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[Kevin Wood]

Virtually by default, all speedos over guestimate your speed so as to stroke the ego of the driver and the car manufacturer.

When I registered the Westfield the requirements of the single vehicle approval test (which may or may not be the same as for full type approval) were that the speedo was not allowed to indicate below the true speed of the vehicle. From memory, at an indicated 70 MPH, the true road speed had to be between 58 and 70 MPH. Had it been 71 MPH it would have failed. The vehicle was run on a calibrated rolling road to measure this.

Compare your speedo with a GPS and you'll find it indicates over the true speed (GPS speed is pretty accurate on the straight at a constant speed). I've tried it in every car I've had and a few more, and I don't think I've ever come across one that under-reads.

Kevin

[DaveL]

Virtually by default, all speedos over guestimate your speed so as to stroke the ego of the driver and the car manufacturer.

When I registered the Westfield the requirements of the single vehicle approval test (which may or may not be the same as for full type approval) were that the speedo was not allowed to indicate below the true speed of the vehicle. From memory, at an indicated 70 MPH, the true road speed had to be between 58 and 70 MPH. Had it been 71 MPH it would have failed. The vehicle was run on a calibrated rolling road to measure this.

Compare your speedo with a GPS and you'll find it indicates over the true speed (GPS speed is pretty accurate on the straight at a constant speed). I've tried it in every car I've had and a few more, and I don't think I've ever come across one that under-reads.
Kevin

...I have when some numpty put  bigger wheels on a motor I bought at auction. Was pulled by one of Brucies associates!! nice man took my word and the receipt from auction house, that I had just got the motor.

Put proper sized tyres onto  the car and flogged. Turned a nice cheap car from auction into a not so cheap car, are well you live and learn.
 8-)
DaveL

[Marks DTM Calib]

Every speedo I have checked has indicated the speed at 3mph above the actual, this is the needle on the speedo, in theory it will also get worse as the tyres wear....

[Dave-C]

Just occured to me, some forces had used to be ZERO tolerance...  as Mark says 3mph and worse with tyre wear....  how could they enforce  ZT?   No doubts several folks have lost their licences for a few over!!!!

[TheBoy]

Well this has actually happened....some chap not being aware of the speed limit traveled up and down the same road several times each time being caught speeding and yep think he got something like 9 points in one day.


Few months back but that's basically what happened.....

My mate's missus got done twice by same camera on the same day, in 2 different cars....

[sounds2k]

... but if your speedo was showing 54MPH then your actual speed would probably be around 51MPH (if 3MPH out) or as much as 49MPH if 10% over-reading ... somehow I don't think they'd prosecute you for being 1MPH over the limit, even if it was 3 times along the same road ...

[The Cambelt Kid]

I heard that if you were caught twice in one journey that you would be done once.  I'm not 100pc sure how true this is, maybe i was told a load of bottom fluff?