Checking the condition of tires and their pressure, designating tires and wheel rims, rotating wheels (Mercedes-Benz S-Class W140)

Please note! On the S420 and S500 models, summer tread pattern tyres may only be used on light alloy wheels, while winter tread pattern tyres may only be used on light alloy and steel wheels.

Depending on the model and equipment, tires and wheels of different sizes may be installed. The wheels have a pressing depth of 38 mm. The pressing depth is the distance from the center of the wheel to the thrust surface of the brake disc or drum. The wheel bolts for steel and alloy wheels are the same size.

Note: When installing alloy wheels from other manufacturers, different bolt sizes may be required.

Technology is improving. It may be that older models may have different tire pressure values. The dimensions specified in the vehicle documents are decisive.

For sporty driving, it is recommended to increase the pressure in the front and rear tires by 0.2 bar. When increasing the pressure, you should proceed from the basic value for different load conditions.

Winter tires are usually 0.2 bar higher in pressure than summer tires. The recommendations of winter tire manufacturers should be taken into account.

Since winter tires have a speed limit, a sign indicating the maximum speed must be mounted within the driver's field of vision.

Disc designations

Example 6Jx15

Wheel width in inches	6
Letter designation of the height and contour of the side flange of the disk rim	J
Solid deep disc designation	x
Disc diameter in inches	15
Permissible lateral runout on the side edge of the disc:	0.8 mm
Permissible radial runout on the disk seat:	0.5 mm

Tyre designation

Example: 195/70 R 14 89 H

Tire width in mm	195
Height to width ratio (the height of the tire cross-section is 70% of the width)	70
Speed class, H: up to 210 km/h (on new tires it is not always given).	H
Radial design	R
Disc size in inches	14
Load capacity parameter	89

Note: If individual width to height ratio information is not available (for example, 175 R 14), then we are talking about a "normal" ratio. It is 82%.

Note: If there is an M+S designation between data 14 and 89, these are winter tyres.

Designation of the permissible maximum speed

H

Note: Speed symbols apply to both summer and winter tires. The speed letters are listed in Specifications.

Date of tire manufacture

The production date is indicated on the tire in the manufacturer's code

Example: DOT CUL2 UM8 019 TUBELESS

DOT	Department of Transportation (US Department of Transportation)
CU	abbreviation of manufacturer's name
L2	tire size
UM8	tire performance
4600	date of manufacture - 46th working week of 2000
TUBELESS	tubeless (TUBETYPE - tire with tube)

Regularly checking your tires will help you avoid the hassle of being stopped on the road due to a flat tire. In addition, such checks provide valuable information about possible problems with the steering and suspension before serious damage occurs.





The tires are equipped with built-in tread wear indicator strips that are exposed when the tread depth decreases to 1.6 mm, after which the tires are considered worn. This value represents the minimum permissible tread depth; in most cases, it is recommended to replace tires with a tread depth of 2 mm or less. Tread depth can also be determined using a simple and inexpensive device known as a tread depth gauge.

Pay attention to any unusual tread wear. Tread defects such as cavities, bulges, flat spots and more severe wear on one side indicate a violation of the front wheel alignment angles and/or wheel balancing. If any of these defects are detected, contact a tire repair shop for correction.

Check the tire carefully for cuts, punctures, and stuck nails or tacks. Sometimes, after a nail has punctured the tire, it will hold pressure for a while or deflate very slowly.

If you suspect a "slow puncture," first check the valve nipple for leaks. Then inspect the tread for any foreign objects lodged in it or previously repaired punctures that have begun to leak air again. If you suspect a puncture, you can verify its presence by wetting the suspected area with soapy water. If there is a leak, the solution will begin to bubble. If the puncture is not too large, the tire can usually be repaired at any tire shop.



Carefully inspect the inside sidewalls of the tires for signs of brake fluid leakage. If any, have the brake system checked immediately.

Maintaining the correct tire pressure increases their lifespan, helps save fuel, and improves overall driving comfort. A special pressure gauge is required to check the pressure.

Recommendations

Always keep an accurate pressure gauge in your glove compartment. Gauges built into air hose nozzles at service stations are often inaccurate.

Always check tire pressure when tires are cold (i.e. before traveling by car). If you check the pressure on warm or heated tires, this will lead to overestimation of the pressure gauge readings due to thermal expansion of the tires. In this case, you should never lower the pressure, because after the tire cools down, it will be lower than normal.

Unscrew the protective cap from the inflation valve protruding from the wheel disk or from the hub cap, then press the pressure gauge nozzle firmly onto the valve. Read the readings of the device and compare them with the recommended values Specifications. Remember to replace the protective cap to prevent dirt and moisture from entering the valve mechanism. Check the pressure in all four tires and inflate them to the recommended pressure if necessary.

Don't forget to maintain the required pressure in the spare tire.

Checking the air pressure in the tires

Note: Checking air pressure should only be done on cold tires.

Unscrew the valve cap.



Tire pressure is checked once a month and also during maintenance (including spare tire). When checking, use a special pressure gauge or a pressure gauge built into the compressor.

Note: Do not rely on the pressure gauges built into the compressor nozzles used to inflate tires at petrol stations.

In addition, air pressure should be checked before each long trip, as this increases the temperature load on the tires.

The required tire pressure is indicated on the sticker located on the inside of the fuel tank cap.

Note: When using winter tires, the air pressure should be increased by 0.2 bar relative to the set value.

The air pressure of the narrow spare tyres is indicated on the sidewall of the rim. The air pressure in the tyres changes depending on the change in the ambient air temperature by 10°C by approximately 0.1 bar. This should be taken into account when checking the air pressure in the tyres indoors, especially in the cold season.

Example:

Temperature in the garage	About + 20°C
Outside air temperature	Around 0°C
Set air pressure in tires	Prescribed value, + 0.2 bar

Note. The tire pressure values given for a light vehicle load are the minimum values that ensure comfortable driving. Increased tire pressure, provided for a heavy vehicle load, has a positive effect on vehicle controllability even under light load and is entirely acceptable. However, rolling smoothness is somewhat reduced.

Checking the tire valve

Note: The valve extensions used must be checked for damage and contamination that could cause leaks. If necessary, the extensions must be replaced.

Unscrew the protective cap and extension.





Apply a small amount of soap solution or saliva to the valve. If an air bubble forms, tighten the insert (3) - use the projection of the metal protective cap (2).

Check the valve again. If bubbles appear and the valve cannot be tightened, it should be replaced (work of the service station).

Be sure to reinstall the protective cap.

Examples of typical tire tread wear

Lateral wear

Underinflation causes the tire to overheat while driving due to excessive deflection, which means the tread is not pressed down sufficiently onto the road surface. This results in loss of traction and excessive tread wear, not to mention the risk of tire failure due to overheating.

Check and adjust pressure.

Incorrect wheel alignment (wear on one side)

Repair or replace suspension parts.

Too sharp turns

Slow down!

Central wear

Excessive pressure

Overinflation of a tire results in accelerated wear of the center tread, reduced traction, harsher ride, and an increased risk of fatal tire damage.



Check and adjust pressure.

If you had to inflate your tires to the pressure specified for this purpose in order to transport heavy loads, Specifications pressure values, do not forget to release it after this when switching to normal operating mode.

Uneven wear

Front tires may wear unevenly due to improper wheel alignment.

Incorrect camber or runout

Repair or replace suspension parts.

Suspension defect

Repair or replace suspension parts.

The wheels are out of balance

Balance the wheels.

Front wheel alignment is incorrectly set

Adjust the front wheel alignment angles.

Note: Frayed edges of the tread pattern, which is a sign of wear, are best detected by touch

Wheel rotation

Note: Wheel rotation is only permitted if the front and rear wheels are the same size

Rotate the wheels every 5,000-10,000 km depending on tire wear. Make sure to maintain the direction of rotation of the wheels (for directional tires).

Rotation must be performed before characteristic signs of tire wear appear. A characteristic sign of wear for front tires is wear of the shoulder area of the tread, and for rear tires - the middle of the tread.



Each time you rotate the wheels, you should thoroughly clean the inside of them. After rotating the wheels, check and, if necessary, adjust the air pressure in the tires (see above).

Wheel mounting bolts may become loose if they have not been tightened to the specified torque Specifications tightening torque. After replacing the wheels, check the tightening torque.

Use only genuine "MB" mounting bolts marked with a star "Mercedes-Benz". Other bolts may come loose.

Lightweight spare wheel

If a tire is damaged, the lightweight spare tire can be used as a normal tire; it is recommended, however, to replace it with a normal wheel as soon as possible, as it is designed for a limited mileage of up to 20,000 km.

When changing tires, the spare tire can be mounted on the working wheel if the tire matches the design of the working wheel tires. If the tire is older than 6 years, it is recommended to use it only if the tire is damaged.

Models with tires size 245/45R18

Attention! If a spare wheel of a lightweight design is mounted, then due to different tire sizes, it is necessary to take into account the change in the dynamic properties of the car. Adjust your driving style to the traffic situation.

Replace the lightweight spare tire with a standard tire as soon as possible.

Models with AMG equipment

Warning! There is a risk of accident! If a lightweight spare wheel is mounted, the dynamic properties of the vehicle must be taken into account due to the different tire sizes. Adapt your driving style to this situation.

The lightweight spare wheel is intended for short-term use only, provided that the prescribed tyre pressure is maintained and the maximum speed is 80 km/h.

Operation with more than one lightweight spare wheel is not permitted.

Wheel replacement

Attention! Stamped steel wheels, light alloy wheels with 15 and 6 holes (7 Ѕ Jx16). When changing tires, the spare wheel can be used as a working wheel if the tire is new and the design of the wheel and tire corresponds to the design of the working wheels and tires.

See Section Jacking and towing in Introduction to this Manual.

Wheel mounting bolts

Replace wheel mounting bolts that are damaged or show signs of rust.

Do not lubricate bolts with oil or grease.

If the thread in the wheel hub is damaged, you cannot continue driving. You must contact a service station "Mercedes-Benz".

Clean the mating surface of the wheel and hub.

Use only genuine "MB" mounting bolts, marked with a three-pointed star "Mercedes-Benz". Other bolts may come loose. Tighten the bolts to the specified torque (150 Nm).