Tyre Wear

When we observed in RealClassic magazine that two similar classic bikes were using their tyres very differently, and wondered what it could mean, RC readers provided all kinds of answers…

Tyred and Bemused

My Norton Commander needs a new rear tyre, which comes as a surprise. It’s many years since I wore a tyre out in about four months. It’s not even as though that particular Norton has been the mainstay Norton, either; my other regular ride still has a decent amount of groove in its Avons. Both Nortons are basically the same; the eccentric rotaries which I enjoy so much. But they have one considerable difference; one has a full fairing and hard luggage, while the other doesn’t. Their mileages this year have been similar, but the tyre wear is considerably dissimilar. Is it the weight of all that plastic? I did wonder about this, but was unconvinced. Extra weight puts more load on the rear tyre when accelerating at the same rate, and more load on the front when doing the deceleration thing, but I wouldn’t have thought it was enough to matter.

I have developed a new theory. When riding the unfaired bike I tend to avoid big fast roads like dull carriageways and monotonous motorways. The lighter machine is much more fun on the twisty stuff, where the heavy tourer reduces journey times by cruising at quasi-legal speeds on dull roads. If the theory is correct, then the wear pattern on the balding rear tyre should leave it with plenty of tread on the edges and a lack of groove in the middle. And yes; it is exactly like that. The edges of both tyres, which have ridden similar mileages, are almost identically treaded, while the centre grooves of the heavy bike are almost gone. QED?

There is another thing. When riding the faired bike on those long dull roads I find myself arriving earlier than I’d anticipated; I do in fact ride it about 10mph faster on average and cruise along with the rest of the outer lane traffic. Not so on the unfaired machine, where the battering does get tiring. I read somewhere once that wear rates rise exponentially as a function of speed. Is this true? Both front tyres are identically worn. How can that be?

Meanwhile, the tyres on Rowena’s MT350 have plenty of tread left but – judging from the skid mark on the drive – little in the way of grip. They are far from worn out. So should they be replaced?

FrankW

Sidewall Info

You are correct in assuming that tyres do have a shelf life and have a host of markings and information on the sidewall. These indicate information for load and speed ratings, tyre size and aspect ratio, rim size, etc. The part that refers to the date of manufacture, and hence its age, is the group of numbers that follow the DOT information on the tyre. The DOT refers to information initiated by the Department of Transport in North America and will consist of a collection of letters which are codes for the factory, size, brand, construction and pattern. The last four digits, often in a lozenge shaped space, indicate the week and year of manufacture.

This is very useful when making a decision as to whether to change a tyre or not especially if it has lots of tread left. Personally it would make me clench if I had to chuck away a tyre with plenty of tread but if the rubber is no longer able to grip the road then the date markings allow informed decisions to be made. If the bike is used for shows only then old tyres would be OK I guess but if you intend riding it you must decide for yourself.

In this picture you can see that the numbers 0309 appear at the end of the DOT information. This tells us that the tyre was manufactured in week 3 of 2009. (Note: prior to year 2000 the year was denoted by one figure only, this being a number 1. A triangle after the number 1 denotes the decade 1990 to 1999). The date of manufacture coding is an obligatory requirement within Europe.

Check your tyres and see what they tell you. You may find a DOT brand on the tyre without the last digits so check the other side of the tyre, the DOT info less the date is often branded on both sides, and you should find the full information. This information also applies to cars, trucks and buses so it is very useful to know especially if you buy part worn tyres for your car. I am sure there is a shelf life for tyres and a point after which they should not be fitted, I think its five years but don’t quote me. Ultra violet light gets to the rubber and makes them less able to work as designed.

Jake Fawcett

The Intricacies of Aging

You are right of course, there is an age limit. When I rode my oif T120R over from France (where I bought it) to Southampton, I came home via Vintage Tyre Services to get new tyres on. The old ones looked perfect but were new in about 1975.

I was alerted to the case of an MGB owner who bought some new old stock tyres from an autojumble. At moderate speed on the motorway one let go, the car rolled and he was killed, the passenger survived but with injuries. The police report at the inquest stated that the tyres were in excess of 20 years old. Another statement from the tyre manufacturers put the safe service life of a tyre at six years. Regular bike and car users will have worn their tyres down to the canvas by then but as the classic owner rarely gets that much use then the tyres never wear out. I’ve seen some awful examples, but what really saddens me is that owners are prepared not only to risk themselves but other road users too. This applies as much to the £100k E-type as it does to the £100 rattler. But do you know where the most neglect is? Trailers!

Tyres age in three different ways: