Wheelbase of a Trailer

Lookup what wheelbase is

 

Track, not wheelbase, it's the word you're looking for. Generally, most modern 102" trailers use axles that take the wheels out to 102".

The exceptions I most often see are trailers retrofitted with super singles, which narrows the track. There's also a manufacturer of high-mount carhaulers that uses 96" track axles on a 102" chassis. Looks like a toy.

 

No, they are still (or should be) running parallel to the drives, just offset 3 inches to the outside on each side.

 

On crowned roads they're always slightly out of alignment to one side or the other, even if everything has the same track width.

 

Most cars have a slightly wider track on the front axle than the rear axle. As long as the midpoint of each axle (halfway between the outer left side and outer right side) is lined up it's not a problem.

 

You are confusing TRACK with WHEELBASE. Most 102" wide trailers have a 102" TRACK axle, but there are (were?) exceptions, like rigs used in severe northern conditions, where rutted wheel tracks were the norm, so sometimes a 96" (old standard) axle TRACK was was the norm. Most tractor units used to come with a 96" wide axle, because there used to be both 96" wide and 102" wide in service, and in some states, 102" wide rigs were not allowed on back roads.