As stated in other threads I am doing my fisrt interstate tow, can any one tell me is it normal tor the tug speedonread differant to the GPS speed there seems to be a variant of 7kph eg Navara speedo/ cruise control reads 99kph while GPS reads 82kph road side radar reads 82kph all equipment on Navara is factory standard eg wheels tyres, any ine have ideas and if speeddo is out can it be fixed oh and wheels & tyres on poptop jayco are standard
Regards
Bobstar52
Bunkerbob said
08:09 AM Oct 28, 2013
It is very unusual for the clock to read higher than the road speed. ADR (Aust Design Regs) say that the vehicles speedometer can read less than the actual road speed but cannot read more. I have an older GQ Patrol and when my speedo reads 100, the GPS says I am only doing 95. 105 for 100, 110 for 105, etc. I would see about getting it looked at. Reading lower isn't a real problem as you can't be busted for doing less, but they now nitpick for speed, i.e. being booked for 63 in a 60, etc. If this vehicle is still in the warranty, take it to the dealer. Don't be fobbed off. If they say it is normal, it isn't and tell them that you will take it up with Nissan Australia, or email Paul Gover at the Melbourne Herald Sun. He is a grat exponent of putting pressure on car companies.
bill12 said
12:43 PM Oct 28, 2013
Think yourself lucky-my speedo is up to 15% off !When it reads 110kph , the gps reads 95kph! I have a 97 ford courier diesel, and trust the gps. The prior owner spruiked how quick it was and how good the fuel figures were, and was miffed when I told him.Very reliable ,and comfortable, though.If its illegal to be so inaccurate, how do I fix it? Bill
PeterD said
04:20 PM Oct 28, 2013
The attached file is an extract from ADR 18-03. You will note that the calibrations are made at only a few speeds. There is also no specification of the linearity of the instrument.
There was mention in a message above that the accuracy could be out by a s much as 10% + 6 km/h. The 6 should only be 4.
-- Edited by PeterD on Monday 28th of October 2013 04:23:22 PM
The speedometer in your vehicle is produced and calibrated according to Australian Design Rule (ADR) 18/03, which states: - Vehicle speedometers to indicate a speed equal to or higher than actual vehicle speed and no more than 10% + 6 km/h higher than actual speed. For example: If the actual vehicle speed was 100km/h, the vehicle speedometer must indicate no less than 100km/h and no greater than 116km/h.
The speedo cannot read less than the actual speed, so this argument won't wash with a speed camera!!!!!
Hope this helps
Grumpy Old Man
brian said
05:23 PM Oct 28, 2013
Bunkerbob wrote:
It is very unusual for the clock to read higher than the road speed. ADR (Aust Design Regs) say that the vehicles speedometer can read less than the actual road speed but cannot read more. I have an older GQ Patrol and when my speedo reads 100, the GPS says I am only doing 95. 105 for 100, 110 for 105, etc. I would see about getting it looked at. Reading lower isn't a real problem as you can't be busted for doing less, but they now nitpick for speed, i.e. being booked for 63 in a 60, etc. If this vehicle is still in the warranty, take it to the dealer. Don't be fobbed off. If they say it is normal, it isn't and tell them that you will take it up with Nissan Australia, or email Paul Gover at the Melbourne Herald Sun. He is a grat exponent of putting pressure on car companies.
I think that you will find that you have that A-about.
The design rules require that the speedo may read higher than the actual road speed but not lower, and in fact most speedos now read around 5kph faster than you are really going.
Also bear in mind that a GPS speed indication is a time/distance based calculation. If you are going in a straight line, it will be fairly accurate, however, depending on the update rate of the processor, when on winding roads or on a bend, the GPS may indicate that you are going slower than you really are due to the fact that it measures your distance travelled in a straight line versus time between updates.
Keith19837 said
05:31 PM Oct 28, 2013
Bobstar52 wrote:
Hi all
As stated in other threads I am doing my fisrt interstate tow, can any one tell me is it normal tor the tug speedonread differant to the GPS speed there seems to be a variant of 7kph eg Navara speedo/ cruise control reads 99kph while GPS reads 82kph road side radar reads 82kph all equipment on Navara is factory standard eg wheels tyres, any ine have ideas and if speeddo is out can it be fixed oh and wheels & tyres on poptop jayco are standard
Regards
Bobstar52
G'day Bob. One reason is this; when vehicle manufacturers set their vehicle's up, they are fitted with a standard set of tyres for that vehicle. These standard fitments are usually the basic steel wheel with razor blade narrow tyre such as seen on army and most government type vehicles. But the manufacturer know that the consumer wants a little extra style so along comes the Special Vehicles Division, the dealer, or after market crowd who decide to 'dress up' the vehicle with wider tyres, thicker tread etc etc. The profile (aspect) of a tyre is a direct percentage of the tyre's width and even a slightly wider tyre will cause a higher relative profile thus giving the speedo a lower reading than is actually the case. When fitting wider tyres, the profile percentage MUST be reduced accordingly e.g. a 225/70/16 tyre is 225 mm wide, 70% of that width is the profile and in this case a 16 inch wheel. So if we decide to fit mags and fancier tyres we might say go to a 255/70/16. We now have a 255 mm tyre with a profile of 70 %. Our tyre is now some 20mm taller (if my math is correct) and tyre is now turning slower for the same speed which puts our speedo out. The upshot of all this is that when we increase our tyre width over the manufacturer's base wheel and tyre, we need to decrease the percentage of profile so that the tyre remains at the same height. Unfortunately, getting the right width/profile ratios can be a bit difficult and are choices are limited.
For what it's worth.
oldbobsbus said
06:00 PM Oct 28, 2013
I have experienced much the same problem with most of the vehicles I drive and that can be as many a 5 per week.
As I am never in a hurry to get anywhere and desperate to retain my driving record so I just accept that the unit reading the highest speed is correct and drive by it... I'm not one for holding up traffic so I do the legal limit according to the instrument I am driving by..
Works for me..lol.
justcruisin01 said
10:13 PM Oct 28, 2013
I drive a couple of different vehicles & the speedo reading is lower than than GPS; eg, 110 clock =100gps.
Have checked gps with road side speed warnings at road works & both are the same.
brian said
11:16 PM Oct 28, 2013
justcruisin01 wrote:
I drive a couple of different vehicles & the speedo reading is lower than than GPS; eg, 110 clock =100gps.
Have checked gps with road side speed warnings at road works & both are the same.
Wouldn't that underlined statement indicate that the speedo reading is higher than the GPS, not lower as you suggest?
Bobstar52 said
01:34 AM Oct 29, 2013
Wow that spaked some discussion hey , thanks all for the imput, looks like a lot of you folk have the same issue , as the speedo seems to be lower than tne speed limit I will go by that save getting booked and save on fuel , again thank you all its been a big help
oldbobsbus said
06:49 PM Oct 29, 2013
Diggings wrote:
Back in the day you could buy different ratioed speedo drives, they were colour coded, not to sure about vehicles now
Gee that takes me back a while to my Holden days I think there is a couple of different coloured ones out in the workshop somewhere... everything is electronic these days.. and I don't understand them anymore...
But there is one advantage with an electronic speedo it doesn't clock up miles when you are flat towing your car..
-- Edited by oldbobsbus on Tuesday 29th of October 2013 06:50:28 PM
Diggings said
12:53 AM Oct 30, 2013
Back in the day you could buy different ratioed speedo drives, they were colour coded, not to sure about vehicles now
Just Roman said
12:12 AM Nov 8, 2013
I also have a navara and speedo reads 100 and gps reads 95, with 255/70/R16 tyres, yet someone I know fitted nissan Pathfinder wheels and tyres to his Navara now his speedo reads 100 and his GPS reads100.
John
Hi all
As stated in other threads I am doing my fisrt interstate tow, can any one tell me is it normal tor the tug speedonread differant to the GPS speed there seems to be a variant of 7kph eg Navara speedo/ cruise control reads 99kph while GPS reads 82kph road side radar reads 82kph all equipment on Navara is factory standard eg wheels tyres, any ine have ideas and if speeddo is out can it be fixed oh and wheels & tyres on poptop jayco are standard
Regards
Bobstar52
The attached file is an extract from ADR 18-03. You will note that the calibrations are made at only a few speeds. There is also no specification of the linearity of the instrument.
There was mention in a message above that the accuracy could be out by a s much as 10% + 6 km/h. The 6 should only be 4.
-- Edited by PeterD on Monday 28th of October 2013 04:23:22 PM
Hey Bobstar,
The speedometer in your vehicle is produced and calibrated according to Australian Design Rule (ADR) 18/03, which states:
- Vehicle speedometers to indicate a speed equal to or higher than actual vehicle speed and no more than 10% + 6 km/h higher than actual speed.
For example: If the actual vehicle speed was 100km/h, the vehicle speedometer must indicate no less than 100km/h and no greater than 116km/h.
The speedo cannot read less than the actual speed, so this argument won't wash with a speed camera!!!!!
Hope this helps
Grumpy Old Man
I think that you will find that you have that A-about.
The design rules require that the speedo may read higher than the actual road speed but not lower, and in fact most speedos now read around 5kph faster than you are really going.
Also bear in mind that a GPS speed indication is a time/distance based calculation. If you are going in a straight line, it will be fairly accurate, however, depending on the update rate of the processor, when on winding roads or on a bend, the GPS may indicate that you are going slower than you really are due to the fact that it measures your distance travelled in a straight line versus time between updates.
G'day Bob. One reason is this; when vehicle manufacturers set their vehicle's up, they are fitted with a standard set of tyres for that vehicle. These standard fitments are usually the basic steel wheel with razor blade narrow tyre such as seen on army and most government type vehicles. But the manufacturer know that the consumer wants a little extra style so along comes the Special Vehicles Division, the dealer, or after market crowd who decide to 'dress up' the vehicle with wider tyres, thicker tread etc etc. The profile (aspect) of a tyre is a direct percentage of the tyre's width and even a slightly wider tyre will cause a higher relative profile thus giving the speedo a lower reading than is actually the case. When fitting wider tyres, the profile percentage MUST be reduced accordingly e.g. a 225/70/16 tyre is 225 mm wide, 70% of that width is the profile and in this case a 16 inch wheel. So if we decide to fit mags and fancier tyres we might say go to a 255/70/16. We now have a 255 mm tyre with a profile of 70 %. Our tyre is now some 20mm taller (if my math is correct) and tyre is now turning slower for the same speed which puts our speedo out. The upshot of all this is that when we increase our tyre width over the manufacturer's base wheel and tyre, we need to decrease the percentage of profile so that the tyre remains at the same height. Unfortunately, getting the right width/profile ratios can be a bit difficult and are choices are limited.
For what it's worth.
As I am never in a hurry to get anywhere and desperate to retain my driving record so I just accept that the unit reading the highest speed is correct and drive by it... I'm not one for holding up traffic so I do the legal limit according to the instrument I am driving by..
Works for me..lol.
I drive a couple of different vehicles & the speedo reading is lower than than GPS; eg, 110 clock =100gps.
Have checked gps with road side speed warnings at road works & both are the same.
Wouldn't that underlined statement indicate that the speedo reading is higher than the GPS, not lower as you suggest?
Gee that takes me back a while to my Holden days I think there is a couple of different coloured ones out in the workshop somewhere... everything is electronic these days.. and I don't understand them anymore...
But there is one advantage with an electronic speedo it doesn't clock up miles when you are flat towing your car..
-- Edited by oldbobsbus on Tuesday 29th of October 2013 06:50:28 PM
John