The tire pressure monitoring system or TPMS is now a common feature in many cars right now. The reason is that you do not need a gauge to know the PSI in your tires and have them inflated or deflated accordingly.
When buying a car, you also get a spare tire. It could be a full-size spare tire or a donut spare tire. We will focus more on the donut spare for illustration in our case.
In most cases, the donut spare tire will not have a TPMS sensor. Take note that there is no legal requirement that such tires have the TPMS sensor. In case you decide to add one, it would be at your own cost and might not be necessary for most people.
Should Spare Tires Have TPMS
Most people might not find the need for having the TPMS because this is a tire you would not be using more often. Once you have the main tire fixed, out with the donut tire.
TPMS for the other tires of the car is quite important. Its job would be to read the tire pressure and update you in real-time about whether you need to inflate the tire to keep it within the right range.
For the TPMS to work, it needs the sensors to also be in good condition. It is the sensors that relay this information and now it is displayed on the dashboard. In case you have faulty sensors, then the readings might also get faulty. Thus the need to replace the sensors.
Here is a video on how the TPMS works
Just because we have said that the TPMS is not a must for a donut spare tire, it does not mean you should not watch the donut tire pressure.
It is best to also check it monthly as you would do for the other tires mounted on the car. The worst can be when you have a flat, but you cannot use the donut tire because it is also low on pressure.
Since it will not have a TPMS, you need a tire pressure gauge to know the level of air pressure in the donut tire. You can do this at a gas station and add more air pressure that is needed to make it useful when the time comes.
The Law on TPMS and Spare Tires
All the cars produced in the US past 2007 are mandated to have a TPMS system. It is for this reason, that someone might wonder if it will be illegal to drive around with a donut tire having no TPMS.
So far, there is no specific law mandating that spare tires to have TPMS. it is understandable considering you would not be using the spare tire for long.
Most people who are used to the TPMS system would want to get their main tire fixed and back on the vehicle as soon as possible.
Do not worry much about driving with a spare tire without a TPMS as it is not an offense. Just make sure you observe the safety guidelines for driving around on a spare tire, especially the donut tire.
Take note that you can still use the car even if the other tires do not have TPMS. This is because the TPMS is not a mandatory safety feature such as a seatbelt that every car should have. No officer will give you a ticket for not having TPMS.
TPMS Light and Spare Tire
First, you will get the TPMS light on the dashboard indicating you have a flat tire the next time you use a spare tire.
The main reason for this message is because the TPMS cannot read a sensor from that side of the axle, thus it identifies it as a flat tire. So long as it is on the side you have added the spare tire, it should not scare you.
Expect this light to remain ON until the normal wheel has been replaced.
Once the normal wheel is fixed back to the axle, drive around for a few miles and the TPMS will turn off the light on the dashboard. It just needs a few miles to check the system again before resetting the light.
As you can see, there is nothing to worry about when you see the TPMS light easily while driving around with a spare tire.
Here is a video with details on why your TPMS light is on and how to turn it off
How Much Air to Put in Donut Spare Tire?
As mentioned earlier, you always have to check the pressure level in your spare tire too just to be sure it will do the job when the time comes.
One thing to note about donut spare tires is that they need to be filled with more air than the normal full-size tires of your car.
The reason for using more air is that the contact surface is small, so more air is needed to help the tire keep up with the weight of the car.
Check the donut spare tire marking to understand how much air to use. The tire manufacturer would always indicate the recommended pressure to use for the right performance.
In general, the donut spare tire needs around 60 PSI to work correctly. This is a lot more than what you usually use for the normal tires which is around 32 to 40 PSI.
What about those with full-size spare tires?
It is not new to find people buying full-size tires and using them as spares. New cars nowadays do not even have the donut spare tire, but rather a kit to help you patch the tire and keep going.
In case you have a full-size spare tire, just use the normal PSI like the one in the other tires. So, for a passenger car, ensure the full-size spare tire has 32 to 40 PSI matching the other tires on the car already.
How is a donut spare tire different from normal tires?
The material used to make the donut spare feels like hard plastic compared to the rubber used for normal tires. We also find that the donut tire would be significantly smaller than the normal tires, making it easy to fit in the car.
How fast should you drive on a donut spare tire?
Most manufacturers recommend that you do not go beyond 50mph when driving on a donut spare tire. Also, do not drive around on a donut tire for too long, have the main tire repaired as soon as possible.
How should you care for your donut spare tire?
You should consider checking the air pressure of the donut spare tire each time you check the other tires too. Also, if it is worn, make sure it is also replaced to have a good tire whenever you need it.