Pressure needs to be checked always on cold tires: during driving of the tire heat up, and pressure increases in them. If to measure pressure right after a trip, the result will be distorted.

Recommendations about check of pressure in tires are given below.

1. You carry out an inspection of pressure in tires regularly each 3–4 weeks.

2. Pressure drop approximately for 1,5% a month is norm for the branded tire. If this value is more, check the tire for STOA.

3. Pumping gates always should be closed caps as at hit of dirt in the gate can jam the valve, and it will hermetically not be closed.

Fig. 7.27. In Mercedes of the E-class the ordered values of pressure of air in tires are specified on a sticker on a reverse side of the hatch of a gasoline tank

Fig. 7.28. Wear of the tire as a result of long operation with an insufficient pressure in it

4. Pressure in tires should not fall below the installed values specified in the table on a reverse side of the hatch of a gasoline tank (fig. 7.27) as it results in the characteristic increased wear of tires (fig. 7.28).

Fig. 7.29. Wear of the tire as a result of long operation with the elevated pressure of air in it or frequent trips at the maximum speed

5. Pressure upon 0,2–0,3 bars above norm has some advantages: steering becomes more sensitive, tires wear out more slowly (fig. 7.29), and even fuel consumption is a little cut. Shortcoming: the damping properties of tires decrease.

Fig. 7.30. Spot of contact of the tire with the road: And — with a normal pressure all working surface of the tire contacts to a paving; In — at elevated pressure the tire contacts to only expensive middle part of the working surface; With — with a low pressure the spot of contact falls on edges of the tire

Fig. 7.31. Scheme of shift of wheels

TECHNICAL DICTIONARY Pressure in tires Pressure in tires defines a form and the size of a spot of contact of the tire with a paving (fig. 7.30) and, thus, term of its service, and also fuel consumption and road performance (with an insufficient pressure of the tire react it is inexact also with lateness on the movements by a wheel).

PRACTICAL ADVICE Correct shift of wheels 1. If you in a luggage carrier have a new spare wheel, you can save. Important only that on sale there were tires with the same drawing of a protector of the same producer. Then it is possible to buy one more tire, and "obuvka" for one axis is provided. 2. Purchase of new tires can be delayed if to rearrange wheels as follows: back and forward on one board (not on diagonal!) and with observance of the identical direction of rotation (fig. 7.31). In this case there is more uniform wear. 3. The lack of this method is that at wear it is necessary to replace at once all four tires. Besides, because of shift through certain intervals of a run it is more difficult to distinguish on the nature of wear possible violations in a suspension bracket, steering or shock-absorbers. 4. When replacing always you watch that anyway on one axis tires of one producer, with an identical profile and term of operation were installed. 5. Other option of shift considers that tires on forward wheels wear out quicker. When they reach minimum admissible level of height of a protector of 1,6 mm, forward it is possible to rearrange tires from back wheels (with preservation of the party) if they, of course, are not worn out to a limit yet. Thus, you need only two new tires for a back axis. 6. The basic principle is that on a back axis it is necessary to install tires with smaller wear of a protector as it influences in a decisive way course stability of the car. At damage of the tire of a forward wheel on the way the car nevertheless keeps controllability whereas damage of a back wheel almost inevitably leads to a drift.