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UNMUFFLED: Decoding sidewalls

Published:Saturday | January 16, 2010 | 12:00 AM

Hello Mario,

I recently acquired a 2005 Toyota Duet. My car did not come with a user manual, and frequent visits to the 'dealer' did not result in my getting one. I gather that tyre pressures are important to maintain for good fuel economy and extended tyre life. But I don't have access to the information. I also need to know what those markings on the tyre mean.

-Cheryl, St Mary

Hello Cheryl,

Tyre pressure management is important to how your automobile feels on the road and is a definite factor when a driver needs to maximise tyre life and efficiency (mileage). Tyre pressure controls the size and shape of the tyre's contact patch, or footprint, which in turn affects rolling resistance. Soft tyres are harder to roll, which eats gas mileage. Tyres with insufficient pressure also get hot - a condition that if persisted in will cause the tyre to degrade rather quickly.

Unfortunately, although it is so easy to check your tyres, it is easy to put off this vital chore for another time! A quick walk around your car before you start off in the morning - or before any drive - is a good habit to get into. A tyre with little or no air is immediately obvious. Not so obvious is a Radial tyre that is underinflated. So a quick press on the sidewall will tell if the tyre needs air.

The problem of the missing manuals is all too common - especially if your car is a 'used deportee'. However there is a used-car dealer with a heart - KACS, a used car outfit owned by Jamaica Used Car Dealer Association past president Kenneth Shaw, located at 37 Dunrobin Ave, Kgn 10. It has most of the 'deportee' manuals translated and for sale. They do not have the manual for every single 'deportee', but they do have access to most. If you can wait, they can probably order it. Cost is JA$3,000. According to the manual for your car, your front tyres should be inflated to 26 pound per square inch (psi), and your rear tyres to 28 psi. If your car is loaded to its full complement, then three psi should be added to the front figure. The rear remains the same.

tyre pressure

The correct procedure, after setting the correct pressure on the tyre pump, and removing the tyre valve cap is to use your car key or similar blunt instrument to depress the valve plunger inside the valve. This will release air. Count to eight when doing this, then release the plunger and pump the tyre until the inflator stops ringing. When this is done it allows all tyres pumped at that pressure to equalise. Remember, your car's pressure settings are different front to rear.

Tyre markings can be cryptic, and numerous. Usually the most prominent one bears the tyre manufacturer and model of the tyre. In our example, the tyre's manufacturer is TRIANGLE - its batch code is 07/06 and the model is TALON SPORT . The tyre is designated 205/50/R15 86H, with a wear factor of 400, traction and temperature indicators of A and A respectively. What do these markings mean?

The most important markings are the batch code, which gives the date of manufacture and the tyre designator 205/50/R15 86H. The first three digits in the designator are the width of the tyre in millimetres; the second two, the aspect ratio of the tyre, and the last three digits include a letter first (in this case, R, which is the construction style - Radial - followed by the wheel diameter the tyre is supposed to fit. Aspect ratio is the width of the tyre divided by the width of the sidewall. The final three characters - the 86H means that the tyre has a load rating of 86 - see table (1) - and the speed rating is H (See table (2). The batch code translates to the seventh month of the year 2006. Tyres should be rejected at point of sale if the tyre is older than five years as the robber tends to degrade over time.

On www.modified.com, an automotive enthusiast website, Dan Barnes wrote: 'Treadwear is determined on a controlled government test course. It is a comparative scale, meaning that a tire graded 200 would wear 50 per cent better than a tire graded 150. Keep in mind, however, that in the real world, driving habits, road conditions, climate and a host of other factors can make a big difference in what the actual tread wear will be. (Usually the greater this index, the less traction is available from the tyre, and the tyre lasts longer - and vice versa.)

'Traction grades (AA is best, then A, B and C) represent how well a car is able to stop on wet pavement under controlled conditions. The government tests on both concrete and asphalt, since both have different grip qualities. Note that the government test has only to do with wet braking, not with cornering, acceleration, hydroplaning or any other traction characteristics.'

Finally, there is the temperature rating, which measures how well the tyre resists heat generation and how well it dissipates heat under controlled laboratory tests. Sustained high temperatures can reduce tyre life because of the degeneration of materials in the tyre. Grade C means that the tyre simply conforms to the safety standard set forth by the government. Grades of B and A are higher levels of performance beyond the minimum required. These tests are done on a tyre that is properly inflated and loaded properly. Excessive speed, under-inflation or other tire abuse can cause any tyre to fail.