yeah, spot on there, this is why police allow a 10% error margin on speed limits, ie, 77mph in a 70zone, if there's larger wheels etc. they might give an advisory to get the speedo sorted, same goes for speed cameras, cameras in 70 zones tend to be set at 79mph from what i was told by a traffic cop a month or 2 ago, and larger wheels will not give that much of a difference in speedAnd dont worry about the speedo thing. It is such a small change that it wont affect you at all. It only really has a significant difference at speeds over 70mph. for example if your speedo is saying your doing 70, your probably doing 76mph, thats how insignificant the innacuracy is, and the speedo innacuracy decreases the slower you go.