Odometer corrections anyone?

Talking to a mate recently, recommended a speedo place to get his cruiser back close to square. Speedo place put a gadget into the speedo drive and got him to drive a measured 100m. By this method the speedo, when the speedo was showing 100kph, actual was 96kph. They made a small gearbox for him which connects to the speedo drive and the cable/transducer plugs into that. He got a new GPS and thought he'd double check his new adjustments, GPS showed, over 3 seperate attempts, 1. odometer 100km, GPS 91km. 2. odometer 101km, GPS 98km. 3. odometer 100km, GPS 105km. It's a Garmin thingy with a colour screen. When he went back to the supplier of the GPS, he was told that terrain had to be taken into account and that if travelling through hilly areas, the GPS will not read accurately.

I personally have no opinion, I don't have a GPS and can't do my own testing. Perhaps it comes down to the quality of the GPS unit...

The GPS is accurate to about 10metres , but it measures in a straight line point to point .

Hi 3 ltr Patrol.
Course it won't read accurate. Speedo reads over the ground. GPS reads as crow flies.. Will not give true speed or true distance.
Any testing gotta be done on the flat. in straight line.
GPS was, like Sat Nav b4 it. Developed for planes,and misiles. in straight flight .That's why we use them successfully on yachts and fishing boats.
Originally my Speedo reading 9km's slow on GPS. fitted 265 x75 tyres. now reads 2 1/2 to 3 slow. Much nearer to radar readings.
As far as economy goes tank empty. Fill tank. We can't do anything about it. so just keep on doing..
Enjoy everybody.
Regards
Macka.

macka posted this followup
>GPS reads as crow flies.. Will not give true speed

Rubbish.

Mike Harding

As Mike has diplomatically put it AKIK GPS is pretty much dead accurate with there as the crow flies directions. I do however dought my Garmin GPS accuracy when measuring distance travelled. It will measure distance travelled vs as the crow flies. Certainly accuracy is further degraded when set to battery save as when you stop it shows you still travelling for some distance. I have found no reason to dought the gps speedo reading. I also heard that the odo works differently to the speed o eg Just because the speedo is 10% out doesnt mean the odo is (different tyres will obviosly make a difference to both) I reckon if these things are a big concern to you when calculating fuel usage Try getting a job that pays more and forget about it and enjoy the travell (last bit tounge in cheek)

Don't worry be happy.
At least we are keeping the, Arabs , Govt, Oil co's and many more happy n rich.
Just burn the stuff and keep going.

GPS speed is correct because it calculates speed from rate of change of position

Hello Mike Harding..
I was talking steepish hills .You find a steep hill and go up it at a decent speed. There will be a variation in readings,'Tween your gps and speedo. (Known differential of course) It can't calc, vertical accurately. Because the Yank's have put in Random, Elevation Variances. To cover their arses from missiles in windows,Bunkers etc.
I've used GPS for 15yrs.and Sat Nav b4 that. Still got my original Garmin 65 on yacht.(Lovely old thing that it is.)along with the Garmin 205 Plotter. That's showing my age. and they're both still going. Which says a lot for Garmin Products and their reliability. Best toy ones on market.
Regards All
Macka