Tyre Punctures & Tyre Fires

December 7, 2006 at 3:05 am Leave a comment

Rarely seen in passenger tyres, but still occurring in multiwheel trucks, is a tyre fire.  Having reached ignition temperature by being run flat for a considerable distance, the flames can spread to a neighboring tyre, where they are fed by the pressurised air (oxygen) inside the tyre casing. So the safest way to reduce the flame’s intensity is to let the air out. Strangely enough, one very effective way is to get a kind policeman to shoot it. An arrow tipped spear gun, fired from a safe distance at the middle of the sidewall, will also do the trick. Best done from a distance, but make sure he’s a good shot, as you don’t want to puncture the fuel tank, do you!

Passenger tyres run flat behave differently. On the front axle, the driver knows almost immediately, because the steering is affected, becomes heavy, wants to steer to one side. On the rear, on a straight road at speed, centrifugal force allows the tyre to stay on the rim, it only being distorted where the tyre meets the road. Provided the road is straight, you can run 10 k.m. or more without knowing a rear tyre is flat. Once bends appear in the road, it’s a different story, because the handling falls away.

A very destructive crease (or knuckle) appears in the sidewall low down, which melts or destroys the casing cords at that point right around the tyre, and the whole sidewall falls out! You can end up with three rings, two of which are still firmly locked to the rim.

If you haven’t a spare wheel, or worse, only a bottle of gooey gunk, you’re stuck!

So, you find yourself stuck without a spare. What can you do?

A lot depends where you are.  Your first requirement is to make sure that the car is in a safe position. Your second port of call should be your motoring service organisation, or your new car roadside assist program, which will move you to that safe position. Be sure to explain your predicament, and if possible, the tyre size on your car. Keep in mind that some luxury off-road vehicles don’t have a spare at all, which doesn’t help motorists in your situation. Calling your service shifts the responsibility to them to get you going again. However, if the tyre size is not common, you may be stuck for days while a new tyre is located, generally through the good offices of the vehicle distributor, your motoring organisation, your insurance company, or a large tyre chain. Lots of phone calls involved in this. A temporary fix might be to try a wrecking yard for a wheel and tyre with the same wheel stud pattern, and the same overall tyre diameter, even if it is a different profile. The wheel nuts might have to be changed to match the substitute wheel. The authorities would probably frown on this, but desperate needs may need desperate measures.  Then drive slowly and carefully home, and get a new tyre fitted as soon as possible. Don’t delay or procrastinate.

If you found a temporary spare that looks a bit like a motorcycle tyre in your boot, then be aware that these are a high pressure tyre (40 p.s.i or so), and have a speed limit of 80 km/k, because purely and simply, they don’t match the other tyres on your car, so it can’t possibly handle as well.

Entry filed under: Tyre safety & maintenance. Tags: , , , .

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