I just got back from a 4000km tour with no issues. The car ran beautifully. I have a new GPS toy and I noticed that my speed is reading about 6% lower than actual at highway speeds. I have new tires on it that is correct for the model and year (205-55-15) according to door pillar info.
Why is the speed off by so much and is there any way to adjust?
Txs

 

Mine has about a 4% error to the low side. When I'm driving 76 mph (display), I'm actually going about 79 mph. I don't think you can adjust it.