Not 100% sure but I think it relates to the number of pulses (revolutions of the wheel). The standard setting is 3795 that relates to a very big diameter tyre that doesn't exist in M3W terms, hence the error. The new Blockleys are a little larger in diameter than the used Avons, so a smaller number. New Michelin Commander II are smaller diameter and they must rotate more times over the calibration distance, so a bigger number (not smaller as you say). There is also a calibration feature that you can use over a known distance of a mile (or maybe a km?). I have not done a metric speedo but I assume the same system applies.
This makes sense. The bigger the diameter, fewer the turns - so the number - to make the same distance.
About the Michelin Commander II, as you pointed out I made the mistake to write it otherwise. Totally correct. Sorry for the confusion.
If we know the outer diameter of any of these tyres we can calculate the distance this number is referred to. Has anyone the outer diameter of the Avons or the Bockleys? Just for curiosity.
What’s clear is that this is something to be done. I mean the calibration. Not Only to be sure the real speed we drive at, but also because the mileage as the speedo is set from Factory is false by at least the 6%. Nothing to scream about, but the more realistic the better.
Thanks Planenut for the instructions. I will do it as soon as possible. I hope to find the calibration plug easy, but I guess it won't be... as my M3W has heated seats.
