When your tyres are under-inflated, rolling resistance is higher than normal, the engine has to work harder and you therefore consume more fuel.
Changes in temperature cause natural variations in tyre pressure. Pressure falls when the temperature drops, so remember to regularly check and adjust the pressure of your tyres, particularly when the temperature drops sharply in winter.
Using "winter tyres" considerably increases rolling resistance on dry ground. They contribute to safety in poor weather conditions but should be removed when driving conditions improve.
Under-inflated tyres can overheat, reduce road-holding capacities, and suffer wear and damage, even blow out. For your safety, respect the pressure levels recommended by the manufacturer, which apply to cold tyres.