Speedo and satnav show different speeds - which is more accurate?

My Garmin nüvi 1300T satnav consistently shows 4mph less than the speedometer reading on my Qashqai 1.6 Acenta manual, checked on a level road. For example, at 30mph on the speedo the satnav reads 26mph. At 70mph, the satnav reads 66mph. Which should I trust?

Asked on 16 June 2012 by GB, Saffron Walden

Answered by Honest John
In this circumstance your Garmin will be accurate, the car's speedo will over-read and the speed warning sign will over-read. But with speeding revenues down, I'm now hearing of drivers getting done for just a few mph over the limit, despite ACPO guidelines, so take care.
Similar questions
When the cruise control on my Volvo XC70 is set at 60mph the TomTom says I am doing 58/59. When setting the cruise control to 61mph TomTom says I am doing 60. Which is likely to be more accurate, please?...
With all the technical wizardry in modern cars, why do speedometers routinely over read? I've used GPS/Satnav units in many different cars and the cars speedo is always over reading. Spookily this over...
I have recently taken a subscription for Road Pilot, which warns one of speed cameras and shows my speed on my iPhone (which is fixed onto my car windscreen). I notice that typically my car speedometer...
Related models
Very comfortable front seats with good ride. Feels well built. Strong Renault sourced dCi diesels. Elevated driving position and good visibility.


Value my car