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Use our tyre size comparison tool to check how two tyre sizes differ in width, sidewall height, overall diameter and rolling circumference. It helps you understand whether an alternative tyre size is suitable for your vehicle before buying.
Thinking of changing tyre size or fitting bigger wheels? This free tyre size comparison calculator checks a new tyre size against your original one, showing the change in overall diameter, sidewall, rolling circumference and the speedometer error so you know your actual speed before you buy. Enter both sizes below, then find the right tyres for your car or browse tyres by manufacturer. All of this is provided to you before purchase, so you can be certain you are not breaking the speed limit. Enter both sizes and we will help you find the correct tyres for your vehicle. Alternatively, browse all available tyres by manufacturer.
Enter your current size and the new size exactly as they appear on the sidewall, then press Compare.
The metric format of a tyre size is 205/55 R16, for example. In this format the first number is the section width in millimetres, the second number is the profile of the sidewall as a percentage of the width, and the last number is the diameter of the rim in inches. This is the diameter of the wheel the tyre can fit. Our tyre size calculator can help if you have no idea what this means.
Based on the tyre specifications, the calculator determines the total diameter and the rolling circumference for each measurement and calculates the difference between your current tyre size and the new tyre size. As long as this difference is about 3% or less, the fitment and gearing will be appropriate for standard passenger vehicles.
The goal of plus sizing is to get a larger diameter wheel, but the overall diameter should remain the same or similar. To maintain the same overall diameter, and with it the same rolling circumference, speedometer and odometer readings, while keeping the fitment comfortable, use the tyre size comparison calculator before making your purchase.
If the overall diameter is larger, that will result in speedometer error, where the speed displayed on the speedometer is less than the actual speed. A smaller diameter will have the inverse effect. Our tyre size comparison calculator will compare the sizes and the speedometer error, giving you the speed you need to know.
After deciding on a size, you can find and compare tyres of that size from popular tyre brands and book a tyre fitting.
Jump straight to some of the UK's most-searched tyre sizes:
To keep the speedometer accurate and the tyres free from contact with the bodywork and suspension, you should keep the overall rolling diameter within around 3% of the original size. More than this and you can start to have rubbing issues and speedometer inaccuracies, as well as issues with gearing.
Larger tyres have a greater overall diameter and cover more distance in the same number of revolutions. This causes the speedometer to show a slower speed and the odometer to measure a shorter overall distance. Smaller tyres do the opposite. This tyre size comparison calculator can show you the speedometer inaccuracies for a range of speeds.
Plus sizing is the practice of increasing the wheel size of the vehicle while decreasing the tyre sidewall height to maintain a similar overall diameter. Typically, this is a one-inch increase in wheel diameter and a corresponding decrease in tyre height along with an increase in width. Use the tyre comparison tool to keep the rolling diameter within the appropriate range.
In order for a different size tyre to fit your wheels, the profile and width can change, but the diameter cannot. The new width must also fit the rim. It is always a safe bet to use the size recommended by the manufacturer of the vehicle.
In the UK you can use a different tyre size providing the following conditions are met: the tyres on the same axle must match; the tyres must meet the vehicle's load index and speed rating; and the rolling diameter must be close to standard. Non-standard wheel or tyre sizes must be reported to your insurer.
Check pressures, tread depth, speed ratings and more with our quick and easy tyre tools.
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