Question regarding tire dimensions

[Eavamnba]

I have bought new tires for my EX35 with the dimensions 255/55 18". But when I drive the car, I get a warning symbol for low tire pressure.

I'm a total n00b regarding cars and this is my first car. I bought the tires at a well-known tire shop and they said they fitted well on the car.

Any advice would be highly appreciated.

[ProudNissanFreak]

Are they full on air? Balanced properly?

What year is your EX?

[minimo3]

When you had the new tires installed, did they transfer the TPMS (Tire Pressure Monitoring Sensors) from the old tires? Check your valve stems, they should be silver metal ones and not black rubber pieces. If the shop didn't transfer them to your new tires the car will display the low pressure warning. Also when tires are replaced sometimes it takes some time for the car to detect the changed TPMS. Shouldn't take more than half an hour or so of driving around.