In some cases, it could be a gear shift but our cars run up to 66mph in 2nd gear (8250rpm shift) so that's not the issue. Are the times in the same test? If not, there are a myriad of conditions that can account for the difference including but not limited to track condition and temperature, ambient temperature and humidity, altitude and barometric pressure. When you have read the results of one test, you have read the results of one test. I hope this helps.I have an m6 convertible which bmw quotes 0-62 in 4.6, why do i sometimes hear that it is 0-60 in 4.3? How can 2 mph make such a big difference?