HGV tyre blowout: what to do, why it happens and what a fitter needs

A blowout can damage far more than the tyre and can leave debris or bodywork exposed to traffic. Driver training, the vehicle handbook and road-authority instructions take priority over anything written here.

What happens in a blowout

A steer-axle failure pulls the vehicle towards the burst tyre; a drive or trailer failure is usually felt as vibration, a bang and a pull, sometimes with a loss of air on the affected side. The instinctive reaction, braking hard, transfers weight forward and increases the pull and the risk of a jackknife or rollover.

Keep control first

• Grip the steering wheel firmly with both hands and steer to keep the vehicle straight.
• Do not brake hard. Hold, or very slightly increase, the throttle for a moment to stabilise the vehicle, then ease off gradually.
• Let the vehicle slow using engine braking, then brake gently once you are well under 40 mph and in control.
• Signal and move left when it is safe. On a motorway, aim for an emergency area, a hard shoulder or an exit; on other roads, get off the carriageway if you can.

Stop in the safest available way

Follow your trained breakdown procedure. If the vehicle is in a live lane or a dangerous position, stay in the cab with your seat belt on, hazards on, and call 999. If you can get to a place of relative safety, leave by the side away from traffic, get behind the barrier and call National Highways on 0300 123 5000 or use the SOS phone. Do not step into traffic to inspect the wheel and never place a warning triangle on a motorway.

Do not assume it is only a tyre

A failed casing can damage air lines, mudguards, lighting, bodywork or the adjacent tyre on a twin fitment. Heat from a binding brake or a failing wheel bearing can be the reason the tyre failed in the first place, so adjacent systems need to be assessed before the vehicle continues.

Why HGV tyres fail

• Under-inflation makes the sidewall flex, building heat that weakens the casing. TyreSafe identifies it as the leading avoidable cause and recommends pressure checks at least monthly and before long trips.
• Overloading has the same effect and is common on trailers loaded beyond the tyre's load index.
• Age and ozone cracking weaken casings even with plenty of tread. Since February 2021 tyres over 10 years old are prohibited on the front steered axles of HGVs, buses and coaches, and the date code must be legible on all tyres fitted to HGVs and trailers over 3.5 tonnes.
• Kerb and pothole damage creates sidewall bulges that fail later at speed.
• Heat from sustained high speed, hot weather, binding brakes and bearing failure; rubber compounds begin to break down at sustained temperatures around 93°C.
• Retread failure, usually on casings that were already damaged or over-age.

The legal position

For vehicles over 3.5 tonnes the minimum tread depth is 1 mm across the central three-quarters of the tread width, around the whole circumference. Exposed cords, bulges, cuts to the cord and tyres over 10 years old on a front steered axle are dangerous defects that attract an immediate prohibition at a DVSA roadside check. Read the date code as the last four digits of the DOT string: 5210 means week 52 of 2010.

Information for the fitter

Mobile commercial tyre companies target 45 to 90 minute attendance in most areas, but only if they leave with the right tyre. Give them:

• the tyre size and load and speed index from fleet records or a safe photograph of a matching tyre (for example 315/80 R22.5 156/150L);
• the axle and wheel position, and whether it is a single or twin fitment;
• the wheel type (steel or alloy) and whether the rim is on the ground;
• vehicle type, whether it is laden and the approximate weight;
• any collateral damage you can see from a safe position;
• whether wheel nuts or a hub were recently worked on;
• the precise location, direction and access for a service van.

Confirm the replacement basis

Ask whether the offered tyre is new, a retread or another permitted category, its specification, whether a casing or disposal charge applies, the call-out, labour and VAT. Out-of-hours attendance typically carries an uplift. The fitter must decide after inspection whether any repair is lawful and suitable.

Before continuing the journey

The attending competent person should assess the adjacent tyres, the wheel and any damage to lines, guards and lighting. Record the fitted tyre, the pressure set, the torque process (and any re-torque instruction) and whatever follow-up inspection your maintenance system requires.