Weather and temperature affects the air in your car tyres. When the temperature is cool the pressure is lower, when the temperature is warm, the pressure is higher. The air in your tyres are what supports the weight of your car, not the tyres.
Car manufacturers will recommend your tyre pressure. This will usually be displayed on the front doors, petrol cap or the car handbook. The pressure will be related to the size and type of tyre. It will also factor in the weight of your vehicle.
If you want to check what your pressure level should be, Tyre.safe.org have a useful tool that helps you identify what your car manufacturer recommends. You will need to enter your make and model.
The change in temperature will affect your tyre pressure. If the weather is cold then that means there is less tyre pressure as opposed to hot weather.
Lower pressure can :-
Increase fuel consumption
Compromise grip and handling
Sun Exposure can influence the tyre pressure. In the sun, your tyres will absorb the heat, which will pass onto the air inside.
Many cars are fitted with a tyre pressure monitoring system, find out more about the TPMS here.