245 is the tyre width in millimetres, 45 is the sidewall height as a percentage of that width, R means radial construction, and 18 is the wheel diameter in inches. These numbers need to match your vehicle specification so the tyre seats correctly, maintains the intended rolling radius and keeps speedometer and safety systems working as designed. When shopping, also match the load index and speed rating shown on your door jamb or handbook.
Look for the tyre information label on the driver door pillar, fuel flap or in the handbook. It will list the approved load index and speed rating, sometimes with different values for normal load, full load or high-speed driving. Choose a 245/45 R18 option that meets or exceeds those ratings, and if your car specifies XL (reinforced), select an XL-marked tyre to maintain the intended support and handling.
Only if your vehicle manufacturer approves the alternative size for your exact model and wheel width. Changing size alters rolling circumference and sidewall shape, which can affect ride, handling, clearance to suspension and wheel arches, and the accuracy of driver aids. If you are considering a change, check the placard for approved alternatives or confirm with the vehicle maker, then buy the exact size and rating listed.
Some cars are set up for runflats from factory, while others are not. If your vehicle requires runflat construction or is supplied without a spare wheel, sticking with runflats can preserve the intended behaviour in a puncture and avoid mobility issues. If you want to switch from runflat to standard, confirm it is suitable for your car and consider how you will deal with punctures, then replace tyres in axle pairs to keep handling consistent.
Summer tyres suit warmer months and drivers prioritising dry and wet grip at typical UK temperatures. Winter tyres improve traction and braking in cold weather, especially on slush, ice and snow. All-season tyres aim to cover both, making sense if you want one set year-round and regularly drive in cooler conditions. Decide based on your local climate, mileage and routes, then compare tread patterns and EU label ratings to pick the best balance for your car.