Hi there,
I don't know which car you have - is it a mainstream manufacurer model ? or a more specialised model ? or a sought after car with specialist's dealing with various aspects of ownership, servicing and maintenence?
Some cars indeed, you can find the overlay and 'convert' it that way - but it's still only half the story. Remember the clock 'hand' will sweep around the speedomter range in KPH calibration, so may need a specialist unit to 'change the number of pulses' the unit recieves in order to sweep around in MPH calibration. If the decals manufacturer is reputable then they may have done the printing correctly so that the MPH calibrated intervals 'on display' match up with the sweeping hand's KPH calibrated movement correctly. If it's one of those stick on jobbies off ebay you should find out as much about them as possible first before you buy.
I suggest you find one of the SVA test centres around the country and see if they list any preferred suppliers for this kind of adjustment, I vaguely recall seeing adverts for Speedo Calibration and conversion specialists, but I can't quite place them, have a search on Yahoo and Google and see what that turns up.
the reason for asking which car you have, is that in many instances, finding spare parts for certain cars can be quite difficult or time consuming to source. Overall though, I think many of the European left hand drive cars that are here, the cars do have the MPH reading in smaller fonts on the same speedo - I think! - else if not, it seems many of them are 'normal' bread and butter type cars for which just swapping out the whole speedo unit out of a breaking/parted out UK car is the quickest and easist way to do it !
It's when you have rarer cars things can get a bit more complex!
Hope this helps!
Cheers! DtM! West London & Slough UK!
