Lorries across 3 lanes of a 4 lane motorway.. surely this is wrong?

Oh I know it shouldn’t do. It does because the previous owner fitted non-standard wheels and tyres. The tyres are slightly wider so there are fewer rotations per mile. Hence the under-read.

You do know, don't you, that it's a limit, not an obligatory speed?

What car do you have and how do you know that it shows slower than what you are driving? Is it a fault because law states that they are not allowed to make them to show slower than what you are driving.

They obviously can, because mine does.

In practice it isn’t a problem because I know it does and just allow for it.

You’ve had random luck with your cars, I think. Mine have always read low; I had one at the point I started using a satnav which turned out to be the full 10% allowed low.
the road sensors near us agree well with satnav speed not what the speedo indicates.

"I think this myth"

I also had heard of this so I thought that I would check it out.

"Every 30mph road sensors around schools etc accurate detects when you are at or over the limit"

That's interesting. My experience has been the opposite. There are three of these near where I live. Two show the speed recorded of any vehicle passing and one only shows a speed when it is over 30 mph.

I drive a Ford Mondeo and typically if I'm driving at 33-34 mph then these sensors show my speed as 30 mph.

Start campaigning to get all freight back on the goods trains and off the roads. Much better for the environment and the roads and peoples sanity.

I think you've misread the OP. The issue is not lorries passing her, but having to go into the fourth lane to get past three lorries in a row in the other three lanes.

Agree at 30 most cars and vans are close but by 50 it varys. I run a fleet and some vehicles are close 1o2 but my personal car is about 4mph out. I drive for a living and do a lot of miles never found a car at 60 or 70 to be 100% accurate. I tend to use Waze or Google maps all the time especially in average speed limits to ensure I’m doing the speed limit if appropriate.

I think they are allowed a 10% leeway but in practice tend to be set a little low. I tend to use Sat nav so I compare what speed Im driving to the speedometer. I think it was a Volvo estate that was bang on Volkswagen polo was about 6-7% under. Current car is a Toyota and is about 5% under. I like it as it means I never speed.

I’m not convinced this is true - independent sat nav devices, whether TomTom/Garmin or the google app on my phone agree with the speeds on every car I have ever driven. Every 30mph road sensors around schools etc accurate detects when you are at or over the limit… I think this myth is used to justify speeding - ‘oh no officer, I wasn’t speeding, the tachometer is inaccurate’, doesn’t really wash, does it?

I drive to the speed shown on the satnav if possible in an 50 zone and still find lorries tailgating because true 50mph is less than the 56mph their speed limiter lets them drive at. They should, obviously, be obeying both the speed limit and not tailgating - much of the discussion around car speedos reading high is irrelevant to that.

as to the blockages cause by trucks overtaking trucks - I’ve not noticed those being too bad, they’d be helped if car drivers would also drive less close together and not exceed the speed limits to allow people to pull out to go round slow rather than hogging the overtaking lane.

Yes, because they're overtaking the lorry next to them.

It's what the lane is for, why are you struggling with this? They're following the rules of the road.

Yeah it’s got fuck all to do with speedometers. It’s just basic dangerous driving if you don’t adjust your speed downward to the car in front (unless you overtake it).

It doesn’t matter if their speedos are more accurate, a massive lorry with a long braking distance still shouldn’t be tailgating a car. You know, on account of it being dangerous driving. ‘I was frustrated because they were driving a few miles below the speed limit’ isn’t going to mitigate wiping out a family.

You need to get your car checked then as they can’t show slower.

They can’t. They’re not out by accident. They are specifically calibrated to show x when you are doing y and are set by the manufacturer. That’s the only reason they vary. BMW have 28mph showing as 30 in the dash whereas Peugeot chose 27 as 30.

They can show you going slower, but they shouldn’t. The speedo in my car shows me going slightly slower than I am actually travelling.

The standard of driving has significantly decreased. Lorry drivers are included in this. I drive for work across the country and see it all. However, that’s why they aren’t allowed in the “fast lane”, so that we can go round them. I have no qualms with waiting behind until they get past the other. It really is efficient for them.

im much more bothered by the absolute pricks in lane 3 of 4 going slower than me in lane 1.

The great thing about lories is that they tend to be very predictable.
They drive at a very stable speed.
Don't loiter in their blind spots.
If they're bunching up, they're likely to want to overtake before they have to adjust their speed.

The same and having also driven on bluelights the wagon drivers are fantastic. Not the same can be said for cars, buses and taxis.

But that’s the issue the lorry’s will be doing exactly 50 as they have calibrated speedos. You with your cruise set to 50 on your speedo is more likely doing 46-47mph - I use Waze or Google maps in my car and to do 50 the speedo reads 54

This is my point entirely.

i find to do 50 my speedo reads 54.

That’s what the overtaking lane is for… to over take (go round them)

I drive quite a lot and to be honest generally I find lorry drivers to be courteous and letting me in on zip merging stretches of roads, they tend to leave appropriate stopping distances too. If I want to overtake I just go in the outside lane. I do try to be mindful of their blindspots too. The only exceptions are on country lanes when they should not be there and on the roads down to Dover where I have seen totally crazy behaviour and so I always try to avoid any trucks on those motorways.