Original equipment wheels that come on a car are designed so that they fit snugly around the center of the wheel hub. This is important because that takes the load off of the studs, so they’re not what’s holding all the weight and forces of the car. Aftermarket wheels are designed to be able to fit multiple vehicles, which may have different sizes of hubs.
Because of that, you need centering rings that take up that gap and make the wheel fit tight to the hub. But as important as it is to remember to put those on, you have to remember to take them off when putting OEM wheels back on. This car came into the shop and the technician found that the aftermarket center ring was still on the hub under the OEM wheel, which prevented the wheel from being properly mounted, which is definitely a big safety hazard. The customer is lucky that the wheel didn’t come loose while driving.
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