Automtive maintainence -- Tyres

Tires are the number one aspect of car maintainence. They form the single contact of the car with the road. You can upgrade your brake lines, brake fluid, brake rotors, calipers, pads and discs. You can bleed and bed the brake system. You can stiffen your springs and dampers, lower the car's ride height, change your wheel adjustment and improve the steering mechanism, install stiffer anti-roll bars and brace the chassis. You can turbocharge the engine and swap the motor oil and change for lighter rims and more aerodynamic downforce -- but all of these combined will not be as good as a nice tire. Because the tire is the only contact with the road. If you cannot put all this extra performance down through the tire and against the road -- it is insignificant.

Understand, brakes do not slow down the car or stop it. They slow down the rotation of the tire, and the tire slows down the car. The same goes for acceleration and steering and to a certain degree -- for dampening. Hence, driving on bad tires is like driving with a faulty brake system. In fact, modern brake systems have turned so reliable that they never fail completly, so you always have at least some precent of pressure that can still be sufficient to get home. Tires, on the other hand, wear quickely and can give you the same result you might attribute to a failure of the braking system.

The problem is that the tire's contact patch which is pressed against the road is quite little, quite like a man's footprint. See for yourself: Take two pieces of paper and put them in front and behind a tire. Try and get them closer to one another by sliding them under the tire. At a certain point, the paper sheets will meet resistance untill they could no longer be pressed under the tire. The gap left between them -- is the area in contact with the road. This little patch of rubber, is even smaller because road tires (and most tires used in racing street cars in circuits) have a tread that means that some of the rubber in the area of the patch is not on the ground at all. 

So, this little patch, made of nothing but rubber, has to accelerate us (and keep us in a static speed when cruising in highways), slow us down and stop us, turn us aside and keep the car is the requested direction while resisting the side force, dampen bumps and carry the weight of the car and it's passengers/luggage, sustain pressure, physical forces, bumps and heat, divert water, dirt, snow and other things from the way, give feedback to the driver, etc...That's a lot of effort in a day! For instance, on the wet, the tread of the tire has to clear significant amounts of water which, in highway speeds, can be more than one gallon per second!

I have seen cars that stopped significantly further away in emergency braking tests, spun while braking and/or cornering, were not responsive to driver's inputs, very uncomfortable to drive, and produced bad tire and gas milleage -- all due to bad tires in particular. Tires are involved in more car crashes than any other part of the car -- it's not a stuck gas pedal or faulty brakes that could kill you, it's worn tires! Whether they explode, peel off or simply not stop you fast enough or get you into a slide, tires equall safety and bad tires make the car work against the driver.

Tire Choice

Tire maintainence begins with the choice of the tire. There are differences in qualities of tires. For road drivers, the basic parameter is the manufacturer: It should simply be a tire that is made by a known Manufacturer. Here are some examples: GT-Radial, Continental, Bridgestone, BF-Goodrich, GoodYear, Pirelli, Michelin, Falcen, Toyo, Kumho, Yokohoma, Dunlop, Maxis, and others.

Other aspects of tire choice involve the tire rating and type: Tire rating, like all the data regarding a certain tire, are printed on the sidewall of the tire. They rate Temperature, Traction and Treadwear. Each of them is rated between A (or AA) and C. Treadwear is rated in figures. You should go for anything above C. The "Traction" rating in particular, relates to how well the tire stops on the wet -- which might not offer a good indication for how good it is on the dry, so a tire that has AA traction, might be just as good as one with A or even B -- on the dry. Treadwear states how quickely the tire is being worn. Basically, softer rubber wears out faster, but gives more grip. Therefore, drivers who do not make long trips, can go for tires with relativelly soft rubber that give more grip but less treadwear. Treadwear should never go below 200.

The type of the tire relates to it's function: It can be an all-season tire, a winter tire, a road tire with M + S (mud and snow) rating, snow tire,  ice tire and racing tire. Do not drive in the summer with winter/snow/ice/mud and snow tires and do not drive in snow/ice with allseason/race tires. Do not drive roadcars with race tires. Generally look for anything written on the tire with the word "Performance" on it -- these are normally very good tires. In freezing conditions, look for a sign of a mountain with an ice flake inside it -- stating that the tire is adecuate for heavy snow.

Good tires don't come for free but overall, tires are one of the cheapest car parts and the most important -- so changing them to new tires will actually pay out quickely in terms of milleage and in avoiding collisions. Remember, the tire should come from a known manufacturer, have good ratings and be suitable for the conditions.

So, we have bought new tires, but what about their placement? You have probably heared the rule of  "placing the good tires on the rear." The goal of placing the good pair of tires on the rear is to avoid the car skidding into a situation called oversteer, where the car skids with it's tail and spins around. This happens when the rear wheels have less grip and slide first. So, by placing the good tires on the rear, we avoid oversteer. There is also a school of thought that is for placing the good tires in front -- mainly because that's where the bigger brakes are. 

Our advice is simple: The good tires go...ON ALL FOUR WHEELS. If there is a doubt as to where to place a new pair of tires, this means that at least two tires are already worn to a point where still riding on them is perillous. When you have such a doubt, now is the time to replace all four tires. This way you get both a stable car that does not oversteer, and also good braking -- and not for a significant change in the amount of money spent.

Tire Replacment

By now we have covered the subjects of purchasing new tires and placing them on the car's wheels. But, there is more to it. First, we begin with when to REPLACE tires. There are several criteria, and since tires are both relativelly cheap and very crucial for safety and performance, we should be strict and if any single one of these criteria is present -- we should replace tires:

- If the tire appears significantly worn, damaged or dry -- we should replace it (no matter how much it has travelled or how old it is). Before every drive, take a few second, to look at the tires and search for cracks and damages.

- If the tire has did a sum of 70,000km, it's time to replace it. Even if it still looks good and new, and even if it is still new -- this tire has probably lost over 50% of it's abilities.

- It the tire has passed the age of three years -- it should be replaced. No matter how much miles it did (even if it wasn't used at all) or how good the tire appears to the naked eye -- the rubber undergoes a process of expanding and shrinking under weather changes and it also dries out -- making the tire lose some 20% of it's qualities already when just two years old, and about 50-60% when three years old.

- Tire Tread Depth: With all but Slick racing tires, the tires should have a deep tread for any moist the tire might come in contact with. The popular penny test indicates that the tread depth is larger than 1.7, which is just above the legal minimum of many countries. A safety criteria is a minimum of 3 mm.

A tire's age is determinded based on the date that appears on the tire. It is the only date that in printed INTO the rubber. It usually consists of a letter, and than four figures. For instance, 2610 -- which stands for the 26th week of the year 2010. 1709 stands for a tire that was "born" in the 17th week of 2009.

Tire inflation

Now we reach the most complex subject of all of these, and none-the-less important than the above: Tire air pressure. Tire pressure is measured at PSIG or BAR. I will use the PSIG measurements I'm used to. They represent the pressure created by the amount of air which is squeezed into a tire. More air results in more pressure and less air -- in less pressure. When referring to tire pressure, it's important not to associate it to baloons. In the tire, air pressure has a much more crucial structural role: More air means a stiffer tire and less air means a softer tire.

If you remember, I previously mentioned that tires made of softer rubber have more grip but wear out sooner. But, when we look at the tire as whole, things are bit different. The side force generated when turning the car works on the tire, distorting it somewhat. A stiffer tire resists the side force and distorts less and can provide more grip and less wear. That's why the fear of the tire exploding if we overinflate it is not justified -- unless the tire is extremlly overinflated.

Tire pressure also changes the shape of the tire. Many people believe that less pressure will make the tire scrubb against the ground which means more rubber against the tarmac which means more grip. This is not a true assertion. Why? Because it is made based on looking on the tire from the outside. If we could look on the tire from below (say, if the tarmac was transperent), we could see that -- because less air means that the tire is softer and flexes more -- it is pressed agains the surface but it also flexs and folds so that the center of the tread -- where most grip comes from -- is folded and lifted from the surface. This is catastrophic for grip, tire wear and especially for braking. 

On the contrary, overfinlation below the "right" pressure, results in the opposite. The tire, which recieves a convex shape when underinflated, is now rendered into a concave shape, which makes it grip the road with the center of the tread, and not so much with the shoulders of the tire (corners of the tread). This is better because the center of the tread is both more durable and more grippy, and also in adverse conditions because this kind of tire tends to penetrate through water, snow, mud, gravel and whatever might cover the road surface, and find grip below. If in doubt, overinflation is better than underinflation!

Note: Many people believe that off-road drivers tend to underinflate their tires. They do not! In off-roading, underinflation is used in very specific situations, like deep mud or dune driving (driving on loose, dry sand). In this case, the convex shape of the tire captures sand inside it which gives it more grip. In shallow mud, mould and alike -- the underinflated tire will capture the mould of mud in it's folds -- which would make it slide over them rather than grip the more grippy earth beneath them.

But, why should there be any doubts regarding tire inflation? After all, the manufacturer states clearly how much pressure to put in each tire. This is all very true, but some variants change the pressure:

1. Heat: After driving on tires to the gas station, the tire sometimes heats-up considerably. If you feel noticeable warmth when you touch the tire's sidewall -- it is hot and the air inside it has been expanded by the heat. Say that the pressure in the tire before you started to drive was 30PSI. In the station you might reach a measurement of 33PSI. Now, let's say the tire is undefinflated and only has 26PSI, at the station this might appear as 28PSI, and you will have to inflate it to 33PSI instead of 30. This is another advantage of overinflation -- you can always bleed out the excessive air later.

2. Load: Three healthy adult passengers in the back seat increase the weight of the car significantly. For such cases, you will find that the manufacturer specified different figures for inflating the tires when the car is loaded. Inflating tires with more pressure for a loaded car is something most people fail to do, but it is very important, especially in long trips, and it severly reduces the grip of the loaded vehicle.

3. Performance: In racing, you deduct the correct pressure in the practice sessions. After a few laps, you check the tires for wear and temperature. If underinflated, the contact with the road will be in the tire's shoulder, so it will be more hot and mor worn. If overfinflated, the heat and wear would be more evident in the center of the tread.

4. Accuracy of the check: Different guages give readings in different accuracy. The least accurate kind was/is used in old gas stations where the you aim the pressure you want with by rotating a dail. These pumps should never be trusted (they can mislead you by more than 10 PSI!). Most modern gas stations have digital guages that are more accurate, but it's still advisable to use a personal guage. Pencil guages are the least accurate type of personal guage, but they are cheap, easy to carry around and resistant to blows -- so they are my choice. 

Digital guages are more accurate and some dail guages are even more accurate -- but the differences here are very slim and these guages are cost more, harder to carry around, and can be knocked out of callibration by a blow without you even knowing about it. A pencil guage will mislead you by a maximum of 0.6 of a PSIG.

The frequency in which we need to check air pressure is in times considered as once a month. But this is too much. It's best to check once every two weeks. This way, there is no need for dramatic inflation, and the whole procedure takes a few seconds, faster the fueling the car. Remember to put the caps back on the air nuzzle once done!

If we rate the different parameters of a tire, the most important is wear, than comes milleage, age, tire quality and tire inflation, but the differences are not very significant.

Front tire failure

If one of your front tires do fail and blow-off when you drive, it's important not to panic. You can still control the car.  Slow down steadily and keep on steering the car carefully at a low speed. Some states in America and Europe have special stop-zones alongside the road where you can stop. If the road does not have such a stopping point -- DO NOT STOP ON THE SHOULDER OF THE HIGHWAY. The risk is like nothing you ever experienced. Get on the shoulder and drive slowely enough so that no significant damage be caused to the rim, untill you reach a safe place to stop. The risk exists even if the blown tire is on the side of the car which is not facing the road.

Rear tire failure

This can cause a spin-out that is usually beyond the ability of the driver to control. The choice is to brake really hard to stop the spin, and try and get to car slowely to a safe stopping zone.