SatNav: how accurate is the GPS speedo?
18 April 2009, 12:08 PM
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SatNav: how accurate is the GPS speedo?
Just bought my wife a TomTom XL 22, which she insisted on having in use all the way down to the house in France, and back.........this despite the fact that I've driven the SAME route over 40 times now and NEVER got lost
Anyway, it did OK, except for getting a bee in it's bonnet and wanting us to go via Paris
I did notice that it gives speed LIMIT and actual speed data. However, the actual speed it showed was ALWAYS about 5-8mph LESS than that shown on my speedo.
So............which ought I to trust?
Anyway, it did OK, except for getting a bee in it's bonnet and wanting us to go via Paris
I did notice that it gives speed LIMIT and actual speed data. However, the actual speed it showed was ALWAYS about 5-8mph LESS than that shown on my speedo.
So............which ought I to trust?
18 April 2009, 12:18 PM
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If you are travelling at a relatively constant speed and relatively straight, then the GPS is very accurate.
My Supra speedo was about 14 mph over at higher speeds, my current Focus ST is about 4-5 mph over.
(most speedo's are calibrated to be over slightly)
Steve
My Supra speedo was about 14 mph over at higher speeds, my current Focus ST is about 4-5 mph over.
(most speedo's are calibrated to be over slightly)
Steve
18 April 2009, 12:38 PM
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I suppose everyone's must be then. I was doing an indicated 80mph on French motorways, which is the limit, and was about the same as everyone else.
If I went at gps 80 mph, I was overtaking everyone.
If I went at gps 80 mph, I was overtaking everyone.
18 April 2009, 05:57 PM
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Remember that by law speedos must be spot on OR over-read by less than 10%. So you should be reading a maximum of 76/77 at an accurate 70. My Passat (2001) is about 3/4mph out at 70 or 80, so fairly accurate.
The GPS will be about spot on at a constant speed in a straight line, as someone has said.
Dave
The GPS will be about spot on at a constant speed in a straight line, as someone has said.
Dave
18 April 2009, 06:16 PM
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Wot you doing in here? I thought you only went into sport now?
No tiles, a bit of electrics, a bit of MASSIVE woodwork, and LOTS of fighting with ivy, brambles, nettles, thistles, weeds and the stupid mole etc that take over the garden when your back is turned
However, Mr Mole is no more.............the "Detaupeur" did it's lethal job first night there
Beer? Sounds good.
Get the postcard?
No tiles, a bit of electrics, a bit of MASSIVE woodwork, and LOTS of fighting with ivy, brambles, nettles, thistles, weeds and the stupid mole etc that take over the garden when your back is turned
However, Mr Mole is no more.............the "Detaupeur" did it's lethal job first night there
Beer? Sounds good.
Get the postcard?
18 April 2009, 06:31 PM
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I dabble when the offensive emails and pm's subside
Your not talking about your lovely wife are you Jeffrey 
Better than making bombs with poles and lighters I guess
Ofcourse it does. We had a good laugh last time mate
I did, and Natalie noticed it straight away on the fridge
Ofcourse it does. We had a good laugh last time mate
I did, and Natalie noticed it straight away on the fridge
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18 April 2009, 07:31 PM
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My mates dads satnav records maximum speed. Whilst checking the unit out I noticed the max speed was 186mph!!! He told me he'd done that on an undisclosed UK road in one of his cars ( quite achievable, he has a nice collection).
After some weeks I mentioned to my mate that I'd seen his dads top speed and was well shocked. He then pointed out that the top speed was achieved... on Eurostar. B*stard.
After some weeks I mentioned to my mate that I'd seen his dads top speed and was well shocked. He then pointed out that the top speed was achieved... on Eurostar. B*stard.
18 April 2009, 09:11 PM
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That's funny !
My local train hit 91 mph ! Rattly old buses that they are...
Mine is 1 mph out at 100 mph, OZ alloys and R888's. 5 mph at 80 mph on std wheels.
dunx
My local train hit 91 mph ! Rattly old buses that they are...
Mine is 1 mph out at 100 mph, OZ alloys and R888's. 5 mph at 80 mph on std wheels.
dunx
19 April 2009, 09:26 AM
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19 April 2009, 05:13 PM
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If the authorities are so insistent that *speed kills* they would have the speedo accuracy tested at the MOT. But hey, what do I know obviously ....
Dave
19 April 2009, 09:15 PM
#13
I went through one of those speed checkers that display your speed as you drive past, warning of the speed you are doing, TomTom 720 matched the speed given by the speed detector (30 mph) yet my odo showed 35mph ..... This on a 52 plate Transit.
The WRX was out by 3mph (27 on the odo,) at the same speed of 30 mph.
The WRX was out by 3mph (27 on the odo,) at the same speed of 30 mph.
20 April 2009, 08:33 AM
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Mention of speed checkers has just reminded me that I passed one of those signs in Doncaster which tells you of your speed, and in the Scoob, and indicated 40 on the speedo was shown on the sign as 35.
I REALLY can't see those being inaccurate, or they encourage folk to speed, so maybe the car's speedod ARE way out.
At least they are low: less chance of being done for speeding by the scammers
I REALLY can't see those being inaccurate, or they encourage folk to speed, so maybe the car's speedod ARE way out.
At least they are low: less chance of being done for speeding by the scammers
20 April 2009, 10:09 AM
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So when floating around hell (I mean Scun.thorpe), I stick to exactly my speedo, not slightly over as I did with the Scoob.
20 April 2009, 10:42 AM
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My speedo always reads slightly under the sat nav, i was a bit pi55ed off the other week, as i had been on a private testing facility, and seen the speedo hitting speeds of 150+, but when i checked the sat nav some days later it showed the maximum speed achieved as 134mph, which got me thinking, my car (a WR1) has 18" alloys as standard, but is just a gay coloured STI in reality, which have 17"alloys as standard, so do prodrive re-calibrate the speedo, or just leave them as they left the factory?
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