I've been driving this to work over two months with GPS app running on the phone. And the speedometer is off showing faster than it's actually doing. At 70mph it's 4.5 mph slower than the speedo is displaying. It's even worse at 90+ but that's because it's a linear progression. Suspect that the deviation is from tire/rim. However they are factory. Could the factory set the calculations with another tire/rim configuration? And can this be adjusted? Newer electronic speedos have a adjustment just for this situation.