On this page
- Why does the spare wheel go flat?
- What pressure should the spare wheel have?
- How often should you check the spare wheel?
- Can a spare wheel "expire"?
- Which signs show it needs replacing?
- What should you do if you find the spare is flat after a puncture?
- Unusable spare and a punctured tyre in Milan?
- Frequently asked questions
Why does the spare wheel go flat?
The spare wheel goes flat because all tyres slowly lose air over time, even when they're not being used. After years in the well without being checked, it's easy to find it very low or completely flat.
An aged valve or a corroded rim can also contribute. The problem is that you only notice when you need it: after a puncture, perhaps at night or far from home.
What pressure should the spare wheel have?
The spare wheel should be at the pressure specified by the manufacturer. For a full-size spare it's usually the same as the other wheels (or the higher of the front and rear values, according to the handbook); for a space-saver it's often higher than for the normal wheels.
The space-saver's value is generally printed on its sidewall or label, as well as in the owner's handbook and sometimes on the tyre pressure label on the door pillar or inside the fuel filler flap. For using a space-saver see space-saver: how far and how fast.
How often should you check the spare wheel?
It's worth checking the spare wheel every time you check the pressure of the other tyres, and in any case before a long journey. Many drivers forget it precisely because it's hidden away in the boot.
The seasonal tyre change is also a good moment: you can ask the tyre specialist to check it along with the others.
Can a spare wheel "expire"?
Yes, in the sense that the rubber ages even if it doesn't cover any kilometres: over the years the compound hardens and cracks can appear. There's no expiry date printed on it, but you can find out its age.
The last four digits of the DOT code on the sidewall give the week and year of manufacture: for example 2423 means week 24 of 2023. To read all the information on the sidewall, see how to read a tyre size.
Which signs show it needs replacing?
The signs that the spare wheel needs replacing are visible if you check it carefully.
- Cracking on the sidewall or between the tread blocks.
- Deformation from sitting flat or squashed for a long time.
- Bulges or swelling (see bulge on a tyre).
- Worn tread, if the wheel has been used in the past.
- Rusty or bent rim, or a damaged valve.
If in doubt, have it assessed by a tyre specialist before relying on it.
What should you do if you find the spare is flat after a puncture?
If you find the spare is flat after a puncture, don't fit it as it is: driving on a deflated wheel is as dangerous as driving on the punctured tyre.
- If you have a 12 V compressor (including the one from the repair kit), inflate it to the correct pressure before fitting it.
- If you don't have a compressor, consider whether the hole in the original tyre allows you to use a kit (see how to use the repair kit).
- Otherwise, stay safely where you are and ask for assistance.
Unusable spare and a punctured tyre in Milan?
If you're in Milan or the surrounding province with a punctured tyre and an unusable spare wheel, SOS Tyre comes out 24/7, in 30 minutes on average, to wherever the vehicle is. Call +39 377 326 0999 or read what to do with no spare wheel.
Frequently asked questions
Does the TPMS sensor also monitor the spare wheel?
On most cars, no: the tyre pressure monitoring system watches the wheels that are fitted, not the one in the boot. That's why the spare wheel's pressure needs to be checked manually with a gauge.
Can I inflate the space-saver with the kit's compressor?
Generally yes: the repair kit's 12 V compressor can also be used without sealant, to inflate the space-saver to the specified pressure. Check the kit's instructions for how to use it in inflation-only mode and how long it can run continuously.
Is a spare wheel that's never been used but is many years old safe?
Not necessarily. Even without any kilometres the rubber ages and can lose elasticity. Check the year of manufacture from the DOT code and the condition of the sidewall: if there are cracks or the tyre is very old, have it assessed by a tyre specialist before using it.
After using the spare wheel, should I re-inflate it before putting it back in the well?
Yes. When you remove it and put it away, check that it's at the correct pressure and in good condition. That way it'll be ready for the next emergency. If you've used it for a long time or on poor roads, have it checked for wear too.