Air pressure within a tire forces its bead against the wheel rim and ensures that they rotate as a single unit. When more traction is needed for an off-road vehicle's tires, drivers will often lower the air pressure to cause the tread to spread out and create a larger contact patch. This practice can create a safety hazard as there may not be enough pressure to secure the tire to the wheel. In certain situations where there is a lot of pressure pushing the tire to one side or the other, the bead of the tire may come off the wheel. It is also possible for the tire to have more traction on the ground than there is friction between the tire and wheel. In this case the wheel would spin within the tire without being able to turn the tire. Beadlocks are therefore designed to "lock" the bead of the tire onto the wheel.
A standard beadlock is designed to clamp the tire bead between an outer and an inner ring. The inner ring may be welded onto a standard wheel or may be formed as part of the wheel when the wheel is made in the factory. The outer ring is then bolted onto the inner ring with the bead clamped between them. Anywhere between 16 and 32 bolts are used around the circumference of the wheel to keep the clamp tight. The rings and bolts can cause problems with balancing the wheel and tire because all the added weight is on one side.
It is important to note that most standard beadlocks clamp only the outside bead. This is fine in most cases because the outside bead is the side that comes unseated most often while off-roading.
An internal beadlock is very much like an inner tube within the tire that pushes the bead of the tire tight against the wheel. The internal beadlock is inflated via its own valve stem. The side of the beadlock closest to the tread, the "case", has a layer of thick fabric, generally polyester, which keeps the beadlock from inflating too far up into the tire. This forces the sides into the tire which compresses the bead of the tire against the wheel.
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Cut away view of internal beadlocks within tires.
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Cross-section view of internal beadlocks.
Some people will want their vehicle to look like it has beadlocks without actually paying the additional cost of real beadlocks. Many wheels are therefore made to look like beadlocks but they don't actually lock anything. The off-road community generally refers to these as "streetlocks" since the owners typically don't use them for off road use.