235/45/20 235 refers to the width, 45 refers to the Aspect ratio, and 20 for the rim size. http://www.carbonbla...nformation.aspx Messing with the wheels in changing the rim size and tyre profile will mess with the speedo reading. It'll inaccurately point somewhere where in fact you might be actually going slower / faster hence safety and obvious financial problems, like speeding.. Messing with the wheels in changing the rim size and tyre profile will mess with the speedo reading. It'll inaccurately point somewhere where in fact you might be actually going slower / faster hence safety and obvious financial problems, like speeding.. Not only that, if you mess with your rolling diameter to the point that it is a fair bit of a change (3% is usually the maximum change recommended), if this is in the negative direction (smaller) then that means that for a given speed, your wheels will be rotating faster. Your brakes will then be working harder as a result. Thanks, That link is helpful!