Friday, 4 May 2012

Wheel Anatomy : Structure

The outboard face is the part of the wheel you can see when it is bolted onto the car. We often refer to it as the “cosmetic face” but it is also the structural face of the wheel, since the other side is essentially required to be an open cylinder. This makes the outer face less directly vulnerable to impact damage, since it is simply easier to bend the open cylinder than the structure, but it can also make the damage that does occur a lot worse.

Center Bore
Structurally, the empty space inside the center bore is one of the most important points on the wheel. This hole fits over the end of the axle when the wheel is bolted on. It is this fit between the axle seat and the center bore that truly holds the weight of the car, as lugnuts only serve to keep the wheel on the axle. For this reason, OEM wheels are made to fit closely on the axle seats of their designated cars. When buying aftermarket rims, care must be taken to ensure that the center bore is the same or larger than the OEM size - large enough to fit over the axle. Most correct aftermarket wheels will have center bores that are larger than the OEM size, and so the gap between must be filled by “hub-centric spacers” to avoid damaging both wheels and lugnuts.
Around the center bore there is generally a substantial piece of metal interrupted only by the bolt holes. We call this the plate. The plate is the core of the wheel, the point of contact to the axle seat, the lug bolts and the lateral surface of the rotor. Everything else on the wheel is connected back to the plate.
In essence, the spokes are the structures between the plate and the outer edge of the wheel. They are designed to tie the wheel together, support the outer edge and resist impacts. Spoke designs vary wildly, from the classic 5-spoke patterns to intricately overlapping multiple “Y”-spoke extravaganzas. It's important to note that the strength and damage resistance of spoke designs also vary, because if a spoke gets cracked by an impact the nature of the structural relationship is such that attempting to repair it by welding would be unwise and possibly dangerous.
Although it also refers to the outer part of a 3-piece wheel, the dish is generally thought of as that portion of the wheel that comes out beyond the spokes. A wheel where the spokes are sunk inches below the lip is a