#x2019;s tread design and compound provide lower rolling resistance and longer removal mileage than standard tires, said Michelin, adding to the overall cost savings.
The X-One is currently available in two tread designs: the XDA drive, an OE exclusive to Freightliner until mid-2003, and the XTA trailer, available as OE to any trailer maker. Both are out in size 445/50R22.5, and have the same outside diameter as Michelin’s popular 275/80R22.5 low profile size, according to MATT.
Up to the Task
Randy Clark, MATT’s vice president of marketing, said both X-One models and accompanying aluminum wheels are currently available through 375 Michelin dealers and the entire T/A truckstop network. And the cost for one X-One is comparable to a set of traditional duals, making it economically feasible for fleets to convert, he said.
Clark said the X-One was originally intended for specialty applications, but driver and fleet acceptance allowed the tire to spread to other applications like regional and national over-the-road fleets, he said.
The biggest concern fleets expressed was what would happen if the one tire went flat. “If you lose one tire on a dual set, you’re going to have to replace the remaining dual anyway because its been overstressed,” he said.
Clark said Michelin conducted rapid air loss tests on the X-One with both a loaded 76,000-pound dry van and a full tanker two key applications for the tire. A small explosive was used to puncture the sidewall at 60 mph, both on straight roads and at the apex of a curve. Clark said in both cases the vehicles easily maintained control, and the flattened tires didn’t disengage from the wheel.
Later this year, MATT will introduce two new X-One patterns: the XDE for high load spread axle applications, and the XDA-HT for high scrub, high-torque applications. Plus, Michelin is adding an extra belt to all X-One models to increase their load capacities above the current 10,200 pounds/axle.
According to Ibrahim Janajeh, a Michelin engineer instrumental in the X-One’s development, the tire was extensively tested over 200 million road miles before it was rolled out last November. Currently, some 40 truck fleets are actively using the X-One some on drive axles, some on trailers and some at both positions.
Janajeh said the X-One can be used on the same axle as a set of duals, or on one axle with duals on the other. Testing, he said, shows the wider tire/wheel package has no impact on wheel bearings, and truck brakes run cooler as the super wide allows better air flow than traditional duals.
Super wides are an entirely different breed of tires compared to wide base radials, said Janajeh. The lower profile makes the X-One five inches shorter than wide base tires, and the flat crown radius is less sensitive to load variations compared to wide base tires. And X-Ones are run at 100 psi vs. the 125-135 psi of wide base tires, he added.
Michelin testing showed the X-One drive tire delivers 21% better rolling resistance than standard drives, and the trailer version is 14% better than standard trailer units, Janajeh claimed. In terms of weight savings, a set of four X-One drives and accompanying aluminum wheels weigh 456 pounds less than eight low profile duals on aluminum wheels, Janajeh said.
The X-One’s unique Infinicoil zero degree belt is the key element in the tire’s performance, said Janajeh. The belt is applied as a single, continuous strand, with 400 meters of coated steel wire being wound on each X-One. The belt helps reduce belt flex and shoulder strain on the extra wide tire, thereby reducing heat stress, he said. And the wound belt helps maintain the tire’s flat crown shape and reduce shoulder stress.
Clark said the Infinicoil technology, developed specifically for this tire, adds cost and time to the manufacturing process, but is necessary.
North American Production
Michelin’s X-Ones are produced on a specially-designed, dedicated tire builder at its 1.2-million-square-foot Spartanburg, S.C., plant. While the non-union truck tire plant is 23 years old, the equipment and processes used are all quite modern, according to plant manager Skip Sherlock.
While Michelin won’t reveal the capacity of the 1,100-employee plant, industry estimates say the plant can produce 5,500 radial 17.5-, 19.5-, 22.5- and 24.5-inch truck tires per day.
Spartanburg is organized into five distinct process sections where tire components are produced, assembled, cured, inspected and warehoused. Production processes are heavily, but not totally automated, leaving much to the craftsmanship of employees.
At least at Spartanburg, Michelin uses an extruder system that pre-forms ribs into the tread stock; individual tread elements, sipes and shoulder blocks are formed by the molds. The extruder sits spider-like on the plant floor, gobbling up selections of tread rubber at one end and spitting out pre-formed multi-compound tread stock from the other.
The extruder used to produce X-Ones is a three-head co-extruder. Pre-formed treads for the super wides are produced complete with shoulder wings and undertread each with its own rubber compound ®“ maximizing the entire process. Sherlock said the co-extrusion system allows the blending of compounds that promote different performance characteristics, like mixing one compound for long original tread life with another for enhanced traction and still another for heat resistance.
Mixed and extruded under high heat and pressure, X-One treads receive a lengthy water bath to cool them to room temperature, preventing the stock from curing itself, said Sherlock.
Slow But Focused
The horseshoe-shaped multi-station X-One builder sits on a raised platform. The building tambor rides on a mini-rail system, moving station-to-station as each element is aligned and applied. As one casing is being produced on one side of the shoe, its matching belts and tread are being assembled on the other. The Infinicoil belt layer is applied to the casing before the belt/tread package is mated to its casing at the middle of the U.
Sherlock admits the X-One production system is slow and focused more on quality vs. quantity. Not surprisingly, Michelin won’t say what its X-One production capacity is end to end, it takes 10 to 15 minutes to build one unit, and it has only one X-One builder at Spartanburg ®“ but stated firmly that it will gear up to meet market needs.
Once built and moved to a conveyor system, human hands won’t touch the tire again until it hits final inspection. The X-Ones are cured on the plant’s regular line using standard Michelin-designed mold presses. The curing room is highly automated, with each green tire reaching its assigned curing press via computer control.
Each cured tire goes on very long conveyor ride long enough to air-cool the cured tire nearly two hours before it reaches final inspection. Each finished tire is visually inspected for flaws, and tires are randomly pulled from each production lot for x-ray and shearography testing, and to be run on a force variation drum. From there, finished X-Ones ®“ as with all Michelin truck tires ®“ are stacked, warehoused and shipped.