Safe Speed Forums

Whilst driving to work yesterday afternoon, I noticed a police car at a junction up ahead. I didn't know if he was nicking motorists so I slowed down to the 30 limit and he pulled out ahead of me.

Followed a few car lengths behind on the road leading up to my workplace and he was doing 40mph. Had I been in front rather than behind I'd have been nicked and handed a fine and 3 points on the license.

Similar thing happened when I was driving home from Nottingham late last year, I was doing exactly 40 in a 40 when an off-duty police car approached from behind and overtook me at a set of lights.

One set of rules for them and another for everyone else, hardly setting a good example is it?

Devils Advocate: Perhaps he was driving at a speed suitable for for the road and conditions...Which is basically what we all want to do!

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"Are you sh**ing me?"
"John Spartan, you are fined one credit for a violation of the verbal morality statute."

Perhaps he just had a more accurate speedo?

Which is by far a more likely explaination.

Whilst doing my IAM bike training (Passed the test by the way) my observer questioned my inability to ride at the speed limit commenting that I was continually 5-7 mph below it measured on GPS and his Speedometer. I was adamant that when he felt I was not using the conditions to allow progress I was in fact at the speedlimit. I then did an observed run using my GPS, and we compared speeds and sure enough the speedo on my bike is "fast" by 5 mph increasing slightly as speed increases.

I raised this with BMW (they make the bike) and they stated that all speedo's on their bikes are common and that it is impossible for them to calibrate accurately given the wide choice of tyres available.

The Police car speedo is generally calibrated and therefore likely to be more accurate than the civillian car.

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Former Military Police Officer and accident investigator

Plus the fact that the manufacturer's speedometer generally reads slightly high for obvious reasons!

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"Are you sh**ing me?"
"John Spartan, you are fined one credit for a violation of the verbal morality statute."

But whether the Police speedo is more accurate or not doesn't really matter much. Mr Average driver is going at exactly the speed limit according to the best information available to them (and watching it to almost the exclusion of everything else), and spots that Mr Police driver is going significantly faster.

It doesn't matter whether Mr Police driver has a super accurate calibrated speedo or not - everybody else thinks that he is speeding and therefore that it is one rule for us and that they are above it.

I think my speedo is reasonably accurate, given the speedo cable was replaced not long after I bought the car having snapped the old one removing the dashboard to replace some bulbs. Prior to that there was some wobble in the needle so it was certainly less accurate then.

We have a few radar-operated electronic signs near to where I live, and they light up when I'm only 2-3mph over the limit if that, so I wouldn't say my speedo was out by 10mph at the speed I was travelling.

Incidentally, when said old cable snapped it was just over a month before my local garage had time to replace it, I never had any problems in that time driving without a working speedo passing these electronic boards several times and only setting one off on one occasion, and I managed to pass a Gatso in Norwich a few times without setting that off either. I would say I have a reasonable grasp of speed, and proof, if it were needed, that one does not need to keep their eyes glued to their speedo in order to drive safely!

it is (i think) illegal for the manufacturers to sell a car whos speedo reads too slow. hence they will read fast, usually by a fair %.

at vehicle speeds (tens of mph) on an open road a gps is more accurate (in my experience) than your speedo.
my speedo is close to 10% out @ 70mph (i.e. 70 on the speedo reads under 65 on the gps).

Near Chester this week saw a police car go thorugh a lightb that had been red for about 2 secs. The pro-police and pro-camera perosn who was with me said almost exactly the same thing.

Respect fo the police amongst their staunchest supporters is plumetting daily.

And I'm sincelerly concerned where this will end.

He was not being hypocritical, you admit to exceeding speed limit ( especially in a 30 limt ) and you were not pulled over


It is a serious point though, even more so with Camera "safety" vans ( whose sole aim is to catch people speeding ). But was police car a Traffic Car or Non-Traffic? In my experience it does seem to be the non-traffic vehicles, small low powered diesels and Transit Vans, that are more likely to be setting a bad example.

Fair point, but if speeding is such a serious offense they should not be doing it in the first place either.

This is rural Nofolk/Suffolk border we're talking here, we hardly see ordinary coppers about let alone traffic cops. But yes, ordinary police car it was. Less likely to have a regularly calibrated speedo. Somehow, I find it unlikely that mine is out by 33% at a true 30mph.

The last time I checked my speedometer by timing against the kilometre posts on the motorway, it over-read by 7% at an indicated 50, 60 and 70 mph. I know it doesn't automatically mean it is 7% over-reading at lower speeds but I was surprised the other day to have a speed-check sign (not a speed camera) flash 31 mph when approached at an indicated 29 mph.

Hmm, last night came across another cop car seemingly over the limit. Wouldn't have a problem if the authorities weren't making such a big show out of being a few mph over the limits. The worst thing this time was that they didn't even give a signal when turning left onto a housing estate, lucky I was a few car-lengths behind.

Anyhow, what this thread serves to highlight is that surely it's pointless getting people to stick rigidly to limits when we can't even be sure we're getting accurate readings from our speedos? Perhaps speedo calibration should be part of MOT testing, anyone know how often a speedo needs calibrating to ensure a high degree of accuracy?

The problem with speedo calibration is that it depends on the exact ratio between axle revolutions to distance covered (with mulitplication factors depending on intermediate gearing). This means that it is highly dependent on effective wheel radius - the distance between the center of the axle and the road.

However making up part of that distance is a variable - the tyre. There are two factors to the variable too, the wear and the pressure. So a new tyre running at too high a pressure could be up to 2 centimeters larger than a soft (but not flat) worn tyre. So the accuracy of the speedo is changed by getting new tyres or changing the pressures, and this is likely to happen between MOTs. Worse, the change will typically be the purchase of new tyres and they are larger than the old ones so you now will be going faster than the speedo says.

It is possible to get relatively accurate speed measurements in a non-calibrated car through a GPS system, but not all the time, as in built up areas, tunnels, etc the signals get interrupted. However with such a system you can mentally note what the correction is for common limits (30, 40, 50, 60 & 70) by using the GPS where it does get a clear signal, and then applying it. So if at GPS 30, your speedo read 29, at GPS 40 your speedo read 42, at GPS 50 speedo reads 54, etc. You remember those numbers, and know that you can drive at an indicated 54 in a 50 limit tunnel.

Maybe in future the cars will all have Sat-Nav, and will be able to auto-calibrate the new heads up display speedo by automatically doing exactly this, and everybody will know exactly what speed they are doing all the time. In the meantime we can be grateful that GPS doesn't work everywhere because it stops the big brother tracking your car road charging mechanisms, until the point when the electronics incorporate inertial as well as GPS systems and will basically track your car through the same technology that guides cruise missiles...

i did read a few years ago that because of the nature of their 'gearing' it was actually impossible for a cable speedo to give a accurate speed... it would have to be either higher or lower.

when i was a car trader i noticed that all vauxhall speedos seemed to read fast but ford ones seemed to read low (but this was pre GPS so i was never able to check)

I regularly do 40mph+ in 30 limits. I'm not "setting a bad example", i'm driving at that speed because i've been trained and i feel it's safe for the time and conditions. Is that not what we all want here, safe driving for the conditions? I might then approach a school, still in the 30 zone, but decide that 20mph is more appropriate to navigate safely round the 4x4's parked up....

I wouldn't dream of 'pulling' you for doing 40mph in a 30 unless you're driving was well below standard. I'm not a traffic Officer and i have no 'targets' to meet......

Well said - thats what we all want - safe driving for the conditions, which is sadly not reflected by the sometimes ridculous politically set speed limits

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"Are you sh**ing me?"
"John Spartan, you are fined one credit for a violation of the verbal morality statute."

It's called discretion

As said umpteen times before... depends on what we see people do and to large extent on their attitude when we stop to speak about it.

On the other hand... if a scam cops you at 35 mph and above....

And this is the real problem....fining for 35 mph on an empty road is not common sense. We'd probably ignore it .... 45 mph? Posibly we'd think "this one's up to no good" but generally -we are not too fussed over "slights"

However, I like to think that self and lads on our patch behave on and off duty

(Apart form on here - where I can let my hair down and chill out a bit. .)

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Take with a chuckle or a grain of salt
Drive without COAST and it's all your own fault!

A SMILE is a curve that sets everything straight (P Diller).

A Smiley Per post
FINES USfor our COAST!

Approach love and cooking with reckless abandon - but driving with a smile and a COAST calm mind.

Just asking.... Does Rupert the Bear get about everywhere, or just in Cumbria?
Maybe Ian H can tell me.... or is it a closed shop? I have the annuals, I was supposed to get the badge, but it never materialised!

I have been on the receiving end of discretion, and was a passenger in a car that went the wrong way down a one way street by mistake. An officer assisted in setting the driver right, and said no action would be taken, because it was clearly an error which was unlikely to be repeated, and the driver had shown skill in avoiding and not inconveniencing oncoming traffic - despite their frantic hooting and hand gestures!

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Time to take responsibility for our actions.. and don't be afraid of speaking out!