Technofile - the rod end bearing

Browse pages
Current page

1

Current page

2

Current page

3

Current page

4

Current page

5

Current page

6

Current page

7

Current page

8

Current page

9

Current page

10

Current page

11

Current page

12

Current page

13

Current page

14

Current page

15

Current page

16

Current page

17

Current page

18

Current page

19

Current page

20

Current page

21

Current page

22

Current page

23

Current page

24

Current page

25

Current page

26

Current page

27

Current page

28

Current page

29

Current page

30

Current page

31

Current page

32

Current page

33

Current page

34

Current page

35

Current page

36

Current page

37

Current page

38

Current page

39

Current page

40

Current page

41

Current page

42

Current page

43

Current page

44

Current page

45

Current page

46

Current page

47

Current page

48

Current page

49

Current page

50

Current page

51

Current page

52

Current page

53

Current page

54

Current page

55

Current page

56

Current page

57

Current page

58

Current page

59

Current page

60

Current page

61

Current page

62

Current page

63

Current page

64

Current page

65

Current page

66

Current page

67

Current page

68

Current page

69

Current page

70

Current page

71

Current page

72

Current page

73

Current page

74

Current page

75

Current page

76

Current page

77

Current page

78

Current page

79

Current page

80

Current page

81

Current page

82

Current page

83

Current page

84

Current page

85

Current page

86

Current page

87

Current page

88

Current page

89

Current page

90

Current page

91

Current page

92

Current page

93

Current page

94

Current page

95

Current page

96

Current page

97

Current page

98

Current page

99

Current page

100

Current page

101

Current page

102

Current page

103

Current page

104

Current page

105

Current page

106

Current page

107

Current page

108

Current page

109

Current page

110

Current page

111

Current page

112

Current page

113

Current page

114

Current page

115

Current page

116

Current page

117

Current page

118

Current page

119

Current page

120

Current page

121

Current page

122

Current page

123

Current page

124

Current page

125

Current page

126

Current page

127

Current page

128

Current page

129

Current page

130

Current page

131

Current page

132

Current page

133

Current page

134

Current page

135

Current page

136

Current page

137

Current page

138

Current page

139

Current page

140

Among the wreckage of a German fighter plane was found the future for racing car suspensions. Keith Howard reveals the origins of the rose joint.

Compliance. If you had to encapsulate the essential difference between race car and road car suspensions in a single word, that would be it: compliance, the reciprocal of stiffness. Road car suspension systems require carefully applied compliance to achieve acceptable ride quality and provide isolation from the noise and vibration generated at the tyre contact patch. So they make liberal use of elastomeric suspension bushes, meticulously positioned and dimensioned in modem cars so as to cause minimal compromise of wheel control. In a racing context, by contrast, refinement is barely an issue and accurate wheel control paramount, so rubber bushes are anathema.

Look closely at any modem race car, particularly from the senior formulae, and you’ll find it littered with a component which has become truly ubiquitous because of this: the rod end bearing. It is used to pivot suspension arms, at either end of anti-roll bar drop links, in gear linkages, on pedals: anywhere, in fact, where a low friction, very low compliance, zero play and, above all, adjustable pivot is needed.

Reel back 40 years, however, and the rod end bearing – although already widely used in aircraft – all but disappears from view. Right into the late 1950s/early 1960s even Formula One cars more commonly used (horror!) rubber bushes in their suspensions, albeit stiff ones. It was the desire to eliminate this parasitic suspension compliance, particularly with the development of wider, grippier tyres, and to incorporate increased suspension adjustability that brought the rod end into the picture and how.

In essence the rod end is delightfully simple, cornprising two, or at most three, principal components: a pierced ball with flattened poles which provides the articulation; a banjo-shaped housing into which the ball is secured during manufacture; and, in the most sophisticated types, a thin, usually PTFE-based, self-lubricating liner which is interposed between ball and housing to ensure low friction. What attracts the race car designer to the rod end is that it is,able to sustain high radial loads and, thanks to the male or female screw thread incorporated into its shank, is inherently adjustable, making it an ideal pivot in suspensions and elsewhere.

The origin of the rod end bearing has an edge of intrigue about it. Reel back another two decades to the first year of World War II and the desperate days of summer 1940. One of the first Messerschmitts to be shot down – presumably a Bf109E, although I haven’t been able to confirm that – crashes into a field, where its wreckage is pored over by Air Ministry experts. They are surprised to find a component in the flight control system that nobody in Britain has ever seen before: the rod end bearing.

It’s such a simple, elegant, effective device that Rose Brothers, later Rose Bearings Ltd, is asked to copy it for British aircraft to use. In due course, the same happens in the US with the HG Heim company. So intimately do these two manufacturers become associated with the rod end that to this day it is still commonly referred to as the rose joint or heim joint on either side of the Atlantic, the loss of capital letters a sign of how the names have become generics. Both companies still exist, albeit now as part of larger groups, and both still manufacture rod ends.

The first race car to employ a rod end bearing may well have been the Vanwall. Rose Bearings has a record of supplying a special order to Vandervell in 1957 (and to Rover a year earlier – but for what?) and photos of the front suspension of the 1958 car clearly show a rod end at the outboard extremity of its long radius arm. Later Rose made bearings to order for Cooper (1958) and Lotus (1960) among others, but the list is inevitably incomplete: as well as there being other sources of rod ends, Rose may have supplied off-the-shelf items of which there’s no record. In the US rod ends were certainly in use by 1959: the Watson-Offy Indy car of that year had them at both ends of its rear radius arms.

It’s all somewhat academic anyway because the rise of the rod end was gradual, as a perusal of early ’60s Formula One cars shows. By 1961/2 when the Lotus 25 was designed, for instance, rod ends were more widely deployed: Chapman used them at the outboard end of the lower front wishbone and rear radius arm, at both ends of the upper and lower rear lateral arms and at either extremity of the rear anti-roll bar drop links. Five years later, in the Lotus 49, the rod end was truly entrenched it was used virtually everywhere it could be.

Prior to the rod end’s adoption the Metalastik bush had held sway: two coaxial metal cylinders, the smaller to carry the mounting bolt, the larger to press-fit into the wishbone eye, separated by a thin layer of rubber. An odd choice, you might think, given that today a solid metal bush would be preferred, as it is in road cars adapted for track use. But rubber served an essential purpose in those days of gas-welded wishbones and suspension pick-up brackets: it provided enough ‘give’ to accommodate manufacturing tolerances.

The articulating ball of the rod end was likewise forgiving of dimensional inaccuracies, and without the cost to wheel control introduced by rubber. Also it facilitated, for the first time, the wide-ranging adjustability of suspension geometry we now take for granted although whether the teams and drivers had much idea how to juggle all the new variables at their command in those early years is another matter. Today the rod end continues to perform essentially the same functions, largely unchanged, although some F1 constructors are now incorporating spherical bearings – basically rod ends without the shank – directly into their carbon fibre composite push rods and suspension arms.

The next time you tuck into a Cadbury’s Roses chocolate would be an apposite time to reflect on how the simple rod end bearing transformed racing practice. Because, believe it or not, the name of the chocolates that grow on you derives from the fact that the clever machine originally developed to wrap them was designed by Rose Brothers the very same whose name would later become synonymous with the rod end.

Our thanks to R G Bearings for providing the NMB E-series stainless steel rod end used in the photograph. ‘Rose joint’ is a registered trademark of Rose Bearings Ltd.

Related articles

Related products