I stumbled upon this really nifty utility on the internet. Kouki Tech has this really cool Flash-based utility where you can easily compare different tyre and wheel sizes both through hard numbers (end result of circumference, diameter, sidewall height) as well as visually see how different the tyre sizes will be. It’s very useful if you want to change to a tyre size that’s different from your car’s original size. The utility will also tell you how off your speedometer reading will be. Click the image above to access the Visual Tyre Size Calculator by Kouki Tech.