You can’t beat a spread-axle trailer for flexibility, but those axles sure beat up tires. Measuring a minimum of 10 feet from spindle to spindle, and often 10-feet plus 1-inch to account for slack tape measures used by enthusiastic inspectors, each axle is treated as a separate single axle and can therefore carry 20,000 pounds. With 40,000 pounds between them, that’s about 6,000 pounds more than you can squeeze onto a standard 60-inch tandem group.
The spread-axle group works against tires in two ways: the weight, and the lateral forces exerted on the tire during tight turns. The trailer will have a pivot point between the two axles, and that point will depend upon the center point of the load on the axles. It’s rare that such a pivot point would center between those axles and distribute the weight evenly. Usually one axle – often the front – takes the full brunt of those forces most of the time.
Drivers can have a large influence on how long tires survive in a spread-axle application. Sensitive drivers will try to avoid jacking the trailer around 90 degrees to the tractor and dragging the tires through the arc of the turn. Other drivers? Well, you can almost see the little chunks of rubber peeling off the tires as the suspension creaks and groans its way through the maneuver.
“The spread-axle application is one of the most demanding in the industry because of the tremendous forces that are transmitted to tires,” says Mahesh Kavaturu, Goodyear marketing manager for commercial long-haul and regional tires. “Combine this dynamic with the extra weight that spread-axle trailer axles can carry due to their configuration, and scrubbing emerges as the biggest threat to tires in spread-axle applications.”
Fleets can expect severe shoulder wear and accelerated tread face wear due to the lateral scrubbing action.
“Trailer tires are designed primarily to defend against free-rolling axle wear and sidewall/shoulder damage created by curbing,” says Tom Clauer, senior manager of commercial and OTR product planning at Yokohama Tire. “However, tread design and compounding can have an impact on minimizing the damage created by the lateral sliding of the tire on one or the other axle.”
Rib-type tread designs fare better on spread-axle trailers than lug treads. The deeper the lug, the more susceptible they are to tearing. Lug tires can be more prone to tearing than rib tires simply due to the volume of rubber in their tread area.
“Even lug tires moved back from a drive position to be run-out usually have 50% or less tread,” notes Clauer. “You could, depending on their design, expect to have significant lug tearing and chipping from the lateral sliding, and if they have certain wear patterns in them, it could exasperate the condition by being placed on a trailer.
“If lug tires are to be moved to the trailer position, then the shallower the tread the better. It’s always a gamble to make such moves, because the potential of ruining a casing could be costly,” Clauer adds.
Speaking of casings, there no particular reason to avoid using retreaded tires on spread-axle trailers, assuming you have a good tire maintenance program in place and inflation pressure is checked religiously. One might imagine how the high scrub forces on a tire being dragged sideways through a tight turn might be inclined to peel the tread off the casing, but Kavaturu says that’s not the case.
“In general, excessive scrubbing should not have a negative impact on retreading if the casing, as a whole, has been properly maintained over the course of the new tire’s initial service life,” he says. “Goodyear UniCircle retread products are designed to resist scrubbing and withstand other forces inherent in the spread-axle application.”
Tough tires for a tough application
With today’s boutique selection of treads for specialty applications, several models are available for spread-axle applications.
Michelin, for instance, offers the MRT XZE SA, an all-position retread designed with rounded shoulder and tapered tread extensions to resist the high scrub and shifting footprint stress in spread-axle applications. For off-road applications where chip and cut resistance is important, there’s the MRT XTY SA.
Michelin’s Oliver Rubber division also offers three specialty retreads for spread-axle trailer: the Oliver Spread Axle with rounded shoulders to resist tread tearing, the Regional A/P- all-position retread with rounded shoulders, and the Rugged Service Rib.
“Tires that work well in a spread-axle application are ones designed to withstand a high lateral scrub environment,” says Sharon Cowart, director of B2B product marketing at Michelin North America. “Tires for these applications are formulated specifically with compounds that resist scrub.”
Bandag has a spread-axle tread offering too, the BTL-SA (Bandag Trailer Linehaul-Spread Axle). The tread features tough shoulders to withstand the scraping, scrubbing and lateral stress created when trailers corner.
On the retread side, Goodyear has a match for its G619 RST, designed for spread-axles. The G619 UniCircle retread is engineered to replicate the performance of G619 RST tire, so it’s a good fit for fleets that want to maintain the original tire performance on casings designed to hold up to the curbing as well as the lateral stresses in the spread-axle environment.
Goodyear’s G619 RST is the company’s premier offering for this application, with a special compound that resists scrubbing and curb damage. It also boasts a deep, 18/32-inch tread depth for long life.
“In general, we’ve designed the Goodyear G619 RST to help minimize tearing and scrubbing and to optimize the casing durability,” Kavaturu notes. “The compounds found in the tire are similar to the compounds that are built into our steer tires, and the casing design is steer-like, as well. These features were deliberately applied to the tire to enhance its general robustness, which is much-needed in spread-axle applications.”
Tires optimized for spread-axle usage from Michelin include the XTE and the XTE2. Michelin says these tires are formulated specifically with compounds that resist scrub.
Bridgestone’s R196 features wide, continuous shoulder ribs to fight turning side forces and resist tearing and a belt package that protects against side forces encountered on spread-axle and multi-axle trailers.
Yokohama’s candidate for spread-axle specialty tires include the RY023 and 108Rs. Clauer says both tires have a deeper rib tread, rounded shoulders, and minimal siping.
We couldn’t find a wide-base single tire optimized for spread-axle applications, possibly because those tires haven’t proven hugely successful where lateral forces on the tire and tread scrub is severe. But that doesn’t mean they can’t be used with care.
“Wide-base tires are more beneficial in straight-line, long-haul applications where fuel consumption and – in the case of tankers and other weight-sensitive applications – the ability to optimize payload are main concerns,” Kavaturu points out.
“Wide-base singles tires have unique belt packages designed to support the wide tread face and contain the pressures required to carry the weight,” notes Clauer. “This application can create stress on those features and be a challenge for the tire overall. However, a well-maintained fleet with disciplined operators can function with no more, and in some cases, fewer issues. In a nutshell, ultra-wide-based tires in both spread- and closed-axle trailer configurations perform extremely well.”