Under-inflated tyres are extremely common and cause real problems: longer stopping distances, vague steering, faster wear on the shoulders and measurably worse fuel economy. A cordless inflator makes checking pressures a two-minute job you can do at home.
Find your correct pressures
The number on the tyre sidewall is the maximum the tyre can take, not the pressure your car wants. The correct figures are on a sticker in the driver’s door shut, inside the fuel filler flap, or in the handbook.
Most cars list two sets: normal load and full load. If you are carrying four people and luggage, use the higher figures.
Check cold, not warm
Driving heats the air in a tyre and raises the pressure, typically by a few PSI. A tyre checked after a motorway run will read high, and if you set it to the correct figure while hot it will be under-inflated once it cools.
Check before driving, or after the car has sat for a couple of hours.
The routine
- Remove the valve cap and keep it somewhere you will not lose it
- Push the connector on squarely; a hiss means it is not sealed
- Read the current pressure before adding air
- Set the target on the inflator and let it run
- Check the reading, then refit the cap
- Do all four, and the spare if you have one
What else to look at while you are there
- Tread depth: the UK legal minimum is 1.6mm across the central three quarters
- Uneven wear, which suggests alignment or persistent under-inflation
- Cuts, bulges or embedded objects in the sidewall and tread
- Age, shown by the four-digit DOT week and year code
What TPMS is telling you
Most cars since 2014 have tyre pressure monitoring. Direct systems use a sensor in each wheel and report actual pressures; indirect systems infer pressure from wheel rotation speed and only detect a relative difference.
After adjusting pressures on an indirect system you must reset it, or it continues comparing against the old baseline. The reset is usually a button or a menu item, and skipping it is why the light sometimes stays on after inflation.
A TPMS warning is a prompt to check, not a measurement to trust. Always verify with a gauge.
Punctures, and what a sealant can and cannot do
Many cars now carry a sealant kit instead of a spare. Sealant works on small tread punctures and does not work on sidewall damage, on a large gash, or on a tyre that has been driven flat.
- Do not remove the object before using sealant; it helps seal around itself
- Follow the kit instructions on driving distance and speed afterwards
- Treat a sealed tyre as a temporary repair and get it inspected
- Tell the tyre fitter sealant has been used, as it affects the repair
- Check the sealant bottle’s expiry; it does have one, typically four to five years
Using an inflator without flattening the battery
Cordless inflators avoid the issue entirely. Twelve-volt units plugged into the accessory socket draw a significant current, and inflating four tyres with the engine off can leave you with a car that will not start.
Run the engine while using a 12V inflator, or use a cordless unit. Let a small compressor rest between tyres; they overheat, and thermal cut-outs on cheaper units trip partway through the job.
Frequently asked questions
How often should I check tyre pressures?
Monthly, and before any long journey. Tyres lose pressure naturally even without a puncture.
Do I need to adjust pressures in winter?
Cold air contracts, so pressures drop as temperatures fall. Check more often through winter rather than deliberately over-inflating.
