Safe Speed Forums

I was driving my girlfriends car and i KNOW i was doing 75mph.

i cant count for invisible technicalties but i can assure you the needle was between 70 and 80 smack on middle so as far as i am concerned i was seeing the car travelling at a "reported" 75mph

ahaaaa didnt think of that... yes its top of the range and has GPS speedo

how accurate is the GPS speedo ?

Quasar wonder if you were in Northamptonshire at the time.

There is an increasing suspicion that the LTI 20-20 laser gun can be tweaked in some way so that they read a few mph high, typically about +10%. This could then bring in those just over the posted speed limit, but below the set threshold, and so increase the tally of convictions for the operator.

Of course no motorist can complain about, or defend against, this as they were, after all, above the speed limit, but not above the normal discretionary allowance, so should not have got a speeding ticket.

I am aware of an increasing number of cases where this appears to be happening. It appears to be too consistent to be due to the slip effect.

It would be interesting to know of how this might be achieved with the LTI 20-20, perhaps by fiddling with the cosine correction, to about 25 degrees, or some other tweak. If you have understanding of how this might be achieved it would be interesting to hear about that.

Quaser if you have been sent two photos of your car by the police I would like to examine them to see if it is possible to determine your actual speed. Please send a PM.

Far moreso than the mechanical one in the car, which is allowed to read +/- 10%

is this possible, it will open a minefield if the operator has to tweak his camera to get a conviction then tweak it back to do a check if they do any checks that is, any idea how it is done

everyone knows you can break the tamper proof seal, and then whilst doing your duty in order to increase the number of convictions if your prior opinion does not work you can tweak the settings to get a reading, this is of course after you have tried to get the slip factor which only operators know how to do, then after this at the end of the shift, reset the tweaked settings, re seal the device with a tamper proof seal that we all have in our pockets, the time and date of calibration we obviously copy every time

Not so. Your speedo must indicate -0/+10% of the true speed. IOW, it must not underread. In practice it is very rare to find a speedo that is completely accurate, and most overread to some extent.

Not so. The accuracy specification only applies to motor manufacturers. There is no check and no specification for speedo accuracy after the sale of a new car.

Speedometer Accuracy

Lord Allen of Abbeydale asked Her Majesty's Government:


Whether, in the light of the increasing importance of speed limits, they have any plans to make it easier for the private motorist to have his speedometer tested for accuracy.[HL839]


Lord Whitty: The Road Vehicles (Construction and Use) Regulations 1986, as amended, allows the use of speedometers that meet the requirements of EC Community Directive 75/443(97/39) or ECE Regulation 39. Both the EC Directive and the ECE Regulation lay down accuracy requirements to be applied at the time of vehicle approval for speedometers. These requirements are that the indicated speed must not be more than 10 per cent of the true speed plus 4 km/h. In production, however, a slightly different tolerance of 5 per cent plus 10 km/h is applied. The requirements are also that the indicated speed must never be less than the true speed.

A vehicle meeting these requirements would not be able to travel at a greater speed than that shown on the speedometer and a driver could not, therefore, inadvertently exceed speed restrictions. Her Majesty's Government have no plans to introduce instrument tests.

I can but refer you to the posting by the claimed camera operator, Camera Partnership Staff, of Sat Nov 11, 2006 12:22 am at;
http://www.safespeed.org.uk/forum/viewt ... highlight=


It is, however, my belief that there is likely to be a much simpler way by which this can be achieved, but which has not yet been revealed.

pity i thought there might be something written down to prove they do this

You wouldn't expect any LTI 20-20 operator to openly admit to fiddling the speed measurements.

I don't yet have enough "proof", but enough to indicate serious suspicion and a cause for concern. I would like to get more evidence for at least another half dozen cases in Northants and then move on from there. You wouldn't expect any LTI 20-20 operator to openly admit to fiddling the speed measurements.