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If "LT" precedes the size description: these are
light truck tires according to U.S. manufactur-
ing standards.
If "T" precedes the size description: compact
emergency wheels with high tire pressure that
are only designed for temporary use in an
emergency.
Tire width: tire width : shows the nominal
tire width in millimeters.
Aspect ratio: aspect ratio ; is the size ratio
between the tire height and tire width and is
shown in percent. The aspect ratio is calcula-
ted by dividing the tire width by the tire height.
Tire code: tire code = specifies the tire type.
"R" represents radial tires; "D" represents
diagonal tires; "B" represents diagonal radial
tires.
Optionally, tires with a maximum speed of over
149 mph (240 km/h) may have "ZR" in the
size description, depending on the manufac-
turer (e.g. 245/40 ZR 18).
Rim diameter: rim diameter ? is the diame-
ter of the bead seat, not the diameter of the
rim flange. The rim diameter is specified in
inches (in).
Load-bearing index: load-bearing index A is
a numerical code that specifies the maximum
load-bearing capacity of a tire.
Do not overload the tires by exceeding the
specified load limit. The maximum permissible
load can be found on the vehicle's Tire and
Loading Information placard on the B-pillar on
the driver's side (Y page 316).
Example:
Load-bearing index 91 indicates a maximum
load of 1,356 lb (615 kg) that the tires can
bear. For further information on the maximum
tire load in kilograms and lbs, see
(Y page 322).
For further information on the load bearing
index, see "Load index" (Y page 322).
Speed rating: speed rating B specifies the
approved maximum speed of the tire.
i
Tire data is vehicle-specific and may devi-
ate from the data in the example.
Regardless of the speed rating, always observe
the speed limits. Drive carefully and adapt
your driving style to the traffic conditions.
Summer tires
Index Speed rating
Q up to 100 mph (160 km/h)
R up to 106 mph (170 km/h)
S up to 112 mph (180 km/h)
T up to 118 mph (190 km/h)
H up to 130 mph (210 km/h)
V up to 149 mph (240 km/h)
W up to 168 mph (270 km/h)
Y up to 186 mph (300 km/h)
ZR...Y up to 186 mph (300 km/h)
ZR...(..Y) over 186 mph (300 km/h)
ZR over 149 mph (240 km/h)
R
Optionally, tires with a maximum speed of
over 149 mph (240 km/h) may have "ZR" in
the size description, depending on the man-
ufacturer (e.g. 245/40 ZR18).
The service specification is made up of load-
bearing index A and speed rating B.
R
If the size description of your tire includes
"ZR" and there are no service specifications,
ask the tire manufacturer in order to find
out the maximum speed.
If a service specification is available, the
maximum speed is limited according to the
speed rating in the service specification.
Example: 245/40 ZR18 97 Y. In this exam-
ple, "97 Y" is the service specification. The
letter "Y" represents the speed rating. The
maximum speed of the tire is limited to
186 mph (300 km/h).
R
The size description for all tires with maxi-
mum speeds of over 186 mph (300 km/h)
must include "ZR" and the service specifica-
tion must be given in parentheses. Example:
275/40 ZR 18 (99 Y). Speed rating "(Y)"
indicates that the maximum speed of the
tire is over 186 mph (300 km/h). Ask the
tire manufacturer about the maximum
speed.
All about wheels and tires
321
Wheels and tires
Z
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