Hi again

Can any one tell me what figure to put in to my speedo in order for it to read correct.

I have an acewell speedo with 1 pick up sensor mounted in the rear brake drum.
My tyres are 185 70 13

Hope you can help

Cheers

Your theoretical circumference is 1851mm, so use that to start with.

After that the only way to check its right is at the sva test, or follow another car at a known speed.

See:
http://www.carbibles.com/tyre_bible.html

Just over half way down there is a calculator for circumference.

David

Or calibrate it using the marker posts on any motorway. I believe they are a set distance apart.Can't remember the exact figure.

I used a tom tom sat-nav to check mine on a very short run, twas perfect at sva.
john.