vibration at the front wheels under all conditions of loading shall not
exceed 2.0 hertz. Torque rods shall be provided, if available as
manufacturer's standard or option to increase longitudinal and lateral
18.104.22.168 Full--air rear suspension. The rear axle with full air
suspension shall have four air springs of adequate diameter. The
suspension design shall be such that the natural frequency of vertical
vibration about any transverse axis shall not exceed 1.5 hertz at rated
capacity for required GVW. Full air system shall have none of the
spring weight carried on anything other than air springs. No other
spring medium such as leaf, coil, or rubber springs may be used in
conjunction with the air springs. The full air system shall incorporate
four radius rods to control lateral and longitudinal movement. Radius
rods shall transmit driving and braking forces to chassis and body.
Each end of the radius rods shall be equipped with rubber bushings that
do not require periodic lubrication. Suspension system shall include
locking devices to lock up the suspension to preclude damage when
lifting and towing the vehicle from the rear.
3.4.9 Axles. Axle ratings shall be at least equal to the load
imposed on each axle, measured at the ground, when vehicle is loaded to
required GVW. The drive axle shall be furnished at the front or the
rear. Torque rods shall be furnished for the rear axle(s) if available
as manufacturer's standard or option. Axle gear ratio furnished shall
enable vehicle performance required in 3.3.1. Unless a two-speed axle
is specified, a single reduction drive axle shall be furnished.
22.214.171.124 Two-speed axle. When specified (see 6.2), a two-speed
axle shall be furnished, equipped with electric, vacuum, or air shift
and provided with ratios which will permit proper gear splitting. Gear
ratio shall provide performance specified in 3.3.1.
126.96.36.199 Traction control. When specified (see 6.2), the vehicle
shall be furnished with a traction control on the rear axle. The
traction control shall actuate automatically to insure that power is
transmitted to the wheels having traction when the opposite wheel loses
traction. Maximum traction capabilities shall be maintained at all
times under each drive wheel for the life of the vehicle.
3.4.10 Wheels, rims, tires, and tubes. The vehicle shall be
equipped with single front and dual rear wheels, Rim size, tire size,
type and load range (ply rating) shall be the same for all wheels on the
vehicle. Tire and rim ratings shall conform to Tire and Rim Association
recommendations, for the type and size of tires furnished. When
specified (see 6.2), 10-stud disc type wheels shall be furnished.