I think my speedo calibration may be out by around 13% as the same journey in my 98 wrx shows 39.5 miles & in my standard Primera reads at 35 miles.

Wondered how its altered from km to miles in the first place & if this is adjustable ?

Thanks

 

Miles x 1.6 = Kms Kms x .625 = mls.
To check your trip or audometer:
On the motorway you will see striped posts at the edge of the hard shoulder at 100m intervals. They are marked. eg. 17/6.... 17/7 and so on.
This means 17.6Km from the start of that particular M-way.
Log the post number and re-set your trip or log the audometer and then run for upwards of 10km to get an accurate figure. You can then work out by what %age your trip etc over reads.
There are a number of companies who can re-calibrate your speedo if you think that is necessary.

 

Also have you changed the wheels at all on your WRX?

Different size wheels usually have a different rolling circumference and may throw your speedo out.

Rich

 

Cheers for the advice I'll compare it to another car over a measured distance

It has 205/45/17's on which I believe to be the closest rolling radius to oe.