Tyre pressure is checked casually or not at all, and the two most common errors both produce a reading that is wrong in the same direction.

Check Them Cold

The single most important condition. Driving heats the air inside a tyre, and warm air is at higher pressure.

A tyre checked after a motorway run can read several PSI above its cold pressure. Setting it to the placard figure while hot leaves it under-inflated once it cools, which is the opposite of what you wanted.

Cold means the car has been standing for a couple of hours, or has driven less than a mile or two. First thing in the morning is ideal.

Forecourt Gauges Are Unreliable

Public air lines take heavy use and are frequently inaccurate, sometimes substantially. They are also used at the end of a journey, when tyres are hot.

A gauge you own, used at home on cold tyres, gives a considerably more reliable figure. A compressor with an accurate built-in gauge and a preset shut-off, of the kind at olarhike.net, removes both problems at once.

The Routine

  • Check monthly, and before any long journey
  • Check all four, plus the spare if there is one
  • Use the vehicle placard figure, not the tyre sidewall number
  • Note that front and rear frequently differ
  • Use the loaded figure when the car is fully loaded
  • Replace the valve caps, which keep dirt out of the valve

Monthly Is Not Excessive

Tyres lose pressure naturally through the rubber and around the valve, typically a small amount each month regardless of whether anything is wrong.

Add a temperature drop and a tyre that was correct in September can be noticeably low by November without any leak at all.

What Under-Inflation Costs

An under-inflated tyre flexes more in the sidewall, which generates heat. Heat is what destroys tyres, and severe under-inflation at speed is a recognised cause of blowouts.

It also increases fuel consumption, lengthens braking distances, and wears the outer shoulders of the tread while the centre stays fine.

What Over-Inflation Costs

Less contact with the road, so less grip and longer braking distances. A harsher ride. And wear concentrated in the centre of the tread.

Neither error is harmless, which is why the placard figure matters rather than approximately correct.

While You Are There

Checking pressure is the natural moment to look at the tyres properly: tread depth, uneven wear, cuts, bulges and anything embedded in the tread.

Uneven wear across a tyre usually indicates an alignment or suspension issue rather than a pressure one, and it is worth mentioning at the next service.

When to Stop and Get Help

A tyre that keeps losing pressure has a leak and needs inspection. A visible bulge in the sidewall means internal damage and the tyre should not be driven on.

Neither is a job for a compressor.