How Spare Tire Mounts Work

Choosing a Spare Tire Mount

This spare tire mount simply attaches to your trailer hitch.
This spare tire mount simply attaches to your trailer hitch.
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Automobile and trailer manufacturers have managed to find places to stow tires in just about every available location: on the trunk, in the trunk, on the roof, under the car, on the side and even right on top of the engine. When adding a spare tire mount, however, your options aren't as limitless.

If addin­g a spare tire mount to a vehicle, you'll want to be able to secure the spare without adversely affecting performance or safety. If you add a spare tire mount to the back of your vehicle, will you still have access to your trunk? If you mount it on the roof or in a truck bed, will you miss the lost cargo space? Offset and extra-offset trailer mounts help out with some of these problems by positioning spares away from the part of the vehicle or trailer to which they're mounted.

With trailers, you face a similar situation. While having an extra trailer tire on hand could save you a lot of grief in the event of a flat, the last thing you want to do is limit your payload. Your spare tire doesn't have to hang there, though. Some designs mount the spare tire on a small, rotating axle beneath the trailer tongue, the part that extends from the payload to attach to the tow vehicle. This arrangement allows the spare to serve as a dolly wheel when the trailer's unhitched.

­Once you're done choosing a spare tire mount and have evaluated where you can realistically install it, you had better make sure you have the right tires in mind. That's right, not all tires or tire mounts are the same. Whether you're looking to haul a spare for your truck or your trailer, knowing the wheel's bolt pattern is essential. Your spare tire may have four, five or even eight bolt holes.

Next, you'll want to determine the bolt circle, which is the center-to-center diameter of the imaginary circle that the bolts outline. With even bolt numbers, you'll simply measure the distance between two opposing holes. With odd numbers, you'll measure the distance between a hole and the halfway point between the two bolt holes opposing it. If your wheel has five bolt holes and the bolt circle is 4.5 inches (114.3 mm), then your bolt pattern would be 5 on 4.5. While some spare tire mounts are universal and will accommodate any bolt pattern, others will only work with certain measurements.

Know what you need? Read the next page to find out how that spare tire mount will become one with your vehicle or trailer.