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Old 09-09-2006, 07:23 AM
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GPS Speedometers

Hey Guys: I need some comments please. I recently discovered a company (this is a fancy way for saying read an add in a hot rod magazine) that markets GPS speedometers. I contacted them directly, asked the standard 50 questions, got the standard sales pitch. At the end of this exchange, which included, "we never hear back from customers so our product must be so good we consider it bullet proof", I asked for an end user reference to contact so that I could talk to someone who is acutally using the product so as to get their input. Well, they did not have someone for me to contact right off the top of their heads. So they took my number and said they would call back, three days ago. And the funny thing about this reference thing is that they quoted two people who they "claimed" are customers about their experience with the system in their add. So why not give me their contact information so that I can talk to them directly? Anyway, after no response from the company with a reference I then realized that I have the greatest reference group on the planet at my finger tips on this website. So, I would be most appreciative is someone, anyone, who has any experience with a GPS speedometer system would provide me with their input.

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Old 09-11-2006, 08:55 PM
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I have two GPS's that compute speed although neither is marketed as "speedometers." What I do know is that a GPS has to get readings from several satellites to compute location, then use the change in location over time to get speed. Neither of my units give continuous readings but rather update the speed every few seconds. A GPS speedometer won't work in a tunnel, under trees, or any where else that doesn't allow a clear view of several satellites.
I can't see how they would be as accurate either. What if you go through an s curve? I think the GPS would compute a straight line distance.
I just installed TPI gauges with a programmable speedometer that uses a sender mounted on the transmission where a mechanical cable would mount. Regardless of tire size or rear end, it is just a matter of pushing a few buttons, driving a mile, and pushing a few more buttons to calibrate the speedometer.
I h ope this helps
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Old 10-16-2010, 12:03 PM
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TO Pa-Farmer

Hi, I am trying to calculate my TPI-Tech speedometer and can't tell you how many times I have push that darned button! I am getting all of the correct readings and can get it set up but after I drive the mile and stop, push the button one time, the readout says calculating and never goes to done. I've tried doing step 5 and setting on each of the letters (L N H) and then step 4 after each. No luck. Any suggestions?
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Old 10-02-2011, 01:52 AM
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Gps Speedometer

AS far as a GPS speedometer Speedhut has the best one on the market that i know of. I know a few folks that have then also and they have never had a problem with them, yes you will loose them in a tunnel but i have never lost signal even while driving down town Foort worth around the tall buildings. Little pricy but sure was easy to hook up i did not have to figure any gears tire size are anything just hook it up turn it on and it will start working with in 4 seconds or less most of the time now it want work sitting in the garage but as soon as you pull out it goes to work. very accurate and you can see what you ran in a 1/8, 1/4 mile what direction your going trip meter and more and no i do not work for the company just a satisfied customer. Cost around $250 and they have a complete gage set if you want one here is the link for the site. not sure if this is ok and i am sure if it is not some one will tell me.
http://www.speedhut.com/

GOD BLESS AMERICA
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Old 10-02-2011, 05:24 AM
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My Garmin GPS seems just as accurate as the speedo in our 2005 Chevy........Sure, there are a couple of drawbacks, but not $250 worth...After all, you just want to see how fast you are going down the highway, not so much in parking lots etc
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Old 10-02-2011, 05:31 AM
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How true $250 is steep but life time warranty no questions asked, does Garmin give you that? I had to save for it but I have never had any issues with it and very easy to hook up.
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Old 10-02-2011, 05:45 AM
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I have a Garmin 255W ($75 from Target last fall) that I used to set my electronic VDO speedometer. The VDO would not set via the "drive 2 miles and push the button" method, but only via the pulses transmission/driveline speed. It s accurate to a mph and I was able to get it 'right on' fairly quickly. The VDO speedo plus the Garmin were less than a Speedhut GPS speedo,

I'm not suggesting a GPS speedometer is bad, but that it might be a good idea for them to 'mature' a bit first and maybe a few more brands available for competitive quality, features and price. Being among the first users ain't always the best nor least expensive

Dave W
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Old 10-02-2011, 06:32 AM
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Quote:
Originally Posted by papas32
How true $250 is steep but life time warranty no questions asked, does Garmin give you that? I had to save for it but I have never had any issues with it and very easy to hook up.
Can a GPS speedo tell you where the nearest Walmart is?.........lol
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Old 10-02-2011, 07:10 AM
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Garmin will get you there..others get you lost..

Sam
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Old 10-02-2011, 07:27 AM
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Originally Posted by OneMoreTime
Garmin will get you there..others get you lost..

Sam
Let's just say that the Garmins wont get you quite as lost

I'm going to hold graveside services for my 5 y.o. NUVI 750 later this week. It went into cardiac arrest once too often yesterday and I'll be euthanizing it

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Old 10-02-2011, 07:28 AM
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I bought a Garmin Nuvi 1350LMT for my daily driver last May. $160 at Costco. I was pleasantly surprised with it's features.

It displays the vehicles speed, and the speed limit for the road you are driving on. Of course it also provides navigation and has content for USA and Canada, has lifetime free map updates and lifetime free realtime traffic advisories. I mount it right in front of my speedometer on the daily driver and it is dead nuts accurate, don't need the car's speedometer any more.. On trips I use it to find the nearest McDonalds when the grandkids have to pee or whatever.

If I was completely redesigning the dash in my street rods, I would consider building something like this in permanently in the layout.
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Old 10-02-2011, 08:17 AM
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GPS speedometers are getting popular in boats. I have driven, and waterskied behind boat with them, a lot.

GPS systems get speed by two different methods. Both methods depend on having a good fix to GPS satellites.

The first method was explained already. The GPS gets a fix, a exact location, and then in a little while gets another fix. It knows how far apart the two points were, and the time it took to travel to the new point, and calculates the speed. But this is the average speed you were going between the two points, not the speed you actually are going. Errors also occur if you are going in a circle, because GPS assumes a straight line. This method requires a fix on several satellites.

The other method GPS uses it it locates a satellite low on the horizon, directly in front or behind you, and it listens to the radio frequency transmitted from that satellite. It knows what frequency the satellite should transmit on, and compares the difference, using Doppler shift, and then calculates the speed, similar to radar speed systems. I believe 73 HZ Doppler shift = 100 MPH. This method requires a fix on only one satellite, but the satellite has to be low on the horizon, and in front or behind you. Low on the horizon is not a good position to get a strong GPS signal.

My experience in boats has convinced me that GPS is not always accurate. It changes slightly when moving at a constant speed, and sometimes drops out altogether. In boats, GPS is an alternative to measuring speed, because of the difficulty of measuring speed, and distance on water. On my boat, I use GPS as a backup system, to initially calibrate the Airguide speedometer, and then I use the Airguides to tell me how fast I actually are going. Airguides are the old pitot tube pressure gauge system.

In a car, with a more or less solid connection to a hard surface, and a direct correlation between driveline speed, and the speed of the car, I think GPS speedometers are an expensive, non reliable solution to a problem that really does not exist.

Especially when you can get navigation systems that give you a lot more useful information for less. Just do not depend on the information navigation systems give you. People have died here in Oregon, by following GPS directions into roads closed for winter, or otherwise impassable.

Last edited by DanielC; 10-02-2011 at 08:24 AM.
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Old 10-02-2011, 10:01 AM
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My TomTom will not only give me an accurate speed, it will tell me if I am speeding. I haven't had this feature since my 1968 Corvette, speedo will 'BUZZ' when you go over the set speed. Show me a car today that will do this.

GPS doesn't work so well in the deep mountains, tunnels are a hit and miss thing because some have cut windows where signal will penetrate.

Note to threewindowdeuce:

Read your instructions a bit more, run the vehicle at a steady 30, 60, etc. mph, when you come to your marker post, click the button, drive the measured 'flying' mile, click the button to stop the count. Let the speedo calculate and retain result into its memory and your done.
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Old 10-02-2011, 10:46 AM
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Quote:
Originally Posted by poncho62
Can a GPS speedo tell you where the nearest Walmart is?.........lol

No need for that thing to tell me that since I usually have my wife in the car!
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Old 10-02-2011, 11:45 AM
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With the Dakota Digital speedo, you don't need a "flying mile" it's calibrated by the number of pulses it recieves from the tranny pulse generator during the "measure mile" for example mine came with a 16K tranny pulse generator, one would think it would produce 16K pulses for a mile....... mine produces 1752 pulses in a mile. I used my hand held Garmin GPS, zeroed the garmin, pushed the auto calac on the speedo, started driving in a straight line, when the GPS said one mile, I stopped and pressed the auto calc button again......1752 pulses, repeated the whole process again, 1751........ had the wife drive beside me and we verified the speeds..... dead on.
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