First, sorry for my bad english, Im french canadian . I just purchase a 2008 g35x whit 65 000 miles on it. Last week, i was on the highway, following my girlfriend.She was at 120km/h and me 110???? But the tires of both car are the right size.What make me "slower"on my dash than my girlfriend?

 

Girls are always faster than guys?

If you are running stock wheels and stock sized tires than thats a pretty interesting question. The one thing to also try is to use a GPS or app on a smartphone to see which of your cars is actually correct.

 

Good idea.

 

Maybe HER car is off? Try testing it against another car to make sure.

 

Since you and your g/f both have OE size wheels and tires take your G to Nissan and ask them to check it....if it's that important.
Gary

 

Update. I Check my speed whit a GPS and the speed of the CX-7 is the same as the GPS... For my G:120 km/h on the cluster and 112 onGPS. .... Any idea??

 

Tire size and or speed error. I've read in the past that manufacturers will permit their speedos to be slightly off and on the high side in favor of safety and a 'sense of speed'. I don't know if I believe this though.
I know when I bought new tires and they were overall smaller diameter my speedo was way off. Over the course of a year or two I would estimate the smaller tires resulted in an additional 1000 miles on the odometer than I had actually driven.