This tool combines features of a tire size calculator with an easy way to compare speedometer differences for tire sizes. Just enter the original tire size you see on the sidewall and compare it to the desired tire size alternative.
The first number (265) is the tire width in millimeters.
The 2nd number 60 is used to calculate the sidewall height or "aspect ratio", by percentage. So, the sidewall height of a 320/60 R 18 tire is 60% of 320 = 192
The 3rd number 18 (generally preceded by an "R") is Rim Diameter in inches.
This is the diameter of the rims bead seat base, not the diameter of the outer rim edge. The rim edge, or lip, extends past the tire bead seat to hold the bead and stop the tire slipping off the rim.
When we say a rim has a 18 inch diameter, we mean that the diameter of the bead seat base measures 18 inches. The outer rim edge diameter will actually measure more, depending on the design.
If you replace 320/60/18 with 235/60/18 for Odometer reading 1000 the actual distance traveled = 879 ~ (-12.1%)
(If your Odometer is accurate for original tires)
Edit and Copy Tire diagram above to compare or print.
|320/60 R 18 KPH||235/60 R 18 KPH|
To get an accurate difference between your original tires and alternative size tires you should do this:
This tool is here to provide you with the necessary information, but it must be used with caution
You should generally seek professional advice when looking for an alternative tire.
One day you may want to use aftermarket tires different from the factory rubber supplied with your vehicle. Alternative sizes for a tire make sense if you want to influence unique driving characteristics, such as:
Prices for alternative tires can differ significantly from the original tires - sometimes, they are cheaper or more expensive.
The dimensions of a tire are usually specified in this way: 175/75 R14.
This is the maximum speed at which you can drive the tires. If this is exceeded, the tires are dangerous to use. The speed index is indicated by letters, e.g. T (190 km/h) V (240 km/h). You should permanently mount the tires with the speed index approved by the manufacturer.
This is denoted by a LI symbol (Load Index). This describes the maximum load capacity of the tire in kilograms. The load index is represented by numbers, e.g., 91 means that the full load on the tire is 615 kg, and this cannot be exceeded. You should always fit tires with the load index recommended by the manufacturer.
Determining an alternative tire options only gives a meaningful result in a direct comparison with the size approved for your car. If your car already has tires that differ in size from the OEM tires, then the alternative determined by the tire calculator is by no means suitable.
The numbers will not show the true picture. The alternative calculation only gives a correct result compared to the size approved for your vehicle. So always compare the new tires' size to the recommended value. If the tires fitted to your car are already alternatives, the alternative calculated with them may not fit your vehicle.
You can find the permitted tire size for your car in the owner's manual or with the help of our tire calculator.
With a diameter/circumference and speed calculator, you can quickly and easily test whether a speedometer adjustment is necessary for your desired tire size.
When changing the ground clearance, some rounding errors are possible, but they amount to a maximum of 1 mm, i.e., and are irrelevant.
The speedometer may show a maximum of 8% too much and no km/h too little. Please note that the speedometer display is slightly ahead of the factory original on most vehicles.
If you want to go through the tire conversion process to improve your driving experience, you should know the safe limits. By installing the alternative-size tires, you change not only the way your car behaves but also the way other vital systems function after this sudden change. So to stay within the safe threshold, keep the difference at 3% of the original diameter/height. This cautious approach will save you from faulty brakes and other problems.
The tire aspect ratio is, in simple words, the relationship between the width and height of the tire.
The aspect ratio is the width of the tire divided by its height. The higher/taller the sidewall (or “profile”), the bigger the aspect ratio. The wider and shorter the tire, the lower the aspect ratio.
Car owners often resolve to lower aspect ratio to get better performance and improved control over the vehicle. But that must be done with extra caution and ideally with help from a professional.
Because if you mount a lower aspect ratio tire on the same diameter wheels, you'll need to increase the tread width to keep the speedometer and ECU readings consistent. And compensation can be tricky sometimes.
To calculate the sidewall height, multiply the ratio (70 or 0.70) by the width (225): 225 millimeters x 0.70 = 157.5 millimeters. The number 15, or R15, is the diameter of the wheel in inches.
The most reliable source of information is your car's manual, it contains all the necessary information. You can also use the recommended tire size values from the manual to test your chosen alternatives using our tire size comparison calculator to get a better idea.
Also, by changing one size up in tire width and one size down in aspect ratio (the proportion of the tire's height to width), you will stay within a reasonable range.
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