Another silly question.

Is there a particular reason why trailers have the spare tire mounted on the passenger side of the vehicle (right side)?

That's usually the side with the tack access and so you want to tie your horse there.. spare tire is kind of in the way.

The discussion came up today because my mom was finally getting around to mounting her spare tire, and her boyfriend insisted it had to be on the right side because that's where it was on everyone else's trailer so he figured there's a legal/technical reason for it. They compromised by putting it in the dressing room, but it got us wondering why its always on the right side?

If you have a flat tire you will likely pull to the right.  If tire is on the right side you will not be standing in traffic trying to remove the spare from the trailer.

An old "spare" thread....

http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=11275

We have a Sidekick with a street side mounted spare. It's mid tack and main entrance door is on the curb side. The awning braces are also affixed to the curb side.

 Various trailers have entry doors mounted on both sides, and the awnings will vary as well. If a trailer has a LQ, the area under the goose will often be utilized for batteries and propane cylinders. These differing configurations and equipment, will determine what space is available for the mounting of spare tires. The braces for an awning could interfere with the placement of a tire, as well as a door that may swing around to the side when it is opened and latched.

You can mount the spare in any place that is most convenient. There are no hard and fast rules.

Gard