How accurate is vehicle speed on a GPS ?

Lepton1 · Jun 5, 2016

Hammer166 said: ↑

If you're seeing variations in the mountains, remember your speedometer is measure a two-dimensional speed, and GPS may be using a three-dimensional speed, although your vertical component shouldn't ever be enough to noticeably affect the speed.
Click to expand...

Note to self...

"If my speedometer is pegged at 90, but my GPS shows 0, things are bad."

Hammer166 · Jun 5, 2016

x1Heavy said: ↑

Im going to have to sit down and think this through. What you are asking me to consider is very close to figuring glide slope and resulting ground speeds in aviation.

If you consider the GPS system, it generates a perfect sphere and where it intersects with another sphere generated by a satellite GPS number two, and that intersects a third sphere with GPS Number three you have now what is necessary to find the center inside those three, discarding results that point to space you have the location on the planet. If you have 4 or more GPS Satellites that can see you, the more precise you are going to be.

My head hurts if I have to understand that the vehicle speedometer is #### and it is not accurate. That's almost like living 50 years of your life and then being told your name is a lie.

Why have that #### speedometer if it's going to be crap anyway? Remember that driving 2000 miles somewhere to be JIT to the minute, preferably 15 minutes prior to appointment time arrival is ideal. The amount of deliberate error in the speed sensing and reporitng system inside the truck, dashboard and cabling etc. Is going to be enough to make you late and be told to come back tomorrow.

It's going to make me feel put out because if all this wonderful pre-cisse tech on the truck, communciations, computers and electronics made to be thrown out the window because half the Nation's 18 wheelers have #### speedos that don't work properly.

I think I better go pour a coffee and think about this some more. Maybe I grab a speedo from a Police car and throw THAT into the truck.
Click to expand...

If you think truck speedos are bad, jap bikes are atrociously optimistic. 10% is pretty common

SteveScott · Jun 5, 2016

Did a little experiment today. Made a run from Oregon to central California on the I-5. When I got to Redding I was exactly 200 miles from my destination. My Rand McNally GPS said that I would arrive in 3 hours and 20 minutes if I maintained 60 mph. The road is dead flat for the entire distance so I set my cruise control for 60mph on my GPS. My speedometer had me at 57 mph. What I found interesting was that my available time clock on my Qualcomm was using up time faster than real time. By the time I arrived the gps time was exactly correct but my Qualcomm clock used 7 more minutes than the gps and my watch.

So my clock is going faster than real time and my speedometer slower. If I had any hair left I would be pulling it out about now. Is there a financial advantage for my employer if I drive less time? I suppose over a long period it can add up to a lot of money?

Log in or Sign up

Forums

Find Trucking Jobs

How accurate is vehicle speed on a GPS ?

Lepton1 Road Train Member

Trucking Jobs in 30 seconds

Wait, employers can't reach you!

Hammer166 Crusty Information Officer

SteveScott Road Train Member

Trucking Jobs in 30 seconds

Wait, employers can't reach you!

Log in or Sign up

Useful Searches

Find Trucking Jobs

How accurate is vehicle speed on a GPS ?

Lepton1 Road Train Member

Wait, employers can't reach you!

Hammer166 Crusty Information Officer

SteveScott Road Train Member

Wait, employers can't reach you!