Speedo's over read by around 10% as a safety margin for mfrs. Imagine if they under read and you were given a speeding ticket for going over the limit when your speedo read under. US lawyers would have a field day and bankrupt mfrs in no time.
Some are more extreme than others, I believe Peugeots are at the high end but 7-10% over read is pretty standard. Your satnav will be pretty close to spot on so check what that reads when your speedo is doing 30, 40, and 70mph to see how your own car fairs.
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I used to have an S40, V60 and XC60 so I am allowed here, honest.
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