Trailer swing clearance

Did you ever think that there is more to clear than just the trailer to cab or sleeper? If you draw a straight line from kingpin to any object you can see if clearance exists. But does that margin remain constant as the combination turns a corner? If your geometry teacher was good about application, you would know that this is where the Pythagorean Theorem comes into play. A-squared plus B-squared equals C-squared. Sure, we all recall the rhyme, but how does that apply to a truck?

Imagine these scenarios Back of Cab or Sleeper

• A = distance from kingpin to side edge of trailer.

Example: 51 inches

• B = distance from kingpin to forward face of trailer.

Example: 36 inches

• Square both A and B numbers and then add the results together.

Example: (51 x 51) + (36 x 36)

• Find your phone & calculate the square root of the sum.

Example: (2610 + 1296) = 3897 sq. root 62.4 inches

This means you need at least 63 inches between the 5thwheel position and the back of the cab or sleeper to avoid contact in a turn.

Landing Gear

• A = distance from kingpin position to position of mudflap.

Example: 51.5 inches

• Half tire dia. (20.5) + Half axle spacing (27) + Standard tire to mudflap dim. (4) + 5th wheel position (0)

• B = distance from kingpin position to edge of vehicle mudflap (or outer tire).

Example: 48 inches

• Half the width of the trailer

• Square both A and B numbers and then add the results together.

Example: (51.5 x 51.5) + (48 x 48)

• Find your phone & calculate the square root of the sum.

Example: (2652 + 2304) = 4956 sq. root 70.4 inches

This means that when the 5th wheel is placed at the calculated spot (in this case zero or bogie) you will need 70.5 inches to the landing gear to clear the mudflap bracket in a turn.

Interesting point. Trailers do not have a standard landing gear position. Beyond that, most people who encounter interference within a sales tool result believe that decreasing the overhang dimension will resolve the issue. If you have mudflaps on your vehicle, they are usually the item that influences the equation most. So feel good about the sales tool results, but understand what it takes to resolve the issues, and what questions you should be asking the customer.