Your Wheels Are Two-Faced, Part One
First things first, the essential core. Around the center bore is a hefty metal plate with the function of connecting all the major players in the wheel - the lug bolts/holes, wheel core, and axle. This sweet spot spoons the surface of the rotor. This configuration happens at the center of the wheel and is responsible for the integrity of the entire wheel-axle setup.
Not to be forgotten, is the stem used to air-fill tires that must protrude through the wheel surface. This consists of a small hole drilled in the wheel to make way for the air valve. This hole can make one side of the wheel lighter than the other, meaning a good spin balancer will have to compensate for it. Valve stems come in all types, from snap-in rubber stems to fancy metal stems with rubber gasket seals.
Anything but a bore, the circular hole in the middle of the wheel is perhaps the most exciting aspect of wheel fit and performance. The center bore refers to the size of the hole where the spigot/axle fits through. This bore is also known as spigot size, and refers to the diameter of hole, usually measured in millimeters. The wheel’s center bore must match the spigot size of the car's axle seat.
Original Equipment Manufacturer (OEM) wheels are made to fit snugly on their original axle seats of their designated cars. However, when dealing with aftermarket wheels, care must be taken to ensure that the size is the same or slightly larger than the OEM center bore size - large enough to fit over the axle. Many aftermarket wheels are designed to accommodate this and will have center bores larger than the OEM size. Hub-centric spacers can be used to fill the overage and keep the wheel functioning properly.
Our list continues next month, so stay tuned…
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