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4.1.3. Indexes of speed of tyresThe index of speed (e.g. T) after marks of the size of the tyre (e.g. 185/65 R 14 86T) specifies admissible maximum speed (vmax) for the given tyre.
Tyres for the corresponding car are necessary for selecting so that their as much as possible admissible speed was more maximum („depending on a design) speeds of the car.
If in a concrete case it is a question of the car having the interstate permission to operation the maximum speed of the car pays off as follows.
The formula for cars with Vmax to 150 km/h.
Vmax = 1,03'V + 3,5 km/h.
Example: the specified maximum speed V = 145 km/h.
Vmax = 1,03'145 km/h + 3,5 km/h = 152,85 km/h.
In this case it is necessary use the tyre with an index Q or with higher index of speed.
The formula for cars with Vmax about 151 km/h.
Vmax = 1,01'V + 6,5 km/h.
Example: the specified maximum speed V = 163 km/h
Vmax = 1,01'V163 km/h + 6,5 km/h = 171,13 km/h.
In this case it is necessary use the tyre with an index S or with higher index of speed.
Cars with the typical permission of EU.
If in a concrete case it is a question of the car with the typical permission of EU the maximum speed pays off for all cars under the formula.
Vmax = 1,05'V.
Example: the specified maximum speed V = 172 km/h.
Vmax = 1,05'V172 km/h = 180,60 km/h.
In this case it is necessary use the tyre with an index T or with higher index of speed.
Use of tyres with higher index of speed is supposed. The same concerns and tyres with higher index of loading.
THE NOTE
Instead of the letter v it is necessary to substitute specified in the car passport in column 6 the maximum speed. The given transformation is necessary, as all cars for technical reasons develop various maximum speeds within admissible admission laws.

