Speedo vs Sat Nav vs Speed Camera's
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Speedo vs Sat Nav vs Speed Camera's
I've just borrowed a friends Tom Tom for Le Mans and it's the first time I've had Sat Nav in the car and have an observation.
I know std speedo's are crap, but I expected the BMW's to be vaguely accurate. According to the Tom Tom the speedo is under reading by a good 7mph and this is at speeds around 60-80.
So how accurate are Sat Nav speed read outs and how do they compare to proper timing gear and speed camera's.
I understood that Datron etc also used GPS. Does the Datron stuff have quicker sampling rates for more accuracy or is the Tom Tom reading pretty close and the BMW's speedo is actually crap?
Whats your experiences? Going by the Tom Tom I could be driving faster and not worry about it
Ta
I know std speedo's are crap, but I expected the BMW's to be vaguely accurate. According to the Tom Tom the speedo is under reading by a good 7mph and this is at speeds around 60-80.
So how accurate are Sat Nav speed read outs and how do they compare to proper timing gear and speed camera's.
I understood that Datron etc also used GPS. Does the Datron stuff have quicker sampling rates for more accuracy or is the Tom Tom reading pretty close and the BMW's speedo is actually crap?
Whats your experiences? Going by the Tom Tom I could be driving faster and not worry about it
Ta
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Speedo under-reading? Not likely.
Has it different wheels?
Sat navs are spot on 100%, checked mine against all our tacho'd lorries.
My bmw is 2/3 mph over at all speeds I've checked, and that's a 95 - run off diff so more accurate than your old cable driven that are typically 10% over at all speeds.
Has it different wheels?
Sat navs are spot on 100%, checked mine against all our tacho'd lorries.
My bmw is 2/3 mph over at all speeds I've checked, and that's a 95 - run off diff so more accurate than your old cable driven that are typically 10% over at all speeds.
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My Garmin sat nav reads about 10% slower than the speedo readings as well?
I thought it was highlighting the safety cushion that manufacturers build into the speedos?
I thought it was highlighting the safety cushion that manufacturers build into the speedos?
#4
Testing the future
tomtom is very accurate if you hold a steady speed for a while. i guess you meant over reading? i.e. that your speedo shows 68, but the satnav shows 60? if not, there is something wrong, perhaps different size wheels as suggested?
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10% is typical on older cars, modern abs/diff read are pretty accurate, but always read over, unless wheels/rolling radius has changed.
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My dad used to have a 5 series back in 2002 ish, that over-read by 10% as well. Personally I think it is a scam to make services come round faster! If your speedo over reads by 10% then you are going to get your car serviced 10% more (even with the smart service intervals I think!)
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im sure the sample rate of proper timing gear is higher than tom tom!
tom tom seems to sample once a second? datron etc is far more accurate than that.
but they must all use the same gps sattellites? so would be pretty good i'd say
tom tom seems to sample once a second? datron etc is far more accurate than that.
but they must all use the same gps sattellites? so would be pretty good i'd say
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Yes tomtom is 100% spot on as its done by gps. My tomtom reads 78mph when the vans speedo shows 80 so not far out at all. Whereas i know my mates Audi A3 used to read 70 on the tomtom with the speedo showing 79-80! same with his Passat come to think of it. Most other new-ish cars/vans i know are only out by about 2 or 3 at the most, so maybe its a german thing if your bmw is a fair bit out too.
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They know your location within a metre, so accurate.
#14
Testing the future
and yes they all use the same satellites, but some systems are more sensitive than others and have more channels so can theoretically be more accurate
#15
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gps accuracy is about 15m, so roughly about 1%
gps can be even more accurate with the right codes, down to about 30cm's, but these codes are tightly guarded and licensed
gps can be even more accurate with the right codes, down to about 30cm's, but these codes are tightly guarded and licensed
Last edited by GARETH T; 11-06-2008 at 10:42 AM.
#20
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sorry, my last post didnt really help
just reading a little, the standard civil channels can be improved down to 30cm's and the military codes down to a few mm's
just reading a little, the standard civil channels can be improved down to 30cm's and the military codes down to a few mm's
#21
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All cars are setup about 10% over reading. The comment about servicing your car more often as a result is not correct since the odometer is correctly setup. If you travel at 60mph on the speedo for 10 mins, you wont cover 10 miles.
All big manufacturer cars will do this no matter how new. My brothers 56 plate audi 4a underread by exactly 10%.
Satnavs speed calculations are accurite to 0.001% I beleive and use a doppler shift from multiple satalites to work our your exact velocity (velocity not being the same as speed).
JAmes.
All big manufacturer cars will do this no matter how new. My brothers 56 plate audi 4a underread by exactly 10%.
Satnavs speed calculations are accurite to 0.001% I beleive and use a doppler shift from multiple satalites to work our your exact velocity (velocity not being the same as speed).
JAmes.
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my Audi A6 speedo is Always about 10% about at all speeds vs garmin satnav
however my TT is out by about 2-3mph from 30 till about 100 then its spot on at about 110 not looked long enough at sat nav at higher speeds
Nige
however my TT is out by about 2-3mph from 30 till about 100 then its spot on at about 110 not looked long enough at sat nav at higher speeds
Nige
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[QUOTE=cossiegreg1;3351213]how bad are cossies? obv cant speak for every cossie but just in general[/QUOTE
at 50 on my speedo on the cos its 51 on tom tom, 100 is 103 on tom tom.
at 50 on my speedo on the cos its 51 on tom tom, 100 is 103 on tom tom.
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