Specifications for D.O.T. Trailer Wheels

The Department of Transportation (DOT) and the Federal Motor Carrier Safety Administration (FMCSA) determine what regulations commercial motor carriers must follow in terms of safety. A commercial driver must perform a pre-trip inspection of his vehicle each day, to make sure all parts meet DOT regulations. Safety of the driver and the traveling public depend on how compliant companies are with those regulations. One of those many parts that must be inspected are the wheels. Semi tractor and trailer tires and wheels are deadly if they become disengaged while moving at interstate speeds. Daily safety checks ensure wheels meet DOT specifications.

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Wheels and Rims

Match the wheel and tire for maximum load safety.
The wheels and rims on a trailer cannot be broken and there cannot be any visible cracks. Wheels on trailers are constantly under large amounts of pressure. The weight of a trailer, in combination with the weight of the load may cause stress fractures in the wheel or rim. Wheels and tires have specific weight recommendations, if they are mismatched, cracks can form which will allow air to escape from the tire. Eventually the tire will go flat and could cause an accident if tread were to separate.

Stud or Bolt Holes

Out of shape bolt holes could mean an air leak.
Wheels have 10 bolt or stud holes. The bolt holes cannot be elongated or stretched out of shape. They must be round. Elongation from over-torquing or uneven torquing can happen when under-trained mechanics use air-powered tools. Proper torque is required to prevent cracks or elongation. Misaligned bolts may also cause stress on the holes, causing fractures which will allow air to escape and the tire to go flat.

Nuts or Bolts

Bolts can become loose and fall out.
Missing or loose bolts are also a violation of DOT regulations. Mounting tires in a warm area, then exposing them to colder outdoor temperatures, can cause metals to contract, causing bolts to become loose and fall off. Improper torque can cause bolts to fall off as road vibration and constant turning puts pressure on the bolts. When a bolt is missing, there is added pressure on the bolts on either side of the missing bolt. These remaining bolts may become loose, break and fall out. Eventually, the tire could fall off.