15"

15-inch wheels are a classic size for light cars, historic and club racing and gravel rallying, where a tall tyre sidewall and low wheel weight count. This section holds 15-inch wheels of 6.4 to 6.7 kg in 7, 8 and 9 J widths, with four- and five-stud patterns.

Rim diameter decides how much of the wheel’s height is tyre. On a 15-inch rim the sidewall is tall, so it soaks up bumps, gravel and kerb strikes and gives a progressive feel at the limit. The trade-off is slower steering response, as the sidewall flexes before the contact patch follows the wheel.

Low weight is the other advantage. A light wheel cuts unsprung mass, helping the damper keep the tyre in contact on a broken surface, and lowers the inertia the engine and brakes must overcome. The limit is brake space: a 15-inch barrel leaves room for modest discs and calipers only, so check any uprated brake kit first.

Choose in this order:

• Bolt pattern: 4×100, 4×108 or 5×120, the stud count and the diameter in millimetres of the circle they sit on. The pattern must match the hub exactly.
• Width: 7 J, 8 J or 9 J, the figure being the rim width in inches between the flanges. Each tyre size has an approved rim width range, so check it before choosing a wide rim.
• Offset: ET 15 to ET 35. ET is the distance in millimetres from the rim’s centreline to the mounting face, and a lower figure places the wheel further out.
• Load rating: 400, 475 or 525 kg per wheel. Two wheels share each axle, so the rating must reach at least half the maximum axle load; these figures suit light cars.
• Finish: gloss anthracite or matt black.

Check the wheel’s centre bore against the hub spigot, and fit a centring ring if the bore is larger, so the wheel is hub-centric. Use bolts or nuts with the seat type the wheel needs and a length that suits its mounting face. On gravel and kerbs, check the rims for dents and cracks after each event, and check the fastener torque between sessions.