How Spare Tire Mounts Work

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.

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That spare tire mount isn't going to install itself. If you find the task too intimidating, you can always pay a professional to install it at a garage. Otherwise, until scientists create a robot tire mount that will do the work for you, you're going to have to bust out a few tools.

The exact nature of the required installation depends on the type of spare tire mount you picked out. This means installation might be as simple as tightening a few bolts. On the other hand, you might have to figure out from whom you can borrow a welding torch. Let's look at a few varieties of spare tire mounts and what all's involved in sticking it on.

Trailer hitch mounts: As the name implies, these spare tire mounts connect to trailer hitches. Simply remove the drawbar or hitch cover and slide the mount's end into the receiver tube. Then, all you have to do is lock it in place with a hitch pin or hitch lock. Just make sure the mount fits your hitch size. If the pieces rattle too much, you can also install a hitch stabilizer to smooth things out.

Bumper mounts: If your truck or trailer has a bumper, you may have another mounting option for your spare tire mount. Bumper mounts attach to the bumper with U-bolts, which are long, two-headed bolts bent into a "U" shape. These special bolts go around the bumper and screw into the spare tire mount, locking it firmly in place.

Tongue and frame mounts: Some trailers, such as those used to haul boats, are essentially metal frameworks. Technically, you can latch a spare tire mount to any portion of the frame, so long as it doesn't interfere with the payload or the towing vehicle. Various spare tire mounts are made to work under these conditions. Once you've found a suitable location on the trailer, these spare tire mounts are easy to install. The mount attaches to one side of a trailer beam and a pair of long, narrow pieces goes on the other. Screw four bolts into place, and the trailer beam is sandwiched firmly between the two pieces. In addition, some models attach with U-bolts.

Horse trailer mounts: Horse and livestock trailers often boast a rather simple spare tire mount design. Horse trailer mounts consist of a single, rectangular piece of metal with its ends bent down to form two legs. Installation typically calls for these legs to be welded to the trailer, usually atop the raised gooseneck between the trailer and the hitch.

Truck bed mounts: Granted, you can always just throw a spare tire into the back of the truck unsecured, but this doesn't really help you protect against theft or possible damage. Several different spare tire mount designs actually attach to portions of the truck bed. Some lock into the side, near the wheel well, to save room. Others bolt to the center of the bed on an angled metal tripod or even allow you to mount the spare under the bed. It all comes down to what you plan to use your truck for.

If none of these designs fills your requirements, don't despair. You can find spare tire mounts designed to fit specific needs, such as those made for RVs or Jeeps. A number of mounts are designed to attach to roof racks. If you've thought about sticking a spare tire mount to your vehicle, some enterprising individual probably has as well.

Want to make sure you have all the parts you'll need? Read about spare tire mount kits on the next page.

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You've taken a close look at your vehicle or trailer and evaluated your spare tire needs. You have even read up on how to install it. The last thing you want is to get home from the automotive parts store and find out that you have to make a second trip because you're missing a few essential items. Luckily, many stores sell spare tire mount kits to ensure you have everything you need to make it all come together.

The exact contents of a tire mount kit depend entirely on the variety of spare tire mount you've decided on. For instance, some tongue or frame mount kits include the spare tire mount and the bolts, screws and back pieces required to attach and assemble it. But while one manufacturer includes all the necessary parts in a kit, others don't -- and you're on your own for tools. While a kit such as this is more general, other kits work with specific vehicle models.

Think of those kids' snack packs that contain crackers, a little cup of cheese and a plastic spreading paddle. They include everything you need to assemble a few cheese and cracker sandwiches. If you want peanut butter and crackers, however, you'll need a different kit. If you were able to wrap your head around this fact of life in second grade, then you're well prepared for the realities of purchasing a spare tire mount kit. Make sure you know what you need, ask a professional if necessary and check to make sure the spare tire mount kit has all the necessary pieces.

You can haul far more than spare tires with vehicles and trailers. Explore the links on the next page to learn much more about towing.

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