[WxmJax]

Not sure which would be closer to actual speed but I was using my Nokia phone GPS sat nav and while that was reading 73mph the car's speedometer was saying 80mph.  Tyres haven't been changed (195/65/15) so can't factor that in.

[eye30]

I'm sure Speedo's are set with a + tollerance of circa 10% so yours will be about right.

[CraigB]

There all set to read faster than what you are actually doing to keep you within the limits of the law but your's does appear to be further out than most I've seen "7mph ( 11kph ) difference".

At 100kph ( 62mph ) my vehicle is out about 3 to 4kph ( 2mph )

[Just Rick]

Sounds like You have one of the older FD poverty packs,or new GD active I think they call them,with the stock steel wheels,Cycril when I first bought him he was the same was actually 11kph slow,as it has been said all new cars since the ninties have been made with a safety buffer of up to 10 to 11 percent, but most are around the 5 percent mark

[WxmJax]

No, it's a 2012 GD 1.6 diesel blue active estate with alloys. Just been out now and it's reading (speedo/sat nav) 30/27, 40/36, 50/45, 60/54. Tyres are set at 32psi.

Now edited as I put the figures the wrong way around, the speedo was always the higher mph figure.

[Asterix]

Would be more fair if it was km/h.. 

All readings are 10% off so believe it's all legal, however not desirable.

It's probably a necessity to avoid a claim from the U.S. of A legal system. Can you believe the outrage it would be if an innocent American was speeding because the car wasn't showing fast enough....  

[eye30]

What is the tolerance allowed by law for speedometer accuracy? in the uk?

 ACPO Guidelines on speeding, and the UK law regarding prosecution.

Vehicle construction and use regulations require a vehicle speedometer accuracy to be in the range of -0->+10%.

The implications are that it must never under-read - for obvious reasons - but may over-read.

[asathorny]

Not sure which would be closer to actual speed but I was using my Nokia phone GPS sat nav and while that was reading 73mph the car's speedometer was saying 80mph.  Tyres haven't been changed (195/65/15) so can't factor that in.

Yeah mine is similar, I can safely do 35'ish on the car speedo and know that I am not gonna be flashed by the speeding cam...   

[eye30]

Not sure which would be closer to actual speed but I was using my Nokia phone GPS sat nav and while that was reading 73mph the car's speedometer was saying 80mph.  Tyres haven't been changed (195/65/15) so can't factor that in.

Yeah mine is similar, I can safely do 35 on the car speedo and know that I am not gonna be flashed by the speeding cam...   

Have you actually put this to the test by passing at 35 past a camera?

[asathorny]

Not sure which would be closer to actual speed but I was using my Nokia phone GPS sat nav and while that was reading 73mph the car's speedometer was saying 80mph.  Tyres haven't been changed (195/65/15) so can't factor that in.

Yeah mine is similar, I can safely do 35 on the car speedo and know that I am not gonna be flashed by the speeding cam...   

Have you actually put this to the test by passing at 35 past a camera?

Couple of times inadvertently, and thank heavens 'it's true'   

[eye30]

Not sure which would be closer to actual speed but I was using my Nokia phone GPS sat nav and while that was reading 73mph the car's speedometer was saying 80mph.  Tyres haven't been changed (195/65/15) so can't factor that in.

Yeah mine is similar, I can safely do 35 on the car speedo and know that I am not gonna be flashed by the speeding cam...   

Have you actually put this to the test by passing at 35 past a camera?

Couple of times inadvertently, and thank heavens 'it's true'   

Next time you are over my way i'll take you past 3 new gatso camera's and you can see if these are set at 35 mph

[asathorny]

I never said that the CAMERAS where set at 35 Lester, what the hell have you been drinking 

[Shambles]

I never said that the CAMERAS where set at 35 Lester, what the hell have you been drinking

Maybe he's on speed

[The Gonz]

To answer the original question, GPS readings are far more accurate.
How accurate is a GPS-based speedometer? | GPS Systems

[Phil №❶]

As stated in every GPS manual, neither does the manufacturer of GPS devices guarantee their accuracy.

GPS works by receiving signals from up above and then (using a shortened form of Windows), performs calculations to determine all the information provided. There is a delay, so the readings are never going to be "real time". Due to distance, even the time is actually 4 to 5 hundred milliseconds late.

That said, GPS's are generally more accurate that a purpose designed, erroneous speedo. I've always hated this concept, the speedo should be deadly accurate and if you go over the limit, expect to get pinged IMO. I am quite capable of managing a car's speed.

[eye30]

I never said that the CAMERAS where set at 35 Lester, what the hell have you been drinking 

The cameras are in 30mph zone so doing 35 should not activate them

[Phil №❶]

Last time I checked, 35 was greater than 30. 

[eye30]

Last time I checked, 35 was greater than 30. 

Correct.

But if asa is right then doing 35 in a 30 zone should not activate the camera as within non activation tollerance.

I,e

30 plus 10% plus 2 = 35

[Phil №❶]

O I C,

I assumed 35 actual, not 35 indicated, silly me. 

[mjt57]

No, it's a 2012 GD 1.6 diesel blue active estate with alloys. Just been out now and it's reading (sat nav/speedo) 30/27, 40/36, 50/45, 60/54. Tyres are set at 32psi.

Did you post correct figures here? GPS is reading higher than the speedo in the above figures. The OP had the speedo reading higher.

I have a 2011 (last of that shape with a CRDi 6sp manual) and 17" wheels. According to the TomTom the speedo reads 100 km/h at 98 km/h GPS indicated.

There's a local road with a road-side speed indication. It corresponds with the GPS. 62 km/h indicated for a speedo reading of 60 km/h.

So, it's not out by much, perhaps a needle thickness. But yours seems to have a lot more error.

Being all electronic can they be re-calibrated?

Some motorbikes can have a thing called a 'speedo healer' fitted which corrects errors. Wonder if there is the same for cars.

[asathorny]

Last time I checked, 35 was greater than 30. 

Correct.

But if asa is right then doing 35 in a 30 zone should not activate the camera as within non activation tollerance.

I,e

30 plus 10% plus 2 = 35

Your exactitude should be a standard to which we all aspire       Once we learn how to spell tolerance of course 

[eye30]

Last time I checked, 35 was greater than 30. 

Correct.

But if asa is right then doing 35 in a 30 zone should not activate the camera as within non activation tollerance.

I,e

30 plus 10% plus 2 = 35

Your exactitude should be a standard to which we all aspire       Once we learn how to spell tolerance of course 

Spelt that way as you have to pay, a toll, to come through the mersey tunnel.....unless you are a cheap skate and use the M53 and M56 and add miles to your trip....

[asathorny]

You know very well that I am a cheap skate Lester, I thought it was a club requirement? 

56 every time for me, the only time I came through the tunnel a bloomin lorry turned over and I was two hours late AAAggghhhh.

If I incur tolls or indeed any other travel costs it goes on the invoice    Which I guess means, tax payer funded, YOU Lester, you help to pay my travel Yiiippppppppppeeeeeeeeeeeeeeeeeeeeeee   

[asathorny]

also I am hoping to be back in your neck of the woods bout springtime, so just behave yourself or I shall have you banned from cycling round Heswall millionaires row 

[diablo]

Last time I checked, 35 was greater than 30. 

Correct.

But if asa is right then doing 35 in a 30 zone should not activate the camera as within non activation tollerance.

I,e

30 plus 10% plus 2 = 35

That's about right. I got a speeding ticket a couple of years ago for doing 36 in a 30 zone.  It said on the info on the back that they only prosecute if ii is above 35.

I checked my speedo against GPS a while back and it wasn't far out at all. That probably explains why when I'm following some cars through 30 mph Gatsos they slow down to 27. It is probably showing as 30 on their speedos.

[Lorian]

I've had a ticket for doing 34 in a 30. £60 fine and 3 points at the time. about 8-10 years ago. hand held gun. If i'd have know about 10%+2 at the time I would have maybe challenged it.

[Asterix]

Being all electronic can they be re-calibrated?

On a VW if you have the VCDS computer you can adjust the accuracy of the speedometer, so maybe possible on a Hy as well....

[Mike SX]

The cameras are in 30mph zone so doing 35 should not activate them

This Police Officer WAS only doing 35mph in a 30 Zone 
Policeman Anthony Rees-Thompson who switched number plates to avoid fine is jailed | Daily Mail Online

[Johnno]

I think its better to have it over reading by 10% +2, gives you a bit of lea way,

[The Gonz]

I have no problem with mine underreading. I drive 5-10 under the limit anyway.