Took my MY04 WRX to Scotland for the first time over weekend to see the in-laws. The journey is 300.5 miles door to door. This was the distance recorded by my Toyota MR2 and confirmed by my Tomtom Sat Nav. However, the WRX recorded the journey as 315 miles. I took exactly the same route, except for calling into the services a few more times; to change my daughters nappy to to fill the car with more fuel. This is unlikely to account for the difference of nearly 15 miles.

This could make quite a difference overall in the mileage the car is actually driven:

3,000 miles - 150 miles over read
30,000 miles - 1500 miles over read

I also find that the speedo over reads the speed given by the Sat Nav by about 4 - 6 miles per hour.

The car has had no modifications i. e. tyres/ wheel size changed.

The fuel economy was reasonable. I put £36.00 of petrol in the car; from 1/8 full up to the pump clicking. When I got to Scotland the fuel gauge was in almost exactly the same place.

 

From memory (and I'm sure someone will correct my Swiss cheese brain) but I seem to dimly recall that by law a speedometer cannot display a speed lower than the vehicles true speed. It must also fall within 10% of the actual speed. E.g. at 70mph the speedo should read in the range 70-77mph. This is why your speedo and GPS always differ, most manufacturers err on the side of caution and stump between 5-10% over estimate of true speed.

Or is that so much baloney?? Seems to ring a bell but don't take it as gospel.

As to the distance discrepency ... ermm ... perhaps you 'flew' 15 miles?? Were there a lot of bumps and hump back bridges on the route??

 

You are correct about the over reading of upto 10%.

Both my Legacy Turbo Estate MY93 and my current Outback H6 MY 03, over read by about 7% compared to my Road Angel.

 

I got something right?? Oh my.

Basil Fawlty mode:
A satisfied customer Sybil ... we should have him stuffed