Many of us take tyres for granted until it time to replace them. No-one likes to spend too much so the budget range is popular and this is especially true for those clients that have had to exchange what they thought were perfectly good ones when they failed an ITV inspection. Well tyres are black, made of rubber and have grooves in them wherever you are in the world, so why do some British and Irish tyres not pass the test?
Vehicle and tyre makers set the specification for every vehicle on the road based around what the vehicle is designed to do such as urban driving or negotiating rough terrain on 4X4’s. Also taken into account is the weight of the car and its performance. Tyres are categorised by wheel size, width, depth, weight and speed capacities. This is all shown on the side of the tyre such as 205/ 65/R16/ 95 W where 205 is the width, 95 the height or depth, 16 the diameter of the wheel, 95 the weight code and W the speed code.
So a car with 16 inch wheels could have virtually any tyre with such an internal diameter fitted to it, but these may not be the correct tyre that the manufacturer of the car has specified and this is where the problems begin. If any of the characteristics are incorrect for the car an ITV failure may result. Most vehicles that I see have the correct tyres, occasionally they will have the incorrect width or depth, but the most common cause of failure is because the speed and weight ratings are not suitable.
This is frustrating for the owner as the difference between what has been fitted may be the difference between the manufacturer stating that the tyres allow the car to be driven at 270 KMH (W rating) but the tyres fitted have a maximum speed rating of 240 KMH (V rating). Now I haven’t come across anyone who habitually drives at more than twice the permitted speed, so why these tyres will be deemed unsuitable is as mystifying as to why the makers set the standard so high in the first place, nevertheless it is cause for ITV failure as the fitted tyres are not what was specified!
Normally cars from the continent meet the required spec’s, but cars from the UK and Ireland may not; this is probably because common sense is applied when considering the speed ratings rather than slavish adherence to what seems over specification, but I am standing to be corrected by a rubber boffin.
Back when tyres had inner tubes a mix of radial and cross-ply was not permitted and in a similar vein tyres in Spain must be identical on the same axle, I guess to ensure consistent grip especially in wet weather when the grooves disperse the water. Ironic that this seems more important to the Spanish when the rainfall back home is a tad more frequent.
Here’s an odd tyre story. My ageing Merc’ has cruise control which is a godsend when coasting the motorways. It packed up and Joaquin my local mechanic was baffled, so he replaced a couple of the more obvious possible culprits from the local car graveyard which is staffed by folks from my village so “mate rates” apply. Still no joy so Joaquin took the car off to a main dealer where a buddy of his happens to be in charge of the service department, talk
about “it’s not what but who you know”! We were both bemused to be told that it is because the incorrect tyres had been fitted and were 5mm too shallow- yeah right.
Last week I replaced all 4 tyres ensuring that they were as prescribed. Ah joy, I am back to cruising foot-free. Goes to show how important the correct tyres, depth tread (minimum 1.6mm) and correct pressures are