With the general cost of motoring increasing, vehicle owners must understand where these costs come from and reduce their costs. Tires and the rate of wear are essential considerations for the cost-conscious driver.
Smaller tires wear faster. The smaller the tire’s circumference is, the more times each part of the tire’s surface will touch the ground over a set distance. Many other factors influence tire wear, e.g., driving style, speed, vehicle maintenance, and quality of road surfaces.
In modern times, it seems as though everyone is struggling to make ends meet; smaller tires may be cheaper but is this a foolish economy due to the rates of replacement? Learning to choose the correct tire size for your vehicle involves balancing tire performance with longevity.
Does Tire Size Affect Tire Longevity?
The tire diameter is calculated by applying the formula “Diameter * πd” (Pie equals 3.14 for all you who had to suffer through this in school).
A fifteen-inch tire will therefore have a circumference of 15*3.14 = 47.1 inches. Similarly, an eighteen-inch tire has a diameter of 56.62 inches.
To travel 100 miles, therefore, a 15-inch tire will rotate 134,522 times, whereas an 18-inch tire will only rotate 111,903 times. That means that each part of the 18-inch tire will touch the road 22,619 fewer times than a fifteen-inch tire.
Simplistically put, that means that an 18-inch tire will be able to travel 117 miles with the same wear as a 15-inch tire. That equates to a 17% improvement in tire life. Tire size is directly proportional to longevity; the smaller the tire, the shorter its life expectancy.
Does Perception Match Reality?
The vehicle’s measuring systems (speedometer and trip meter) are calibrated against a factory-specified tire size. This instrument measures the rotation of the wheels as opposed to the actual distance traveled.
If the car travels for a set distance using different tires, it will register a higher distance on the smaller tires and a reduced distance for larger tires.
For example: assuming the factory tire size is set at 18-inches, and the vehicle travels 100 miles. The 18-inch tires will log a distance traveled of 100 miles, while the 15-inch tires will log 117km.
Over a given distance, although the vehicle’s trip meter will show the same distance traveled, the 18-inch tires will have traveled 100 miles, whereas the 15-inch tires will have traveled 117km. The vehicle’s trip measure will make it appear that the tires have worn to a similar extent for the distance shown on the trip meter. A more accurate estimate of tire wear per unit of distance traveled is GPS units which measure actual distance traveled and not the number of wheel rotations.
Is Tire Size The Only Factor Influencing Wear Rates?
The tire size does not exclusively dictate tire wear rates. Other variables which affect tire wear are:
- Driving style
- Where the vehicle is Used
- Road surfaces commonly traveled
- Inflation pressures
How Fast The Vehicle Is Driven
Speed is a critical consideration in influencing tire wear. At high speeds, road surfaces generate friction, which in turn cause high temperatures. Therefore, driving at excessive speeds for a long time will cause the rubber to weaken and the tire to wear down.
The counter to this argument is that drivers are more likely to drive at high speeds on motorways and other roads which have suitable surfaces.
Vehicles with larger wheels may be geared to more performance (i.e., driven at higher speeds) and therefore could well experience increased wear compared to cars with smaller tires driven on the same roads.
Driving Style
Driving style is the factor that has the most impact on the life of a tire; it is even more influential on tire wear rates than speed!
Sudden braking, fast acceleration, and making tires squeal as you go around corners are the factors that have the most significant influence on tire wear. Driving like this might give you adrenaline surges but will negatively impact your wallet; you’ll be forever replacing your tires!
To positively impact the life of your tire, try to practice the following driving style:
- Keeping abreast of the traffic flow when you move off from a stop
- Accelerating gently but consistently
- Maintaining a sufficient distance to the car in front so you can stop without having to violently brake to avoid an accident.
Where The Vehicle Is Used
Driving on open stretches of well-surfaced roads, with little traffic, at a constant (not excessive) speed is the best condition to ensure a long life for a tire. However, not all of us are blessed with the luxury of driving on well-maintained, quiet roads.
Driving in a city or town with constant braking, acceleration, and even the possible speed hump, potholes, or aggressive curbs has the opposite effect. Driving on pothole-filled country roads can be just as damaging to your tires as driving on well-maintained busy city roads.
Road Surfaces
Long even, tarred, or cemented road surfaces are the best conditions to ensure you get the most extended life out of your tires. Conversely, driving on poorly surfaced roads increases the potential for higher wear and damage.
Potholes are known tire killers causing catastrophic blow-out and wheel damage. In some parts of the world, potholes are such a prevalent issue that insurers exclude the cover from their auto insurance policies, e.g., South Africa.
Driving on gravel or shale surfaces increases the potential for damage, particularly of the tire’s sidewall. Sidewall damage is generally not repairable and necessitates the purchase of a new tire.
If you do drive on these surfaces, exercise caution and restraint. Don’t speed or change direction suddenly and aggressively; gravel is not your friend and will cause damage to your tire if you disturb its rest!
If you regularly drive on these roads, it is recommended that your tires be designed for rugged use. These hard-wearing tires often have a gel film on the inside of the surface, which can reseal more minor cuts when they occur.
Your local tire supplier will be the best person to advise you on which tire is best suited for use in your area and activities.
Inflation Pressure
Correct tire pressures play a huge part in protecting your tires and ensuring a long life expectancy.
Underinflated Tires
- Cause a weakening of the sidewall and make the tire more susceptible to lateral forces. The tire becomes unstable and more liable to “wabble” around corners.
- Underinflated tires run hotter, which in turn causes higher degradation rates.
Overinflated Tires
- Overinflation is just as harmful as underinflation as it causes excessive wear along the center of the tire.
- Overinflation causes reduced traction, as less of the tire tread contacts the road, increasing the risk of losing control, e.g., skidding and wheel spin.
You should regularly check the tire pressure against the manufacturer’s handbook: the left and right wheels must be maintained at the same pressure.
Condition Of The Vehicle
The vehicle’s condition is a significant factor in determining the life and health of the tires. Tires wear out more quickly and unevenly if the:
- Wheels are misaligned and not balanced properly
- The suspension is worn, has faulty or loose components such as aging bushes or leaking shock absorbers
- The steering system is defective and not correctly aligned
- The braking system is worn or defective, resulting in unequal forces applied to each wheel.
Conclusion
A smaller diameter tire will have more wear over a set distance than a higher diameter tire. However, the tire’s diameter is not the most important factor when considering tire wear; other factors influencing tire wear are speed, driving style, location, road surfaces, level of tire inflation, and vehicle condition.