If you've been shopping for aftermarket wheels at all, you've probably heard the term, “hub-centric” in regards to a set of wheels, usually as a selling point. Or maybe you've been cautioned to avoid “lug-centric” wheels, although perhaps the warning is a little fuzzy as to what that is, or why to avoid them. The actual concept is pretty simple, but it almost never gets explained in a simple way. The most common misconception I see is that there are specific wheels that are “hub-centric” or “lug-centric”, when in fact the terms properly refer to how the wheel actually fits onto the car.
Nearly all OEM Wheels are designed to be hub-centric. The automaker designs an OEM wheel to fit on a certain car or range of cars. The center bore of the wheel is sized to fit perfectly onto the axle of that car. This is a hub-centric connection, as the wheel is centered by it's connection to the axle hub. The lugnuts hold the wheel firmly to the mounting plate, but it is the wheel-to-axle connection that actually holds the weight of the car. This is quite an important distinction, as the lugnuts are designed to handle lateral forces that push the wheel away from the mounting plate. The forces that the hub and center bore connection are designed to withstand – the weight of the car forcing downward and impacts forcing upward – are at right angles to the forces that the lugnuts are designed for.
Hub diameter is therefore an extremely important consideration when fitting new wheels, whether OEM or aftermarket. If the hub diameter is smaller that the axle, the wheel will simply not fit. Most aftermarket wheels are therefore made with larger hub diameters to ensure that they will fit on a wide range of cars. This means that when the wheel is installed, there will most likely be a space between the axle and the hub instead of a firm contact. The wheel is therefore lug-centric, as the wheel is centered by the lugs rather than by the hub. There are some people who will say that driving on lug-centric wheels doesn't really matter as long as the lugnuts are the self-centering cone type, as they will adequately center the wheel. These people are wrong. Driving on lug-centric wheels means that any impact will apply shear force to the lug studs, forces at 90 degrees to those the studs are designed to handle. This can cause the lug studs to bend, leading to a vibration in the car as the wheel slips around on the mounting plate, and possibly damaging the wheel's center bore if it has enough play to contact the axle. To prevent this kind of thing, aftermarket wheels will usually need hub-centric spacers, small rings of metal or plastic made with various inside and outside diameters so as to fit inside the wheel hub and then fit over the axle, making a lug-centric fitment into a hub-centric one. Some aftermarket wheel makers advertise that all of their wheels are in fact hub-centric – what this means is that they provide the proper spacers for the customer's car, not that they custom-make their wheels for the many hub diameters out there. Most good wheel retailers, online or otherwise, will provide the correct spacers as part of the fitment package. If you do need to shop for a set, try one of the better online stores. In Real Life, most tire retailers will also either carry spacers or will know who does. Do not make the mistake of thinking that spacers are optional equipment, or that a retailer is trying to upsell you on some useless accessories. Hub-centric spacers are actually about as necessary for aftermarket wheels as lugnuts are. Keep the proper fitment for your wheels and you'll be driving happy for a good long time.