easy removal of the tire from the wheel and. when in
place. it provides a seat for one side of the inflated tire.
A standard wheel consists of the RIM (outer lip
that contacts the bead) and the SPIDER (center section
that bolts to the vehicle hub). Normally the spider is
welded to the rim. Common wheel designs are as
Drop Center Wheel
The drop center wheel (fig. 8-35) is made in one
piece and is commonly used on passenger vehicles
because it allows for easier installation and removal of
the tire. Bead seats are tapered to match a
corresponding taper on the beads of the tire.
Semidrop Center Wheel
The semidrop center wheel (fig. 8-36) has a
shallow well, tapered-head seat to fit the taper of the
beads of the tire. It also has a demountable flange or
side ring. which fits into a gutter on the outside of the
rim. holding the tire in place.
A safety wheel (fig. 8-37) is similar to the drop
center wheel. The major difference is that the safety
wheel has a slight hump at the edge of the bead ledge
that holds the bead in place when the tire goes flat.
A split wheel (rim) (fig. 8-38) has a removable
bead seat on one side of the rim. The seat is split to
allow for its removal so tires can be easily changed.
Some bead seats also require the use of a lock ring to
retain the seat. These wheels are used on large
commerical and military vehicles.
LUG NUTS, STUDS, AND BOLTS
Lug nuts hold the wheel and tire assembly on the
vehicle. They fasten onto special studs. The inner face
of the lug nut is tapered to help center the wheel on the
hub. Lug studs are special studs that accept the lug
nuts. The studs are pressed through the back of the hub
or axle flange. A few vehicles use lug bolts instead of
nuts. The bolts screw into threaded holes in the hub or
Normally, the lug nuts and studs have right-hand
threads (turn clockwise to tighten). When left-hand
threads are used, the nut or stud will be marker with an
"L." Metric threads will be identified with the letter M
or the word Metric.
Figure 8-35.Drop center wheel.
Figure 8-37.Safety wheel.
Figure 8-36.Semidrop center wheel.