Question: How important are tires to handling? What about tire pressure?

Answer:  Tires and handling:

Tires are the vehicles grip on life. The single most important component of the vehicle suspension. All too often the tire is almost an afterthought of the driver these days. How often have you looked at the swaying family wagon next to you on the superhighway and at the half inflated rear tires groaning for mercy from the induced load of dogs kids and trailers. Tire technology has advanced so much that no one even bothers to check tire pressures. And sometimes they get away with it. Consumers want a tire to last as long as the car. What hasn't changed is that the tire is a wear item and does need to be replaced throughout the life of the vehicle, and it needs to be checked and maintained to do it's job during it's life.

In the early days of motoring if a pneumatic tire lasted 500 miles it was an accomplishment, mind you we didn't have debris free smooth highways in those days either. In those early days not getting a puncture was a big goal, the consumer didn't worry about tread compound, grip, ride quality etc. The black rubber balloons that we risk our lives on daily need some respect, care and feeding just like all the other components of the car.

Tire pressure is probably the single most important thing. Yes there are run-flat tires these days but this is meant as a last ditch effort to get you to a place that you can get a replacement -- as are the tiny space savers that are not supposed to ever see highway speeds that we see pounded down the motorway. What we are talking about is giving the tire a chance to deliver its designed performance potential.

The tire is a "balloon" that has fiber reinforced walls so that is has a particular shape. This "shape" that is maintained under load is what maintains the road contact surface of the tire. The fiber reinforcement of the tire can only keep the shape if the correct amount of air pressure is in the tire, as the carcass relies on this pressure for support. If you grab an inflated party balloon with your hands and squeeze the balloon will collapse in the area that you have applied the pressure and the air will move into another area of the balloon that will stretch to accommodate the extra air. If the balloon had fiber reinforcement in its walls it wouldn't stretch and where you squeeze it would fight back - get the picture ? The tire relies completely on this relationship between the air pressure and the carcass construction. So not enough air and the tire can't even come close to doing its job.

Lets look a bit at the basic anatomy of the modern tubeless radial tire. We will simplify this anatomy into four basic parts the "bead" the "side wall" the "tread" and the "tread belts". The bead can be described as the area where the tire seals itself to the rim there is a strong "cable" that is buried or molded into the edge of the tire. The shaped rubber coating around the cable allows the tire to get a tight seal on the rim surface and the strong cable keeps the shape from stretching and allowing the air to escape. Together they lock onto the specially shaped "bead area" of the wheel rim and stop the tire from being pulled of when extreme loads are applied. The loads are applying power to the ground or going around corners. In the case of some extreme machines (some race cars) bolts are actually used to keep the tire bead in place on the rim. But most vehicles rely strictly on the air pressure and the shape interface of the rim.

The next topic is the tread, this is the thick rubber coating on the surface of the tire that rolls on the road. There is a multitude of different "treads"; everything from a smooth surface with just little perforations so that wear can be measured to an assortment of shapes and patterns that are designed for the tires individual specialty. Each tires special tread shapes are designed to enhance the tires ability to develop grip in a particular circumstance or set of conditions. The completely smooth treads are generally meant for smooth dry hard surfaces, like on tires for fork lift trucks that run inside factories on very smooth dry flooring, or on race cars that run on smooth dry race tracks. As soon as another medium is introduced the tread form is altered to help combat the extra circumstance. The race cars that run on smooth dry surfaces have tires that have grooves in the surface when they have to run in the rain the groove shapes are to prevent an effect called hydroplaning where the tire actually rides up on the water film on the surface and provides an excellent friction free surface that has led to a less than fortunate time space coincidence with things like Armco, concrete retaining walls or the soft rear of the vehicle in front . The channels in the tire allow the water to channel away and the higher tread blocks then can contact the road surface to acquire as much grip as possible. If the vehicles chosen traction medium happens to be somewhat softer like the ooze in the back forty that occurs after a few days rain on the farm and ploughing just has to get done then a more aggressive rubber blade tread block is in order to swim through the mud. Huge tires with this kind of tread also make the scene at the local mine and construction sites where these huge loads have to be transported over the worst terrain possible and the surface is anything but hard. Actually most farm vehicles and big stuff like this uses a tire that is filled with a calcium powder to support the tire and make it virtually puncture proof. Some of you may have seen these huge traction getters used in the local fair-ground on the "monster-truck" crushing mere mortal vehicles under the incredible weight guided by the Knight in shinning baseball cap livery at the controls.

This is a second aspect to the tread blocks and that is the composition and construction of the blocks themselves. Again tied to the tires ultimate purpose and intended vehicle style and weight the treads can be made of different hardness of rubber or elastomer. The different "compound" of the tread has different grip characteristics due to the friction coefficient of the rubber. The hardness of the rubber is adjusted to meet the intended operating temperature range of the tire. As the tread blocks squirm under the weight and induced load there is an internal heating that occurs this is called hysteric heat. This one of the three ways that a tire under use builds up its own operating heat. On a race car the rain tires will have a much "thicker" compound layer that the grooves are cut into than the "dry" tire - - in order to increase the traction in the rain if we get the tread blocks hot they will have a higher friction or stick. The racing dry tire operates at a fairy high temperature around 200 degrees F - - the surface of the racing tire at temperature has the consistency of almost tar and provides an incredible amount of grip. More than one racing incident has resulted from a too aggressive driver on "cold tires" - - you have seen drivers weaving back and forth on the race track prior to the start or restart of the field - this is to get "some heat into the tires". If you were to use a rain tire in the dry the tread blocks get to hot too fast and they actually will break down and chunk or fly off of the tire. People that take a normal street tire to the track for "drivers ed" and fun will intentionally shave a new tire to a percentage of the new depth in order to avoid the overheating of the tread blocks from the "squirm heating" effect.

The tread blocks are supported by the tread belts. The belts are layers of fibers or chord that can be made of steel, fiberglass, Kevlar or other fabric like materials that are layered on the carcass to form a sort of floor to support the tread layer on top -- kind of like a foundation for a building. They are near the extreme diameter of the tire so the weight has to be kept to a reasonable level but the stiffer and the more stable the construction the better here is the compromise that has to be addressed by the manufacturer (one of them). The other job of the tread belts is to keep the tire as round as possible while in use and also to keep the tire from growing in diameter as it spins faster. The different speed ratings that is printed on the tire like "X" or "Z" is an indication of how much spinning effect stress the tire can handle. The flexing of the belts also will contribute to the heat build up inside the tire as the higher the air pressure the more support the belts can get from the air and therefore the more stable the tread support.

The side-wall of the tire is also made up of layers of fabric like material combined with the rubber. the stiffer the side wall the more effect the side wall has on supporting the tread belts and therefore the tread and the less the overall flexing the tire carcass as a whole does vehicles with low sophisticated suspensions like trucks and farm equipment usually have a very stiff carcass and side wall tire. Vehicles that have suspensions built for racing and high dynamic side loads like a soft flexible side wall this allows the suspension system to get the maximum tread surface contact in a very dynamic handling situations. Race cars like stock cars tend to use a bit of the farm equipment strategy of the stiff side wall for a slightly different reason -- - in order to keep the carcass temperature under control the tire is made very stiff so that it won't tend to overheat on the high-bank ovals where there is a high level of sustained load. Road racing cars like and can get away from the flexy side wall because cornering loads are intermittent and the tire gets a chance to cool on the straight sections of track - plus the loaded tire switches from side to side as the vehicle negotiates both left and right turns. The bottom line here is that the side walls get support as well from the air pressure in the tire - - the more pressure the more stiff the side wall which we have learned may or may not be good depending on the specific tire and application.

Now back to our original statement about the importance of tires and suspension. We know that tires get hot, we know that we want to control the heat level. We know that tires build heat 3 ways: the friction heat from the road surface tire interaction - - the tread block squirm heat - - and the energy heat that is generated by the flexing of the tire carcass. We now can consider the vehicle dynamics like weight, intended use, and the road conditions that we expect the tire to come to grips with. How the vehicle suspension is designed for the vehicle's intended operational profile in order to take advantage of what the tire is technically capable of delivering as far as performance is the essence of it all - - and the single biggest influence on how the tire can optimally perform is having the proper pressure inside.