Whoever invented the spare tire deserves a medal, plain and simple. It’s one of the most important conveniences adopted into a car, as who’d have guessed that tires can break? Potholes, nails, rocks, trees, can all cause a tire to pop, or become dislodged and lose the air inside.
When this happens it’s unlikely that you'd keep a spare set of tires, and even less likely you’d have an air compressor capable of seating the tire bead and not to mention a way of balancing the wheel after mounting the tire.
The spare tire serves to aid you in your time of crisis, but it’s important to remember it’s not to be taken lightly. The spare tire is not a replacement, but rather a way of buying time. It’s not supposed to last forever, and it won’t so don’t treat it as such.
Spare tires are all rated differently and are indicated as such on the side. They all have a speed rating, but it’s typically understood that spare tires shouldn’t be driven faster than 50 mph. While it’s not recommended to go more than 70 miles, you can stretch the life to 90.
We don’t recommend that, but if you’re in a bind know that it is possible. Stay in the slow lane for the duration of your spare tire journey, and be sure to keep the car as straight as possible. Aside from the gradual sweeping of highways, the car should not be turned and definitely shouldn’t be jerked around or suddenly moved to a different lane. Know your limits, and know that they are 50 mph.
Spare tires are supposed to limp your car to a shop, and nothing more, so the real answer to this question is “as short a distance as possible.” Spare tires aren’t constructed in the same way as a normal road tire. They’re cheap and can’t withstand the abuse a real tire can endure, so it’s important to not push its limits.
Also know that spare tires are typically smaller than the rest of your tires, so the longer you drive on them the more your alignment, brake and tire wear will no longer be uniform, and this will cause all kinds of problems later on the longer it is ignored, all the way to severe steering issues where parts start to break.
There are tires called run flats, which are designed to run for a limited distance after air is lost, but like the spare tire, you shouldn’t abuse the run-flat tire's limits. The only real advantage a Run-flat tire has over a spare tire is that you don’t have to change it out once it blows.
Be sure to look and see what kind of spare tire you have, because some cars are equipped with spare tires that are the same size as your others (as long as they are the stock size), and can be used with confidence.
To be extra cautious, if all your tires are the same size and you get a flat tire on one of your driving wheels, i.e. one of the front tires blows on your FWD car, you should replace it with a non-driving wheel instead of the spare, and then throw the spare where you got the non-driving wheel.
This is because of the rotational difference between a spare tire and a normal road tire, if they are different sizes, results in the drivetrain working harder thus creating more wear, and can then become more damaged.
The bottom line is that spare tires are amazing, but aren’t meant to be used for long periods of time or distances. Ideally, in the case of you hitting a nail or pothole or in some other way suffer a flat tire, you'll be right in front of a tire shop.
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