Hot weather and long motorway trips are a classic recipe for a summer blowout. Heat raises the pressure and temperature inside the tyre, and any existing weakness, low tread, old rubber, under-inflation or a hidden cut, is far more likely to let go. A few summer checks keep your tyres safe when they're working hardest.
Why heat is hard on tyres
As tyres warm, the air inside expands and pressure climbs. Combine that with high speeds, a heavily loaded holiday car and hot tarmac, and a marginal tyre can overheat until the structure fails. Older, perished tyres are especially vulnerable, because the rubber has already lost flexibility. It's why summer sees a spike in roadside blowouts, and why the tyres that fail are almost always ones that were already worn, old or under-inflated before the hot weather arrived.
Summer tyre checklist
Run through this before any long, hot drive:
- Check pressures cold against the recommended figure, and don't over-inflate to "allow for heat".
- Inspect for cracks, bulges and embedded objects before you set off.
- Mind the load. A fully loaded holiday car may need the higher "laden" pressure, so check your handbook.
- Check the spare, as it's often the oldest, most neglected tyre on the car.
Tyre-safety charity TyreSafe puts correct inflation at the heart of tyre safety, so correct pressure is the single best summer precaution. Do the check the evening before a long trip, when the tyres are cold and you have time to sort anything you find.
On a long drive
Take regular breaks, which let the tyres cool and let you spot problems early. If a tyre looks low or feels odd, stop and check rather than pushing on into the heat. A common mistake is to check pressures after an hour of motorway driving and find them "high", then let air out, which leaves the tyres dangerously low once they cool. Always set pressures cold and leave them alone when hot. And know what to do in a blowout before you ever need to, because the right reaction is counter-intuitive.
Caravans, trailers and loaded cars
Summer is towing and holiday season, which adds extra demands exactly when it's hottest. A fully loaded car needs the laden pressure, not the everyday figure, or the tyres will be effectively under-inflated for the weight. Caravan and trailer tyres deserve special attention, because they usually fail on age rather than mileage and may have sat unused all winter. Before a big summer tow, check the age, condition and pressures of every tyre on the outfit, including the spare, since a towing tyre failure can cause dangerous snaking at speed.
How much pressure rises in the heat
As a rough guide, tyre pressure rises by about 1 psi for every 5 to 6 degrees Celsius the air inside warms up. A tyre set to 32 psi in a cool garage can read 36 to 38 psi after an hour on a hot motorway. That is normal, and the manufacturer's cold figure already allows for it.
Two things follow from that:
- Do not let air out of a hot tyre. The gain is temporary. Once the tyre cools it will sit well below the correct figure, and an under-inflated tyre flexes more, runs hotter and is the one most likely to fail on the next hot run.
- Do not add air "for the heat" either. Over-inflation shrinks the contact patch, lengthens braking distances and makes the tyre more vulnerable to pothole damage.
The cold figure is on the door placard, the fuel flap or the handbook, and many cars list a higher figure for a fully loaded car.
If you cannot check before driving, a short trip to a garage forecourt of a mile or two barely warms the tyre and the reading is close enough. After a long drive, wait a couple of hours in the shade before trusting the gauge.
Signs of heat damage to look for
Heat damage shows on the outside of a tyre before it fails, so a walk-round after a hot journey is worth doing. Look for these, and treat any of the first three as a reason not to drive further on that tyre:
- A bulge or lump in the sidewall or tread. The internal structure has separated. The tyre is finished, however good the tread looks; see what a tyre bulge means.
- Blistering or a raised, wavy patch on the tread surface, which is tread separation starting.
- Chunks missing from tread blocks, common after hard driving on soft, hot tarmac.
- Fine cracking in the grooves or across the sidewall, which is ozone and UV ageing accelerated by heat.
- Both shoulders worn more than the centre, the classic sign of running under-inflated, which is what makes a tyre overheat in the first place.
- One tyre noticeably hotter to the touch than its partner on the same axle after a drive. That points to low pressure in that tyre or a brake dragging on that wheel.
The spare deserves the same look. It sits in a hot boot all summer and is often the oldest tyre on the car.
Parking, storage and standing in the sun
Sunlight and ozone age rubber whether the car is moving or not, so a car that stands outside all summer needs its tyres checked as carefully as one that is driven hard. This matters most for caravans, trailers, second cars and anything that sits for weeks between uses.
- Park in shade where you can, or use tyre covers on a stored caravan or motorhome. It slows sidewall cracking noticeably over a few seasons.
- Move a stored vehicle every few weeks so the same patch of tread is not carrying the weight in the heat, which is how flat spots develop.
- Be wary of glossy tyre dressings. Solvent-based products can dry the rubber. If you use one, choose a water-based dressing and keep it off the tread.
- Check the date code on tyres that have done low mileage. A six-year-old tyre with deep tread can still be perished, and heat brings that on.
Storing a set of winter or summer tyres over the season? Keep them cool, dry, out of direct sun and away from electric motors, which produce ozone.
If a tyre fails on a hot motorway
If a tyre lets go at speed, hold the wheel firmly, do not brake hard, let the car slow, and get off the carriageway before anything else. Summer blowouts tend to happen on the fast, hot, loaded runs, so it is worth knowing the drill before the holiday, not during it.
- Grip the wheel, ease off the accelerator and let the speed bleed away. Signal and move left once it is safe to do so.
- Stop as far left as possible, hazard lights on. On a motorway, leave via the passenger side and get everyone behind the barrier, well away from the vehicle.
- If you cannot get off the carriageway or are stuck in a live lane, stay belted in with hazards on and call 999.
- Otherwise call National Highways on 0300 123 5000, or the police in Scotland and Wales, and then your recovery provider. Rules 274 to 287 of the Highway Code (rule 275 for motorways) cover this.
- Do not attempt a wheel change on a motorway. The vehicle needs recovering to a safe place first.
Once you are somewhere safe, a mobile fitter can bring and fit a replacement so the holiday carries on. Our burst tyre page explains what we can and cannot do at the roadside.
Pre-trip tyre check at home
Heading off on a summer trip? We can check and, if needed, replace tyres at your home before a trip, across London and the Home Counties. Call and we will tell you when we can come.
