This may be a stupid question

Greetings

That number indicates the maximum width in millimeters from the outer sidewall to the inner sidewall; in this case 265 millimeters. The number that is directly after the "R", for radial tire, (i.E. P205 55 R16) is the diamater and it must match what your wheel's diamater is (i.E. 16 inch, 18 inch etc.). So if your wheels are 16 inch and they currently have 245 tires, you can purchase a P265 70 R16 tire and it will fit.