The most common tyre pressure mistake is reading the number off the tyre itself. That figure is not the pressure your car needs, and using it is a genuine safety issue.
The Sidewall Number Is a Maximum
The pressure moulded into the tyre sidewall is the maximum the tyre is rated to hold. It is a limit set by the tyre manufacturer, not a recommendation for your vehicle.
Inflating to that figure typically produces a considerably over-inflated tyre: harsh ride, reduced grip, and wear concentrated down the centre of the tread.
Reaching the Figure Accurately
A compressor with a gauge that reads accurately and shuts off at a preset removes the guesswork of inflating and checking repeatedly.
Units with a preset that stops automatically, of the kind at olarhike.net, are considerably easier to use correctly than one that runs until you stop it, since over-inflating and bleeding back down is how most people end up approximate.
Where the Correct Figure Is
The vehicle manufacturer sets it, based on the weight of the car and how it handles. It appears in a small number of consistent places.
- A placard on the driver’s door jamb, which is the usual location
- Inside the fuel filler flap on some vehicles
- In the glovebox, on some models
- In the owner’s handbook
- Frequently with separate figures for front and rear
Front and Rear Frequently Differ
The point people miss. Many vehicles specify a different pressure at each axle, because the weight distribution is not even.
Setting all four to the same figure is a common error and produces uneven handling. Reading the placard properly takes ten seconds.
The Loaded Figure
Most placards give two sets of numbers: normal use and fully loaded. The loaded figure is higher, sometimes considerably.
Before a holiday with a full car and a roof box, that second column is the one to use. Almost nobody does, and it matters more than most people realise for handling and braking.
Never Exceed the Sidewall Maximum
The one absolute limit. Whatever the placard says, the sidewall figure must not be exceeded.
In practice the placard is always well below it, so this only arises if something has gone wrong: a misread gauge, a compressor without a cut-off, or a tyre that was already hot.
Different Tyres, Different Numbers
If the car has non-standard wheels or tyres, the door placard may no longer apply. A tyre fitter can advise on the correct pressure for a different size.
The same applies to a space-saver spare, which usually requires a much higher pressure and has its own figure printed on it.
When Not to Inflate
A tyre with a visible bulge, a cut through to the cord, or one that has been driven on while flat should not simply be reinflated. It needs professional inspection, since the internal structure may be damaged in a way that is not visible.
