Which do I believe?

[Bognor Saint]

On our way here to Chew Bath Valley I pondered again about the differences between the speedo reading and that stated on sat nav. For instance when the speedo reads 60 the sat nav says 55. I know it's said some allowance needs to be given to speedometer readings but are sat nav stated speeds anymore accurate!

 

[Two on Tour]

Both my satnav and dashcam read the same speed as does the speedo app I use for the KPH on the continent.
Van speedo reads 70mph other 3 read 65 mph, what's the chances of 3 being wrong and the van being right ?

 

[Riverbankannie]

On our way here to Chew Bath Valley I pondered again about the differences between the speedo reading and that stated on sat nav. For instance when the speedo reads 60 the sat nav says 55. I know it's said some allowance needs to be given to speedometer readings but are sat nav stated speeds anymore accurate!

Don’t know the answer, BUT ... if you are forecast a rainy day I can recommend a visit to Devizes and Wadworth Brewery. We’ve just come home from a stay nearby at Caen Hill Locks and went on the tour yesterday. The vote from the two guys was “That’s the best tour I’ve ever been on “
It’s a good job I stuck to coffee so that I could drive back to the campsite! 7 beer tastings of third pint each followed by a dram of Pussers Rum.

It was great to see this family firm still in business and thriving, I loved the shire horses and the sign writing studio.
If you ring up they will arrange for large vehicle parking.

 

[Barclaybasher]

Believe the van speedo - it might save you speeding tickets - especially in France !

 

[DBK]

On our way here to Chew Bath Valley I pondered again about the differences between the speedo reading and that stated on sat nav. For instance when the speedo reads 60 the sat nav says 55. I know it's said some allowance needs to be given to speedometer readings but are sat nav stated speeds anymore accurate!

Assuming you are on a straight road and the satnav has a good view of the sky it should be very accurate. A speedometer reading +10% is not unusual. By law they cannot under-read so virtually all are set on the safe side and over-read but at low speed this might be only one or two mph.

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[Clarky]

Speedo always reads under the actual speed to give you a margin below the speed limit.
GPS will be accurate, except there might be a very slight variation when climbing or decending hills and it will be slightly slow at calculating any speed changes.

Richard.

 

[SpeedyDux]

At least I can see clearly the mph reading on the sat nav so I tend to go with that.

Correct me if I am wrong, but as long as you are on a level road the satnav is likely to be highly accurate.

 

[pappajohn]

Sat nag accuracy depends on how many satellites it's picking up but in general it will be more accurate than a speedo.
My last m/h and car were both the same as satnag .... Current car is 3 to 4mph slow at 60mph.

 

[hilldweller]

are sat nav stated speeds anymore accurate!

I've done tests with two GPS receivers at once, they both agreed and the speedo was about 10% high.

Just once, I found that a Kawasaki bike was spot on with the GPS.

 

[Pausim]

I would have expected the speedo reading to be a little above the sat nav one because they are usually calibrated to read a bit high. 5 mph is a bigger difference than I usually get. GPS accuracy can vary with how many satellites are being received and if you lose site of the ones lower on the horizon the accuracy is further reduced. I suspect clever algorithms and rapid recalculations smooth out the readings but perhaps that depends on the quality of the unit.

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[Northernraider]

My satnav is also 5-7mph slower than the Speedo. It also seems to know speed limits better than the signs as it's always changing even when there hadnt been a sign to say so
I trust it more than I trust the van Speedo

 

[wileyfox]

If you have a digital Speedo it will be just as accurate as gps .

 

[Northernraider]

If you have a digital Speedo it will be just as accurate as gps .

Why ?
It's still taking it's reading from the wheels

Satnav is from a satellite

 

[wileyfox]

Does it?

 

[Chockswahay]

If you have a digital Speedo it will be just as accurate as gps .

Nope it won't, as @Northernraider said

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[pappajohn]

If you have a digital Speedo it will be just as accurate as gps .

No, it won't.
It just means it's not connected to the gearbox/final drive by a mechanical link.
It will be calculated by sensors and electronics.

It couldn't use GPS to calculate speed..... What speed will you be doing going through an alpine tunnel where there is no GPS for example.

 

[bigtwin]

Does it?

Yes.

And, for the reasons stated earlier, it’s designed to over indicate the speed.

Ian

 

[old-mo]

Not all car speedo`s are reliable...

When I got pulled on my Harley Davidson, I was doing 126 mph according to my speedo...

But the copper in his BMW said...... Do you realise Sir you were doing 115 MPH on a 40 limit road ...

 

[Northernraider]

Does it?

Yes

Also good for setting the correct time

 

[pappajohn]

UK law, based on EU law, states a speedo can have an inaccuracy of 0 to 10% over actual speed. It CANNOT under read.

If your speedo had a known inaccuracy of 10% you could pass a speed camera in a 30mph zone at 37 mph indicated on your speedo and not flash the camera.

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[Northernraider]

UK law, based on EU law, states a speedo can have an inaccuracy of 0 to 10% over actual speed. It CANNOT under read.

If your speedo had a known inaccuracy of 10% you could pass a speed camera in a 30mph zone at 37 mph indicated on your speedo and not flash the camera.

But thats more than 20%

 

[pappajohn]

But thats more than 20%

No, it's 10% plus 2mph as the law prescribes.

Your speedo shows 33mph (which is a true 30mph with a 10% error)...plus 10%... 36mph on your speedo (but a true 33mph).. Plus 2mph...38mph on your speedo (true 35mph) which triggers the camera but you're only at 37mph (true 34mph..30+10%+1=34) so doesn't flash.

 

[Northernraider]

No, it's 10% plus 2mph as the law prescribes.

Your speedo shows 33mph (which is a true 30mph with a 10% error)...plus 10%... 36mph on your speedo (but a true 33mph).. Plus 2mph...38mph on your speedo (true 35mph) which triggers the camera but you're only at 37mph (true 34mph..30+10%+1=34) so doesn't flash.

Woosh

 

[Feltwell]

Not all car speedo`s are reliable...

When I got pulled on my Harley Davidson, I was doing 126 mph according to my speedo...

But the copper in his BMW said...... Do you realise Sir you were doing 115 MPH on a 40 limit road ...

Nah, Harley's don't go that fast, the tassles fly off...…..

 

[Bart]

No, it's 10% plus 2mph as the law prescribes.

Your speedo shows 33mph (which is a true 30mph with a 10% error)...plus 10%... 36mph on your speedo (but a true 33mph).. Plus 2mph...38mph on your speedo (true 35mph) which triggers the camera but you're only at 37mph (true 34mph..30+10%+1=34) so doesn't flash.

Whooshhh, that just flew right over the top of my head @pappajohn

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[pappajohn]

Woosh

Whooshhh, that just flew right over the top of my head @pappajohn

Believe me, it's right.
A 30mph camera triggers at 35mph
Thats 30 plus 3 (10%) plus 2
If your speedo is 10% (3mph) fast it shows 38mph...at 37mph (actual 34mph) the camera won't trigger
Now, where did I put those paracetamols

 

[Northernraider]

Whooshhh, that just flew right over the top of my head @pappajohn

Mange tout

 

[Northernraider]

Believe me, it's right.
Now, where did I put this paracetamols

I'm confused because surely 10% of 30 is 3 then your 2mph tolerance equalling 35

 

[tonyidle]

Nah, Harley's don't go that fast, the tassles fly off...…..

Damages the plough shares too ..........

 

[pappajohn]

I'm confused because surely 10% of 30 is 3 then your 2mph tolerance equalling 35

Agreed.
But if you have a 10% speedo error that 35 shows as 38mph on your speedo.
BUT... if you pass at 37mph ON YOUR SPEEDO your true speed is 34mph..
34 will not trigger the camera.

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