GPS How Accurate ?

[iand46]

Can anybody confirm how accurate a GPS signal is compared to a calibrated speedo or tachograph?

Maybe a HGV or Police driver have compared their satnav to either of the above to check as Car/Bike speedos can be out by +/-10%

 

[Schtum]

In steady state cruising on a straight and level road, I believe they're pretty much dead on. The only issue is that an NMEA signal only updates at a frequency of 1Hz. So if your speed changes within that 1 second window, the display won't be accurate.

 

[DavidHale]

As the murcans now use GPS to guide bombs onto the heads of Johnny Foreigner I'm guessing their pretty accurate...

 

[sanensafe]

Depends how many satellites your device is "seeing" at the time. I have a Garmin GPSMAP which when picking up 7 satellites is accurate to 13 feet.
I'm so confident of the accuracy that when in a white out in deep snow on hills last year, zoomed in and used this to stay on path right back to base.

Sent from my Nexus 7 using Tapatalk 4

 

[Neil W]

We have tried both Garmins and Tom Toms against three or four speed detection devices plus calibrated speedos and the speed displays on the sat navs are almost spot on ,however, the garmins appear better as they have a faster refresh rate than the tom toms (ie when you alter speed the garmins react within a second but the tom toms will stick on the previous speed for up to four or five seconds- not good when entering a speed limit)

 

[mcinlb]

We have tried both Garmins and Tom Toms against three or four speed detection devices plus calibrated speedos and the speed displays on the sat navs are almost spot on ,however, the garmins appear better as they have a faster refresh rate than the tom toms (ie when you alter speed the garmins react within a second but the tom toms will stick on the previous speed for up to four or five seconds- not good when entering a speed limit)

There's usually a sign at the side of the road

 

[walrus]

In steady state cruising on a straight and level road, I believe they're pretty much dead on.

Key word here is level. In a very hilly area they are less accurate ISTR.

 

[John Armstrong]

Key word here is level. In a very hilly area they are less accurate ISTR.

Even then it's only minor inaccuracy due to cosine calculation.

 

[IJGser]

There's usually a sign at the side of the road

How does that help? Imagine if you can, you where to rely on the GPS to tell you your current speed.

 

[iand46]

There's usually a sign at the side of the road

This won't allow for very inaccurate speedo, sometimes you need to drive at the legal limit but not under to avoid being tailgated on stretches of motorway in roadworks while being aware of the many average speed cameras if you go over.

 

[Schtum]

This won't allow for very inaccurate speedo, sometimes you need to drive at the legal limit but not under to avoid being tailgated on stretches of motorway in roadworks while being aware of the many average speed cameras if you go over.

I've been using Garmins to watch my speed while riding and driving below, at and over the limit for 15 years and about 300K miles without getting nicked once. In fact, I haven't been nicked for 25 years now but that's another matter.......touch wood.

 

[iand46]

We have tried both Garmins and Tom Toms against three or four speed detection devices plus calibrated speedos and the speed displays on the sat navs are almost spot on ,however, the garmins appear better as they have a faster refresh rate than the tom toms (ie when you alter speed the garmins react within a second but the tom toms will stick on the previous speed for up to four or five seconds- not good when entering a speed limit)

Thanks, just what I was after.