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Technical Knowledge

A Guide to Common Wheel Terminology

keltgen wheel
September 15, 2022
min read

Hardly anyone reads the regular old dictionary for fun. So absolutely nobody is going to pick up a sheet of wheel terminology and pore over it for grins. But if you need to order a custom wheel, it helps to be familiar with some common industry wheel terminology. Without any further fanfare, here’s our version of the wheel dictionary.

Back Set

A measurement from the mounting face inboard to the wheel’s bead seat. 

Bead Seat

The surface where the tire and wheel form a sealing seat when assembled. 

Bolt Circle (diameter)

The distance between bolt holes on opposing sides of the wheel (center of hole to center of hole). For example, you would measure from the center of the 12 o’clock hole to the center of the 6 o’clock hole.

Bolt Pattern

A wheel’s mounting pattern, which includes 4 pieces of information:

  • The center (pilot) hole diameter. This is the opening in the center of the disc.
  • The bolt circle diameter from hole center to hole center. (See Bolt Circle above.)
  • The bolt hole diameter.
  • The bolt hole type (flat or some type of tapered design).

Drop Center

The inside diameter of the rim at the point where the center disc is normally welded into the rim.

Dual Holes

Holes added to the center disc to accept a dual wheel application.

Negative Offset (outset)

When a wheel’s hub mounting surface (center) is behind the wheel centerline, or toward the center of the machine. 

Non-Reversible Wheel

A wheel that can only be mounted to the hub from one side of the center disc mounting face. 

Positive Offset (inset)

When a wheel’s hub mounting surface (center) is in front of the wheel centerline, or toward the outside of the machine. 

Reversible Wheel

A wheel that can be mounted to the hub from either side of the center disc mounting face.

Rim (or wheel) Width

The width of a rim (or wheel) measured between the bead seats. 

Rim (or wheel) Diameter

The diameter of a wheel as measured from the bottom of the bead seat.

Valve Guard

Often a welded ring of metal on the wheel to protect the valve stem. 

Questions when ordering a custom agricultural wheel? Call Keltgen Wheel.

If you’re measuring up a wheel for your own machine or a customer’s machine and you have a question about what you need to measure—or how you should measure it—call Keltgen before you spend time scratching out measurements on a napkin or other scrap of shop paper.