Enter your username:
Do you want to login or register?
  • Forgot your password?

    Login / Register



    Results 1 to 13 of 13

    Thread: GPS speedometer

    1. #1
      Join Date
      May 2000
      Posts
      4,151
      Country Flag: United States

      GPS speedometer

      I think I remember seeing this item in a magazine. It's a gps speedometer that you could just plug into your cigarette lighter.



      Anyone know of such a thing?


    2. #2
      Join Date
      Jun 2001
      Location
      Newbury Park, CA
      Posts
      5,821
      Country Flag: United States
      There are handheld GPS units available that have speed capability. The last time I looked they were in the $800 range.
      VaporWorx. We Give You Gas http://www.vaporworx.com

    3. #3
      Join Date
      Nov 2001
      Location
      Sacramento Ca
      Posts
      6,827
      Country Flag: United States
      Almost ALL handheld GPS units work for MPH. I have a Garmin etrex legend. 150 bucks at REI. (200 at target) there are cheaper ones, but Im an avid Geocacher, so the features on mine are needed.
      Last edited by TonyL; 09-19-2005 at 09:02 PM.
      Tony Langlois
      1966 Corvair Monza

    4. #4
      Join Date
      Aug 2004
      Location
      San Antonio, Tx
      Posts
      1,190
      in the new Boating World mag they have the speedo that is done 100% GPS. it would work in a car and you would know how many knots your land yaut (sp?) is going
      Instagram: CamaroAJ

    5. #5
      Join Date
      May 2007
      Location
      Las Vegas
      Posts
      668
      Country Flag: United States
      Bringing up a 5 YEAR OLD thread because "I USED THE SEARCH BUTTON" and found a topic with the perfect title .... lol

      Anyway. With 5 years of progress and advancement in technology... How many people are using one? I just found a speedo I like and they offer a GPS version....
      http://www.speedhut.com/gauge_produc...ometer_GPS.htm

      How accurate are they really?
      Does the GPS signal ever disappear or black out?
      Anyone running gauges from Speedhut (GPS or Not)??
      Rich
      1969 Camaro (in hibernation)
      1972 K5 Blazer - LQ9, 4L80e, NP205, D60, AAM 14BFF => http://67-72chevytrucks.com/vboard/s...d.php?t=423432


    6. #6
      Join Date
      Apr 2001
      Location
      Rockford Illinois
      Posts
      3,947
      Country Flag: United States
      I have a Racepak and the gps works well and it has the anntena mounted under my rear spoiler. i also have a Stewart Warner 200mph speedometer in the middle of my dash. You might ask why?

      In the wondeful state of Ill. you have to have an odometer and the Racepak will sometimes lose the odometer info from what everyone has seemed to experience. The odometer on the SW will also make my insurance man a bit happier when he wants to be sure how many miles I go. It would be no problem I would think if I lost the odometer info from the racepac or the SW but I just wanted to comlply. I have also had a few times the gps was not able to get a signal and the SW was there for me. The SW also sometimes read high and other times low for whatever reasons, not by much but it is off sometimes from the Racepak gps speed.

      If you deduct the cost of things like gps,total data aquisistion, lap times, left and right g forces ,accelerometer for braking and acceleration, and a host of other items and deduct the seperate cost of units from the actual cost of the Racepak you actually get the most number of gauges for the same or less cost of most any other totally complete gauge package from anywhere else.

      I went over my original budget to get the Racepak vs the Autometer Nexus gauges that never came to fruition and now am glad I did.

      Get the right gps and it will give you so much more than just speed and how to get there.
      May The Horsepower Be With You !!!

    7. #7
      Join Date
      Aug 2008
      Location
      Pgh, PA
      Posts
      2,177
      GPS speedos are neat gadgets. They are not as accurate as mechanical (also meaning electric signalled mechanical speedos). A GPS speedo will always lag. If it has at least 4 strong sat signals on level ground, it will be OK. If there is elevation change involved it'll be much less accurate.

      Jim, I'd be willing to bet that your SW speedo is right on, and your Racepak is off - a little high sometimes and a little low other times. Look at the math of it. The SW cannot be both high and low. I'm assuming it's driven off your tranny, right? That means it's a very simple mechanical formula where shaft revolutions are converted to displayed speed. It may be off - but it'll always then be off in the direction - either high or low. By a static variable.

      A GPS, OTOH, takes satellite signals, calculates the time for that specific sat signal to reach the gps, knows the location of that sat , and compares that to the same data coming from other sats. It takes 3 sat signals to get a 2D fix, and at least 4 sat signals to get a poor 3d fix. It's constantly calculating all those vectors. Sat signals are constantly falling in and out. Then you have the sat altitude, all combining to result in something called DOP (dilution of precision). It varies by location and time of day to to these factors.

      Bottom line is that unless you live in the desert, a GPS speedo is simply not an accurate instrument. I'm not saying that the Racepak isn't a good item. Just that the GPS speedo idea is not and probably will never be a recommended solution for cars.

    8. #8
      Join Date
      Dec 2007
      Posts
      284
      I found a free app for my iphone that is a speedometer and distance traveled readout.

    9. #9
      Join Date
      Aug 2004
      Location
      Rustburg, Virginia
      Posts
      3,436
      Country Flag: United States
      I like those Speedhut Revolution guages...
      1970 RS/SS350 139K on the clock:
      89 TPI motor w/ 1pc rear seal coupled to a Viper T56 via Mcleod's modular bellhousing w/ hydraulic T/O bearing from the Viper, 12 bolt rear w/ 3.73 gearing, SC&C upper control arms, factory lowers with Delalums, C5 brakes at all four corners, Front Wheels 17x8's with Sumi 255/40/17 and Rear Wheels 17x9's with Sumi 275/40/17.
      Brief description of the work done so far can be found here: http://www.nastyz28.com/forum/showthread.php?t=112454


    10. #10
      Join Date
      Apr 2001
      Location
      Rockford Illinois
      Posts
      3,947
      Country Flag: United States
      Quote Originally Posted by wmhjr View Post
      GPS speedos are neat gadgets. They are not as accurate as mechanical (also meaning electric signalled mechanical speedos). A GPS speedo will always lag. If it has at least 4 strong sat signals on level ground, it will be OK. If there is elevation change involved it'll be much less accurate.

      Jim, I'd be willing to bet that your SW speedo is right on, and your Racepak is off - a little high sometimes and a little low other times. Look at the math of it. The SW cannot be both high and low. I'm assuming it's driven off your tranny, right? That means it's a very simple mechanical formula where shaft revolutions are converted to displayed speed. It may be off - but it'll always then be off in the direction - either high or low. By a static variable.

      A GPS, OTOH, takes satellite signals, calculates the time for that specific sat signal to reach the gps, knows the location of that sat , and compares that to the same data coming from other sats. It takes 3 sat signals to get a 2D fix, and at least 4 sat signals to get a poor 3d fix. It's constantly calculating all those vectors. Sat signals are constantly falling in and out. Then you have the sat altitude, all combining to result in something called DOP (dilution of precision). It varies by location and time of day to to these factors.

      Bottom line is that unless you live in the desert, a GPS speedo is simply not an accurate instrument. I'm not saying that the Racepak isn't a good item. Just that the GPS speedo idea is not and probably will never be a recommended solution for cars.

      My Racepak is usually running on 7 to 9 satellites and when clocked in the mile at 60mph is right on the minute. The SW is an electrical speedo and not a mechanical driven by cable speedo, it is also the 3 5/8 size in the 200 mph style. It is hard to read at times and when timed in the mile with the Racepak coming up right it is off. At anything below 30 mph the SW is almost impossible to really get a good visual for the correct speed and the Racepak once above 10mph will go down to a crawl and be steady as she goes.

      I truly agree that a mechanical cable driven speedo that is calibrated right is probably more accurate all around but even most of them are driven by the pulse field inside and are at least 3% off.

      I don't know about the cheap $100-$300 gps sytems out there that give you directions and how accurate they are? When I was driving in Matt Altamores 69 and we had the gps going it seemed to be more accurate than his SW speedo too.

      The big thing about the SW speedo is the way you have to set it up. It is totally depnedant on the number of pulses per mile and I had trouble getting it to take the set as did Matt. I had to call Matt and ask him how to do it because the instructions SW gives you don't work. I am going to try to reprogram it one more time in the summer when I am not trying to keep the car running and paying attention to so many other things.

      Either way if you and I are both close to right the error of one and the error of the other could add up to the 3 mph difference between them at around 60mph, which isn't too bad considering if the radar speed warning signs they put on the hiway are correct they are both more accurate than my truck or Vibe are because of the tire differences and the factory preset for what ever they decided.

      This is just my observations. And when you lose all the signals because of a tunnel or other blockage to the signal the SW is a good thing to have.
      May The Horsepower Be With You !!!

    11. #11
      Join Date
      Aug 2008
      Location
      Pgh, PA
      Posts
      2,177
      Jim,

      When I say "mechanical" I'm not just talking about cable driven. I'm considering electric units driven off the tranny as "mechanical" also.

      I think your Racepak is pretty cool. As an overall package, it's pretty compelling. However, as a speedo itself, a GPS driven speedo can never ever be truly accurate. It is simply not mathematically possible due to the effect of elevation changes and dilution of precision (DOP). There are inaccuracies and errors caused by water vapor in the ionosphere, deviation in the actual clock times of the GPS sats themselves, and multipath error caused by signal bouncing in less rural areas. These are just a couple examples. You apparently live in an area that is relatively flat and void of interference - allowing you a more than typical view of sat horizons. That helps you immensely. In general, you can never possibly see more than 12, and in most areas, it's half that at best. Here for example, obstructions in line of sight due to terrain prevent more than 5 or 6 sats the majority of the time. That same elevation change also seriously degrades accuracy in terms of elevation - which means that while you're driving the gps is only really doing a great job in measuring 2 axises of travel. This is also why functions requiring truly accurate data use stuff like differential gps (ie, aviation precision landing systems use differential GPS, which adds land based transmitters to correct errors inherent in the native GPS system - they do NOT function using only sat signals).

      Even pulse driven "traditional" speedos like what yours is apparently can have accuracy issues - however in that case it's not a question of the general "method" but more the quality of the individual "product". It would be interesting to compare the accuracy of SW and Autometer units, for example.

      What this means is that the fundamental differences in accuracy between "traditional" speedos and GPS units boil down to this....

      1) GPS units are simply not reliable "for general use" due to atmospheric and physical obstruction variables such as tall buildings, tunnels, etc.

      2) "Traditional" speedos may have some loss of accuracy, however it will in general be somewhat constant - ie, it's slightly "slow" by a relatively constant percentage. GPS units will vary in no predictable manner. Sometimes it will be right on. Sometimes it will be slow. Sometimes it will be fast.

      I do think if you live in a rural, flat, and relatively dry area it can be pretty accurate in general. And for infrequent use in hobby vehicles it may be pretty cool.

    12. #12
      Join Date
      Apr 2001
      Location
      Rockford Illinois
      Posts
      3,947
      Country Flag: United States
      Quote Originally Posted by wmhjr View Post
      Jim,

      When I say "mechanical" I'm not just talking about cable driven. I'm considering electric units driven off the tranny as "mechanical" also.

      I think your Racepak is pretty cool. As an overall package, it's pretty compelling. However, as a speedo itself, a GPS driven speedo can never ever be truly accurate. It is simply not mathematically possible due to the effect of elevation changes and dilution of precision (DOP). There are inaccuracies and errors caused by water vapor in the ionosphere, deviation in the actual clock times of the GPS sats themselves, and multipath error caused by signal bouncing in less rural areas. These are just a couple examples. You apparently live in an area that is relatively flat and void of interference - allowing you a more than typical view of sat horizons. That helps you immensely. In general, you can never possibly see more than 12, and in most areas, it's half that at best. Here for example, obstructions in line of sight due to terrain prevent more than 5 or 6 sats the majority of the time. That same elevation change also seriously degrades accuracy in terms of elevation - which means that while you're driving the gps is only really doing a great job in measuring 2 axises of travel. This is also why functions requiring truly accurate data use stuff like differential gps (ie, aviation precision landing systems use differential GPS, which adds land based transmitters to correct errors inherent in the native GPS system - they do NOT function using only sat signals).

      Even pulse driven "traditional" speedos like what yours is apparently can have accuracy issues - however in that case it's not a question of the general "method" but more the quality of the individual "product". It would be interesting to compare the accuracy of SW and Autometer units, for example.

      What this means is that the fundamental differences in accuracy between "traditional" speedos and GPS units boil down to this....

      1) GPS units are simply not reliable "for general use" due to atmospheric and physical obstruction variables such as tall buildings, tunnels, etc.

      2) "Traditional" speedos may have some loss of accuracy, however it will in general be somewhat constant - ie, it's slightly "slow" by a relatively constant percentage. GPS units will vary in no predictable manner. Sometimes it will be right on. Sometimes it will be slow. Sometimes it will be fast.

      I do think if you live in a rural, flat, and relatively dry area it can be pretty accurate in general. And for infrequent use in hobby vehicles it may be pretty cool.
      I think we really do agree on this on all counts and I really do live in a flat rural type situation where I do my test. I also have both because I know the total reliability of gps is not going to be there.it just happened to be dead on when I did my test against the SW slower by 3 mph and the SW could be off just because of several pulse counts different when programming and the other times I noticed them to be off could have been accounted for by both being off.

      I would also like to see a test done to see not only the accuracy of the different manufactures but also the different sizes . Like I said , my SW is the 3 5/8 version and it is visually harder to see the accuracy of the dial at the angle I see it in my car. A larger one would have been nice but it wouldn't have packaged as well and it is a redundant gauge for a redundant purpose of recording mileage. I really like the double trip odometer for calculating gas mileage which is something that the racepak doesn't do unless you wanted to program it to, but then that would take up a channel that I would rather use for something else.

      I want you to know that I really like discussing this stuff with you because we really go throughly thru both side of things and that matters to me to know both sides as that is how others get the best info to make decisions including ourselves.

      May The Horsepower Be With You !!!

    13. #13
      Join Date
      Aug 2008
      Location
      Pgh, PA
      Posts
      2,177
      Jim,

      Agreement all around. I'm really interested in hearing how you like the Racepak after you get some miles behind the wheel. I also agree about the form factor. I also have 3 5/8 speedo and tach because of the asthetics - not the function. If mine were a serious competition car, I would have made a different choice. As it is, I don't plan to push the car much on the roads, and on the track you get slips.





    Advertise on Pro-Touring.com