Product Report: Radial revolution

Radial tires rule when it comes to off-road haul trucks, but for other types of construction machinery, they’re still a tough sell. According to Michelin, just 7 percent of backhoes come out of the factory with radials, compared with 79 percent of off-road earthmoving trucks.

To improve the acceptance of radials in this market Michelin introduced a new XMCL radial tire primarily for wheeled excavators, telehandlers and backhoes. The company recently invited the press out to its Laurens Proving Grounds near Greenville, South Carolina, to test drive the new tire and to take a look at another new radial product, its Ultraflex Technology for big scraper tires.

The new XMCL, with its steel crown belt package and puncture resistant sidewalls, has as much as 46 percent more service life than the XM27, the model it is replacing, according to Todd Gillespie, North American training manager for Michelin Agro-Industrial tires. The new radials also carry more weight: 14,000 pounds at 6 mph and 9,900 pounds at 24 mph for the XMCL versus 9,240 pounds and 6,400 pounds for the XM27. The XMCL tires will be availble in 12 sizes including 18, 20, 24, 26, and 28 inches. They will replace both the XM27 and XM37 tire lines.

The construction environment is full of tire killers: roots, rebar, jagged rock and concrete; and often the most vulnerable part of the tire is its sidewalls. To protect this part of its XMCL radial tires Michelin added a beefy, square shouldered sidewall protection rib.

The primary benefit of a radial tire is that the flexible sidewalls absorb bumps and lateral force, keeping what tire manufacturers call the “contact patch” of rubber firmly on the ground. In a bias-ply tire, flex or movement in the sidewalls carries through to the tread, deforming the shape of the contact patch resulting in less traction, more scrubbing of the tread and a hotter running tire.

The toughest part of this pitch is selling a more expensive radial tire to a market segment that eats and abuses tires with some regularity. Michelin uses a total cost of ownership model to demonstrate the more expensive tire is the better long term value since it can reduce flats, downtime and repairs and offer much longer tread life. To drive this point home Michelin showed us a scenario with numbers run through its tire cost comparison software using a real-world example. When all the lifecycle and maintenance issues were factored in, a $761 Michelin radial tire on a Cat 426 backhoe cost 18 cents per hour compared to 27 cents per hour for a comparable bias-ply tire. The bias tire cost less up front but, due to a shorter service life, flats and the costs of repairs and downtime, ended up costing more in the long run.

To demonstrate the performance of the XMCL tires Michelin set up two identical Caterpillar 430E backhoe loaders for us to drive at the company’s test facilities. One backhoe was shod with the new Michelin XMCL tires, the other with a competitor’s bias-ply tires. With a 2,200-pound weight in the loader bucket and the ride control turned off, we took each backhoe up a steep, muddy slope with several tight turns and rutted spots, then descended on a washboard-like surface.

The effect of the radial tires going uphill in the mud was subtle but consistent. Both types of tire slipped, but the radial tires grabbed and dug in quicker each time the tires started to spin. With the bias-ply tires the spinning was just a second or so more prolonged, but when this happens four or five times in 100 yards it tends to make you begin to doubt whether you’re going to make it to the top of the hill. And in real-world applications every extra second of tire spin means more fuel burned, more drivetrain wear and less productivity.

The ruts at the top of the hill also became deeper with each successive pass and eventually the backhoe with the bias-ply tires was unable to negotiate the last turn and had to back down out of its ruts and come up on fresh turf. Going down the hill on the washboard surface, the radial tires were noticeably quieter and less jarring.

In the excavator/digging mode, this type of tire performance won’t mean much, but on the loader end of the machine, the smoother ride and better traction should pay performance dividends. Better traction and a smoother ride translates into less bucket spillage, faster travel speeds and better productivity. And the less a tire slips, the longer it will last and the less likely it is to knife open on a sharp rock or piece of rebar.

Scrapers get Ultraflex
On a much bigger scale, the Ultraflex Technology radial tires for big pull-scraper tractor units were designed to run at inflation pressures 20 percent lower than standard radials or carry 20 percent more load at the same pressure. Michelin designed this tire with an increased deflection zone, the vertical space from the bead to where the sidewall joins the crown. The larger deflection zone gives the Ultraflex tires a footprint that is 22 percent bigger than a standard radial. The bigger footprint enables lower air pressure which in turn reduces soil compaction and adds to a longer life and a better ride.

The lugs on the Ultraflex tires were also angled at 45 degrees, rather than the more typical 23 degrees, which puts more rubber on the ground. And the edges of the lugs – particularly near the shoulder of the tire – are sharply angled, helping them to grab and hold in the dirt much like a cleat on a steel grouser.

To show how much smoother the Ultraflex tires were, Michelin set up a prototype of the new Challenger MT900B series tractors with a pair of traditional radials on one side and Ultraflex tires on the other side of the machine. Then they had us run over an evenly spaced series of railroad ties, one side at a time. Here the Ultraflex tires showed their merits, delivering a smooth ride with barely any jolting or jarring of the machine. Running over the ties on the regular radial tires caused the seat to bounce and the steering to jerk, making it more difficult to control the machine.