What it Does
Corrosion commonly develops in the places (hubs) where the wheels are attached. It is commonly found on the wheel and also on the rotor or drum that goes between the wheel and the wheel hub. This corrosion develops due to dissimilar metals in contact with each other and environmental conditions (humidity, road water, etc.). It is also common to find corrosion between the hub and the brake rotor or drum that attaches to it.
Why This Matters
Corrosion in the wheel attachment area increases the risk of the wheel coming loose. Uneven attaching surfaces, material fatigue, and bind-up can all contribute to this.
Possible Problems and Concerns
Material Fatigue
Corroded metal is not as strong as it used to be. If a wheel is tightened down against or with a corroded surface, material may break off between the wheel and the hub. Lug nuts/bolts that felt tight pulling against the corroded surface(s) can quickly loosen when this happens. That corrosion was holding the rim away from the hub. Once it breaks, the rim can move closer to the hub, which will relieve tension being held by the lug nut/bolt. We want that tension because that’s what holds the wheel on.
Bind-Up
Wheels are commonly installed via “hub-centric” mounting. In this case, a portion of the hub fits just right through the hole in the middle of your wheel. If corrosion sets in on either of these surfaces, that corrosion can hold the wheel away from the hub. The wheel may also cock sideways as the lug nuts are tightened down. While the lug nuts may feel tight at the moment of installation, the vehicle’s weight, vibration, and road forces may loosen them over-time. If the rim overcomes the corrosion and moves closer to the hub, this will relieve tension on lug nuts/bolts.
We also encounter hub-centric corrosion when removing wheels. This can seize the wheels in place even with the lug nuts/bolts removed. The required removal force can range all the way from a light tap or a good tug to hard but controlled hits with a dead-blow hammer.
Uneven Surfaces
A tight fastener won’t always stay tight. Surface asperities and vibration contribute to fastener loosening, and this can be true even when bolting two flat surfaces together. If corrosion results in an uneven surface being bolted to a flat surface, or two uneven surfaces being bolted together, the fastened joint is put under abnormal stress, and vibrations, weight, and road shocks may cause the wheel lug nuts/bolts to work llose.
End Results
The consequences of a wheel coming off can be severe. The vehicle may be damaged mechanically, and the odds go up of being involved in an accident. The wheel and tire assembly may actually keep rolling on its own, and due to its mass and speed, it may kill a pedestrian or animal or cause property damage.