When should you change to new tires?

One important and frequently overlooked component of your car is literally where the rubber meets the road. I'm talking about your tires. All four of them (five if you count the spare in the boot, two if you ride a motorcycle, or eighteen if you're like Optimus Prime).

Getting a grip on the importance of tires....

Brakes stop wheels from spinning. It's the tires that stop the car from moving. If your tires can't grip the road, your car will continue to move long after your wheels have stopped turning.

When you turn the steering wheel, the wheels turn accordingly, but it's your tires that make your car move in the direction of the front wheels. If your tires lost their grip on the road, your car will continue to move forward instead of in the direction of the wheels (this is called under-steering).

When you accelerate from a stationary position, the spinning motion of the wheels is translated into forward acceleration by the tires. If your tires did not bite into the road, you will still be here long after others have gone....

The tires on the cars that you and I drive have grooves or treads. These are not for decorative purposes but have several functions, one of which is to remove water from under the tire when travelling on a wet road. If the tire is unable to do this, a layer of water that forms between the tire and the road will result in loss of grip and control (this effect is known as hydroplaning) in the same manner that a water skier glides over wafer.

Formula 1 cars have tires with practically no treads, called "slicks" for ultimate grip on dry surfaces. Of course, they are not meant for driving on wet roads, so when it starts to pour, the drivers have to very cautious to avoid spinning out of control.

How deep is your groove?

"Wear Bars"

Still within spec (>1.6mm)

Over time, due to wear and tear, the treads in your tires will grow shallower. Their ability to evacuate water will become diminished up to a point where they have to be replaced for safety reasons.

In the US / UK, regulatory requirements are for tire grooves to have a minimum of 1.6mm. I'm not aware of any such regulation here in Malaysia, yet. Then again, the laws here are still catching up with the rest of the world (rear-seat belts only became mandatory fairly recently) and we're still using only Euro 2M grade fuel.

Back to the groove, so, how does one measure tread depth? One way is to use a specialised measuring tool or gauge, which is possibly only available at the tire shops. No, your standard ruler is not accurate enough to measure 1.6mm.

Another method that seems to be quite famous is to use a coin, and make some visual reference, example, "using a US penny, as long as any part of Lincoln's head is obscured, the tread is deep enough". Trouble with this method is the non-standardization of coins, and parallax error (where the position of the observer affects the outcome of the measurement).

Fortunately, tire manufacturers nowadays are incorporating "wear bars" into their tires to clearly indicate when the groove depth is no longer safe.

Of course, when checking for tire wear and tear, don't always assume that tire wear out evenly. Tires that are over-inflated will wear out faster in the center, while tires that are under-inflated will wear out faster at the sides. Keep tires inflated as recommended by the vehicle manufacturer.

I do not have any experience with filling tires using Nitrogen (which you have to pay for at the tire shop), so I can neither confirm nor deny the claimed benefits associated Nitrogen-filled tires. Anyone out there have any stories to share?

Of course, if you use your car under "extraordinary" circumstances (drifting or on track), you may have uneven wear on one portion of your tire. So, when checking the condition of your tires, do rotate and look all around them.

Though different tires are made with dissimilar compound composition according to their individual manufacturer's processes, in general, high-performance tires tend to be softer. This is what makes them so "sticky" with superior road-holding. Unfortunately, as a result, they tend to wear out faster. My current tires, Goodyear Eagle F1 Asymmetric, are just over 2 years old, but are quite worn out already (of course, I have brought them onto the tarmac of the Sepang F1 circuit twice, so it's somewhat expected!).

Happy Birthday, Tires!

3+ years old. Still usable for another year....

5 years old. Times up!!!

Speaking of age, do you know how old your tires are? No, the clock does not start ticking only when you buy them from the tire shop, but as soon as they roll off the assembly line. Tire manufacturers indicate the tires manufacturing date on the sidewalls, in the form of a 4 digit date code. The first 2 digits indicates the work week, while the next 2 digits indicate the year.

In general, you should use tires which are more than 5 years old, as the material becomes hardened and brittle over time. An old tire has an increased risk of blow-out, especially when travelling at high-speeds / extreme temperatures.

Not many people seem aware of the tire manufacturing date code, so the next time you change your tires, do make it a point to confirm the date code of your "new" tires with the dealer. Don't accept a tire that is already above 3 years old, no matter how cheap it is. Safety comes first!

Also, take note of this when purchasing 2nd hand tires. Yes, sales like these do take place from time to time, especially on web forums. Even if the tires are minimally worn out (you remembered about checking the groove depth, right?), the tires might already be close to their "expiry date"....

Double or Nothing

When changing tires, ideally, changes should be made in pairs, unless the other tire is relatively new with deep treads too. Using a new tire on one side of the car, paired to an older worn out tire on the other side of the car would compromise the handling characteristics and result in a less stable ride. And since the new tire now has a more recent manufacturing date, you will end up having to replace the other tire sooner (ending up with the same problem of mismatched tires).

Should new tires go in the front or in the rear? Contrary to intuition and common believe, new tires should always go to the REAR. Why?

If the front tires lose their grip, the car will have a tendency to carry on moving forward. This is known as under-steer. While not so good on the racetrack, for normal drivers, this is kind of behaviour is predictable and safe, as it's easy to control.

If the rear tires lose their grip, the back of the car will have a tendency to swing around (over-steer). If one has no experience, this can easily develop into an out-of-control spin.

Therefore, new tires with their better grip, should go to the rear, for safety reasons!

A, B, C (Alignment, Balancing, Crossing)

In order to keep tires performing optimally and prolong their useful life (through minimizing wear and tear), do consider to get the following done at regular intervals (every 10,000km):-

• Alignment. Front and rear pairs of tires should be parallel and pointed in the same direction. If the are not, the will be increases resistance to forward motion (imagine a skier slowing down by turning both skis inwards), which results in higher wear and tear. While doing alignment, they will usually adjust the camber angle too. Ideally, the tire should have a slight negative camber (good for cornering), but too much of it would result in uneven wear at the edge of the tire.

• Balancing. Each tire in not perfectly symmetrical along the axis. These geometric imperfections cause vibration when the wheel is turning, effect amplified at high speeds. Placing counterweights at specific points on the rims during balancing serve to ideally eliminate these vibrations which can only be felt at high speeds. Nonetheless if not corrected will result in an unstable ride, with increased tire wear.

• Crossing or rotation of tires. In general, the front tires wear out faster than the rear ones, more so in a front-wheel driven car, because the front wheels have to steer the car as well as move it. Crossing or swapping tire positions ensures that all tires wear out evenly. The usual pattern for crossing tires is to swap the front and rear tires on the same side. Since some tires actually have a rotation direction and can be mounted wrongly if swapped to the other side of the car. Look on the tire for "ROTATION==>" and "SIDE FACING OUTWARDS" indications. Some cars have different front and rear tire sizes. In this case, with directional tires, no rotation is possible.

Some of us may spend just 30 minutes in our cars daily (work is just a short drive away, but too far to cycle or walk). Others may spend long hours at the wheel. Regardless, it's important to be aware of the condition and age our our tires, as it does not pay to skimp on this very important component of our car.

When the time comes, don't be a cheap-skate - change it!!!