CURRENT SPEED

PAUL-R-S · Posted: Sat Jan 07, 2006 2:11 pm Post subject: CURRENT SPEED

ive been using my ttn5 with the tomtom gps reciver for about 4 months now. ive noticed that the fast im driving the further out the speed thats being displayed is from my speedo. ive tried it in 2 different cars (both fords).

is anyone else having this problem and can it be relied apon ?

badgerdid · Occasional Visitor Joined: Dec 08, 2005 Posts: 41

Mine always seems to be 4 miles an hour less than my speedo says, this is with pda through bluetooth.

mikealder · Posted: Sat Jan 07, 2006 2:48 pm Post subject:

Paul, this topic has been covered before, the last time http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&p=178074&highlight=#178074 although a search will reveal loads more, car speedos are well known to be inaccurate when compared to GPS, but you do need to be aware of the limitations, straight, flat roads offer the best speed data, other factors can mess up the GPS signal, but I would say trust it over and above the data from your cars speedo - Mike

PAUL-R-S · Posted: Sat Jan 07, 2006 4:13 pm Post subject:

cheers mike.
i went through a speed trap before xmas car said 55 and tt was saying 50.

not heard anything yet so fingers crossed will be ok

lupos0_1 · Posted: Mon Jan 09, 2006 9:33 am Post subject:

Speed Camera Database?? Embarassed

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martike · Regular Visitor Joined: Aug 02, 2005 Posts: 194

It’s very easy to check the accuracy of your speedometer : drive at a set speed on a road with distance markers, check the time it takes to cover a certain distance, calculate your speed, then check it against your speedometer reading.

It’s not unusual for the speedometer error to be as much as 8 or 10% and it usually overstates your true speed.

peterc10 · Posted: Mon Jan 09, 2006 4:29 pm Post subject:

The easier way is to use your sat nav. As long as you are doing a constant speed on a reasonably straight and level road it will be right to within a gnats whereas your speedo could be out by up to 10%. It is certainly more accurate than pressing stopwatches when yoy pass markers in approximate positions.

martike · Regular Visitor Joined: Aug 02, 2005 Posts: 194

Checking your GPS by comparing it with a speedometer which has been checked by comparing it with GPS doesn’t make a lot of sense. You need an independent method, and a good old time/distance/speed manual calculation is a very easy way to do it (within certain limits of accuracy).

julianbarker · Lifetime Member Joined: Apr 12, 2005 Posts: 431

The time/distance/speed calculation is what your GPS is doing. It is doing it several times a second and giving you the averaged results - which is why it is pretty accurate. The reason why roads that are not flat or straight induce errors is because they affect the averaging of movement across the geoid used in the GPS calculation. Also, becasue it is an average, if yo uare changing speed, the average will not show your current speed. Even so - most GPS figures will be lots more accurate than a speedo in most situations.

gnattycole · Occasional Visitor Joined: Jan 12, 2006 Posts: 3

I find that UK/European cars tend to over read the speed after about 45mph. Every time I drive in the USA car speedos seem spot on to the single unit there. I think it's a ploy to let folk think they're doing 80 when they're in fact doing the motorway limit in the UK. Keeps the plods happy I suppose.

mav36 · Occasional Visitor Joined: Dec 06, 2005 Posts: 3

Hi guys,

I have both tt300 and tt5 for pda - i don't recall it ever showing my speed!! is there some thing i need to do to either for it to show my speed,
I am fairly new to all this sat nav stuuf, sorry if its an obvious or stupid question

mikealder · Posted: Fri Jan 13, 2006 12:29 am Post subject:

Mav36, for TTN5,x go to preferences then status bar preferences (use the RH arrow to get to it) then tick the speed check box and it will display speed in the lower RH corner of the display when in use - Mike

mav36 · Occasional Visitor Joined: Dec 06, 2005 Posts: 3

Mike,
Thanks for the advice, will give it a go and let you know how I do,
once again,many thanks

Robin2 · Posted: Sat Jan 14, 2006 8:18 pm Post subject:

European Construction and Use regulations make it obligatory for new car speedos to be between 0 and 10% fast. This means that most car makers pitch it somewhere near the middle of that range to allow for manufacturing tolerances.
Robin
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cfalz · Occasional Visitor Joined: Jan 17, 2006 Posts: 4

My TomTom reads a couple of miles slower than the speedometer in my car. That is consistant with the portable radar signs that I pass periodically that the police put out to remind you of how fast you are going. I've been impressed with the accuracy of the gps speed rating. :D

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