Tire repair kit in new cars: double pressure check and replacement rules
Car manuals now spell out how drivers must use the emergency tire repair kit that replaces the spare wheel in new cars sold in Brazil, such as the BYD Dolphin Mini and the Volvo EX30. The kit pairs a 12 V electric compressor with a bottle of sealing liquid that closes punctures temporarily and inflates the tire so the driver can reach a workshop without changing the wheel on the road.
The seal is only temporary, and the manuals impose strict driving limits. “If the pressure is between 1.8 bar (26 psi) and 2.8 bar (39 psi), you may drive at a maximum speed of 80 km/h (50 mph). Replace the valve dust cap. Replace the sealant bottle and the hose after use,” says the Volvo EX30 support manual.
Pressure and time figures set by the manufacturers
The factory system injects the sealing liquid through the valve while the compressor restores the air pressure inside the tire. The movement of the wheel spreads the product across the inner surface. Capacity, filling time and driving distance vary among makers such as Renault, Volvo, Continental and Osram.
- Maximum puncture diameter on the tread: between 4 mm and 6 mm, depending on the equipment maker.
- Maximum compressor run time during the first inflation: 10 to 15 minutes.
- Minimum pressure required at the first inflation: 1.8 bar.
- Initial driving distance to spread the sealant: 3 km to 5 km, at speeds between 20 km/h and 60 km/h.
- Minimum pressure on the second gauge check: 1.3 bar.
- Maximum range with the tire temporarily sealed: up to 200 km.
- Usual shelf life of the sealant bottle: up to 5 years.
Jorge Alexandre Onoda Pessanha, professor at the Escola de Engenharia da Universidade Presbiteriana Mackenzie, said the figures in the manuals do not guarantee a repair in every case. The shape of the hole, the condition of the rubber and any internal damage affect whether the air stays in. The kit does not seal side cuts, wheel damage or structural harm caused by driving on a fully deflated tire.
According to the specialist, the sidewall flexes constantly while the car moves, which rules out the liquid in that area. “An injury in that region can compromise the integrity of the casing, and simply sealing the air leak does not restore its mechanical strength,” the professor said.
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Roadside procedure when the object stays in the tread
When the sharp object is still stuck in the tread, the usual technical guidance is to leave it in place before starting the procedure. The driver must follow a safety sequence on the road to apply the product and test whether the tire holds air.
- Parking and warning: stop away from traffic, turn on the hazard lights, engage the parking brake and place the warning triangle.
- Visual check: confirm the puncture is on the tread and that there are no side tears.
- Connection: attach the sealant bottle to the compressor, screw the hose onto the tire valve and plug the cable into the vehicle’s 12 V socket.
- First inflation: run the compressor to inject the liquid and air. If the minimum pressure is not reached within the device’s time limit, the repair is not viable and the car needs a tow truck.
- Distribution drive: drive the short distance set by the carmaker so the gel covers the hole from the inside.
- Final check: stop in a safe place and read the gauge again to confirm the tire kept its pressure.
If the reading at the second stop falls below the safety floor, the driver must stop the trip at once. The Renault user manual says that after 3 km the driver should stop and check the pressure. “If the pressure is above 1.3 bar but below the recommended pressure (see the label on the driver’s door frame), adjust it. Otherwise, contact a brand representative: the tire cannot be repaired,” the manual says.
Contran rule and other emergency options on the market
In Brazil, the omission of the spare tire, jack and wheel wrench in cars that leave the factory with alternative systems is governed by Resolution No. 913/2022 of the Conselho Nacional de Trânsito (Contran), the national traffic council. The federal rule requires the sealant kit and the inflation device even in cars with run-flat tires, which have reinforced sidewalls that allow short trips without air pressure.
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Besides the carmakers’ original kits, the aftermarket sells aerosol instant repairers, such as the MP10 from Mundial Prime, sold for about R$ 25 per can at retail. The can holds both fluid and propellant gas and is limited to one can per tire. Another emergency method uses an elastomer cord, known as macarrão, which requires removing the object and widening the hole with a probe before inserting the material from outside.
TPMS sensors and replacing the repair kit
In vehicles with direct tire pressure monitoring, known by the English acronym TPMS (Tire Pressure Monitoring System), the electronic sensors sit next to the air valves and come into direct contact with the chemical injected. In cars with indirect TPMS, which calculates air loss from the wheel speed sensors, there is no physical contact with the liquid. Gel products supplied in factory kits are designed to be washed out and to be compatible with the sensor, but unsuitable products can block the reading and require replacing the sensor and the valve.
After use on the road, the 12 V electric compressor can be kept for future emergencies. The sealant bottle is single-use and must be replaced even if product remains in it. On arrival at the workshop for the final assessment of the casing, the driver must tell the tire technician that sealing fluid is inside the tire before the wheel is removed.
