Back in the mists of time, motorists used to change their own tyres – by hand. No doubt there are diehard enthusiasts who still do this but for us mere mortals, there are car tyre bays. Here’s how a car tyre is changed – by machine.
To be attended to on a tyre machine, the car wheel with the tyre to be replaced must be taken off. Enter the trolley jack and powered wheel nut wrench. Almost without exception a key or adaptor to cope with the locking wheel nut is needed now. Soon enough, the errant car tyre will be detached from the car, complete with wheel.
Now the fun begins! We’re contemplating separating a big, tough rubber ring from the big, heavy metal wheel it’s been embracing, probably for many miles. The tyre fitter can unscrew the tyre valve and let the air out, but he can’t make any impression on the car tyre/wheel combination without mechanical assistance. This is why the tyre machine has powerful, compressed air-powered jaws, better known as the bead breaker. With the deflated car tyre placed correctly, all the fitter need do is press on a pedal. The jaws seize the tyre and separate the bead from the wheel rim.
The failed car tyre now has to go up in the world. More accurately, it has to lie flat on the tyre machine, with the wheel clamped firmly in place. More compressed air is used to let the machine seize the wheel firmly. Then, the fitter will place the hooked head of the tyre machine by the car tyre’s bead. Lifting the broken bead carefully over the wheel rim with a tyre lever, the fitter will flip it over the machine’s head. Another press of a pedal releases compressed air, causing the wheel to rotate. The tyre machine’s head peels the upper bead of the car tyre up and off the wheel rim. Repeat the process for the lower bead and that’s it – the old car tyre is off.
Now for a spot of wheel preparation. The old tyre valve’s inner fitting is sawn off and the valve is drawn out. The old balance weights will be peeled off or unclipped and, in some instances, the fitter will use a hand wire brush to clean corrosion off the wheel rim. Then, after having replaced the tyre valve, the fitter will apply a special compound to the wheel rim and the new car tyre. This stuff is a lubricant that will make fitting the new tyre easier. However, where there has been an air leak between the old tyre and the wheel, the fitter will brush on a special sealant.
The tyre machine comes into play again now. Once cleaned, lubed (or sealed) and re-valved, the wheel is ready to accept the new car tyre. The machine is simply used in reverse order, the push the new tyre over the wheel rim, bead by bead. Using a compressed air line, the fitter will then inflate the new car tyre. Sometimes, the tyre/wheel will need encouragement to seal but the tyre will eventually seat itself – sometimes with a loud bang – when air pressure builds up. Throughout the car tyre-fitting process, the tyre machine has done most of the heavy work, while the tyre fitter carried out the intelligent tasks.
So, are we finished? Not quite – the wheel and car tyre combination need to be balanced. There’s another machine for this. Having placed the wheel on the tyre-balancing machine and clamped it on firmly, the fitter will close a safety guard and start the machine. The machine spins the wheel up to a given speed, which is usually about 200 revolutions per minute. Now it’s the balancing machine’s turn to be clever. Using its sensors and electronics, the machine will tell the fitter how heavy the balance weights need to be and exactly where they must go. Using the machine’s recommendations, wheel weights will be fitted and the newly balanced wheel taken up to speed again. Fine-tuning can be done but it’s rarely needed.
What used to be done manually, and could lead to sore hands and backache has been done quickly and efficiently. Should you watch from the comfort of the waiting area, you’ll know exactly what the fitter was doing at each stage of the tyre change…and why!