Speedo in Lexus 250

Normally I would expect your speedo to be around five percent fast, in other words it's reading five percent higher than the actual speed you're doing. Under the law it could be as much as 10 percent fast, but on average most cars appear to be closer to five percent. You could have the speedo checked by an instrument maker, but I would suggest you first check it against an overhead speed indicator on a nearby highway. While they are not necessarily 100 percent correct, they are a good guide. You could also check it against a GPS unit, which would give you a good indication of a problem.