You may have heard that because air expands in hot weather, it is safer to let some out of your tires in advance. It is a story that has circulated for years at repair shops, from fathers, and in community posts. But if you trace why tires burst in summer, the conclusion is exactly the opposite.
3-line summary
1. Summer tire pressure should be increased, not lowered
2. When the air temperature is 30°C, road surfaces can reach 70°C
3. A tread depth of 1.6 mm is the legally mandated replacement point
Where did the advice to let air out come from?
The logic itself sounds plausible. As gases warm, they expand, so the idea is that letting out some air beforehand can offset the pressure that rises while driving.
The problem is that a tire is not a balloon.
A tire with low pressure has a larger contact patch and its sidewalls flex more with every rotation. This repeated deformation generates heat. The heat the tire produces itself is far greater than the heat it receives from outside.
In other words, letting air out increases heat rather than reducing it. This is why a considerable share of summer tire-burst accidents begins not with overheating, but with insufficient tire pressure.
Road surfaces can reach 70°C
Summer roads are far hotter than they feel. On a day when the air temperature is 30°C, asphalt surfaces can reach around 70°C, and highways exposed to sunlight for long periods can heat up to nearly 60°C.
Driving over them at high speed for an extended period can cause what is known as a standing wave. This occurs when the portion of the tire surface that contacts the ground is compressed again before it returns to its original shape, leaving a wave-like deformation at the rear of the tire that continues to follow it.
If this condition persists, heat concentrates in that area and the tire eventually bursts. What makes this phenomenon frightening is that there is very little time between when the driver notices something is wrong and when the tire bursts.
This is why tires need to be checked before long summer drives—not merely as a maintenance habit, but because of this physics.
So how much air should you add?
The reference value differs by vehicle. When you open the driver's door, a sticker on the inside pillar lists the recommended tire pressures for the front and rear tires. Some vehicles also list a separate value for when the vehicle is fully loaded.
If you are preparing for high-speed, long-distance driving in summer, industry guidance commonly recommends inflating tires about 10–20% above that reference value. This helps reduce heat-related deformation and delay standing waves.
One point can be confusing. The number printed on the tire sidewall is the maximum pressure the tire can withstand, not the recommended pressure. You should not inflate to that number as a target. The reference should always be the value listed on the sticker by the vehicle manufacturer.
Measurements are most accurate in the morning. Immediately after driving, the tires are already warm, so the reading will be higher.
Check wear with a 100-won coin
Tread depth is just as important as tire pressure.
The legal limit is 1.6 mm. Tires must be replaced once they wear down to that point. There is a small triangle marking on the tire sidewall; if you follow that marking into the tread, you will find a raised bar measuring 1.6 mm high. When this bar is level with the tread surface, the tire has reached its limit.
There is also a way to measure it at home. Insert a 100-won coin upside down into the tread. If more than half of Admiral Yi Sun-sin's helmet is visible, it is time to replace the tire. The distance from the coin's edge to the helmet is roughly equivalent to this standard.
However, 1.6 mm is the absolute minimum threshold for passing or failing, not an indication of a safe condition. The ability to push water away on wet roads begins to decline much earlier, so many recommendations advise replacement at around 3 mm to leave a margin.
This is the figure that stands out most
According to reporting citing an analysis by the Korea Road Traffic Authority, tire defects account for more than 5% of traffic accidents caused by vehicle defects.
But when highways are considered separately, that share rises to more than 30%.
It means that the same component carries six times as much risk when the road changes. Personally, I think this contrast is the most persuasive figure in the discussion of summer tires. It explains why tires that seemed fine around town repeatedly cause problems on vacation trips.
Three minutes before departure
Check the tire pressure. Most modern vehicles display readings for all four tires on the instrument panel. If yours does not, check them using the air pump at a gas station.
Try the coin test. Check all four tires, and inspect both sides of each tire, since the inner and outer edges can wear differently.
Run your hand over the sidewalls. Cracks or bulging areas are dangerous even if tread remains. They often develop after scraping against a curb.
Account for your load. Recommended tire pressure changes when the vehicle is fully loaded with people and luggage. Follow the fully loaded specification shown on the sticker.
Rest every two hours. This also gives the tires time to cool. Simply stopping briefly at a rest area allows a substantial amount of heat to dissipate.
Because appropriate values vary by vehicle type and tire specification, it is safest to check the vehicle manual and manufacturer guidance for specific figures.
Conclusion
The advice to let air out in summer holds true only if you think of tires as balloons. In reality, heat is generated not by the outside temperature but by the tire's own deformation, and that deformation increases as tire pressure falls. It takes just three minutes to check before leaving for vacation.
References
- Michelin Korea, “Tire Tread Depth and Legal Limit” — https://www.michelin.co.kr/auto/advice/tyre-basics/tyre-tread-depth
- Michelin Korea, “How to Read the Tire Wear Indicator” — https://www.michelin.co.kr/auto/advice/change-tyres/tyre-wear-indicator
- eKorea, “Risk of Tire Bursts During Heat Waves: Highway Driving Checkpoints” — https://www.ekoreanews.co.kr/news/articleView.html?idxno=81395
- The Herald Business, “Tire-Puncture Accidents Surge During Heat Waves... Raise Tire Pressure” — https://mbiz.heraldcorp.com/article/2043136
- Hankook Tire, “Tire Safety Management Tips for the Rainy Season” — https://www.hankooktire.com/kr/ko/company/media-list/media-detail.630267.html