JIS News

Motorists are being cautioned not to mix different types of tyres on their vehicles, as this has been found to be a contributing factor to many of the accidents on the roads.
Manager of Advanced Insurance Adjusters Limited, K. Michael Webster, speaking at the Traffic Authority’s seminar for certifying officers held recently in Ocho Rios, St. Ann, said that after years of investigating accidents, he has found that mismatched tyres ranks high on the list of vehicular problems that have caused accidents.
Mr. Webster, who conducts car inspections for the insurance industry, said that if he detects defective tyres during his inspections, then that policy is not recommended for renewal.
While the casing of tyres may look the same to the untrained eye, they vary in construction methods and the material used. There are three tyre types: radial ply, bias ply and bias-belted. Mr. Webster advised strongly against mixing radial tyres with belted tyres.
“Never mix them, they should never be mixed,” he cautioned, noting that such a practice can and has caused “vehicle directional instability.” The configuration of the chords on radial tyres, he explained, enables the walls to work independently of the bias-belted ones, particularly on cars.
He pinpointed taxi operators as some of the main culprits in this practice, noting that they are often unaware of the potential implications of such action.
According to Mr. Webster, in older vehicle designs, the mixing of tyres can interfere with the mileage reading, as the speedometer is usually calibrated for a particular tyre size. “When you mix them, the speedometer no longer calibrates properly and will never tell you what the true mileage is, as it will not read correctly,” he pointed out.
Tyre mixing also poses a problem for newer vehicle models, Mr. Webster said, explaining that because most newer vehicles are computerised and equipped with an Anti-locking Braking System (ABS), “if you have mixing of tyres, especially sizes, and you get a rotation on one wheel, which is spinning faster than the other wheel, you are totally confusing the computer,” he said. He said that this can also affect the locking system.
Radial tyres have ply cords, which run across the centre line of the tread and around the tyre. The two sets of belts are at right angles to each other. Most belts are made of steel wire, but others are made of polyester or other substances.
Bias ply tyres, on the other hand, are usually made with nylon and the cord strips are arranged diagonally, that is at a bias, to the centre line of the tread. Alternate plies are reversed to cross at a 30 or 40 degree angle. Bias belted tyres are similar to bias ply, but have additional layers, cords or ‘belts’ circling the tyre beneath the tread.

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