The Venerable Bead: How the Professionals Change Car Tyres

In the past, people used to change car tyres by hand. Some still might but this arduous procedure has been semi-automated for a long time. Here’s how professional tyre fitters change a car tyre, using a tyre machine.

As the tyre to be replaced will probably have been in service for a long time, it’ll be reluctant to part from its wheel. The beads, where they abut the wheel, will be firmly stuck and this is where the tyre machine’s first weapon comes into play. After unscrewing and removing the valve to let the air out of the tyre, the fitter will position the wheel in the jaws of the bead breaker. One press of a pedal and the bead is ‘broken’ – separated from its location.

Next, the fitter will lay the wheel flat on the tyre machine, clamping it into place. Since wheels – especially alloy ones – are both delicate and expensive, the equipment is designed to not touch the wheel rims directly. Having levered the upper bead upwards over the wheel rim, the fitter will engage the hooked head of the tyre machine under the bead. Another pedal press sets the machine rotating, to skin the tyre off the upper rim. Repeating this process for the lower bead separates the old tyre from the wheel.

A little preparation of the wheel comes next. The old valve body is sawn off inside the wheel and if necessary, the inner faces of the wheel rims are cleaned. The old wheel balancing weights are removed. Having pulled a new valve into place with a special tool, the fitter will coat the wheel rims and the new tyre’s beads with a special compound. This is a lubricant that eases the fitting process though sometimes, a material with sealing properties may be needed.

The penultimate stage of tyre fitting is essentially the reverse of the removal of the old tyre. The fitter uses the tyre machine to force the new tyre on to the wheel, bead by bead. Finally, a compressed air line is used to inflate the tyre, until its beads pop outwards to seal against the inner faces of the wheel rim. Throughout the process, the tyre fitter has done the controlling, while electricity and compressed air have done the heavy work.

This leaves just the wheel balancing. The fitter will have already positioned the tyre correctly in relation to the wheel, using a coloured dot marking on the tyre. However, balance weights are virtually always required and there’s a machine to help with this task. The tyre fitter will clamp the wheel onto the machine. When the guard is closed and the machine starts, it will take the wheel up to a fixed speed, usually about 200 revolutions per minute.

Using its onboard sensors and electronics, the balancing machine points out where the wheel weights should be fitted and how much they should weigh. Having fitted the weights – stick-on or clamp-on as appropriate – the fitter will run the machine once more, fine-tuning the balance with other weights if necessary.

As we can see, what used to be an hour or more’s hard work is done in minutes. What’s more, if you watch the proceedings from the waiting area, you’ll know exactly what’s happening in the tyre bay!

Merityre are a leading UK independent supplier of car tyres. Why not visit their website at www.merityre.co.uk and see where you can buy your next set of tyres.

Tyre Hieroglyphics - What Car Tyres Sidewall Markings Mean

Have you ever noticed that tyres have moulded markings on their sidewalls? You’ll probably have spotted the maker’s name but does the rest mean anything to you? Can you tell what 205/70R14 88 T is all about? Perhaps not yet but understanding these codes could save your life. Why? If they show your tyres aren’t the right ones for your car you can arrange replacements.

We can start by breaking down the example above; the markings denote the tyre size, construction, and load and speed rating. How? Like this…

205 – This is the width of the tyre’s section in millimetres. The section 205 is a little over eight inches wide.

70 – This is the tyre’s aspect ratio, the sidewall’s height expressed as a percentage of its width. Here, the height is 70 per cent of the width. ‘Low profile’ tyres are fashionable so aspect ratio figures go as low as 30. Ultra-low tyres like this give tremendous grip but you pay for it, in a poorer ride quality and very little protection for your wheels against kerbs, potholes and speed bumps.

R – The next letter indicates the tyre’s construction. Here, R means radial.

14 – This next number is also simple. The figure 14 refers to the diameter of wheel the tyre will fit, in inches.

88 – Not so simple but extremely important. This tyre load index is a code for the maximum load capacity of the tyre when driven at its maximum rated speed. The figure 88 denotes a rating of 560 kilograms. Car tyres need to be correctly rated for load.

T - The last letter indicates the tyre’s speed rating. The letter T means the tyre can cope with extended use at a maximum speed of 118 miles per hour. The top speed rating is Z, which appear on tyres for cars capable of maintaining 149mph and above.

There are other tyre sidewall markings but most are for the attention of the tyre fitter. Markings show the tyre complies with EEC, ECE and US regulations. There might be an arrow symbol showing the tyres’ direction of rotation and there’ll be a ‘TWI’ mark indicating where the running surface’s tread wear indicator lies. There will also be a safety warning, perhaps the country of manufacture, whether the tyre is tubed or tubeless, and coloured markers showing the fitter where to fit the tyre in relation to the wheel’s valve.

All these are largely for the fitter’s information but there’s one marking you’re advised to note. The last four digits in the ‘DOT’ code reveal the tyres’ date of manufacture. Four-digit codes began after 2003 so if you see, for example, the code 3 0 0 8, the tyre was made in the 30^th week of 2008. You should never use tyres over 6 years old but a good tyre fitter won’t fit ‘new’ tyres that are beyond their sell-by date.

It’s true that checking your tyre markings could save your life, simply because underrated tyres could fail, especially under high speed/load conditions. The right tyres could save you something else –under-specified car tyres can invalidate your insurance.

For more advice about which car tyre is best for your car then ask our experts at Merityre.co.uk.