345 is the tyre width in millimetres, 30 is the aspect ratio showing sidewall height as a percentage of the width, R means radial construction, and 21 is the wheel rim diameter in inches. Always match these numbers exactly when replacing your tyres to ensure correct fitment and safe handling.
345/30 R21 is a popular fitment on Bugatti Chiron variants and Koenigsegg models. The specific vehicles using this size can vary by model year and trim level, so always confirm the correct size from your door-jamb sticker, fuel cap label or owner's handbook before purchasing.
You should only fit an alternative size if your vehicle manufacturer explicitly approves it. Changing from 345/30 R21 can affect speedometer accuracy, handling balance, ABS calibration and fuel economy. If you are unsure, match the exact 345/30 R21 specification printed on your existing tyres or listed in your owner's manual.
Summer 345/30 R21 tyres deliver the best grip and shortest braking distances in warm, dry conditions. Winter 345/30 R21 tyres with the three-peak mountain snowflake symbol are designed for temperatures below 7°C and perform better on ice and snow. All-season 345/30 R21 tyres offer a year-round compromise and are a practical choice for UK drivers who prefer not to swap sets seasonally.
The required load index and speed rating for your 345/30 R21 tyres are printed on your existing tyre sidewall, typically as a code like 91V or 104T immediately after the size marking. Always match or exceed these values — never fit a tyre with a lower load or speed rating than specified. Your vehicle handbook and the label inside the driver's door frame also list the correct ratings.
