275 is the tyre width in millimetres, 45 is the sidewall height as a percentage of the width, and R18 is the 18 inch rim diameter. Because this is a wide fitment with a relatively short sidewall, choosing the correct load index and speed rating for your vehicle is essential.
Many vehicles that use this size specify Extra Load (XL) to carry the weight and cope with higher pressures. Check your door jamb sticker or handbook for the required load index and match or exceed it when buying, as choosing a lower rating can affect safety and legality.
Only switch if your vehicle manufacturer permits it. Some cars are set up for run-flats with specific pressure monitoring, suspension tuning and puncture mobility expectations, so moving to non run-flat may require carrying a repair kit or spare and keeping tyres matched across each axle.
Summer tyres suit warmer months and prioritise steering response, while winter tyres are safer when temperatures regularly drop below 7C. All-season tyres are a strong year-round option for mixed UK conditions, especially if you want one set to handle wet roads and colder mornings without changing tyres twice a year.
A change in profile alters the overall rolling diameter, which can affect speedometer accuracy, ground clearance and how the car’s systems behave, especially on AWD vehicles. Stick to the sizes listed on your vehicle placard or handbook, and if you are considering an alternative, confirm it is manufacturer-approved before ordering.
