If you have ever had the misfortune of experiencing a flat tire, or worse still, a blowout, then you can appreciate the importance of carrying a spare tire. When driving on a long journey, carrying a spare tire is absolutely vital, as you may not otherwise be able to get assistance to get you somewhere safe. A spare tire, however, is not a permanent replacement for a damaged tire. So how long can you drive on a spare tire?
It is worth remembering that a spare tire is not the same as a regular one. It's not as durable. Spare tires have fewer layers of steel and polyester beneath the rubber, which means they won't last as long. This is good news generally speaking, because it means that you are carrying less weight since the spare takes up less room in the rear of the car. But it also means that in the event of a crisis, you can only use the spare for a certain amount of time.
A spare tire will have a smaller contact surface with the road, because it is narrower. This increases your stopping distance, and makes an emergency stop much riskier. Other functions of your car, such as anti-lock brakes and traction control are going to be less efficient too. If you use the spare tire for too long, then you run the risk of causing damage to other parts of the car, which are optimized for a regular, full-size tire.
As a general rule, you should drive on a spare tire for the shortest distance possible. Use the spare to get you to the next available place where you will be able to get mechanical assistance where you can purchase a replacement tire. The spare is there to get you out of an emergency situation. It is a lifeline, not even a medium-term substitute for a proper replacement. Fit the spare, and then work out the shortest possible route to safety. Make sure to take into consideration the driving conditions. A slightly longer route on a highway might be better than remote rural roads, for example, in case you need to call for assistance.
That aside, the limit of your spare tire will be documented in your owner's manual and will, technically, differ from one vehicle's make and model to the next. If you run into trouble and you are a long way from assistance, then you may have to look for alternative means of help if the minimum distance is greater than the safe limit stated in the manual. If in doubt, contact your dealer for assistance. A mechanic will always be able to give you the best advice for your car.