The tyres in size 225/50 R18 are designed for SUV, passenger and sports cars. From the designation of the size each user can read four kind of information. Firstly, there is the exact tyre's tread width expressed in millimetres (225). Secondly, the tyre's profile height is known (here it amounts 50% out of 225 millimetres of the tyre's tread width). Next there is the "R" which denotes the radial construction of the tyre. Number 18 is the diameter of the wheel's rim in inches (18) which can be installed with the tyre in size 225/50 R18. You're welcome to do the shopping!