Thursday January 16 2014

What is wrong with my low profile tyres?

By Paul Kaganzi

I recently fitted low profile tyres to my Toyota Mark II but my ride has become more uncomfortable as I feel the potholes more. Is there a link between the poor suspension performance and the low profiles?

The noise you describe under the dashboard of your Toyota may be generated by a faulty air vent flap.Low profile tyres are usually wider with thinner side walls. Many newer vehicles today come with low profile tyres. These kind of tyres are popular because they accommodate better-looking and stylish alloy wheels.

Low profile tyres improve road grip to provide better car handling characteristics as well as allow sufficient space to fit bigger size brake calipers and pads. These features are important for faster high performance vehicles. However, low profile tyres by nature of their thin walls tend to transfer uneven road imperfections or stress faster to the different suspension components such as shock absorbers, ball joints and rubber bushes. Low profile tyres tend to get damaged much easier than the normal profile tyres because the side walls tear easily or deflate more rapidly when you hit sharp potholes.

Manufacturers of high performance or faster vehicles try to
mitigate these problems by fitting specially tuned electronic or pressurised suspension kits to improve damping of road shocks. Newer high performance cars also use reinforced tyre side walls that sometimes ‘run flat’ or allow you to drive on a punctured or damaged tyre for a certain distance at limited speeds up to 80 kph. If you must have low profile tyres on your Mark II you may consider replacing
your shock absorbers for more heavy duty ones.

Recently, my Toyota RAV4 made in 2003 started misfiring and releasing a very bad smell in the exhaust. After extensive tests my mechanic concluded that the exhaust catalytic converter was damaged. The mechanic dismantled the exhaust pipe and showed me the damaged catalytic converter. Now I have to buy a very expensive section of the exhaust pipe with the new catalytic converter. I am not sure why this catalytic converter was damaged and whether the new one will not get damaged too. Can you throw some light on what could have damaged my catalytic converter?
Richard Segawa.

The catalytic converter (CAT) is an oval or cylindrical device designed to break down pollutants in the exhaust smoke emitted from internal combustion engines. It is oval or cylindrical and fitted in the front part of the exhaust about a metre after the engine manifolds. Most post 2000 year motor vehicles sold in modern countries with strict environmental legislation have their exhaust pipes fitted with the CAT. When we buy these used vehicles they come fitted with these gadgets.

CATs are damaged by a couple of factors, usually avoidable if the driver or vehicle owner takes the necessary precautions. Damage usually involves overheating and melting of the CAT ceramic material which blocks the exhaust pipe and prevents free flow of exhaust from the vehicle engine. The outcome affects engine performance and leads to serious damage.

There are several causes of CAT failure all of which are maintenance related. The use of leaded fuel as opposed to the legitimate unleaded fuel releases harmful excess levels of lead which damage the CAT. Excess or unburnt fuel overheating after entering the exhaust is a major factor. An engine that is well maintained operates at peak condition by burning the fuel efficiently.

A poorly serviced vehicle with incorrect ignition timing, damaged piston rings leading to engine oil intrusion in the
combustion chamber, damaged ignition

wires or coils, faulty sensors which mislead the engine computer to deliver excess fuel, dirty air cleaner elements, damaged spark plugs, clogged fuel injectors or dirty engine valves coated by excess carbon deposits caused by after effects of poor burning (petrol and diesel engines) will lead to inefficient engine combustion cycles which do not burn all the delivered fuel and instead release it through the exhaust chamber. This excess fuel will cause more burning in the exhaust which overheats the catalytic converter beyond temperatures it is built to withstand.

This will melt the ceramic CAT. You can avoid this situation by regularly servicing your engine and replacing damaged components with genuine parts. Use of additivated (with additives) Shell Fuel Save unleaded (petrol) or diesel will keep your engine valves and injectors clean to ensure more efficient fuel burning which prevents CAT damage. Besides, Shell fuel Save’s lubricating formula improves upper engine cylinder piston movement to give you better instantaneous ignition and more kilometres covered per litre (better fuel economy).

Thank you for the information you usually put in My Car magazine concerning car troubles. I have a NOAH car of 1997 series, which I bought in December 2012. Whenever I am driving on a rough road, the body keeps knocking on the frame hence producing sound like that of a drum. What could be the cause of this, and how can it be solved?

Your description of the noise made by this Toyota Noah is not specific. Any kind of noise in your car suggests that something is damaged. However there is a need to determine whether it is from the steering system, axle suspension bushes or the body.
When a vehicle is moving over uneven or rough terrain the following components will work harder: steering linkages (tie rod ends and rack ends), axle suspension (shock absorbers and bushes, stabilizer bar and link bars) and body suspension (engine and gearbox mountings).
You will need an experienced mechanic to test drive this car and identify the source of the noise you are hearing before dismantling the car to fix it.