The underlying cause of most premature tire failures today is the same one it has always been: improper inflation. “About 80 per cent of failures are related to air pressure maintenance,” says Brian Rennie, director of sales engineering at Bridgestone Canada. “That’s been the key since day one, since pneumatic tires started.” And it continues to cost truck owners money in increased maintenance.
The good news is the problem is easily preventable. Investing about $20 in a good-quality pressure gauge and a little time on a regular basis will ensure you get the most out of tires on the heavy trucks on your farm. And be sure the pressure gauge you use is right for the job. You want one that will give precise readings in the pressure range the tires operate in. That likely means investing in more than one gauge.
And there is no point checking tire pressures unless you know what they should be. The exact number depends not only on tire size and type but also the load you expect it to carry. “It’s not the tire supporting the load,” says Rennie. “It’s the air inside it.”
On heavy trucks, that could mean using different pressure settings for tires mounted on different axles. “You need to identify the proper inflation pressure.” he explains. “That’s dictated by the load, which may dictate different inflation pressures for the front as opposed to the driver or trailer positions.”
A tire retailer will have a chart of inflation pressures for various tire sizes under different loads, but you can also find the information online. Bridgestone’s website, www.bridgestonetrucktires.com, includes a chart of standard Tire and Rim Association pressures, the industry standard. There is some room to fine tune those recommendations to suit your specific application, but Rennie cautions the table pressures should be considered minimums. Any adjustments should be made on the high side of the table numbers.
Drivers of heavy commercial trucks are required to make daily pre-trip inspections of their rigs, which includes checking tires. Although in some provinces that same regulation may not apply to farm truck drivers, Rennie recommends they, too, conduct regular pre-trip inspections, paying close attention to tire condition each time. Unusual wear patterns on tire treads can point to a variety of problems ranging from incorrect inflation pressure or misalignment to mechanical suspension failures.
“Interpreting the appearance of the tire can tell you a lot about your vehicle and pressure maintenance,” says Rennie. “You can read the tire (wear) and gain a lot of understanding from it. Underinflation, overinflation and mismatched inflation can initiate the development of various types of irregular wear.”
The increased sidewall flexing caused by underinflation will also cause a tire to overheat during a trip. That makes sudden and premature failure a real possibility, especially when the truck is carrying a heavy load.
“Underinflation is probably the worst case scenario,” adds Rennie. “It wears faster. And it affects fuel consumption. We have a rough estimate of over one mile per gallon (decrease) for every 20 PSI of under inflation.”
Rotation & Alignment
Heavy-truck tires should be rotated at least once during their life to ensure consistant wear rates. Each one should be moved to the opposite side of the truck and to a different axle. It should have its direction of rotation reversed.
The truck should also have its alignment checked regularly.
If you find a tire has a deep cut that exposes the metal cords, it should get immediate attention and possible replacement. If moisture comes into contact with the cords, it can cause rust and eventually breaks, leading to a sudden failure. “Exposed steel needs to be repaired or the tire needs to be removed for replacement,” says Rennie.
When replacing a tire from a set of duals, you need to pay close attention to matching the pair. Generally, the diameter of the replacement tire should be measured to ensure it’s within the industry standard of a maximum of a quarter inch of its partner. And, when installing new tires, match duals by brand and tread type. Not all new tires of the same size rating built by competing companies will be exactly the same. “We did a survey of that,” says Rennie. “There is probably double the industry recommended standard (in diameter) between brands and even within brands between patterns (tread types). Just because you have the same tread depth doesn’t mean the casings are the same dimensions.”
When you go shopping for replacement tires, be sure to select a type designed to suit the kind of road surface your truck travels on most of the time. Tires that perform well during long hauls over pavement may not be the best option for short trips on gravel roads. †