Tire tactics
With military equipment playing such a prominent role in world news recently, I thought it might be interesting to see how tires spec'd for these vehicles compare to those used on over-the-road trucks.
In terms of similarities, both must support loads, transfer driving and braking torques, generate cornering forces, and cushion impacts from the variety of surfaces traversed. Military tires, however, tend to be vehicle-specific designs that incorporate mobility and damage resistance features that go well beyond mixed-service truck tires.
Tactical vehicles comprise the largest segment of military trucks used in off-road applications, and are generally divided into three size categories: light, medium and heavy. The High Mobility Multipurpose Wheeled Vehicle, aka “Humvee,” is a typical light military vehicle. It's fitted with aggressive tread 37 × 12.50R16.5LT radial tires. On-board inflation systems are also spec'd, allowing tire pressures to be tailored to the terrain.
Modern radials, unlike bias-ply tires, can be designed to be very durable under much wider ranges of inflation pressure and footprint length. Low inflations, and corresponding longer footprints, allow these tires to perform well in sand or as flotation tires. They can also be very durable at high speeds in over-the-road use when inflated to higher pressures.
Medium tactical vehicles, such as the traditional 4 × 4 and 6 × 6 AWD transports, are typically equipped with 11.00R20, 14.00R20, or 395/85R20 tires. A majority are tubeless designs, even though they're fitted to flat base rims. This is accomplished by using two-piece rim designs, which include sealing O-rings, similar to the mounting systems used on larger earth-mover vehicles.
Heavy tactical vehicles include a wide array of larger trucks, tractors, and specialty trailers, which are tailored to transport specific equipment and weapons systems. Popular chassis configurations are 8 × 8 and 10 × 10 AWD units with tires mounted as singles. The most common tire size for these trucks is 16.00R20, usually fitted as tubeless designs to enhance durability, minimize downtime, and reduce maintenance.
Mobility is the word that best describes the overall design emphasis of military tires. Large-diameter tires are preferred because they provide added ground clearance and lower spring rates, which help cushion ride on rough terrain. Other advantages include better traction and flotation in soft soil or sand.
Sidewall designs are also different for many military tire applications. First, additional long-term weathering resistance is sometimes required to meet stringent military tests, which assure that tires remain ready for duty even after long periods of storage and exposure to sunlight.
Second, extra sidewal-abrasion damage resistance may require heavier, thicker rubber reinforcement for use on rock, debris, or other adverse surfaces. New technology and materials have been applied to military radials, greatly upgrading their performance, yet retaining the softer ride and improved fuel efficiency typical of their commercial counterparts.
Modern linehaul radials routinely deliver tread wear, casing durability, and fuel efficiency so reliably that some operators take them for granted. This is due in some part to intense competition among tire makers, whose products are compared every day out on the road. In contrast, military vehicles may sit for long periods of time, but are expected to perform at high standards on short notice. Judging by recent events, mission accomplished.
