Does anyone know if and so how you can calibrate, more precisely what/where the adjustment is for speedo calibration? I have a 97 wrx import with a kph-mph conversion box fitted to the clocks that is working but has approx 10% error. Not a real prob just annoying having to keep working it out everytime a camera appears

 

Does your speedo read over or under the 'real value?


Most non-adaptor boxed speedos read probably between 5 and 10% over the actual speed; this is quite normal.

Checked on a GPS thingy mine reads around 7% over.

But in answer to your question I have no idea if there is any manual adjustment in speedos; never heard of it myself.

 

my dads 22b reads over by 8mph @ 80mph!

my RA reads spot on 130mph @ 130mph


(gps)

 

There's no adjustment on the speedo itself.

The max permitted error on new cars is +10%, -0%. Because no car maker can manufacture a speedo 100% accurate they aim for the middle of the permitted band ie +5%. Your average speedo will therefore read somewhere round 5% fast and there's nothing you can do about it.

This means it's legal, you are dead chuffed because you think your car is going 5mph faster than it really is, you go in and pay the robbing dealers £200 for a service after 9500 miles instead of a month later with 10000 miles.

You might find there's an adjustment on the kph/mph converter, not sure as I don't know how they work. Look for a tiny screw head that you can twiddle with a jewellers screwdriver. If not tough, live with it, just cheer up with the fact that every other driver on the road is doing the same.

 

One of the reasons they are not able to make accurate speedos is because the rolling circumference of your tyres changes according to wear!

Very rough calcs indicate approx 2% from new tyre to mnimum tread.

Also, I imagine tyre pressures and maybe even tyre types could affect it.

 

Thanks folks for your replies, most of it I had already taken into account - even looking for a little thing too twiddle . scary thinking that they plan it for the servicing thou!!! Just as well I am a DIY'er - no comments please!

JC