1115 Adhesion factor

The stopping distance of a wheel is greatly influenced by the interaction of the rotating tyre tread

Table 11.1 Stopping distances for various vehicle speeds and brake efficiencies

Vehicle Stopping distance for various braking

Table 11.1 Stopping distances for various vehicle speeds and brake efficiencies

Vehicle Stopping distance for various braking

speed

efficiencies (m)

km/h

100%

90%

80%

70%

60%

50%

10

0.4

0.4

0.5

0.6

0.7

0.8

20

1.6

1.8

2.0

2.3

2.7

3.2

30

3.6

4.0

4.5

5.1

6.0

7.2

40

6.4

7.1

8.0

9.1

10.7

12.8

50

10.0

11.1

12.5

14.3

16.7

20.0

60

14.4

16.0

18.0

80.6

24.0

28.8

70

19.6

21.8

24.5

28.0

32.7

39.2

80

25.6

28.4

32.0

36.6

42.7

51.2

90

32.4

36.0

40.5

46.3

54.0

64.8

100

40.0

44.4

50.0

57.1

66.7

80.0

Table 11.2 Adhesion factors for various road surfaces

No.

Material

Condition

Adhesion factor

1

Concrete, coarse asphalt

dry

0.8

2

Tarmac, gritted bitumen

dry

0.6

3

Concrete, coarse asphalt

wet

0.5

4

Tarmac

wet

0.4

5

Gritted bitumen tarmac

wet

0.3

6

Gritted bitumen tarmac

greasy

0.25

7

Gritted bitumen, snow

compressed

greasy

0.2

8

Gritted bitumen, snow

compressed

dry

0.15

9

Ice

wet

0.1

and the road surface. The relationship between the decelerating force and the vertical load on a wheel is known as the adhesion factor (ua). This is very similar to the coefficient of friction (u) which occurs when one surface slides over the other, but in the case of a correctly braked wheel, it should always rotate right up to the point of stopping to obtain the greatest retarding resistance.

Typical adhesion factors for various road surfaces are given in Table 11.2.

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