How does my car know what the speed limit is?

65 plate Focus, it shows me the speed limit but how does it know? Most of the time it’s clearly quite confident, sometimes it’s greyed out so is obviously a bit unsure – does it read signs? Just know what the limits are everywhere on the map? Secret signals from Skull Island? How does it know? Can I trust it?

If your car has satnav then it’s built into the maps

Some cars supplement that with cameras to .pick up temporary limits

No, you can’t fully trust it. It’s up to you in the end but it’s still useful

There’s a little man under the bonnet

Can I trust it?

Do you have your own eyes and a brain ?

If your car has satnav then it’s built into the maps

Some cars supplement that with cameras to .pick up temporary limits

No, you can’t fully trust it. It’s up to you in the end but it’s still useful

Interesting, ta – so I could do with finding out how to update the 3 year old maps, then! 🙂

Do you have your own eyes and a brain ?

Mostly. Heading south out of Birmingham city centre on the A38, it shows 30 until you get past where Pebble Mill used to be, then somewhere along there it switches to 40. No signs – is the 30 zone actually 40? Is the 40 actually 30? Do I trust it?

How would you tell what the speed limit was without the car telling you?  I’d use that method 1st and the car as a 2nd guess.  It’s loaded onto the maps as mentioned, but Ford maps are sketchy at best usually.  there’s an SD card that Ford will update for you for a kings ransom.

Mine reads the signs.

I also have a 65 plate Focus. It uses the satnav, and I have noticed that it’s out of date.

It appears that updated SD cards are available on eBay for about £45 – I have not tried them. My car has maps version F4, the latest are F7, 2019

If it’s as crap as the Toyota system in our hire car last month, I would ignore it. Use your eyes.

Our cars have cameras to read the signs (including overhead gantries as variable speed limits change) and you can set the active cruise control to decrease/increase as the speed limits allow. Impressive tech.

Are you sure it doesnt have a camera in the windshield?

Hired a new Astra last year that had it, also an S-Max which had the option to link it to the speed limiter – bad idea as it read a side road when I was accelerating from a set of lights in a merge zone and capped the car at 20 until I realised what it was.

My 2011 E-class has it but it was the first iteration without the link to the speed limiter which I am quite glad of. It will overrule the stored speed limit in the sat nav and display what it reads. Was even able to cope with the dual speed limits in France.

somewhere along there it switches to 40. No signs – is the 30 zone actually 40? Is the 40 actually 30? Do I trust it?

If its a built up area and no signs then its 30.

If its out of town and no signs its 60 (or nsl)

If its DC it’s 70 (or nsl)

Anything else has to be signposted.

Can I trust it?

Do you have your own eyes and a brain ?

🤣🤩🥂

Your Focus has a camera/laser built into the cluster on the windscreen behind the rear view mirror. It works fairly well but sometimes reads the speed limit sign on the back of HGV’s and then tells me the limit is 80!

Not all Focus models have the camera. Mine is the same year as the OP’s and the cluster housing is there but has nothing in it.

It works fairly well but sometimes reads the speed limit sign on the back of HGV’s and then tells me the limit is 80!

It does sometimes show 80! I’d wondered why it did that, interesting – cheers. 🙂

If its a built up area and no signs then its 30.

Or 40, there are two main roads out of Chippenham heading east/west, one each side, and there’s little to differentiate them, both have housing along one side, one has a field, the other did have, now has a business park, one is 30, the other 40. Oh, and both have street lighting.

Or 40, there are two main roads out of Chippenham heading east/west, one each side, and there’s little to differentiate them, both have housing along one side, one has a field, the other did have, now has a business park, one is 30, the other 40. Oh, and both have street lighting.

Nearly – if there’s street lighting in a 30 limit there’s no requirement for repeater signs, there is if it’s a 40 limit though. In your example the 40 limit will have some repeater signs, the 30 won’t.

So if there are street lights and you haven’t seen a sign for a while, it’s safe to assume it’s a 30 limit.

and there’s little to differentiate them

As above, speed limit signs on one of them will be the main difference 😉

Just for the avoidance of any further confusion, the title of this thread is not “how do I know what the speed limit is”. 🙂