Wire wheels: worn hub and wheel splines

Wire wheels on Jaguar XKs

All Jaguar XK’s of the Special Equipment version were supplied with 16” wire wheels starting 1951. Also standard cars could have wire wheels as a factory option from that moment onwards.

clip_image002 Early Rudge Whitworth wire wheel

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 by Jaguar 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 may become even highly dangerous! In addition, some guidance is provided in checking whether a wire wheel can still be safely fixed to the car.

clip_image002[4]

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] Very early 1912 advertisement

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 Short Hub

35

52

62

36

42

62.5

75

37

52

73

88

37

62

82.5

100

57

72

92

112

55

80

102

124

58

90

111.5

136

56

100

123

150

59

120

137

168

63

Two wire wheel types are normally used on British sports cars: type 42 and 52. Jaguar opted for their post-war cars for the Type 52 wire wheels. The (course) thread of Jaguar wire wheels has a top angle of 60° and a pitch of 8 TPI (or 3.2 mm).

clip_image002 Rear wheel splined hub Jaguar XK 140

Dimensional requirements for Type 52 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 2.627” or 66.7 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 2.707” or 68.8 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 2.840” or 72.1 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 2.790” or 70.9 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 (72.1 – 70.9 =) 1.2 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 52 spline has a contact height of 72.9 – 70.2 = 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!

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