Invented to deal quickly with frequent punctures, this rapid-release system became standard in Grand Prix racing and lasted until the 1960s. Keith Howard describes why the knock-off hub-spinner is even more ingenious than it looks.
Legend has it that the centrelock wheel — originally known as the QD (quickly detachable) wheel — came into being as a result of two Coventry men sharing a car one day during the early 1900s. One of them was John Pugh, whose father Charles had established the Whitworth Cycle Co in 1891 and three years later rescued the ailing Rudge Cycle Co to form RudgeWhitworth Ltd. The other was Victor Riley of the rival Riley Cycle Co.
When the car they were travelling in suffered a puncture, the two men agreed there must be a better way of dealing with a flat tyre than the Stepney rim system then in use, whereby rim and tyre were removed from the wheel and a replacement slid into place. Inspired by this shared experience, Pugh and Riley each designed centre-lock wheels that could be quickly removed by undoing a single large wheel nut, although the details of their fixing arrangements differed.
Legend also has it that, following many years of consequent patent litigation between their two companies, Pugh and Riley agreed to bury the hatchet in a train carriage on the eve of WWI.
Whatever the truth of these two incidents, the essentials are correct. Rudge-Whitworth, Riley and the Goodyear Wheel Company were all involved in prolonged legal wranglings as to who owned the intellectual rights to the detachable wheel, right up until the outbreak of hostilities in 1914. In fact the Great War intervened in more ways than one. Once it was over, Riley considered there were bigger fish to fry and withdrew from wheel manufacture, despite having supplied a remarkable 183 car makers worldwide by 1912. Rudge-Whitworth continued.
Amazingly, the Rudge-Whitworth wheel was originally sold as what today we’d call an aftermarket fitment. Automobile tyres were in their infancy in the early years of last century and tediously puncture-prone, so being able to repair a flat tyre quickly was important. Pugh’s centre-lock wheel was fast to remove and replace but, like the Riley equivalent, it required changes to the hub as well as to the wheel itself.
So hub and wheel kits were offered as replacements for the most popular cars of the time, some hubs even induding brake drums. If everyday motoring was blighted by tyre unreliability, in the emerging sport of motor racing it was a major issue. Being able to change a wheel quickly in the event of a puncture, or when the tyres were worn, could win you races. So it was inevitable the detachable wheel should find its way into competition. Some people fretted about retaining a wheel with a solitary nut — particularly one that lacked the Riley wheel’s evolving positive locking arrangements — but they didn’t appreciate the subtlety of Pugh’s design.
By an apparent miracle, it was self-tightening. In its essentials the Rudge-Whitworth wheel comprised three key components: a splined hub and two pairs of matching tapers (conical surfaces), one comprising the inboard end of the hub and the inboard wheel centre, and the second the retaining nut and outboard wheel centre. These tapers served three functions. First, they automatically centred the wheel on the hub. Second, they transmitted a significant fraction of the drive and/or braking torque so as to reduce the load on the hub splines. And third, they made the wheel-retaining nut self-tightening — or as Donald Bastow (ex-Rolls-Royce, ex-Bentley, etc) was to express it many years later, “perhaps more importantly, not self-loosening”. To picture why, imagine that the nut loosens slightly so that the tapers on the wheel and nut touch at only one point on their circumferences.
Because the male taper is now of smaller effective diameter than the female taper, rotation of the wheel on the hub under braking will cause the nut to rotate on its thread. If this rotation is in the correct direction — which is ensured by using differently handed threads on either side of the car— then the nut will automatically retighten itself.
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 wheels where the male taper is on the spinner (such as those fitted decades later to Special Equipment versions of the original Lotus Elan) the thread sense is reversed.
If it sounds a precarious arrangement, competition proved otherwise. At the 1908 TT race, 21 of the 35 entrants used Rudge-Whitworth wheels, and only one of the finishers didn’t By 1913, the use of detachable (Rudge and Riley) wire wheels was universal in grands prix, and they were widely employed immediately after WWI on such LSR contenders as Henry Segrave’s Sunbeam Tiger and Parry Thomas’s 1926 Babs.
Italian Carlo Borrani licensed the RudgeWhitworth design for his famous wire wheels, which Ferrari used on its grand prix cars into the early 1960s. Rudge’s wheels were also used by German giants Auto Union and Mercedes during the 1930s, proving themselves well able to transmit engine power in excess of 500bhp and sustain speeds of over 250mph in the Rekondwoche runs. All with just a couple of firm, not heavy, blows of a copper-faced hammer to tighten the eared spinners — a refinement of the original Rudge design introduced by Peugeot in 1913, in place of a large spanner.
But the 1930s weren’t kind to Rudge. Profits had been largely spent on its motorcycle racing exploits, so when the Great Slump struck, there was nothing in the kitty to tide the company over. The Receiver had to be called in and Rudge was sold off piecemeal. When John Pugh died, broken-hearted, in 1936, only the motorcycle business remained.
EMI, of all people, eventually bought that with the intention of moving operations to its Hayes factory in Middlesex, but war with Germany once again intervened. Jaguar acquired the rights to Rudge’s wheel business and together with Dunlop continued to exploit the design — first with wire wheels, then disc wheels — long after WWII finished, on the XICs, C-type, D-type and E-type. Similar designs were used by others like MG. Simple, effective, failsafe, the Rudge-Whitworth wheel was an object lesson in how a little original thought can save a lot of engineering complication. So why isn’t it still used?