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[Squatch]

Not of the highest importance - but good for pub topic..anyone know if the plod calibrated speedos are 100% accurate? Normal speedos give you an extra 5/10 mph..

[Sad]

I can't say that they're going to be 100% accurate, but when the cars are still in use by the force I imagine they'd need checking every 12months or so making them as accurate as possible...

[Radar]

I would say they would be right on the money - I got stopped once and question the accuracy and was shown a report which stated the speedo was tested for accuracy that very morning  

[Sad]

Just found this:

'8.2.  Calibrated speedometers must be tested weekly, over a measured distance, and before the completion of a tour of duty during which any speeding offence is detected.'

from:
http://www.kent.police.uk/About%20Kent%20Police/policies/p/p04.html

Doesn't say how accurate they have to be though...

HTH...  

[Squatch]

Very interesting...thank you all. I remember some speedos that were atrocious - old Jags come to mind! And anything Italian...

[Sad]

When I've got the Tom Tom going in my Mig I'm surprised at how accurate the speedo is.  It's only about 3 or 4 mph out at 80, ahem, sorry 70    

[Proz]

When I've got the Tom Tom going in my Mig I'm surprised at how accurate the speedo is.  It's only about 3 or 4 mph out at 80, ahem, sorry 70    

Im the same with the Navman  

[hotel21]

Police calibrated speedos are certified accurate to less than 1% from IRS at Nottingham who pretty much have the UK market to themselves.

A standard speedo is required by legislation to be accurate to within 10% either + or -.  That said, 99.9% of them read high as it boosts the drivers ego sometimes to see a magic number on there - 100mph? - and the car is only actually doing 90....

Calibrated speedos are supposed to be checked at the start and the finish of a shift over a measured distance, just like any other piece of calibrated speed enforcement kit.  Allegedly.  Apparently.  Sometimes......

[hotel21]

[movedhere] Omega General Help [move by] hotel21.

[Kevin Wood]

Calibration of the speedo is one thing, of course, but wheels and tyres have an influence too. In fact, they are probably the biggest contributor to the uncertainty on an Omega because once you've got a signal from the wheel sensors it's just a matter of measuring frequency, which is easy to do to this level of accuracy.

Kevin

[hotel21]

The initial calibration takes into account the rolling circumference/diameter of the wheels/tyres, assuming tyres are 'mid worn' through their tread depth, so I have been told.  That way, if brand new tyres are fitted to the car the speedo will read slow and vice versa when tyres are worn.

We used to get patrol car tyres changed at 3 to 3.5 mm which, when you think theres only about 7 or 8 mm max when new, would easily achieve the less than 1% certified.

[Andy B]

.... to be accurate to within 10% either + or -.  .......

I thought it was +0% -10%  :-/   :-/
ie it could never read slower than actual road speed.

[Kevin Wood]

.... to be accurate to within 10% either + or -.  .......

I thought it was +0% -10%  :-/   :-/
ie it could never read slower than actual road speed.

That is certainly the case at SVA/IVA. I had to calibrate my kit car to read high because if they run it at 70 on the rollers and it reads a gnat's under, it's failed.

The probem is, it means that even if manufacturers are making relatively accurate speedos they are already aiming at having them read high.

IIRC at 70 MPH indicated, the acceptable true road speed range of 57 - 70 MPH was specified.

Kevin

[going crazy]

Would agree with the post above - tomtom says the speedo is out by around 2-3 mph at 7- mph

[PaulW]

In the Elite (non-calibrated), indicated 70mph is 65mph satnav
In the MV6 (calibrated), indicated 70mph is 70mph satnav