Tyres
Tyres are a fundamental part of keeping your car on the road. In reality, the average car weighs approximately one and a half tons and although there are four of them they create a relatively small footprint on the road surface, approximately a patch just over the size of the average adult hand, not much really. So it's vital you keep your tyres in the best condition.
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First things first and most important is the tread depth the legal limit for a car and van tyre in the uk is below 1.6mm within the central three-quarters of the tyre. This means if the tyre is 20 cm wide then the central 15cm must have 1.6mm of tread and the remaining 2.5 cm of each side can be lower than 1.6mm. Having said that the 2.5 cm at each side can not have any damage or cuts that reveal any ply or cords of the tyre. (ply or cords are the internal structure of a tyre and if visible the tyre should be changed immediately). Within the tread pattern of a tyre there are small bumps that are called wear indicators these are there to help identify how close you are to the legal limit, and please remember a tyre below 1.6mm will be 3 points and a fine if the police see it.
One thing I would like to make clear, if your tyre is checked and found to have say 3mm of remaining tread then in reality you must deduct the 1.6mm from the 3mm so in actual fact you only have 1.4mm left before it becomes illegal and should be looking in to getting a replacement sorted.
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Next up is tyre pressure, if the pressure is too low then the tyre can wear unevenly mainly on the edges, and if over inflated they can have increased wear on the centre of the tyre. Most tyres have a maximum pressure on the side wall but please note this is not the optimum pressure for the tyre and must not be used, it is purely for safety. Most car manufacturers have the correct tyre pressures for the car on a sticker located somewhere on the car normally on the inside of the fuel flap or on the driver's doorpost, They can also be found in the driver's handbook. Most local garage workshops should also have the information too.
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On the side wall of a tyre, there are various letters, numbers and codes and they all mean something. The most important one is the size and speed rating. An example of a tyre size would be 205/55 r 16 followed by a letter
205 represents the tyre's width in millimetres.
55 denotes the aspect ratio, which is the height of the sidewall as a percentage of the tyre's width.
R signifies that the tyre has a radial construction.
16 indicates the diameter of the wheel, in inches, that the tyre fits.
The letter at the end of the tyre size indicates the speed rating, I'm not going to go in too much detail about speed ratings, only that if your speed rating is between the letters A to I (with the exception of H) then it's probably not up to the job. Any other letter should be fine unless you own a very sporty little number but it's worth getting in touch with your tyre supplier to double-check.
On a van tyre, you will also have a load rating on the side of the tyre, this indicates the amount of weight a tyre can carry and would normally be a number for example 110 would equal 1060 kg. As a customer it is something your tyre supplier should take care of, you should just make sure the load rating is the same as the old tyre.
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A few other markings on the side of a tyre include but are not always, data of manufacture this is normally set out as 4 numbers eg: 32. 23 so it would have been manufactured on the 32nd week of 2023, Treadwear is again a series of numbers with the word tread wear above, below or to the side, eg: 240. the higher the number the longer the tyre should last.
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There is also a direction of rotation on some tyres and this is normally shown with an arrow depicting the direction it must be fit. On occasion, there can also be inside and outside printed on the side wall, obviously, the inside should be on the inner wall and the outside should be displayed on the outer wall. Both the rotation and inside and outside are important and note should be taken that the tyre is fit in accordance with the side wall instructions as this is a mot fail.
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Finally, the part most tyre fitters hate. The run-flat symbol, this tells you if the tyre can be run-flat (without any air after a puncture) these tyres are normally fit to a car with no spare tyre, the idea is no spare = less weight and therefore can save fuel, also there is the added bonus of not changing the tyre at the side of the road. A few problems with this include if you have a blowout and the tyre sidewall is damaged the run-flat tyre can not be driven on as all the strength to the tyre is incorporated into the side wall of the tyre. They are more expensive and problematic to remove and fit as the side walls are very stiff and have no flex in them, although this is not a concern as a customer as you are not fitting them yourself but it can lead to damage to your wheels and this may be something to approach your tyre supplier/fitter about before the tyre change is carried out.
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Different tyre manufacturers have different codes to depict if the tyre is a run-flat or not.
ROF is used by Goodyear, Dunlop and Bridgestone.
EMT is used by Goodyear.
ZP and ZPS are used by Yokohama and Michelin.
Some but not all just have RFT printed on the sidewall and some are very helpful and have the wording RUN FLAT TYRE.
It's also worth noting that run-flat tyres and the markings on them are not a mot fail. However checking your tyre pressures and condition is advisable before taking your car for a test.
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The very last thing I would like to touch on is four-wheel alignment, tracking and wheel balancing. Four-wheel alignment is exactly what it says, your car is put on to a very sophisticated machine that takes various measurements of all four wheels (castor camber and toe) and displays these on a screen these can then be adjusted by the technician to ensure all the measurements are within the tolerance set by the manufacturer.
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Tracking is similar to four-wheel alignment but only the front wheels are adjusted and it is normally just the toe measurement that is adjusted.
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Balancing is totally different to both four-wheel alignment and tracking, although a lot of people do get confused between tracking and balancing. Balancing is where your wheel is removed from the car and put on to a balancing machine this then spins the wheel to a certain speed, a reading is taken and wheel weights are applied to specific areas of the wheel. The point of this process is to combat vibration through your steering wheel at high speed. All wheels should be balanced after new tyres have been fit.
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