Pressure Carries the Load Not the Tyre
The common assumption is that the tyre is what holds a truck up. It is not. The air inside the casing carries the load, and the casing is only the structure that contains that air at pressure. This matters because it reframes what a pressure check is for. You are not maintaining a component, you are maintaining the load bearing medium itself. A tyre at the wrong pressure is a tyre carrying its axle in the wrong way, no matter how new the tread is. Every consequence discussed in the rest of this guide follows from that one fact.
What Underinflation Does Inside the Casing
A tyre run below its specified pressure flexes more in the sidewall with every revolution. That repeated flexing generates heat inside the casing, and heat is what degrades the bond between the rubber and the cord body. The damage this causes is invisible from the outside. A tyre can look serviceable on a walk-around inspection while its casing is being cooked from within, and the first outward sign is often a separation or a failure at speed. Underinflation is not a slow cosmetic problem, it is cumulative structural damage that you cannot see.
What Overinflation Does to the Contact Patch
Overinflation pushes the tread crown outward, so the tyre rides on a narrower strip in the centre of the tread. The contact patch shrinks and grip drops, wear concentrates in the centre ribs, and the ride gets harsher because the tyre no longer absorbs impacts. A tyre with less compliance passes more of every pothole and kerb strike straight into the casing, which raises the risk of impact breaks. Overinflation usually comes from a single lazy habit: setting pressures cold without checking what the size table actually specifies for that tyre.
The Load Index Only Holds at Its Stated Pressure
The load index on a sidewall is not an unconditional number. Each rating corresponds to a maximum load at a specified inflation pressure, and our size tables list the two together for that reason. If you run a tyre twenty per cent below its stated pressure, it is not carrying its rated load whatever the moulding says. Before fitting, check the load your axle actually puts on each position, find the pressure the size table requires for that load, and set to that figure. This is the single check that prevents most pressure related failures.
Dual Fitment Is About Matching Not Just Pressure
In a dual pair, both tyres must run at the same pressure. If one of the pair is low, it flexes more, runs smaller in diameter and turns slower than its partner. The higher tyre then drags it along, scrubbing tread off both tyres and building heat in the weak one. Because the low tyre is hidden on the inside of the pair, this often goes unnoticed until the tread is ruined or the casing is damaged. Check the inner tyre of every dual set, not just the outer one you can see standing up.
Checking Hot Gives You a Misleading Reading
Pressure rises as the tyre warms up in service, so a reading taken after a run on the road will be higher than the cold specification. That is normal and it is not overinflation. Bleeding air out of a hot tyre to bring the reading down to the cold figure leaves the tyre underinflated once it cools. Check pressures cold, before the vehicle has run, or if you must check hot, expect the reading to sit above the cold target and do not bleed it down. Set your depot routine around cold checks and the problem disappears.
Building a Check Routine a Depot Will Actually Follow
A pressure routine fails when it depends on memory or goodwill. What works is attaching the check to something that already happens: every vehicle through the wash bay, every driver handover, every scheduled service. Put the target pressures for each vehicle and axle position on a card at the air line, taken from the size tables for the tyres actually fitted, not from a generic chart. Make someone accountable for the log. A routine that catches underinflation weekly will prevent the vast majority of pressure related casing damage.
What Pressure Means for Casing Value at Removal
For fleets and distributors who retread, the casing is an asset with residual value, and inflation history is what determines whether that value survives. A casing that ran at its specified pressure comes off the wheel with its structure intact and is a retread candidate. A casing that ran underinflated comes off with separated plies, heat cracking or cord damage that no retreader will accept, and the loss is not just the tyre, it is the retread cycles you had already paid for. Pressure discipline is casing value protection, and it costs nothing but routine.
