Wheel Rims Measuring Guide

Wheels are listed with a complete specification that together describe its size and shape. The specifications can be quite complex depending on the type of wheel rim you require. All of the measurements are vital to ensure a rim will fit correctly onto your vehicle and that the tyre can be mounted and the tyre bead secured.

The most important measurements are:

Wheel Size:  A 'wheel size' marking includes rims width in inches, as well as the rims total diameter in inches. The wheel diameter will always match exactly with the tyre marking's rim diameter. The wheel rim width however will be narrower than the tyre width size they will have fitted to them. So a wheel size of 7.50x22.5 is 7.5" wide and 22.5" in diameter, it will be used on a tyre that also has a rim diameter of 22.5" but that is wider such as an 11" wide tyre such as an 11R22.5 tyre. The 'x' character inbetween the two numbers often means its a welded single piece rim, whereas a '-' can instead mean its a split or multi piece rim that can seperate such as on forklifts or earthmoving equipment. 

Centre Bore Hole Diameter:  The diameter accross the drilled centre hole in the middle of the wheel rim, in mm.

Stud Count:  The total number of stud holes that surround the centre bore hole. 

Stud Hole Diameter:  The internal diameter of each stud hole, in mm.

PCD (Pitch Circle Diameter):  For an even number of studs this is simply the distance between the centres of two directly opposite stud holes. Also known as the Bolt Circle Diameter (BCD). For an odd number of stud holes you can instead measure the distance from the centre of one stud hole to the edge of the wheels centre bore hole, then double this number and add it on to the Centre Bore Hole Diameter figure.

Distance Between Adjacent Studs:  The distance between the centres of two adjacent stud holes. This is only needed if you do not know your exact PCD, and your wheel rim has an odd number of studs, as it can be used in an alternate formula that will calculate or confirm the wheels PCD. 

Offset:  The offset determines how far out your wheel and tyre assembly sit out from your machine. It ties in with your machines track width, that is the distance between your tyre tracks. It's important to work within acceptable offsets / track widths for your vehicle to ensure proper handling, performance and safety. it is measured as the distance between the rims centre plate and the back edge of the rim. If you know the exact offset of the hub then you can provide it, but please specify whether the centre plate is offset towards the front or the back of the wheel, this is known as positive or negative offset, as illustrated in the image below. You can also additionally or alternatively provide the measurement for the front spacing and rear spacing measurements, that is the distances from the face of the centre plate to the edge of the wheel rim. 

Wheel offset is the distance from the middle of the rim to the to the mounting pad. The mounting pad is the rear face of the wheel centre which has the bore and stud holes. On a flat-disc wheel the mounting pad will be flush with the rest of the centre plate, but on a profiled disc the mounting pad will be raised. If the mounting pad is in line with the centre line then the wheel has Zero Offset. If the mounting pad is closer to the front edge of the wheel then the wheel has a Positive Offset, and if the mounting pad is closer to the rear edge then it has a Negative Offset. If we are manufacturing the wheel then we need either the Rear Spacing or the Wheel Offset.

There are other wheel specifications and measurements that may be needed for some wheel rims. These can include:

Centre Plate Thickness:  The thickness in mm of the metal centre plate itself. For larger agri and construction wheel rims designed to carry high loads the centre plates can come in a couple of thickness', with the thicker plates enabling more weight to be supported by the wheel rim. Measure the centre plate thickness through the centre bore hole or stud holes.

Stud Hole Finish:  The stud holes could be countersunk, either on the inside or the outside of the hub, they could be plain or they could have another finish such as counterbored or counterdrilled. Sometimes the stud holes will pressed with a conical stud seat of 60, 80 or 90 degrees that will help the wheel nut seat correctly.

Wheel Well Shape:  Wheels have varying shapes of wheel wells between the outer edges of the rim. They can have a single well in the middle, a double well or other variations. The wheels can also have bead angles of varying degress and styles. All of these well variations are designed to accomodate different tyres and aid their fitting and ensure secure tyre bead mounting. These shapes are often described by letters within the wheel size, such as W10x36, DW18x24, 7.00Ax8, 5.5Jx14.

To pass us your information please fill in the form below and click 'Submit'. Once received we will contact you with a quote and lead time to supply your wheel rims. This form is also available to Download in PDF Format or Download in JPG Format if you wish to print it out.