Speedo or GPS ?

[joeg]

What's more accurate ? (would guess the speedo) my Garmin shows approx. 3-5 miles slower than speedo.............

 

[MoladoGuy]

It doesn't look like you have a lift from your signature so I would assume your Speedo is more accurate. You also have to remember that the Garmin is pulling satellite communications which could slightly off set the actual speeds based on any delays in communication.

 

[joeg]

It doesn't look like you have a lift from your signature so I would assume your Speedo is more accurate. You also have to remember that the Garmin is pulling satellite communications which could slightly off set the actual speeds based on any delays in communication.

No, No lift and my thoughts exactly....................Thanks

 

[Eddo]

What's more accurate ? (would guess the speedo) my Garmin shows approx. 3-5 miles slower than speedo.............

GPS is way more accurate. Just a standard receiver should be accurate to about better than .5 mph. Speedometer are notoriously inaccurate, even on new vehicle with a stock setup. Speed is actually calculate off doppler shift of the GPS signal, not change in position.

 

[hyde]

Eddo, remember the refresh rate of his GPS receiver. I am not sure how well it does, but if it is one of those slow refreshing GPS receivers, it may not be accurate to the second.However if his GPS is always faster or always slower, than there could be a problem.

 

[joeg]

Eddo, remember the refresh rate of his GPS receiver. I am not sure how well it does, but if it is one of those slow refreshing GPS receivers, it may not be accurate to the second.However if his GPS is always faster or always slower, than there could be a problem.

Maybe I'll get one of our local Law types to Laser it for me....

 

[hyde]

Just get a box of donuts. They'll do it for ya.

 

[Eddo]

Eddo, remember the refresh rate of his GPS receiver. I am not sure how well it does, but if it is one of those slow refreshing GPS receivers, it may not be accurate to the second.However if his GPS is always faster or always slower, than there could be a problem.

Most receivers update their measurements(position, velocity, etc) once every second. Garmin may give you an option to change that, but probably not. Alot of the high-end commercial receivers you can set refresh rates some as high as 1000Hz. Anyways if he is accelerate or deaccelerating he could have some issues with delay. However if he sets the cruise control on level ground and then compare it to his speedo and see the difference.

 

[hyde]

I have to check what my GPS update rate is. I am using Pocket PC with Mapopolis, which has pilot data, and it has been very accurate, to the mph. It is a bit off the right, so it thinks I am on the service road sometimes...

 

[Corwyyn]

Well, the easiest way to figure it out is to go for a drive and set your cruise for 60mph, then clock how long it takes you to run a mile on the road. Ten miles would actually be better since it compensate for any minor errors in distance between markers; if you're in Orlando right now I'd say get on the 528 and head for Canaveral. From my experience my Garmin V is always right on as far as speed goes, and my speedo was within 0.5mph before the lift and larger tires - now it reads about 2.5mph slow at 70 so on long trips I use the GPS for speed info.

 

[kjpilot]

I have to check what my GPS update rate is. I am using Pocket PC with Mapopolis, which has pilot data, and it has been very accurate, to the mph. It is a bit off the right, so it thinks I am on the service road sometimes...

Chances are that the map is off of position, especially if you are always shown to one side of the road. The Garmin stuff is awesome, & the newer ones that use WAAS can be accurate within a few feet. The GPS receives a time code signal from the satellites, & uses the difference between those time codes to triangulate your position. It is far more accurate than the mechanical speedometers which have numerous ways to be maladjusted.

 

[JeepJeepster]

Ive noticed that my speed-o is off with the stock tires and is right on with the 245/70/16 tires according to my Delorme GPS for my laptop.

 

[myjeepwalks]

GPS is way more accurate. Just a standard receiver should be accurate to about better than .5 mph. Speedometer are notoriously inaccurate, even on new vehicle with a stock setup. Speed is actually calculate off doppler shift of the GPS signal, not change in position.

I would have to agree the gps would be way more accurate than the spedometer. I'm no expert on this though.

 

[rxraptor02]

I tested mine with a garmin etrex. I set the cruise at 70mph and the gps was showing 65 or something.

 

[hyde]

Chances are that the map is off of position, especially if you are always shown to one side of the road. The Garmin stuff is awesome, & the newer ones that use WAAS can be accurate within a few feet. The GPS receives a time code signal from the satellites, & uses the difference between those time codes to triangulate your position. It is far more accurate than the mechanical speedometers which have numerous ways to be maladjusted.

Maybe, I am always to the left of my heads up. No matter which direction I am going, since it is set up to rotate according to my direction.
I am using WAAS receiver, it is Haicom MMF. The maps are NAVTEQ, although a bit old.

 

[kjpilot]

Maybe, I am always to the left of my heads up. No matter which direction I am going, since it is set up to rotate according to my direction.
I am using WAAS receiver, it is Haicom MMF. The maps are NAVTEQ, although a bit old.

Yeah, It's a weird thing. The GPS can pin point your location with nearly 0 error it terms of lattitude & longitude, & that is all that is needed for speed & distance calculations. When the maps are added, they are like a wrapping paper on a package, prone to slight misplacement. The different programs you are running are probably not quite in synch.

I have a Garmin GPSMAP 96C, which is an aviation hand held unit. The aviation database is hard programmed into the system. In aviation mode, my location on the map is dead on. But when I load in the detailed MapSource maps (from Garmin) & use Automotive Mode, I sometimes show errors of a half a city block. In relation to the map that is, not actual LAT & LONGS

 

[hyde]

I wish google made their maps available off-line for GPS usage on Pocket PC. Those maps have great features.

 

[MoladoGuy]

I wish google made their maps available off-line for GPS usage on Pocket PC. Those maps have great features.

?

http://www.download.com/Google-Maps-for-Mobile/3003-2641_4-10458477.html

Never used it myself but have a work partner who uses it and he loves it.

 

[hyde]

I have that, and I used that on my mobile phone. It requires active connection like GPRS or 3G to get results. You need very fast connection to keep up with GPS refresh. Otherwise it is useless. Still slow though. I have T-Zones and I prefer Windows Live Mobile over this, any day any time. It is much faster and more accurate when it comes to listing, movies, etc..

I also didn't want google to know where I was

 

[Ry' N Jen]

Good day,

GPS

It's why new high end cars use GPS speedometers as standard equipment.
They are not only dead on, but they also interact with the vehicles ABS for speed sensing and automated braking so that people don't rear end one another, but also for "On-Star" as one example, lo jack, and vehicle monitoring so that Mom and Dad can check and see just where, when, and how fast little billy drove his "Parental unit funded" Merc or BMW while piss drunk!

Ta

Ry'