Page 296 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Tyres and wheels C HAPTER 10.1

Intermediate values have to be interpolated. Compen- The following can be assumed for slip S X,W,a :
sation can be achieved by increasing the inflation
pressure. The values are as follows: 1st gear 0.08 4th gear 0.035
2nd gear 0.065 5th gear 0.02
3rd gear 0.05
0

0

0
0
Camber angle 2 20 2 40 3 3 20 3 40 4
Pressure 2.1% 4.3% 6.6% 9.0% 11.5% 14.1% According to DIN 75020 Part 5, the rolling circumfer-
increase ence C R given in the tyre tables relates to 60 km/h and
operating pressure of 1.8 bar. At lower speeds it goes
Taking all the influences into account, such as top speed, down to C R,Stat :
wheel camber and axle load, the minimum tyre pressure
required can be calculated for each tyre category (size C R;stat ¼ r stat 2p (10.1.1c)
and speed symbol). Formulas are shown in the ‘WdK 99’
guidelines from the Wirtschaftsverband der Deutschen The values for r stat are also given in the tables. At higher
Kautschukindustrie. speeds, C R increases due to the increasing centrifugal
force. The dynamic rolling circumference C R,dyn at
speeds over 60 km h 1 can be determined using the
10.1.2.6.4 Tyre pressure limit values speed factor k v . Figure 10.1-16 shows the details for k v as
1
Tyre pressure limit values should be adhered to. These a percentage, increasing by increments of 30 km h .
values are Intermediate values must be interpolated. The circum-
ference would then be:
Q and T tyres 3.2 bar
H to W and ZR tyres 3.5 bar C R;dyn ¼ C R ð1 þ 0:01 k v ÞðmmÞ (10.1.1d)
M & S tyres (Q and T tyres) 3.5 bar
The dynamic rolling radius can be calculated from C R,dyn
as
10.1.2.7 Tyre sidewall markings
r dyn ¼ C R =2p
All tyres used in Europe should be marked in accordance 1
with the ETRTO standards (see Section 10.1.1.1). or, at speeds of more than 60 km h ,
In the USA, Japan and Australia, additional markings
are required to indicate the design of the tyre and its r dyn ¼ C R;dyn =2p (10.1.2)
characteristics. The characters must also bear the import
sizes – the reason why these can be found on all tyres Taking as an example the tyre 175/65 R 14 82 H at
1
manufactured in Europe (Fig. 10.1-18). v ¼ 200 km h (Fig. 10.1-15) gives:
k v180 ¼ 0:7% and k v210 ¼ 1:1%
10.1.2.8 Rolling circumference
and interpolation gives:
and driving speed
k v200 ¼ 0:007 þ 0:0027 ¼ 0:0097
The driving speed is:
k v200 ¼ 0:97%
C R;dyn n M
v ¼ 0:006ð1 S X;W;a Þ ðkm=hÞ The rolling circumference C R taken from Fig. 10.1-15,
i D i G
according to Equation 10.1.1d, gives
(10.1.1b)
C R;dyn200 ¼ 1780 ð1 þ 0:0097Þ¼ 1797 mm
This includes:
and thus the dynamic radius in accordance with Equation
10.1.2 is:
S X, W,a the absolute traction slip (Equation 10.1.4f)
C R,dyn the dynamic rolling circumference in m
r dyn60 ¼ 283 mm and r dyn200 ¼ 286 mm
(Equation 10.1.1d)
the engine speed in rpm
n M
The outside diameter (construction measure) is
i D the ratio in the axle drive (differential)
i G the ratio of the gear engaged OD T ¼ 584 mm and thus OD T =2 ¼ 292 mm

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