We had a Chrysler product that had a speedo that wasn't working at all. It was measured at the tranny and not the wheels.

Why is the gradient off more at higher speeds rather than 'normal' posted speeds?

 

I am an ex sportbike rider & have had my 190mph speedo pegged
with the GPS only reading 162.....this is NOT typical as the bike had
the gearing changed (lowered).

All bikes come from the factory with an optomistic reading of
6-10mph over actual speed....not really sure why.

 

The error in a speedometer is cumulative. The faster you go the more error is added to the equation. So it is more accurate at slower speeds than high. Another thing is that the tires start to deform at really high speeds, elongating in shape and esential becomming talller, also throwing of speedometer readings. Using a GPS is your best bet for getting an accurate top speed reading.

 

What is a good GPS unit to get?

 

Looks like fun. It takes me forever to get my daily up there. I need to buy a fun car!!

 

I always thought that I had fast cars but there is a difference with fast and safe. While they were fast, they didn't feel safe like this car does.
I have had Firebirds that were all faster than anything else in the domestic market, short of the Vette.
Then I have this toy. WOW. It walks up to speed in less distance and stops without protest. Wait until I start to make these features better and I won't be able to stop smiling.
My wife drives a CTS-V which is still faster in a direct line than the targa but it is scary fast in a bad way. 400 hp is still 400 hp unleashed.