
make sure the tire inflation pressure of
all four tires is correct.
Switch on the ignition (page 39).
Make sure the standard display menu
appears in the multifunction display
(
page 164).
Press buttonk orj repeatedly
until the following message appears in
the multifunction display:
Press the reset button on the instru-
ment cluster (
page 154).
The following message will appear in
the multifunction display:
Restart
Run Flat Indicator?
Warning!G
The Run Flat Indicator does not provide a
warning for wrongly selected tire inflation
pressures. Always adjust tire inflation pres-
sure according to the Tire and Loading
Information placard on the driver’s door
B-pillar (
page 366) or, if available, on the
tire inflation pressure label located on the
inside of the fuel filler flap (
page 352).
The Run Flat Indicator does not replace
regular checks of the tire inflation pressures
since a gradual pressure loss in more than
one tire cannot be detected by the Run Flat
Indicator.
The Run Flat Indicator is not able to issue a
warning due to a sudden dramatic loss of
tire inflation pressure (e.g. tire blowout
caused by a foreign object). In this case
bring the vehicle to a halt by carefully apply-
ing the brakes and avoiding abrupt steering
maneuvers.
Warning!G
The Run Flat Indicator can only warn you in
a reliable manner if you have set the correct
tire inflation pressures for each tire.
If an incorrect tire inflation pressure was
set, the system will monitor the pressure
according to the incorrect value.

376 Operation
Tires and wheels
If you wish to confirm activation:
Press buttonæ.
The following message will appear in
the multifunction display:
Run Flat Indicator
Restarted
After a certain “learning phase”, the Run
Flat Indicator checks the set pressure
values for all four tires.
If you wish to cancel activation:
Press buttonç.
or
Wait until the message
Restart
Run Flat Indicator?
disappears.Checking tire pressure electronically
with the Tire Pressure Monitoring
System (TPMS), (USA only)
The TPMS only functions on wheels that
are equipped with the proper electronic
sensors. It monitors the tire inflation pres-
sure, as selected by the driver, in all four
tires. A warning is issued to alert you to a
decrease in pressure in one or more of the
tires.
iThe Tire Pressure Monitoring System
(TPMS) is equipped with a combination low tire
pressure/TPMS malfunction telltale in the
instrument cluster (
page 26). Depending on
how the telltale illuminates, it indicates a low tire
pressure condition or a malfunction in the TPMS
system itself:

If the telltale illuminates continuously, one
or more of your tires is significantly underin-
flated. There is no malfunction in the TPMS.

If the telltale flashes for 60 seconds and
then stays illuminated, the TPMS system
itself is not operating properly.
iThis device complies with Part 15 of the
FCC Rules. Operation is subject to the following
two conditions:
(1) This device may not cause harmful interfer-
ence, and
(2) this device must accept any interference
received, including interference that may
cause undesired operation.
Any unauthorized modification to this device
could void the user’s authority to operate the
equipment.

377 Operation
Tires and wheels
Warning!G
The TPMS does not indicate a warning for
wrongly selected inflation pressures. Always
adjust tire inflation pressure according to
the Tire and Loading Information placard on
the driver’s door B-pillar or, if available, the
supplemental tire pressure information on
the inside of the fuel filler flap.
The TPMS is not able to issue a warning due
to a sudden dramatic loss of pressure (e.g.
tire blowout caused by a foreign object). In
this case bring the vehicle to a halt by care-
fully applying the brakes and avoiding
abrupt steering maneuvers.
Warning!G
Each tire, including the spare (if provided),
should be checked monthly when cold and
inflated to the inflation pressure recom-
mended by the vehicle manufacturer on the
Tire and Loading Information placard or, if
available, on the tire inflation pressure label.
If your vehicle has tires of a different size
than the size indicated on the Tire and
Loading Information placard or, if available,
the tire inflation pressure label, you should
determine the proper tire inflation pressure
for those tires.
As an added safety feature, your vehicle has
been equipped with a tire pressure monitor-
ing system (TPMS) that illuminates a low tire
pressure telltale when one or more of your
tires is significantly underinflated. Accord-
ingly, when the low tire pressure telltale illu-
minates, you should stop and check your
tires as soon as possible, and inflate them to
the proper pressure. Driving on a signifi-
cantly underinflated tire causes the tire to
overheat and can lead to tire failure.
Underinflation also reduces fuel efficiency
and tire tread life, and may affect the vehi-
cle’s handling and stopping ability. Please
note that the TPMS is not a substitute for
proper tire maintenance, and it is the driv-
er’s responsibility to maintain correct tire
pressure, even if underinflation has not
reached the level to trigger illumination of
the TPMS low tire pressure telltale.
Your vehicle has also been equipped with a
TPMS malfunction indicator to indicate
when the system is not operating properly.
The TPMS malfunction indicator is com-
bined with the low tire pressure telltale.
When the system detects a malfunction, the
telltale will flash for approximately 1 minute
and then remain continuously illuminated.
This sequence will continue upon subse-
quent vehicle start-ups as long as the mal-
function exists. When the malfunction
indicator is illuminated, the system may not
be able to detect or signal low tire pressure
as intended.


378 Operation
Tires and wheels
Tire inflation pressure warnings
If the system detects a significant loss of
tire inflation pressure in one or more than
one tire, a message appears in the multi-
function display.
Example illustration
In addition, a warning signal sounds.Restarting the TPMS
The TPMS must be restarted when you
have adjusted the tire inflation pressure to
a new level (e.g. because of different load
or driving conditions). The TPMS is then
recalibrated to the current tire inflation
pressures.
Using the Tire and Loading Information
placard on the driver’s door B-pillar
(
page 366) or, if available, the
supplemental tire inflation pressure
information on the inside of the fuel
filler flap (
page 352), make sure the
tire inflation pressure of all four tires is
correct.
TPMS malfunctions may occur for a variety
of reasons, including the installation of
replacement or alternate tires or wheels on
the vehicle that prevent the TPMS from
functioning properly. Always check the
TPMS malfunction telltale after replacing
one or more tires or wheels on your vehicle
to ensure that the replacement or alternate
tires and wheels allow the TPMS to continue
to function properly.
iIf a condition causing the TPMS to malfunc-
tion develops, it may take up to 10 minutes
for the system to signal a malfunction using
the TPMS telltale flashing and illumination
sequence.
The telltale extinguishes after a few minutes
driving if the malfunction has been corrected.
iOperating radio transmission equipment
(e.g. wireless headsets, two-way radios) in or
near the vehicle could cause the TPMS to mal-
function.
Warning!G
It is the driver’s responsibility to calibrate
the TPMS on the recommended cold infla-
tion pressure. Underinflated tires affect the
ability to steer or brake the vehicle. You
might loose control over the vehicle.


379 Operation
Tires and wheels
Switch on the ignition (page 39).
Press buttonè orÿ on the
multifunction steering wheel repeat-
edly until the standard display menu
appears in the multifunction
display (
page 164).
Press buttonj or k repeatedly
the following message appears in the
multifunction display:
Tire Pressure Monitor
Active
Menu: R-Button
Press the reset button (page 154).
The following message will appear in
the multifunction display:
Restart tire
pressure monitor?
Press button æ.
The following message will appear in
the multifunction display:
Tire Pressure Monitor
Restarted
After driving a few minutes the current
tire inflation pressure values are
accepted as reference pressures and
then monitored.
If you wish to cancel activation:
Press button ç.Checking tire pressure electronically
with the Advanced Tire Pressure Moni-
toring System (Advanced TPMS)*,
(Canada only)
The TPMS only functions on wheels that
are equipped with the proper electronic
sensors. It monitors the tire inflation pres-
sure, as selected by the driver, in all four
tires. A warning is issued to alert you to a
decrease in pressure in one or more of the
tires.
Tire pressure inquiries are made using the
multifunction display. The present inflation
pressures are displayed only after a few
minutes’ travel time.
iRestart the TPMS after adjusting the tire in-
flation pressure to the inflation pressure recom-
mended for the vehicle operating condition. Tire
pressure should only be adjusted on cold tires.
Observe the recommended tire inflation pres-
sure on the Tire and Loading Information placard
on the driver’s door B-pillar (
page 366).
Some vehicles may have supplemental tire infla-
tion pressure information for driving at high
speeds (
page 372) or for vehicle loads less
than the maximum loaded vehicle condition
(
page 372). If such information is provided, it
can be found on the inside of the fuel filler flap.
iThis device complies with RSS-210 of
Industry Canada. Operation is subject to the
following two conditions:
(1) This device may not cause interference, and
(2) this device must accept any interference
received, including interference that may
cause undesired operation of the device.
Any unauthorized modification to this device
could void the user’s authority to operate the
equipment.