Page 291 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 1 0. 1 Tyres and wheels

Tyre load capacity (%)
Top speed of car Speed symbol
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(km h ) V W Y Tyres
210 100 100 100
220 97 100 100
230 94 100 100
240 91 100 100
250 – 95 100
260 – 90 100
270 – 85 100
280 – – 95
290 – – 90
300 – – 85

Fig. 10.1-14 The tyre load capacity shown in the ETRTO standards manual in the form of the load index LI is valid for V tyres up to
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vehicle speeds of 210 km h ; for W tyres up to 240 km h 1 and for Y tyres up to 270 km h . At higher speeds, lower percentages of the
load capacity must be incurred; for VR and ZR tyres, which are no longer made, these values were determined by vehicle and tyre
manufacturers.
10.1.2.6 Tyre load capacities and corresponding with load capacities are valid up to
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inflation pressures 160 km h (see Fig. 10.1-15 and Section 10.1.1.1).
Special operating conditions, the design of the vehicle
The authorized axle loads m V,f,max and m V,r,max , and or wheel suspension and expected handling properties
the maximum speed v max of the vehicle, determine the can all be reasons for higher pressure specification by the
minimum tyre pressure. However, the required tyre vehicle manufacturer. 1
pressure may be higher to achieve optimum vehicle Further, for speeds up to 210 km h the linear in-
handling (see also Section 10.1.10.3.5 and Fig. 10.1-44). crease of basic pressure has to be by 0.3 bar (i.e. by
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0.1 bar per Dv ¼ 17 km h ) and at speeds above
10.1.2.6.1 Tyre load capacity designation 210 km h 1 the tyre load capacity has to be reduced in
accordance with item 10.1.2.6.1. If the tyre load is lower
The load capacities indicated in the load index (item 6,
Fig. 10.1-18) are the maximum loads per tyre permitted than the maximum load capacity, a lower additional
for all tyres up to the speed symbol ‘H’. They are valid up safety pressure can be used in consultation with the tyre
to speeds of 210 km h 1 for tyres marked ‘V’ and up to manufacturer.
240 km h 1 for those marked ‘R’ ‘W’ or ‘ZR’. For vehi- For tyres with the speed symbol ‘W’, the pressures in
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cles with a higher top speed, the load capacity has to be Fig. 10.1-13 apply up to 190 km . After this it has to be
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reduced accordingly. increased by 0.1 bar for every 10 km h up to 240 km h .
Consequently, for tyres with speed symbol ‘V’, at a For higher speeds, the load capacity must be reduced
maximumspeedof240kmh 1 theloadcapacityisonly91% (see Section 10.1.2.6.1).
of the limit value (Fig. 10.1-14). Tyres designated ‘W’ On vehicles, pressure should be tested on cold tyres, i.e.
on the sidewall are only authorized up to 85% at these must be adjusted to the ambient temperature. If the
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270 km h . In both cases, the load capacity values tyre pressure is set in a warm area in winter there will be an
between 210 km h 1 (‘V’ tyre) and 240 km h 1 (‘W’ tyre) excessive pressure drop when the vehicle is taken outside.
and the maximum speed must be determined by linear On M & S winter tyres, it has long been recommended
interpolation. that inflation pressures be increased by 0.2 bar compared
For higher speeds (ZR tyres), the interpolation applies with standard tyres. Newer brands of tyre no longer
to the 240–270 km h 1 speed range. At higher speeds, require this adjustment.
the load capacity as well as the inflating pressure will be
agreed between the car and tyre manufacturers. How- 10.1.2.6.3 Influence of wheel camber
ever, this approval does not necessarily apply to tyres Wheel camber angles e W considerably influence tyre
which are specially produced for the US market and performance and service life. The camber angle should

which bear the additional marking ‘P’ (Fig. 10.1-17 and therefore not exceed 4 even in full wheel jounce con-

Section 10.1.2.5.2). dition. For angles above 2 , the loadability of the tyres
reduces at
10.1.2.6.2 Tyre pressure determination

For tyres with speed symbols ‘R’ to ‘V’ and standard road 3 W > 2 to 3 to 95%

tyres the minimum pressures set out in the tables and 3 W > 3 to 4 to 95%
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