Tyres – Part two
Gareth is back with his ongoing look at the challenges and opportunities represented by tyres. This month; tread
Published: 13 January, 2020
Did you manage to fit that Hayabusa motorbike engine in your smart car then? What speed did you manage to get to on your nan’s private airfield? If you haven’t got a clue what I’m dribbling on about then you obviously didn’t get your last copy of Aftermarket. Darn shame as you missed a corker.
Last time, I touched on tyres, tyre sizes, load index and speed ratings. In this issue I thought it would be only right to include tread patterns and correct fitment of said tyres. After reading this you should be able to make an educated guess about what tyre is best suited to you or indeed what is necessary for your customer’s needs and what tyres are needed in certain situations and – no, I don’t just mean if it snows then go and buy a set of winter tyres. However, I will keep it plain and simple with a hint of humour, just like myself.
Patterns
There are four main tread patterns that I’d like to explain to you. The first is the symmetrical kind. These have no sidewall markings regarding fitment and this, as you may have guessed is the same pattern all over, nothing fancy here! This one is a plain and simple get you to work and back type of tyre. It will hold the road, just as you’d expect, it will dissipate water as expected too, an all-rounder for the better months shall we say. These can be fitted on the wheel anyway you please. The second is an asymmetric pattern. Half the tread blocks for road holding and the rest are for getting rid of all that unwanted water, so this is a remarkable tread pattern engineered for the wet weather but still has very good grip for those hot summers driving through the twisties. The sidewall markings on these tyres are ‘inner’ and ‘outer' or ‘inside’ and ‘outside’. They are designed to be fitted only one way.
The third in the list is a rotational tyre. This is clearly visible by the sidewall markings that have an arrow stating a certain way the tyre must be fitted. Please be careful and remember it is a MOT failure if a tyre Is not fitted in accordance with the sidewall instructions. This type of tyre will also have a tread pattern that looks almost like a continuous arrow pointing in one direction. This tyre is exceptionally good at dissipating water, as you drive through the wet roads water is drained away from the centre of the tread and ejected outwards to prevent aquaplaning.
Winter
“But what about the fourth one?“ I hear you cry. Well, this one is a winter tread pattern, recognisable by the unique three peaks’ symbol. These tyres will more than likely always be rotational with sidewall markings displayed with an arrow. They are characterised by the little wiggly lines in the tread. The real name for these is sipes, and these are designed in such a way that they increase the tyres surface area on the road and this in turn creates more traction.
Winter tyres are engineered with more natural rubber within their compound. They actually stay more supple for longer in lower temperatures. This helps with traction in ice or snowy conditions. However, a winter tyre will only outperform a summer tyre in temperatures of 7°C or lower. Now, there are no laws in our country to say we need to fit winter tyres in the colder months, yet. That said, I can see it on the cards in the future to prevent more accidents. Also, a few customers have seemed to feel a little uneasy when it comes to their insurance and winter tyres. If you’re unsure, just check with your insurance company, you will find that more and more insurance companies find them to be a valuable asset to your car in the colder months and will probably welcome such a safety conscious driver into their realm.
- DVSA urges motorists to make it SAFE
With schools now open again as lockdown is gradually eased, the DVSA has launched a campaign to urge motorists to make sure they are SAFE in their vehicle by doing four basic pre-drive checks:
• Service or health check if needed
• Air in tyres
• Fill up screenwash
• Examine lights and tyre tread
- The shoe’s on the other foot
After my recent articles on tyres and TPMS systems, this month’s topic is wheel alignment, and the massive impact excessive toe-in or toe-out could have come MOT time.
A lot of us can spot alignment issues a mile off. I would worry if after 17 years in the trade, that a technician such as myself couldn’t tell the difference between a tyre that had been toeing-in and a tyre that had been toeing-out most of its life. If you look at a front tyre on a car and only the outer edge is bald (and the tyre has plenty of pressure in) then you walk around to the other side and discover the same issue with that tyre, it would be plain enough to see that the wheel geometry isn’t correct.
Compensate
A car with tyres like this and wheel alignment so far out must handle like it has a mind of its own - like Herbie the Beetle. However, people get used to a car in this state and will compensate to a surprising extent. When we take the car for a test drive, we may come back to the customer and say things like; “there maybe an issue with the tracking” or “the car is pulling rather a lot to one side.”
The customer then looks at us in amazement as if we are saying things just get their hard-earned money from them. We then offer a FREE wheel alignment check, and show them the virtual view on the screen. By Jove, the customer can then see with their own eyes exactly why their tyres have worn the way they have.
I first mentioned toe in and toe out. This is the way the wheels ‘point’ in relation to the forward motion of the car. Look down at your feet. Now keep your heels in position, and point your toes inwards so they point towards each other. If you try walking like this you will wear off the outside of your shoes first.
Do the same again with your heels, but point your toes outwards. This is toe-out and walking with excessive toe-out will wear the inner part of your nice new shoes and that’s the last thing you want. I’m sure you’d like it if your shoes wear evenly. The majority of track cars/race cars will be running with toe-out and negative camber. This will be topic of conversation next time as wheel geometry is a large subject.
Minutes and degrees
I also mentioned minutes and degrees earlier too. A while ago I tried explaining this to another tech and he struggled to grasp the concept of the theory behind alignment/ geometry, but he knew how to set the wheel alignment up on 99% of cars.
Getting your head around the actual maths is a different story. Think of it as a clock; there are 60 seconds in one minute; there are 60 minutes in one degree; and there are 360 degrees in a full turn. Our alignment set-up only works in minutes and degrees as it is really sensitive so no need for seconds-it would be worthless. The wind could blow and move the car slightly and that’s enough to make you panic and pick up your spanners again.
Once the alignment is set-up correctly and you’re happy with the end result, your customer will in turn be very happy. Remember, in the end they are the ones paying our wages, not just your boss. It does help if you have a happy boss too of course.
- MOT decision leaves 1 in 10 at ‘dangerous defects’ risk
The government is being accused of taking “a serious safety risk” by allowing millions of motorists to keep their cars on the road until January 2021 without a current MOT.
- Computer says “oh no” -Online car maintenance queries up 87% as lockdown eases
Garages may be able to pinpoint the kind of post-lockdown work coming through the door, with new research showing that online searches for how to tackle issues with car brakes, batteries and tyres have grown substantially over the last few months
- Tread a mile in your shoes?
We have arrived at the fourth final part on the subject of tyres. This month, the focus is on the MOT, regarding tyres and tread depths. I’m hoping the manual hasn’t changed by the time this is published, (the MOT manual is, after all, changing all the time). As I write this, it states that the legal limit for a passenger car with no more than eight seats excluding the drivers seat used on or after 3 January 1933 is 1.6mm around the whole circumference of the tyre across the central three-quarters of the tread area.
Therefore, if a car was to come to me for a MOT with one or more of its tyres measuring 1.6mm, I would be forced to pass the car with just advisories on the tyres in question. This is a shame as you wouldn’t want to send a car out of your depot with a tyre on the legal limit and 100% worn, would you? The owner could quite easily travel 100 miles or so in the next few hours and their tyres may very well be then deemed illegal If stopped by the police.
“But officer! My car passed its MOT earlier today" may well be their perfidious reply. I suppose all that matters is how the car was presented at the time of test. From a tester’s point of view though, you cannot try and pre-empt what may or may not happen after the test. The car maybe stored in a garage for months at a time for all we know. It may only do 200 miles a year. Regardless of what we think may happen, by following the guidelines and rules set out in the manual you can’t go wrong. As long as the customer in question is made fully aware of the situation and you’ve made the best judgement call you can, then you have done your part and can you sleep at night.
Measurements
Here are some measurements to get your head around regarding tread wear: 8mm-0% worn; 7mm-16% worn; 6mm-31% worn; 5mm-47% worn; 4mm-63% worn; 3mm- 78% worn; 2mm-94% worn. Obviously 1.6mm would be 100% worn. However, as I mentioned, it still passes an MOT as an advisory. A tyre on 2mm also passes but certainly with advisory notice. Me, I give an advisory notice for a 3mm tyre. To me when something is 78% worn, it’s almost had it. If you were to wear a pair of shoes that were 78% worn, I would think that somewhere along the line someone may advise you to replace them too, as they’d look pretty shabby.
The garage I work in receives tyre bookings all the time from cars that have been for an MOT elsewhere, a lot of the time, at a main dealer. For some reason they have advised tyres on 4-5mm tread readings. I’m not sure why, as a 4mm tyre still has some life left in it, and a 5mm tyre certainly shouldn’t be classed as worn. Maybe the testers are overzealous. They should take their tread depth gauge and make sure its calibrated. There was me thinking I was being cautious advising on 3mm! I like to think I’m firm but fair when it comes to testing. I’d like to think others are too. Lastly, don’t forget, the next time you’re out walking in bad conditions and keep falling over, check the tread depth on your shoes, it maybe time to replace them.
