Look inside almost any wheel and you should find various markings which give you pertinent information on the wheel. Typically, they?re marked on the rim and, just for conversation sake, we?ll take into consideration a wheel which is marked “19x7J ET 38.” The first number is quite obvious and represents that the wheel is 19 inches in diameter, while “7” is the width of the wheel and measured from the distance between the flanges that support the bead. The “J” refers to the shape of the flange; easier to understand if you imagine a steel wheel on which the lip is rolled over like a J. “ET” may or may not be present, and if you do see it is the abbreviation of einpress tief, German that translates literally as “pushed in depth,” or offset. The “38” is the offset measurement.
Diameter of the bead seat area of the rim (not measured at the overall rim diameter).
Width measured from the front bead seat wall to the rear bead seat wall. Not measured at the overall wheel width.
Distance from the wheel hub mounting face to the rear outer edge of the rim.
Offset is the location of the flat mounting surface of a wheel relative to the wheel relative to the wheel’s centerline
The difference between the true center of the rim width to the location of the hub mounting face. If offset pushes the tire outward relative to the hub face (deep-dish appearance on the outside), this is negative offset. If offset locates the tire inboard relative to the hub face, this is positive offset.
Negative offset means that the mounting surface is toward the center of the car. A negative offset wheel features more rim area shoved outboard, giving it a “deep-dish” appearance because it moves the tire m further outward in the wheel well. Positive offset means that it’s toward the outside of the car, or the wheel is “pulled in” toward the center. Offset affects many things other than just whether the wheel has the appearance of “sticking out” past the fender. The wrong offset can cause rubbing problems when the suspension is compressed or the wheel is turned. Offset affects the steering geometry’s scrub radius, possibly leading to problems with torque steer or self-centering characteristics. Offset also affects the suspension’s motion ratio, which directly determines the effective spring and damper rates. Potentially, in a very heavily loaded vehicle, or with extreme changes in offsets, wheel bearing life can be affected, but this is more often talked about by truck people than by small car enthusiasts. It’s very, very important that the proper offset wheels be used.
P.C.D. or Bolt Pattern
The P.C.D. (Pitch Circle Diameter), often referred to as the “bolt pattern,” refers to the pitch circle diameter of the bolt holes. The value varies depending on the vehicle type.
P.C.D. or Bolt Pattern identifies the number of fastener holes along with the diameter path of the hole placement. A 5 x 100 bolt pattern indicates five mounting holes, with hole centers oriented along a 100mm diameter.
