Sometimes truck owners treat tires as an accessory that happens to come with the truck or that can be fitted to the truck later on, when the original tires wear out. The problem with that is the word “fit.” Just as trucks can vary widely, truck tires can be very different, too. Not every tire is right for every vehicle or application. Drivetrains also affect tire performance.
To make the best decision about which truck tires to buy – and how to manage their retread lives — you’ll need to understand how drivetrains affect performance.
Downspeeding is a growing trend
In recent years, manufacturers have looked for technology innovations that would meet tough new fuel emissions standards while also improving fuel economy. As a result, heavy-duty highway engines can now generate high torque levels at lower engine speeds. But with shorter piston travel and lower crankshaft speeds, you get greater variation in connecting rod loadings and increased harmonic stress. It’s rather like lugging the engine. So OEMS found they also had to strengthen engine blocks, along with internal engine and transmission components.
Higher torque loadings also necessitated changes in drivetrains. Driveshafts, universal joints and ring and pinion gears are all stronger. Clutches have been upgraded. Trucks with new engines that allow downspeeding also drive differently – or drivers should treat them differently. That means fleet managers have had to invest in re-training, emphasizing how important it is to:
- Avoid wheelspin on low-coefficient surfaces
- Call for a tow rather than rocking the truck back and forth it it’s stuck
- Gently engage the clutch/driveline when accelerating
What’s all this have to do with truck tires?
With drivetrains designed for downspeeding, higher torque is available no matter the road speed, because there is less variance in engine speed from start through acceleration to cruising. That higher torque is transferred from the truck tires to the road surface during acceleration, braking and cornering. That affects both tread wear and casing durability.
Truck tires age for three reasons:
- Chemical degradation over time (whether tires are rolling or sitting). Today’s radial tires incorporate more than 40 individual components, not to mention up to 14 various rubber and steel components.
- Casing fatigue. When truck tires cycle, they deform – flattening against the road surface, then re-expanding – and that puts pressure on the casing.
- Casing stress. This happens as high torque loads “flow” from the metal rim seat through the flexible sidewalls to the tread to the road surface.
You can prolong the life of your truck tires with strategic retreading. For example, you can retread first worn tires with a shallow tread, then use the tires in tag axle position or on a free-rolling trailer. Under this plan the ideal retreaded tire for drive axle use would be one that had a premium casing and shallow tread in its first life. Experts suggest doing this will save you money for both 6×4 and 6×2 applications because casings will last longer.
With downspeeding, drive tires are transferring high torque levels more often. And the engine’s torque curve is nearly flat over a greater percentage of their operating range. This is likely to produce somewhat faster tread wear on the drive tires. It may not be a big difference, but it’s something you should consider when choosing brands and types of truck tires and when planning retread rotation. Don’t forget that tire pressure and wheel lug torque are even more important if you’re running high-torque drivetrains.
In fact, tire experts say proper inflation is the Number One element of any effective tire maintenance program. You can consider outfitting drive axles with a tire pressure monitoring system, or investing in automatic tire inflation systems for trailer axles or for full-floating drive axles as those automatic systems become available.