While some people do not believe in the 4psi rule it seems in recent times there are a growing number of companies who use the method.
Let’s look at how to apply the 4psi rule:
Use the recommended pressure on your tyre placard as a start point, drive for approximately one hour, stop and check the pressure. If it’s gone up by 4psi then your pressures are spot on. This is most unlikely on your first attempt!! So, if they have gone up by more than 4psi, your start pressure was too low. If it has gone up by less than 4psi, then your start pressure was too high. Adjust your pressures by 2psi in the appropriate direction and this will become your starting points for the next cold start.
Let’s work through an example. Your starting pressure is 30psi cold. After one hour driving you check the pressures and they are:
36psi – The increase is more than 4psi, so you should increase your cold starting pressure to 32psi and follow the process again to check the effect of your adjustment.
32psi – The increase is less than 4psi, so you should lower your cold starting pressure to 28psi and follow the process again to check the effect of your adjustment.
34psi – Spot on! No adjustment necessary.
The 4psi method works on any terrain in any conditions. And with a little practice you will be able to get your pressures right quickly with fewer adjustments. Be sure to remember that when you drop your tyre pressures you also need to drop your speed to match. And you will need an air compressor to increase your tyre pressures.