Do you trust the speed indicated on TT?

[danjreed]

Mine seems pretty dead accurate.

Off no more by 1 MPH on the highway...

 

[Pedro2NR]

Thread moved to General.

 

[baggss]

So far I have used my TT in my 2 cars at home and in about 9 rental cars while out on business. All but 1 have been dead on. The 1 one that was off was a rental car and it was off by about 6 Mph.

I'd say the TT is good.

 

[Smokiewolf]

It has been tested against speed dectection devices and certified calibrated speedometers

 

[PiratePast40]

Yeah, that works, set the cruise at 60, and time how long it takes you to travel a mile...

That's one way to do it but there is less error due to acceleration/deceleration if you just watch your odometer at each milepost. You should run it for 10 miles or more to get a good average. If you do it that way, speed and timing are irrelevant.

 

[drledger]

And some areas actually mark a mile so that you can check your speedometer. The TT does read a bit slower in most cases than your actual speed. I am going to make a technical guess about this using my experience with Aviation GPS units. The satellites and gps units give you a ground speed that is from point A to point B but they do not quite get the variance in distance because of slight changes in elevation and in some small tight curves.

 

[Bro. Craig]

Ok, that makes sense. I noticed the speed reporting difference soon after i had the speed shown on my display. I thought, "This TomTom is off." Of course then I thought, "Oh no, maybe my Camry is off." I then did not know which to trust. The TomTom says I am going slower than the Camry said I am going. I'd love to ignore the TomTom's speed, but what if I get to visit with a policeman? So far it has not happened. Maybe that is my answer. I may have my wife get on the interstate with me in her car and just see what the deal is.

 

[adidas1124]

In my Mercedes the speedo above about 50mph is off by 3-4mph according to TT and my Magellan. At above 70mph it gets right again. My Honda Civic was the same way.

 

[Smokiewolf]

In my Mercedes the speedo above about 50mph is off by 3-4mph according to TT and my Magellan. At above 70mph it gets right again. My Honda Civic was the same way.

That's not uncommon for speedometers to be correct at some speeds and a few off at other speeds.

 

[PiratePast40]

I found that long discussion on GPS speed vs. speedometer indicated speed. It wasn't in this forum?no wonder I couldn't find it. It's 8 pages long, but pretty interesting.

http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&t=63445&postdays=0&postorder=asc&start=0

I'm not sure of the validity of that thread. They can't spell tire correctly and they drive on the wrong side of the road!