Tires are one of the more vulnerable parts of your vehicle. Running into a curb while parking, hitting a nail on the road, or countless other hazards can leave you with a flat. And if you don't keep the tires properly inflated, the tires will wear out faster and have a higher chance of blowing out.

A spare tire will offer temporary relief from a flat tire, but it isn't intended to be a permanent replacement. If a tire is too damaged to be repaired or has worn down to an unsafe point, you'll need to buy a new one.

For this reason, a tire warranty can be particularly helpful. This coverage usually guarantees that the tire will last for a certain distance or amount of time, and may also guard against unexpected damage. However, it's important to read the fine print to make sure you understand what the warranty offers.

Many tire warranties are known as "tread life" warranties. Ronald Montoya, writing for the automotive site Edmunds.com, says the warranty estimates the number of miles the tire will be able to cover before the tread depth reaches the unsafe point of 2/32nds of an inch. When the vehicle has different sized tires that cannot be rotated, there are usually different mileage estimates for the front and rear tires.

This warranty becomes useful if the tire wears out prematurely, since you'll be able to purchase a new tire at a prorated price. If the tire was rated for 90,000 miles and needs to be replaced after 75,000 miles, your next purchase will be discounted by about 17 percent.

There are often caveats to this benefit, however. Gordon Hard, writing for Consumer Reports, says the discount will likely be based on the standard retail price of the tire. Once it is applied, it might not save you much money compared to a discount which is being offered by the tire shop or dealership.

In addition, you'll only be able to use a tread life warranty if you've been taking care of your tires. You should regularly check the tire pressure and keep it at the manufacturer's recommended level, since the warranty can be voided if there is uneven wear or other evidence that you have not done this due diligence. You'll likely need to produce documentation showing the odometer mileage when the tire was purchased as well as any record of applicable servicing, such as tire rotation and alignment.

You may only be able to purchase a tire similar or identical to the one you are replacing at the prorated price. In addition, the warranty may only apply if the tire has worn to the minimum allowable tread of 2/32nds of an inch. It can be dangerous to leave the tire on the vehicle until it reaches this level, since it is less reliable in hazardous conditions such as rain or snow. Drivers are often advised to replace a tire earlier than this point, when the tread depth reaches 4/32nds of an inch.

Other warranties are based on a timeframe rather than wear and tear on the tire. For example, Firestone's Gold Pledge Limited Warranty only covers tires that have become unusable within the first three years of purchase or four years of manufacture.

Road hazard warranties will cover the repair or replacement of flat tires. Montoya says repairs are often covered in full, while the replacement cost is prorated based on the estimated mileage remaining.

This type of coverage is often specifically excluded in tire warranties, meaning you'll have to pay extra for it. A road hazard warranty can be particularly useful if you live in an area with a lot of potholes, road debris, or other hazards that increase the odds of a flat tire.

Other warranties seek to guarantee the quality of the tire. These may include a guarantee on workmanship and materials or a uniform warranty to ensure that the tire will not cause vibration or a rough ride.

Warranties typically come with a certain set of exclusions. They may only apply for a certain amount of time, such as the first 2/32nds of an inch of tread. In addition, several costs may not be included. Goodyear's warranty policy notes how the driver will still have to pay for mounting, balancing, and any taxes or fees.

There are also several behaviors which will void the warranty. For example, Firestone's warranty won't apply if there is evidence of improper use, such as vehicle overloading, racing, or tire spinning. Other conditions that void the warranty include filling the tires with anything other than compressed air or nitrogen, improper repair, or degradation by chemicals or excessive heat.

Warranties are often included with the purchase of the tire, and the manufacturer's manual will include the conditions. Before purchasing a separate warranty, review the fine print to find out any exclusions or other conditions.