The Air CTI crew catches up with highway driver Rod Hannifey, president of the NRFA.
The way rubber meets and reacts with the road affects every component and every aspect of your truck’s performance and operation.
The footprint or contact area affects braking, handling, ride quality, truck wear, driver health, road health, and our environment.
A correct footprint is essential for safety, profits, driver health, truck reliability, downtime, breakdowns, and your business.
Unfortunately, most people don’t understand the ramifications of incorrect tire pressures, or even what the correct tire pressures are. Most tire suppliers are in the same boat, as are most truckers.
What is the correct footprint and what controls this footprint?
The correct footprint size for an 11R22.5 tire is 240mm long, 184mm wide. The correct area is 427 square centimeters, or 66 square inches. The tire should deform and settle on the road 37 mm (1.46 “), distributing the load over the entire footprint as evenly as possible.
If the load on the tire changes, the footprint will change, unless the tire pressure is changed to match. Inflation load charts are available from tire manufacturers, tire associations and online. Inflation load tables provide the correct pressures for each tire load to ensure a full and correct tire footprint, optimizing performance. Unfortunately, this does not happen.
This real, scientific information is not taught and is not promoted. This poor distribution of vital knowledge even affects many representatives of major tires. We were hauled over the coals by one of the major tire companies because of our recommendations even though our information came from them.
Our government transportation regulators do not understand the damage caused by improper tire inflation. If they did, our world would be much safer, greener and more profitable.
Everyone knows that underinflation is bad. An under-inflated tire traveling on the highway can overheat due to too much sidewall flex. The heat buildup weakens the sidewall and something will break, causing the tire to explode and potentially cause a crash.
Over-inflation reduces the tire footprint. For example, an empty three-axle 100 psi semi-tire will have a tiny footprint the size of a business card. This tiny amount of rubber in contact with the road will not have much grip. The typical Australian tandem trainer tire is overinflated to 35 percent at maximum legal load. The footprint will be 35% smaller, with less traction, less braking and less directional control. Most 100 psi steer tires are 20% underinflated at 6 ton axle load.
Over-inflation and under-inflation increase tire wear. A 20% over-inflated training tire on Australian roads will wear 22% faster. Optimizing tire pressure for load improves tire life by at least 30 percent. At the same time, under-inflation and over-inflation reduce the life of the housing, again increasing the costs. An over-inflated tire is the leading cause of uneven tire wear and causes 40% more punctures and cuts.
Over-inflated tires bounce off bumps and roughness in the road instead of absorbing impact within 37mm of correct deflection. Over-inflated tires cut the life of your springs, suspensions and bushes in half, and dramatically increase fatigue loads resulting in cracked axle housings, broken springs, blown shocks and breakdowns.
Wheel bearing life is dramatically shortened by over-inflation and uneven tire pressures in twin tires. When a tire is carrying more load, the load on the wheel bearing is shifted, causing a bearing to be overloaded, dramatically reducing the life of the bearing. Of course, uneven tire pressures also wreak havoc with tire wear.
Over-inflated tires act like a rigid wheel, which greatly increases the loads on the powertrain. A properly inflated tire acts as a crankshaft damper, absorbing loads and vibrations, doubling the differential and the life of the transmission. Each explosion in the engine sends a shock wave throughout the powertrain. Over-inflated tires send this shock wave back to the engine, affecting every component. Again, a properly inflated tire absorbs this shock wave, thereby eliminating wear and breakage.
Over-inflated tires double vibration levels throughout the truck, affecting every component from the load to the radiator and intercooler. Correct pressure in the drive tires reduces wear on the suspension seat by 65%. The vibrations kill your truck and your driver.
Whole body vibration is a proven cause of many health problems among truck drivers. The continuous high vibration levels damage the ocular system (eyes), the skeletal system (back), the stomach and the digestive system and the circulatory system. Drivers have the shortest life expectancy of any trade or occupation.
On the outside of your truck, road damage is directly proportional to tire pressure. The higher the pressure, the more damaged the road. We all know that a new pothole will develop within feet of an existing pothole. Our tires simply bounce off the first and hammer the road. Even ripples are caused by over-inflated tires. Correctly inflated tires smooth out ripples.
Our environment is overloaded with dead tires. Recycling tires is expensive and difficult, as we all know when it costs so much to get rid of a tire. A lot of energy, minerals and materials go into making tires. The tires are transported to us from other countries, which aggravates the environmental damage. The waste of CO2 is enormous. Running the correct tire pressures for the load is good business and good for our world.
In fact, using the correct tire pressure will extend the reliable life of any truck by at least 40 percent. It saves a lot of money, pollution and waste.
If we, as a country and as an industry, are serious about our financial future and the future of our country, proper tire pressure is simply the smart way to work.
Equipment to optimize your truck’s tire pressure pays for itself, usually the first year. Safety improvements through the chain of custody really mean that this equipment is essential. Improved driving, reduced driver stress, and easier driving means your staff will drive for you more years, happier, and healthier.
About the Author:
Chet Cline is the owner of Air CTI, an advanced tire inflation system that helps maximize vehicle and tire life.
For more information, contact [email protected]