GPS or Speedo, What do you believe???????

[griz066]

I have a ML Triton work ute and a MN Dual cab and they both differ by 7Km according to my Garmin GPS.

The Dual cab is brand new so tyre size is as per Mitsu specs, the work ute is 2006 and tyre size is as per Mitsu specs.

What do others think and what would you trust?

[Teabag]

GPS will be more accurate....

[Wandering Tassie]

GPS will be correct. That size error is about the same as my Pajero.
The speedo should read less than the GPS. Can save a lot of speeding tickets.

Trevor

[davidy61]

GPS is more accurate.  Speedo's have at least a 5% inaccuracy at least to keep you within the speed limit.

The only speedo I ever had that was accurate was an ex Police Motor Cycle which had been calibrated to be spot on.  Matched the GPS exactly on new tyres, but as tyres wear and circumference varies, so did it, but not by much. 

That being said, the GPS is only good once you are at a constant speed as they only check their positions at very short intervals.  As you accelerate or decelerate, the speed is not accurate.  Once cruising, good.

[Crisp Image]

The  say that they will not take the GPS reading into account as it is an uncalabrated tool.This comes from the local traffic management unit. but I have hard that somone got off because they had their speed recorded on a GPS so Go figure.
Regards
Crisp Image

[OffRoadDave]

I trust the GPS for accuracy as long as you are doing a constant speed as they can be a little laggy in their calculations, but I have tried 3 different gps in my car at the same time (my off road gps, missus on road gps and my phone gps) to compare them and they are all within tenths of a kilometre of each other at a constant speed, with varying speeds they react at different rates.

[BigJules]

I feel vulnerable in a vehicle without the GPS now, as one really doesn't know what speed you're doing. Of course, under ADR, actual speed must be less than or equal to the speedo, but I've driven vehicles with 10% difference, owned a BMW motorbike that was out by that margin and accused them of trying to profiteer by causing me to get it serviced by them more often.

[gunna]

Hi , GPS 95 , Speedo 100 KPH   spot on @ 50
sheeds

[harvs]

The  say that they will not take the GPS reading into account as it is an uncalabrated tool.This comes from the local traffic management unit. but I have hard that somone got off because they had their speed recorded on a GPS so Go figure.
Regards
Crisp Image

Uncalibrated tool. ... That implies that you can't use your cars speedo either, as that is not a calibrated tool.
And while were discussing this, I think it stinks that "traffic safety cameras" operate inside the tolerances of the speedos in our cars. As a result whenever we approach a known speed camera we take our eyes off the  road to check our speed, not what I would call safe driving.
I'm not anti camera in locations that warrant more scrutiny. I'm anti revenue raising. speed/red light are set to a too tight a tolerance, and cameras are popping up everywhere.
Ah that's my rant for the day.

Harvs

[WilSurf]

As all others said: GPS is accurate.

Our new Fiesta is 5 kms out, very very annoying.
Now we drive 75 on the speedo so we are driving 70.
Otherwise we are always been overtaken.

[macca]

I have found that most people I talk too is that the speedo's usually read under by 5 to 8 kph. i am the same as Offroaddave, three GPS's in the car and all nearly identical and the speedo is 7kph out. As far as the cops saying they are not calibrated units I dunno what could be more accurate than an atomic clock, i know i keep my track logs just in case 

[Fivid]

I tend to rely on the GPS more than the speedo.  Falcon is about 6Km out at 100Km so I set cruise on 106 and am overtaking lots of others but never had a ticket.  I have calibrated the Patrol to suit the AT tyres as they are what we use for most highway travel and it is now spot on. 

My original GPS had room for an external antennae, when connected not only did it find a signal much quicker but the accuracy was more consistent and speed when accelerating / decelerating seemed to be better also.  Without the extra antennae I often had spaces for more satellites which it hadn't connected to, with the extra antennae I always had full set of satellites, 15 I think.


Dave

[BeNos]

i dunno if still current but adrs used to allow speedos to be out by 10% either direction. so imo if ever booked for less i reckon id have a pretty good chance at getting off just for that.

[Dion]

GPS is only accurate if you are holding a constant speed and are going in a straight line.

[outback jack]

i travel on the western highway a bit and when i go through the overhead speed checkers i check my speedo, my gps, and the speed checker and they all differ 

[D4D]

I believe both With 265/70/17 tyres on the Prado the GPS and speedo readings are identical across the 0-110 range.

[davidy61]

i travel on the western highway a bit and when i go through the overhead speed checkers i check my speedo, my gps, and the speed checker and they all differ 

Which is the closest to the speed checker, GPS or Speedo?

[outback jack]

if my speedo shows 110 the speed checker says 105 (always) and the gps varies a little but averages 108

[macca]

GPS is only accurate if you are holding a constant speed and are going in a straight line.

Yeah, but the straight line doesn't have to be long though

[Fivid]

i dunno if still current but adrs used to allow speedos to be out by 10% either direction. so imo if ever booked for less i reckon id have a pretty good chance at getting off just for that.

Rules changed a few years ago.  I think it was 2006.  Speedos on vehicles built since then are not allowed to give you a reading where you can be travelling faster than the speed given which is why you usually find speedos are now on the low side of your actual speed.


Dave

[Fivid]

i travel on the western highway a bit and when i go through the overhead speed checkers i check my speedo, my gps, and the speed checker and they all differ 

There are a set of those overhead displays on the southbound lanes of the Hume Highway just out of Wodonga.  They would have to be the most inaccurate things you could use to gauge your speed.  we have three roof bars on the Patrol, virtually never get a reading.  When I had my ute with canopy and three bars on top I very rarely got a reading.  Take the bars off and get readings each time but with very little consistency relating to what the speedo was saying.  If you travel with a trailer it throws readings way out.  I was travelling with a loaded tandem trailer once doing around 90Km/h.  A guy overtaking me in the right hand lane got a speed reading of 112 I think, I got a message saying "Too fast, Slow Down".

And the problem with this?  When Vic brought in the 3Km/h tolerance the minister at the time said that motorists could use these things that were provided at a number of locations throughout the state to ensure their speedos were accurate...  I wonder if that could be used as defence to fight a speeding ticket?


Dave

[Kit_e_kat9]

We are all going to get booked for speeding considering we are actually travelling at somewhere below 1000 miles per hour within the earth's rotation.  I wonder if they take that into account when booking you?  Is it really an accurate reading you've got there officer, I put it a few 100 miles per hour short ... 

"The circumference of the Earth at the equator is 25,000 miles. The Earth rotates in about 24 hours. Therefore, if you were to hang above the surface of the Earth at the equator without moving, you would see 25,000 miles pass by in 24 hours, at a speed of 25000/24 or just over 1000 miles per hour.
Multiply by cosine of your latitude to see how fast the Earth is rotating where you are.
Earth is also moving around the Sun at about 67,000 miles per hour."
From:  http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html

Kit_e

[macca]

We are all going to get booked for speeding considering we are actually travelling at somewhere below 1000 miles per hour within the earth's rotation.  I wonder if they take that into account when booking you?  Is it really an accurate reading you've got there officer, I put it a few 100 miles per hour short ... 

"The circumference of the Earth at the equator is 25,000 miles. The Earth rotates in about 24 hours. Therefore, if you were to hang above the surface of the Earth at the equator without moving, you would see 25,000 miles pass by in 24 hours, at a speed of 25000/24 or just over 1000 miles per hour.
Multiply by cosine of your latitude to see how fast the Earth is rotating where you are.
Earth is also moving around the Sun at about 67,000 miles per hour."
From:  http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html

Kit_e

Aye , Speewa can you explain this to me please

[Estelle]

 Speedos are 'calibrated' and all same model vehicles should read the same as they should use the same components as each other. Theoretically.

What is the difference between a worn set of tyres and a new set. Assume they are 'calibrated' for new tyres, which should give you a reading that is slower than with worn tyres (legal tread of course) - Actual speed being the same.  Percentage? 1- 3% difference?

AT tyres have a deeper tread?

GPS's are not 'spot on' (accuracy will depend on number of satellites 'connected' at the time) but likely to be more accurate than a speedo.

If most modern cars are 'calibrated' to be 'under' (tend to agree with that), you are using the speedo to determine your speed, and find a lot of cars passing you, are the others going by their GPS or knowingly going faster than they are legally permitted?

Really, doesn't bother us if they are going faster, especially when towing a CT. Use the speedo.

[Estelle]

We are all going to get booked for speeding considering we are actually travelling at somewhere below 1000 miles per hour within the earth's rotation.  I wonder if they take that into account when booking you?  Is it really an accurate reading you've got there officer, I put it a few 100 miles per hour short ... 

"The circumference of the Earth at the equator is 25,000 miles. The Earth rotates in about 24 hours. Therefore, if you were to hang above the surface of the Earth at the equator without moving, you would see 25,000 miles pass by in 24 hours, at a speed of 25000/24 or just over 1000 miles per hour.
Multiply by cosine of your latitude to see how fast the Earth is rotating where you are.
Earth is also moving around the Sun at about 67,000 miles per hour."
From:  http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html

Kit_e

There were a couple of words in there I understood, I think.