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Speed signal for aftermarket nav

Discussion in '80-Series Tech' started by tech_dog, Aug 22, 2006.

  1. tech_dog

    tech_dog

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    I'm thinking about adding an in-dash GPS/Nav that requires a speed signal. Since I have 33" tires, I'll have to go through one of the signal correction boxes before I feed the signal to the nav's speed signal input.

    Has anyone done this before with successful results? This seems like the type of thing that could end up requiring a tow truck and a $1500 repair.....

    T.
     
  2. sc40

    sc40

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    i just installed in dash navigation. i did not hook up the speedometer thing. it works for me. but i dont see how on earth it could cause any damage
     
  3. Hants

    Hants

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    Slee sells a speedo gear that corrects for 33" tires.

    http://www.sleeoffroad.com/products/products_speedo.htm

    With it and BFG AT 285's, I'm within 1.5 miles per hour at 70 (compared to GPS speed).

    In thinking (I know -- dangerous!) about why they'd need a speed input, the only reason I can come up with is tunnels or other no-GPS-signal situations.

    The GPS systems I've used either just stop navigating until signal is recovered, or project straight-line (at speedo speed). I've not had a problem with either (usability-wise), and neither is accurate all the time (think: curved tunnels).
     
  4. tech_dog

    tech_dog

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    Yeah... I know I'm obsessive, but I don't want to accept even a 3.2% error. I should be able to dial in the correct speed within .125% with a yellow box.

    Also, the installation guide for the GPS/Nav makes a huge deal about supplying a speed pulse, and even has an optional module to supply the pulse via a wheel magnet if the vehicle can't provide it.

    It appears that the speed pulse is used to provide quicker and more accurate location and speed, in combination with the slightly delayed location/speed from the GPS unit. The unit even has a connection for a reverse gear signal for the same reason.

    I ordered the yellow box last night. The results will either be very cool, or very bad. I'll post results if it ends up cool.

    T.
     
  5. Erratic

    Erratic

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    I don't think the nav cares what size tires are on the car. I know at least the Alpine nav does not. I've installed countless nav units over the years, on cars with many different size tires. Each car has a different speed pulse signal. In the install manual of the Alpine nav units it states that the unit will calibrate itself to the vehicle using the gps as a reference. It can compensate for tire size etc. Don't know if the nav you are using can do that or not. Most nav systems do not NEED a speed pulse, but it can enhance accuracy. The long and short of it is the box will correct your speedo, but I don't think it matters to the nav either way.
     
  6. Waggoner5

    Waggoner5 SILVER Star

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    The nav does not know or care about tire size, but I agree on being more precise. You can purchase an aftermarket speedsensor adapter or tie into the existion one and convert the signal. Dakota Digital sell a piece that is multi adjustable signal converter that will allow you to tab onto the signal wire and convert it to what ever you need.
    G
     
  7. Erratic

    Erratic

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    which nav are you installing?
     
  8. Koffer

    Koffer

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    The Navi will "learn" the tire size by looking at the GPS signal and pulse after driving a little bit. I have installed a Toyota Navi in my 96 and when I hooked up the rev. wire and the speed wire under the PS kick panel at the same harness spot where you hook up the Yellow box .

    HTH some
     
  9. tech_dog

    tech_dog

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    Yep. At the point I first posted, I'd read the instal manual not the user guide. The user guide indicates that you can force a "learning mode" where the unit compares the GPS signal to the speed pulse signal, and comes up with it's best guess at the ratio.

    I don't think having the yellow box in the middle is going to cause a problem.

    Erratic - I'm going to install the Pioneer AVIC-Z1, with XM radio and bluetooth options.
     
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