What should you be looking for when servicing big tires?
Commercial tires have some specialized requirements that your technicians will need to understand. Proper training is essential, as is the right equipment, and knowing when a tire can be repaired or when it must be replaced or retreaded is key.
“There are certain instances in which a tire must be pulled from service immediately,” says Ryan Butler, Continental’s Regional Manager for Commercial Tires in the U.S. Midwest. “For example, if any steel or nylon belts or cords are showing, if it has an audible air leak, and when it reaches minimum tread depth.”
That depth is 4/32nds for a steer tire, and 2/32nds for a drive tire. However, Butler notes that there is a “significant performance gap between 2/32nds,” and says some experts recommend pulling a steer tire from use at 6/32nds, and a drive tire at 4/32nds.
Keeping costs down
If the customer thinks this is too soon, remind him that this helps to protect the casing for retreading—an important consideration in the tire’s lifespan, and a potentially major savings in its overall operating cost.
Many commercial tires have wear bars, Butler notes, which can assist the technician in determining the tire’s fate, and which can also be shown to the customer for verification.
Overall, the signs of a commercial tire on its way out are similar to most of those for other tires, the experts say. These include sidewalls that are significantly chipped or cracking, hard or brittle bead, large blisters or bumps, chunks or cuts, or a crackling sound when the tire has just been inflated. Driver complaints about poorer traction or braking are also a clue.
Matching dual wheels
Dual wheels must always have identically sized tires on both wheels. Putting a larger-diameter tire on one of the wheels will result in faster tire wear and can quickly ruin both tires. The larger tire takes more strain on its sidewall, since it’s handling more of the load, while the smaller tire spins slightly faster and will wear its tread sooner.
Even a small difference between the two will magnify over the number of higher-speed highway kilometres that these tires will see.
Pumping it up
As with any tire, proper inflation is critical, and Butler says commercial tires need special attention. “On most truck tires, the pressure listed on the sidewall is the minimum pressure to carry the maximum load, versus many passenger tires [which] list the maximum inflation pressure on their sidewall. A truck tire should always be inflated following the Tire and Rim Association load and inflation tables, which may call for higher air pressure than the sidewall.”
Technicians need to be trained on inflation procedures, and the proper equipment is required. Tires on multi-piece rims must be inflated in a safety cage, which needs to be able to withstand a maximum force of 150 percent of the tire’s maximum specification pressure.
The cage must be at least a metre away from anything else, including the walls, and can’t be secured to anything—if the tire blows, the cage is intended to deform to dissipate the impact energy.
The technician should be a minimum of three metres away, using a clip-on chuck and extension hose to fill the tire, and wearing safety glasses. No matter how many times a tech has done this job, all the precautions must be taken.