| To compare original tire size to replacement use this calculator. Step 1: To edit "original" or "upgrade" tire shown: Click "original tire" to enter original tire. Click "upgrade tire" to enter replacement tire. Step 2: Select correct units based on tire size format. Step 3: Mouse over "TW" pointer and drag it until the correct "Tire Width" appears. (First number in metric tire size) ex: 205/65 R15 Step 4: Mouse over "AR" pointer and drag it until the correct "Aspect Ratio" appears. (Second number in metric tire size) ex: 205/65 R15 Step 5: Mouse over "WD" pointer and drag it until the correct "Wheel Diameter" appears (Third number in metric tire size normally preceded by an R [Rim diameter]) ex: 205/65 R15 To view results: Solution shows the side by side comparison for the original and new tire size entered. Click on Graph to see how the new tire size will affect your actual speed vs. speedometer reading. Generally, the closer the red and black lines are to each other the better. If you mouse over the plot lines on the graph you can see the original tire speed vs. the upgrade tire speed and speedometer indication. 205/65 R15 94H 205 = Tire width (The tires section width , tread width or overall width. [inches or mm]) 65 = Aspect ratio (The sidewall height of the tire as a percentage of width. Also known as series and profile.) R15 = Rim diameter 94H = Load and speed rating |