Wheel fitment basics.

Lesson 01 / 3 min

Bolt pattern

The bolt pattern is the number of studs and the diameter of the circle they sit on, written like 5x114.3: five studs on a 114.3 mm circle. It has to match exactly.

Some patterns are close enough to look interchangeable, such as 5x114.3 and 5x115. They are not; forcing a near match loads the studs unevenly.

Check the thread size of your studs or bolts, such as M12x1.5 or M14x1.5, and the seat the wheel needs. Conical, ball and flat seats are not interchangeable.

Lesson 02 / 3 min

Center bore

The center bore is the hole in the middle of the wheel that sits over the hub. On a hub-centric fit, the hub centres the wheel, not the studs.

A bore larger than your hub needs hub-centric rings to close the gap. A bore smaller than your hub will not go on without machining.

Lesson 03 / 5 min

Offset and width

Offset, marked ET, is the distance in millimetres from the wheel’s centre line to its mounting face. A higher offset pulls the wheel into the arch; a lower offset pushes it out toward the fender.

Width and offset work together. For your current wheel and the new one, work out how far the inner edge sits from the mounting face and how far the outer edge sticks out. The difference shows whether you gain or lose room at the strut and at the fender.

Check brake caliper clearance too. The spokes need room over larger brakes.

Lesson 04 / 4 min

Tire size

A size like 245/40R18 means a tire 245 mm wide, with a sidewall 40% of that width, on an 18-inch wheel. Keep the overall diameter within about 3% of the original so the speedometer and stability systems read correctly.

Match or beat the original load index and speed rating. Both are on the door placard and on the tire sidewall.

The rim width has to sit inside the tire maker’s approved range for that tire.

Lesson 05 / 3 min

Torque and re-check

Start the nuts by hand, then tighten them in a star pattern to the torque in your owner’s manual, with a torque wrench. An impact gun over-tightens, which can stretch studs and distort brake rotors.

Re-check the torque after the first 50 to 100 miles (80 to 160 km). Wheels can settle, especially alloy wheels.