Confirm it against the tyre size shown on your current tyre sidewall, the driver door placard, or your owner’s handbook. Some models use different sizes across trims, wheel options, or front and rear axles, so match what your vehicle specifies. When ordering, also match the required load index and speed rating printed after the size (for example 94W) to ensure compliance and correct performance.
235 is the tyre width in millimetres, 45 is the sidewall height as a percentage of the width, R means radial construction, and 18 is the wheel diameter in inches. For this size, the sidewall is about 106 mm tall (235 x 0.45), which helps balance ride comfort and steering control. It is designed to fit 18 inch rims and is commonly chosen for stable motorway driving and confident cornering on heavier saloons and EVs.
Use the same or higher load index and speed rating as your car’s original specification. Common ratings for this size include 94W, 95Y and higher-load XL versions such as 98Y XL, depending on vehicle weight and manufacturer requirements. If your car is heavier, frequently fully loaded, or an EV, the correct XL option may be specified by the manufacturer, so check the placard or handbook before you buy.
Only if your vehicle manufacturer approves it, because the overall diameter changes. 235/45 R18 is about 9 mm larger in diameter than 225/45 R18, which is roughly a 1.4% increase, and that can affect speedometer accuracy, clearance, and handling balance. It may also need insurer notification. If you are unsure, stick to the size listed on the door placard or handbook.
It depends on your mileage, location and how often you drive in cold conditions. Summer tyres suit warmer months and drivers prioritising crisp steering and wet braking performance. All-season tyres are a strong year-round choice for mixed UK weather, especially if you want fewer seasonal tyre changes. Winter tyres make sense if you regularly face temperatures below 7 C, ice, or snow, and they should be fitted as a full set for consistent grip and stability.
