This is the first Q&A ses­sion in our three­part se­ries that “torques” about tyres.

Torque (Singapore) - - FEATURE -

When is it a good time to change tyres – ev­ery three years, or af­ter clock­ing 30,000 kilo­me­tres? The best gauge would be the wear indicator, a raised nub found be­tween the main grooves of your tyres. Once the tyre sur­face is level with the indicator, it is time for a change. It does not mat­ter when this hap­pens or af­ter how many kilo­me­tres of driv­ing.

But if your car has clocked 30,000 kilo­me­tres and the tyres have not reached the wear indicator, you should still con­sider chang­ing them, be­cause the rub­ber may have hard­ened and grip may be com­pro­mised. Do not scrimp on tyres, be­cause you never know when you will need max­i­mum per­for­mance from them. If I want to change only two tyres and keep the other two, should I install the new ones in the front or rear? We can imag­ine only a cou­ple of rea­sons why you would end up with a pair of half-worn tyres and an­other pair of com­pletely worn ones.

In all like­li­hood, you did not bother to ro­tate them as in­structed in the car man­ual. And now you want to com­pound the prob­lem by keeping the old, half­worn ones. The other rea­son might be that you man­aged to punc­ture two tyres at the same time, which is quite a rare thing to hap­pen.

If you ever have to re­place just a pair, the rule of thumb is to install the new tyres at the rear, be­cause los­ing grip at the rear is dan­ger­ous for the av­er­age driver.

But if you can, re­place the whole set and re­mem­ber to ro­tate the tyres reg­u­larly. Just four months af­ter I re­placed all four tyres on my car, I started to feel some vi­bra­tion from the rear. When I checked, I no­ticed one of the rear tyres had an un­usual wear pat­tern. It was not worn on one side, as would hap­pen


if the wheel was mis­aligned. In­stead, the tyre had ir­reg­u­lar bumps on its tread all along the cir­cum­fer­ence.

I took it back to the tyre shop, as­sum­ing it was de­fec­tive. How­ever, the shop in­sisted the wear was due to a faulty sus­pen­sion. The other three tyres were fine. What could be the cause? The wear pat­tern you de­scribe is a clear in­di­ca­tion of a worn damper.

While the spring in a sus­pen­sion ab­sorbs the shock from road ir­reg­u­lar­i­ties, it is the damper (com­monly but er­ro­neously re­ferred to as the “shock ab­sorber” or “shocks”) that checks ex­ces­sive body move­ment. When a sus­pen­sion’s dampers are worn, a road hump, for in­stance, would cause the car’s body to bounce on the springs over sev­eral cy­cles. In fact, the os­cil­la­tions may con­tinue if there are fur­ther road ir­reg­u­lar­i­ties. Dampers “dampen” the ex­ces­sive bounce.

In your car, the tyre in ques­tion was forced to con­tin­u­ously bounce on the road sur­face, caus­ing the in­ter­mit­tent cir­cum­fer­en­tial wear.

You should re­place the tyre and both of your car’s rear dampers as soon as pos­si­ble.

There is a lot rid­ing on the tyres of a car, such as safety, com­fort and con­trol, so do re­place them when­ever nec­es­sary.

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