Decided to take up Ray’s suggestion and run a practical test.
I jacked up the rear of my FHC and removed the nearside spinner and wheel. Followed the Jaguar instructions regarding making sure there was no grease on the hub cone and the Dunlop instructions on refitting the wheel and spinner. The spinners are genuine NOS Jaguar made by Albion Brockhurst, wheels and hubs are new and only covered about 1,500 miles since. Spinner tightened up by hand with no binding (as repro spinners tend to). I used a rubber mallet to give the spinner a single whack to ensure it was seated and I could not remove it by hand. I used the Wiggles specified Sharpie to mark the position of the spinner on the wheel. I found there was slight movement in the wheel when I rocked it but less than I expected.
I took the car out through our small village at 30 mph, out on to a country road and felt confident enough to take it up to 60 mph. Moved on to a long straight dual carriagway and looped back at 50 mph (speed cameras!). No knocking noises or other nasties but I did avoid harsh acceleration, braking and cornering. Total distance traveled was about 5 miles and I have to admit I would not have suspected a loose spinner so the self tightening theory began to make sense.
Back in the garage I checked the spinner and found it had not moved at all from the start position; it was exactly as when I tightened it. I jacked the rear up and used a lead mallet to see if there was any possibility of tightening and indeed the spinner moved about 3/4" from the mark. Using a spinner removal tool and torque wrench it tested as above 220lb/ft. So the RW system is indeed ‘self locking’ as Dunlop described in that it will hold the spinner where you left it. It is fail safe in that a loose spinner will not loosen further but neither will it tighten further it seems.
In the interests of experiment I decided to do a second run but this time with a front wheel spinner ‘loose’. Same procedure and route as above but a far more disconcerting experience. Any major application of steering produced a knocking sound from the front. A hard left turn resulted in ‘graunching’ but I was confident the spinner would not loosen further so finished the route. Examination of the Sharpie marks again showed no movement of the spinner relative to the wheel. Three whacks with a lead hammer moved the spinner about 1".
Maybe with more or harsher driving there would be some movement but doing those tests was not an enjoyable experience or indeed really necessary considering the potential danger and spline damage. The spinners are self-locking and provided the Jaguar/Dunlop instructions are followed there should be no reason to expect self-tightening beyond what was set.
Let us not forget that RW made these claims in the 1920’s and 1930’s (when smoking was considered good for your health) and subsequently went bust. Jaguar/Dunlop bought the patent out of receivership, did their own tests and dropped all references to ‘self-tightening’ replacing it with ‘self-locking’.
Anyway, I will get my mallet and leave!
PS In the original Rudge-Whitworth design, the male taper was on the wheel and the female taper on the nut, so the car’s left-hand wheels required a right-hand thread and vice versa. On Lotus Elan S/E wheels the male taper is on the spinner and the female on the wheel so the thread sense is reversed. Same principle in action and only used by Chapman to try and avoid royalties which he failed to do because of what was obvious to everyone, even the Judge.