car speedo and sat nav discrepancy

gazzak_2

shaun_from_Africa wrote: »

If there are 3 lanes, then there must by definition be one in the middle, hence it's the middle lane.
I know that this isn't the official designation but that doesn't mean that the term "middle lane" can't or shouldn't be used for general discussion.

There must be some term to identify the lanes, and what is wrong for inner, middle and outer lanes or nearside, middle and offside lanes?

The OP was referring to a "middle lane" and about driving at the speed limit on it. Whenever someone uses language like this you just know they sit in their middle lane doing 70 with no intention of ever using the motorway correctly. It was a dig at the OP.

ILW

usignuolo wrote: »

Well the sat nav we use is within 1 mile ph same as speedo on OH's current car, at 70mph and higher (we tested it on sunday) and it was also that accurate on his previous car (changed his car last year). I would assume sat nav is more accurate than car speedo as it is measuring speed relative to the orbiting satellites. So I think my car speedo must be wrong.

My problem is if I am driving in middle lane at what I think is 70mph but is actually 64ish, I may be holding up cars wanting to drive at a true 70mph. And does it mean I am safe to over take at 75 mph as my true speed is in fact under 70mph?

Would changing tyres make that much difference?

You should not be in the middle lane unless overtaking.

diesel_dog

mcfisco wrote: »

• Trucks and caravans
• Most people
• Mercedes lane

Shouldn't the last one read as Audi?

mcfisco

diesel_dog wrote: »

Shouldn't the last one read as Audi?

Whatever the current trend is for wannabe high flyers/captain's of industry.
Usually just lower management IT reps, 'ragging' their S Line to the next database meeting - places to be, people to see when you're that important

usignuolo

"You should not be in the middle lane unless overtaking".

I don't sit in the middle lane if the inside lane is empty but it rarely is round where I live. (I drive mostly on the M25 and M3 and M4 within 15 miles of central London). I drive as far left as I can. If I am going faster than the left hand lane I drive in the middle. If you speed up behind me in the middle lane you can overtake on the right. Job done.

If you're travelling at a constant 70mph and everyone on the inside lane is travelling at a constant 65mph then you stay in the middle lane. It would be more dangerous to keep changing lanes.

I don't know about the motorways near you but round my way both the inside and the middle lane are almost always pretty full, with big lorries doing 60ish in the inside lane and cars doing 70 in the middle lane. Cars (Mercs, Beamers, boy racers) overtaking do 70+ in the outside lane. I am always puzzled by where it is people live where the inside lane is empty and they can cruise along it at 70mph.

Chickabiddybex

My Sat Nav told me a one way street is in fact both ways. How can I call my local authorities to tell them to amend the street signs?

almillar

usignuolo - you still haven't answered the question about your wheels/tyres - are they the originals fitted by your manufacturer?
Your speedo is less accurate than your O/H's - you'll just have to get over it. The only people with 'calibrated' speedometers on the road are the police, I don't think it's the car's built in one, and it's an expensive exercise keeping them all up to date and certified to be correct. Best you can do is calibrate your brain to how much your speedo over-reads, so you may think, for example, that you can do '75' on your speedo which is actually 70.

Ultrasonic

usignuolo wrote: »

My problem is if I am driving in middle lane at what I think is 70mph but is actually 64ish, I may be holding up cars wanting to drive at a true 70mph...

(Putting aside the middle lane business...)

Everybodies speedos over-read speed. Without satnavs nobody knew. So all drivers went along thinking they were doing 70 mph when they were actually all going a bit slower. Which is no problem. Some drivers will now go along using a satnav as a speedo, and they will therefore be driving quicker than those following speedos. This doesn't make people following speedos wrong. We're talking about a speed limit, not a minimum speed.

As an aside, if everyone starts using satnav indicated speeds this will likely increase average motorway speeds and consequently drop average fuel economy and boost traffic generated CO2 emmissions.

Edit: Oops - correcting error shaun pointed out below.

shaun_from_Africa

Ultrasonic wrote: »

Everybodies speedos under-read speed. Without satnavs nobody knew.

Bit of a typo there Ultra.
Speedos over-read, they are not allowed to under-read at all.

Carcluster

The sat-nav depends on reception and sampling information - more prone to error. The car's speedo is more connected. Both can be inaccurate, but without getting the car checked, i'd believe (or "drive to") the car reading...