Tyre Tread Wear
TYRES WEAR OUT. “Isn’t that great!” say the tyre dealers. ”Need some new tyres already, and gee, do they cost a lot”, says the motorist. Of course the tyre companies do make a tyre that never wears out. It’s called the “spare wheel” (Joke.)
Tyres wear out because they grip the road, by developing friction. Friction is a study in itself, but without it, you would get nowhere- no acceleration, no braking, no steering. This all occurs where the tyre meets the road. The less movement of the rubber under the footprint, the less the tyre wears- called a steel radial tyre. The less heavy braking, or fast cornering you do, the less the tyre wears. The reason- in order to develop friction, the tyre must slip to develop grip. In order to corner, the tyre surface must distort at the contact patch by slipping. This is happening all the time. When your tyres chirp as you accelerate, or squeal as you brake violently, you are only hearing what goes on all the time.
The A.B.S. braking systems on modern cars pick the point of maximum grip, which is just before the tyre starts to skid, to optimise their brake performance. A.B.S. systems are calibrated to pick this point of maximum grip. They “let go” just before the tyre starts to slide, pulsing far more rapidly, on and off, than even a skilled motorist could do, to maintain maximum braking power. So realise that it is not the brakes that stop the car, it’s the tyre grip. If there is no grip available, like on ice, then you have trouble going anywhere at all!
Due to excessive movement of the tread rubber, the bias ply tyre, which was the normal tyre 30 years ago, reached its engineering limit. It couldn’t go much faster, got too hot, wore fast, and distorted at high speed. Michelin invented and marketed the steel belt radial in 1948, patented its method of construction, and the world’s tyre engineers had to wait till the patents expired. An interim radial tyre, called the Pirelli Cinturato, was developed in this period, which didn’t infringe the patents. At one stage, 44 tyre companies around the world were making tyres of that design.
You were doing well to get 25000 kilometres out of a set of bias ply tyres, and with steel belt radials, this has doubled. Putting steel belts on a radial casing allowed the tyre to develop it’s cornering power at a lower slip angle, so it didn’t wear as fast. Incidentally did you know that hooning around roundabouts can wear your tyres up to eight times faster than straight ahead running?
However, the first radials were down on wet road holding, being skinny by today’s standards. In other words good tread wear and good grip proved dificult to combine in the one tyre. It still is.