I found yesterday that my speedo is reading 5 mph compared to Tom Tom

It got 15” 205/60 R15 tyres on standard Skoda alloys

That all over read by about 4mph I find.

4 hours ago, gav_is_con said:

That all over read by about 4mph I find.

Thanks

19 hours ago, Redestate said:

I found yesterday that my speedo is reading 5 mph compared to Tom Tom

It got 15” 205/60 R15 tyres on standard Skoda alloys

That's pretty typical, if you have a good GPS lock on the sat nav.

I use Google Maps and the speed is usually a few mph out.

It's common to most cars. 70mph on my Octavia is 67mph on Waze.

Trucks have pretty accurate speedos because of the tacho.

I believe the UK regulation states that a vehicle must not underread at all, but may overread by a certain maximum percentage - AFAIK, in order to ensure the instrument is compliant to regulations, all manufacturers opt to calibrate the speedo to read high.

26 minutes ago, Warrior193 said:

I believe the UK regulation states that a vehicle must not underread at all, but may overread by a certain maximum percentage - AFAIK, in order to ensure the instrument is compliant to regulations, all manufacturers opt to calibrate the speedo to read high.

So is that suggesting the speedo is inaccurate then?

If I am using Google Maps on the motorway it will show 67/68mph whilst the speedometer shows 70 - so is the GPS on Google a "true" reading then would you suggest?

No, at an indicated 2MPH overread, your speedo reading is most likely within the manufacturers permitted tolerance, according to UK regulations.

A GPS speed reading is likely to be more accurate than the speedo - provided the vehicle track is relatively straight and there is a constant and clear sight of the minimum number of satellites required (usually 3 or 4 satellites) at acceptable angles to the receiver

I would suggest that if you know you are going slower than the car says you mentally calculate that and if you want to do 70 MPH you drive at it showing 73, or as many do at 75 mph thinking 72 mph with speed cameras is ok.

The reading can ot be the same with New Tyres with good tread depth and tyre pressure high compared to worn tyres and a lower pressure.

I run tyres over the OME size normally and a pretty accurate speedo.

Sometime Miles travelled from a reset and the Total miles on a car are a tenth of a mile different.

And my phone app / GPS reads a bit different in miles covered again by an ickle bit.

Tyre tread wear, a different tyre brand in identical size to original fitting or even changes in tyre pressures can cause small changes to speedo calibration. Remember that the indirect TPMS uses the change in tyre rotation speed to monitor pressures.

I recall when there used to be measured mile markers on roadsides to allow drivers to check speedo calibration - can't say I've seen one for a very long time!

I consider it a very good idea to occasionally check the calibration in correct conditions.

6 minutes ago, Ootohere said:

I would suggest that if you know you are going slower than the car says you mentally calculate that and if you want to do 70 MPH you drive at it showing 73, or as many do at 75 mph thinking 72 mph with speed cameras is ok.

The reading can ot be the same with New Tyres with good tread depth and tyre pressure high compared to worn tyres and a lower pressure.

I run tyres over the OME size normally and a pretty accurate speedo.

Sometime Miles travelled from a reset and the Total miles on a car are a tenth of a mile different.

And my phone app / GPS reads a bit different in miles covered again by an ickle bit.

I'd suggest a little caution if proposing to exceed limit by 2MPH through cameras - I know there's supposed to be an 'allowance' plus a percentage - but I've also seen claims of penalties being imposed at 2 - 3MPH over!

As has been said they all over read

@Warrior193 Oop North in Scotland you will see plenty mile markers for Officers checking.

Oop North in Scotland there was a Pilot Scheme with ZERO over speed tolerances & and Education before financial penalties.

No taking an Education Course instead of prosecution in Scotland by a company run by an Ex Chief Constable or 3 making a nice little earner.

The Advice from the Chief Constables (England Wales) of the 10% plus 2 MPH is certainly not to be trusted in certain areas.

As to the 2 miles over, is that maybe about how accurate what ever system is operating.

I have had plenty bang to right caught speeding incidents, and i am always careful as far as camera vans go.

Average Speed camera routes i use regularly i watch what i am averaging at, and that can be slower than HGV,s from Ireland or Coaches.

There are several locations where i join after a camera or leave before the next camera.

I wonder sometimes about others that have passed the camera before me and go on past the next one at many MPH over the speed limit.

Maybe they think if they see someone that might be local ignoring the limit they can. Like ones that think the posties know.

........................

10 years ago, how time flies.

As did Camera Safety Partnership vans between locations.

I reported one that tailgated me and when let past went over the Commercial Vehicle limit.

Turned out they have no Tacho. Police Inspector that replied who headed the Tayside Safety Partnership claimed it was Not in Service and a Technician was road testing it.

Edited 29 May, 20251 yr by Ootohere

Seeing as whenever I am on the M4 there are some drivers (never Skoda ones, of course!) who treat the outside lane like the Autobahn, I wonder do these cameras actually work? Are they literally snapping driver after driver after driver or are motorway cameras just interested in 100mph and up or something?

Just now, JamieH86 said:

Seeing as whenever I am on the M4 there are some drivers (never Skoda ones, of course!) who treat the outside lane like the Autobahn, I wonder do these cameras actually work? Are they literally snapping driver after driver after driver or are motorway cameras just interested in 100mph and up or something?

M6 Toll is the same - treated as if there is no speed limit.