Category Archives: 03. Back axle & Propellor shaft

Wire wheels: worn hub and wheel splines

Wire wheels on Turners

Many Turners received wire wheels either as a standard factory option or as a later “aftermarket” change. This was (always?) combined with a Girling Type 10 disc brake conversion at the front and required the use of special splined hubs on both axles. See page 19 of the Turner Parts Catalogue below. Turners used both 13 and 15” wire wheels.

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clip_image014 Special splined hubs for Girling Type 10

Wire wheel fixation

Detachable wire wheels have a different way of fixation compared to normal disc wheels, as they are mechanically “connected” to the axle hubs in two ways:

1. In a rotational direction by means of driving splines (serrations) on the (stub) axle hubs and driven splines on the inner wheel centre.

2. In an axial way by means of a (threaded) locking nut preventing the wheel to become disconnected from the threaded axle hub.

This article will not tackle the subject of which wire wheel types have been applied over the years; see the appropriate literature for that. We do want, however, to emphasise the potential danger of wire wheel fixation systems after many years of use (and abuse) to the point where they become even highly dangerous! In addition, some guidance is provided in checking whether a wire wheel can still be safely fixed to the car.

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A – Locking thread on hub (left or right hand thread).

B – Driving splines on hub.

E – Driven splines of wheel centre.

Rudge-Whitworth fixation

The system of detachable and interchangeable wire wheels has been initially designed by John Pugh around 1910 but is better known under the (company) name of Rudge-Whitworth.

The resulting standardisation of detachable wire wheel fixations in Europe dates back to the 1920’s. The basis for this standard was the load to be carried per wheel and the required bearing diameter for that, resulting in a certain cross section for the hub. Note that the wheel type designation in the standard are basically structured around the (metrical!) dimensions of (then available) wheel bearings.

clip_image002[6]  Advertisement 1912

Wear on splines and thread

Over the years the thread of the locking nut and the hub itself may wear but (even more important) the splines on the hub and in the wire wheel centre may wear to the extent that the construction eventually becomes unsafe. Therefore it is wise to regularly check them and more in particular during any XK restoration as the condition and history of axle hubs and wheels are unknown.

Four dimensions are of importance here and have to be checked:

1. The maximum allowed inner diameter of the thread of the lock nut

2. The minimum allowed outer diameter of the thread on the wheel hub

3. The minimum allowed outer diameter of the splined hub

4. The maximum allowed inner diameter of the inner wheel centre splines

Please note that wear of splines and thread is accelerated if the wheel is not fitted tightly!

 

Cross-section of Rudge-Whitworth hubs

The principle wheel type designation according the Rudge-Whitworth standard refers to the maximum size of an outer wheel bearing (in millimetre) which can be used with that hub. The actual hub diameter is measured across the outside of the splines on the axle hubs (not the wheel splines).

Wheel Type

Actual hub diameter

Number of splines

Spline length Long Hub

35

52

62

56

42

62.5

75

62

52

73

88

62

62

82.5

100

78

72

92

112

84

80

102

124

87

90

111.5

136

94

100

123

150

97

120

137

168

101

Two wire wheel types are normally used on British sports cars: type 42 and 52. Turner opted for the smaller  Type 42 wire wheels also due to the rather limited weight of their sports cars. The (course) thread of wire wheels has a top angle of 60° and a pitch of 8 TPI (or 3.2 mm) although some earlier versions may have used 12 TPI (or 2.1 mm).

clip_image002 Alexander-Turner with 15″ wire wheels

Dimensional requirements for Type 42 wire wheels: worn or still OK?

Further to the aforementioned important testing criteria, the survey below gives specific information regarding when a splined hub, wire wheel or locking nut should be replaced.

  1. The locking nut should be checked for wear on the (internal) thread. If a cylinder with an outside diameter of 2.211” or 56.2 mm should fit in the locking nut, wear has progressed to the extent that the locking nut has to be replaced.
  2. If a tube with an internal diameter of 2.291” or 58.2 mm fits over the thread of the axle hub, wear has progressed to the extent the complete hub has to be replaced.
  3. If a tube with an internal diameter of 2.424” or 61.6 mm fits over the splines of the axle hub, the complete hub has to be replaced.
  4. If a cylinder with an outer diameter of 2.374” or 60.3 mm fits in the internally splined wheel centre, the complete wire wheel has to be replaced.

Note that the above dimensional requirements are no more than minimum requirements! As an example: wire wheel constructions fulfilling the above requirements have a remaining overlapping contact height of the splines of no more than (61.6 – 60.3 =) 1.3 mm. Although the contact surface is of course larger due to the 60° V angle of the spline and the length of the spline (here 37 mm), in comparison a new type 42 spline has a contact height of 62.3 – 59.6 = 2.7 mm, meaning that the (safety?) margin has been more than halved.

So don’t use any hubs or wheels with spline dimensions below the above given minimum requirements!