I’m convinced that every classic car enthusiast in the world, will have at least once in their life dreamt of owning a set of wheels with centerlock wheel nuts. They possess a simple beauty, they only require a hammer and they stem back to the very birth of the wheel.
Ever since the invention of the wheel, it has obviously been intended to be mounted in a fashion which allowed the wheel to spin. The fundamental geometry is self-explanatory: the circular wheel requires to be fixed at its center, and this is how we’ve utilised the wheel right from the beginning. So after inventing the wheel, it wasn’t long before we came up with the axle upon which the wheel could be attached. On old carts, this was achieved by simply letting the axle protrude through the wheel and then hammering a wedge through the axle, thereby securing the wheel. Later, we managed to improve this invention by having a thread on the axle and using a nut to secure the wheel which lead to a much more stable rotation of the wheel.
Even after the use of metal had become the norm in the production of wheels, the spokes still remained wooden for a surprising number of years – the old-fashioned design of the artillery wheel was a stubborn one and refused to die. Both the rim and the hub where manufactured in metal by the turn of the century, but well into the 1910s, the spokes remained wooden. Yet, the wheels used on both light aircraft and bicycles had thin spokes of metal, but somehow this development failed to make its immediate transition into the automotive industry. But as performance improved during the car’s early years, the loads and stress of acceleration, braking and not least cornering proved too much for the wooden construction.
But encouraged by the patent of the Rudge-Whitworth hub, the further development of the wheel finally took speed. A suitably strong design was found by utilising two inner rows of tangential metal spokes, while an additional outer row of spokes added the lateral strength required for cornering. The wheels were often relatively deep dished allowing the steering pivot pins to be positioned close to the centreline of the tyres – again in an attempt to add strength and rigidity to the wheel. And of course, with the Rudge-Whitworth hub, exchanging the entire wheel was a lot easier than it had been previously when a new tyre would be fitted to the wheel every time a puncture occurred. This was regarded as a highly luxurious attribute at a time when punctures happened very regularly.
One very popular version of the centerlock application quickly became the winged nut. Especially on the British market, these were called spinners while the accompanying wheels were dubbed knock-off wheels. These winged nuts were either loosened or tightened by striking the wings of the nut with a hammer – which of course perfectly explains the term “knock-off wheels”. The usual arrangement was for the hubs to have right-handed thread on the left side of the car and then a left-handed thread on the right side, which effectively meant that the but would be continuously tightened while the car was in forward motion.
This remained a very common way of securing your wheels to your car even up into the 1960s where the more sporting vehicles were beginning to use alloy wheels. Eventually though, the arrangement still used on current day cars with either three, four or five much smaller conical wheel nuts spread around the center of the wheel was regarded a better and safer way of securing the wheel to the car.
Up through the seventies, the wire wheel and knock-off spinners experienced a revival on the US market. However, their return was in the form of plastic hubcaps complete with faux wires and winged spinners in the very best Liberace style. It was meant to give the buying public a sense of sportiness and class from a bygone era. We probably shouldn’t judge today – but I do…
Eventually though, the vast winged knock-off nuts were phased out as more and more countries introduced legislation against them. They were regarded as dangerous in traffic as they brought unnecessary harm to pedestrians and cyclists. Instead, the already mentioned and much smaller conical wheel nuts took over.
However, a few marques such as especially Maserati resisted and retained the singular and conventional centerlock for as long as they could. They were of course forced to lose the wings, but used a large wingless centerlock instead which required a special and particularly large spanner. This is a system which is still widely used within motorsport primarily due to the speed at which wheels can be swapped – especially with an air impact wrench.