MySwag.org The Off-road Camper Trailer Forum
General => General Discussion => Topic started by: griz066 on July 04, 2011, 12:39:03 PM
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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? :cheers:
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GPS will be more accurate.... :cheers:
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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
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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. :police:
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.
:cheers:
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The :police: 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
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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.
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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.
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Hi , GPS 95 , Speedo 100 KPH spot on @ 50
:cheers: sheeds
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The :police: 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
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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.
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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
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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.
:cheers:
Dave
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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.
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GPS is only accurate if you are holding a constant speed and are going in a straight line.
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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 ???
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I believe both :) With 265/70/17 tyres on the Prado the GPS and speedo readings are identical across the 0-110 range.
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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?
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if my speedo shows 110 the speed checker says 105 (always) and the gps varies a little but averages 108
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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 :cheers:
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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.
:cheers:
Dave
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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?
:cheers:
Dave
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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 ... ;D
"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
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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 ... ;D
"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 :cheers:
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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.
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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 ... ;D
"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.
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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 ... ;D
"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
So speeding 10k over the limit is insignificant in the big picture!!
GS
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So speeding 10k over the limit is insignificant in the big picture!!
GS
Was that 10kph or 10000kph
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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.
:cheers:
Dave
No, you mean the speedo reads higher than the actual speed.
While the GPS position may be out by a several meters, they will be very accurate for interval distance, and the time measurement has the accuracy of an atomic clock. Distance/Time has to be more accurate than any speed measurement that involves rubber do-nuts.
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Was that 10kph or 10000kph
Neither: it's km/hr
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Neither: it's km/hr
technicality
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Having a speedo that is out, mine is reading about 8km/h faster than the sat nav at 80km/h, (the old VW doesnt go much faster than that!!) an about 9km/h if I can get it to 90km/h downhill,
How does this affect the following:
-Fuel consumption calculations, L/100km.
-Odometer reading over a long period of time, say if it curently reads 200,000 kms.
-on a lighter note,.....does this make distances just that much further away????
Cruisindub
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Waiting for the end of the year so i can get a new calender for my old Landy,,,, :D
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a speedo gives you ground speed, a gps gives you your location on the earth. what a gps cant tell is if you are going up or down a hill. compare your speedo to your gps on a flat road and then set your speed at 100 then as you drive up a hill maintain your speed by the speedo and watch the gps speed drop slightly. i use my gps to check my speedo and i havnt had a ticket yet .
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If you want to eliminate all this, get a speedo correction unit if your speedo is electronic, I have a Truspeed in mine.
Get it here, there are other places to get one, this is just the first one I found in Google.
http://www.superlift.com/accessories/truspeed.asp (http://www.superlift.com/accessories/truspeed.asp)
Baz.
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a speedo gives you ground speed, a gps gives you your location on the earth. what a gps cant tell is if you are going up or down a hill. compare your speedo to your gps on a flat road and then set your speed at 100 then as you drive up a hill maintain your speed by the speedo and watch the gps speed drop slightly. i use my gps to check my speedo and i havnt had a ticket yet .
How steep are these hills??? An incline of 10 degrees is quite a steep hill yet will only make a 1.5% difference! (cosine of 10 deg = 0.985)
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a speedo gives you ground speed, a gps gives you your location on the earth. what a gps cant tell is if you are going up or down a hill. compare your speedo to your gps on a flat road and then set your speed at 100 then as you drive up a hill maintain your speed by the speedo and watch the gps speed drop slightly. i use my gps to check my speedo and i havnt had a ticket yet .
Actually my GPS gives me elevation as well as do most.....
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what a gps cant tell is if you are going up or down a hill.
Yes they do.
They are 3-dimensional: longtitude, lattitude and height as long as you have more then 3 satelites.
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happy to put my hand up to say im wrong ;D but im sure i read somewhere that altitude in a gps isnt that accurate as its based on a mathmatical average sea level and assumes the world is perfectly smooth not hilly.
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happy to put my hand up to say im wrong ;D but im sure i read somewhere that altitude in a gps isnt that accurate as its based on a mathmatical average sea level and assumes the world is perfectly smooth not hilly.
I would not expect the indicated elevation (altitude is the distance above ground level) on in car GPS units to be very accurate because over the whole of Australia there are millions of local datum values for reletively small areas, one suburb can have several local datum values ( im unsure of the size of these local datum areas outside of developed areas). When we set up a project at work that will use the GPS systems on our graders and other equipment to auto control horizontal position and elevation we need to calibrate (site cal) the GPS base station to the local area datum value and a minimum of three surveyed control points on site, the base station will then correct the satellite signals before they are sent via radio frequency to the machines, only then we can we obtain the required accuracy which can still vary + - 40mm of the design level throughout the day and day to day.
So as mentioned above I would assume that an average of local datum values (which are in relation to sea level) are used with these in car units to give an indication of elevation and they do not "assume that the world is perfectly flat". but as for how close these units are to being accurate or how accurate you want them to be ??? ??? ???
I might compare one up against the Trimble system one day for interest sake.
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I would not expect the indicated elevation (altitude is the distance above ground level) on in car GPS units to be very accurate because over the whole of Australia there are millions of local datum values for reletively small areas, one suburb can have several local datum values ( im unsure of the size of these local datum areas outside of developed areas). When we set up a project at work that will use the GPS systems on our graders and other equipment to auto control horizontal position and elevation we need to calibrate (site cal) the GPS base station to the local area datum value and a minimum of three surveyed control points on site, the base station will then correct the satellite signals before they are sent via radio frequency to the machines, only then we can we obtain the required accuracy which can still vary + - 40mm of the design level throughout the day and day to day.
So as mentioned above I would assume that an average of local datum values (which are in relation to sea level) are used with these in car units to give an indication of elevation and they do not "assume that the world is perfectly flat". but as for how close these units are to being accurate or how accurate you want them to be ??? ??? ???
I might compare one up against the Trimble system one day for interest sake.
You're describing differential GPS which demonstrates that if you give it an accurately known position (the surveyed point), it is very accurate in determining distances from that reference point. Using the same logic, it is very accurate in determining speed.
To determine speed, you don't need an accurate position, you just need to know how far you've moved in a certain time.
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Let's lighten up, who really cares ???
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Thanks for the reply's you confirmed what i thought but as usual it is way off topic. Time to lock this thread please someone.
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I found some of the techo stuff quite interesting - thanks
:cheers:
Mike