I just drove my wife's Chevrolet Trail Blazer yesterday for few hours and noted that it has huge notable variance on the speedometer as per with two different mobile sat nav (Iphone and Sony).
At 120 km I was getting 110 in GPS, I understand the small variance is acceptable but this 10 km variance seems little big. In my Mustang I get 117-118 in same mobile GPS when I do 120 as per car speedometer.
Any idea how I can fix this variance....?