Do you trust the speed indicated on TT?

[dawgfan]

One of my vehicles matches the speed TT indicates to the mark; however, another vehicle is off by several mph. Leads me to believe the vehicle that doesn't match may have a speedo error. Thoughts?

 

[bel4_20]

I do not believe that there is any better way to measure speed then with satellite. From what i hear it's pretty accurate

 

[Thom]

I would say that the vehicle is off. My car registers about 3 mph faster (above 50mph) than thegps does. My wife's car is pretty much right on...

 

[Rick F.]

The TT is most accurate (as long as you're traveling on level ground). Vehicles have a specific tolerance... something like +0% and -5%, so they're normally on the low side to be safe.

There's a very long thread discussing this somewhere in the forum, but can't find it right now. Interesting read if you have the time.

 

[swisscheese]

I have always assumed the GPS is accurate...

My truck and my 920 differ slightly. I have used a hand held Garmin in cars and it too differed from different vehicles. I have assumed the GPS unit is accurate because speed is calculated using a mathematical formula vs. sensors. This be especially true cruising down the highway at a constant speed.

 

[SShadow]

Yeah, my truck registers about 4km/h faster than the GPS does. Someone explained it that a lot of difference can be had if your tire pressure is higher than rating ns lower than rating, tread pattern is worn vs not worn, etc. Anything that may alter the diameter of the wheel will put your speed off.

 

[starnesc]

I believe that the GPS is the most accurate, especially when you are going at a constant speed. That way it is not trying to correct from a fluctuation of speed.

 

[Gilbert]

Except for some police cars that had calibrated speedometers, car speedometers are not designed to be super accurate.

Honda Canada had a class action because their speedometers were about 3% low and people wanted their mileage warranty to be extended accordingly...

 

[SShadow]

I would think that it would be 3% high to get more warranty...? If the speedo was saying 100 and you were going 97, for every hour you clocked you'd add an extra 3 in mileage on the vehicle.

I'm putting an extra 4 on mine... No wonder my odo seems to be going up so darned fast!

 

[ElectronMan]

I was wondering why people were riding my butt so bad in my commuter Civic. I put the GPS in and turns out when I'm showing 55 MPH I'm really doing about 50 MPH. No wonder people were hating my guts.

 

[Gilbert]

I would think that it would be 3% high to get more warranty...? If the speedo was saying 100 and you were going 97, for every hour you clocked you'd add an extra 3 in mileage on the vehicle.

I'm putting an extra 4 on mine... No wonder my odo seems to be going up so darned fast!

OTOH, you are also getting gas mileage! No need to shop around to save 3 cents on the liter...

 

[Thom]

I was wondering why people were riding my butt so bad in my commuter Civic. I put the GPS in and turns out when I'm showing 55 MPH I'm really doing about 50 MPH. No wonder people were hating my guts.

55 mph? What freeway do you drive on???
My morning commute is usually spent at 75+.

Yea, I'd be saying "WTF is this guy thinking?" if I suddenly closed on you at +25 mph.

 

[bobby101]

i HAVE to trust it, since my speedometer broke years ago, i have it set to warn me at 68- so one day it went off and i slowed down,a few seconds later the CHP patrol car passed me-so i have to thank TT for no ticket!

 

[SShadow]

Our gas is regulated here (and possibly the most expensive in the country at 111.2/litre) so I don't have to drive around to find a bargain... But you are right, I'm probably saving a tiny bit in gas mileage... But if something breaks, that would have been covered under warranty, and I'm just over the warranty period, and my dealer screws me, I'm going to be very annoyed. LOL I think I'm lucky though. My Hyundai dealer has taken really good care of me so far. Hopefully that will remain the case once the warranty is gone.

 

[ElectronMan]

55 mph? What freeway do you drive on???
My morning commute is usually spent at 75+.

Yea, I'd be saying "WTF is this guy thinking?" if I suddenly closed on you at +25 mph.

I work on a large DOE facility where the speed limits are very conservative and the M16 carrying security is extremely tough.

 

[Rick F.]

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

 

[Smokiewolf]

One of my vehicles matches the speed TT indicates to the mark; however, another vehicle is off by several mph. Leads me to believe the vehicle that doesn't match may have a speedo error. Thoughts?

The GPS is right on. I'd recommend you get your speedometer calibrated if you're off by 5mph or more. Typically what causes this problem is using tires or wheels that are not the OEM size.

 

[PiratePast40]

I work on a large DOE facility where the speed limits are very conservative and the M16 carrying security is extremely tough.

OK - I'll bite. SRS, LANL, ORNL, NTS, ANL, Hanford?

 

[PiratePast40]

The GPS is right on. I'd recommend you get your speedometer calibrated if you're off by 5mph or more. Typically what causes this problem is using tires or wheels that are not the OEM size.

It's pretty easy to check your odometer on an interstate with mileposts. Test sections are even more accurate. If you're that concerned (and have a mechanical gear/cable setup), you can buy a new gear based on the error ratio.

 

[Smokiewolf]

It's pretty easy to check your odometer on an interstate with mileposts. Test sections are even more accurate. If you're that concerned (and have a mechanical gear/cable setup), you can buy a new gear based on the error ratio.

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