What he's saying (at least as I read it) is that the nav unit uses the VSS to calculate the speed; it only uses the GPS signal to calibrate it. That could explain how the guy's nav unit and speedo are so far off when they're both pulling from the same data source (the VSS). We're talking about an Eclipse unit, not a Pioneer, so while Pioneer may use the GPS for its velocity readings, Eclipse units may pull from the VSS. (FWIW, true dead reckoning is a method for determining a position based on last known position, velocity (speed and direction), and elapsed time, so it's useless for determining velocity.)beaups said:
Navigation vs. Speedo accuracy
- Thread starter ltnate3
- Start date
If Frogman is correct, and the Eclipse unit uses the GPS to calibrate itself WRT speed, the nav unit is probably correct, and your speedo is probably off. Personally, I'd borrow a handheld GPS unit and use it to see which one's more accurate, or call the local PD and see if they can recommend a place to get your speedo calibrated--that way, you'd know for sure.
One thing bothers me--if your wheels and tires are oversized (ie, their overall diameter is greater than stock), then your speedo should read low, not high. If your speedo reads high and the nav unit is accurate, that means your OAD is smaller than stock...
One thing bothers me--if your wheels and tires are oversized (ie, their overall diameter is greater than stock), then your speedo should read low, not high. If your speedo reads high and the nav unit is accurate, that means your OAD is smaller than stock...
yep best bet is to get another gps (one that doesn't tap vss) and compare them. I would bet money that your speedo is off....and probably due to the wheels maybe being SMALLER than stock (if you went with real low-pro tires). I don't see how the eclipse can be using vss for anything other than reference since vss is only a pulse and the eclipse has no point of reference to understand what distance each pulse represents (since the eclipse wasn't built for your ls specifically).....unless of course it uses the gps signal to figure that out...in which case the eclipse unit is still correct.
one other method to check this would be to go on a trip with a KNOW EXACT DISTANCE. reset the trip computer. make the trip. you'll likely find your car says the trip was 5 percent longer than it actually was. and in that case you are putting more "miles" on your car....
SoonerLS said:
I think the diameter of my tires is exactly the same and my speedo is reading low compared to the GPS. Thanks everyone for the inputs. I guess the next question is should I take it to the dealer to get the speedo calibrated?
94m5
Dmaup's Daddy
Mile and i had to use a gps to set the dip switchs on the converter for the 5speed that we put in the 94. we then drove to Huntsville Al. and back965 miles both ways. the odometer and the gps where both with in a 4 mile reading, i have noticed latley that the speed has dropped some as to wear of the tires. could play with the switches but will wait for new tires and wheels. hopefully from the 95 when we put bullets on it. id