Lexus IS250 models in Australia and I assume every other country have significant speedometre errors. The rim size will determine how inacutate your displayed speed is. You are probebly traveling 10km per hour under the speed displayed on your car if you have smaller rims fitted. Lexus has sold me a dud (RX350) and told me it is lucky I do not have an IS250 as the problem on YOUR car is much worse- !!!! Check your speed using a hand held GPS then demand Lexus fix your car!!