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speedometer inaccuracy

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9K views 16 replies 10 participants last post by  Lil'Trucker!  
#1 ·
Hi all,

Has anyone noticed how far out the d40 speedo is? I set cruise con at 70mph on the speedo, but the actual on gps is only 65.6mph, or the speedo is reading 6.3% over actual speed.

The police have a measured mile near here, for calibrating the 'safety cameras', so I went through at 60mph, so it should have taken a minute, but it was 5 seconds longer, so the gps is good.

Anyway, the theory is that the standard wheels are 30.05", if I put on 285/70/R17's then that will be 32.6" (aka 33's). This will then make the speedo read 8.4% lower, so that an indicated 70mph will actually be 71.1mph, so the error will then be just over 1.5%, but the speedo will then be reading under. I can't remember if it is law that the speedo can read up to 10% over but nothing under in the UK?

If I went for 265/70/R17, then they come up at 31.6", so the speedo would read 1.2% over, so would be ok for UK roads.

Is it just my truck, or are all the nissan speedometers way out? is there a calibration service anyone can recommend?

TIA
 
#3 ·
I believe the speedometer on all Navaras are all the same.

I have compared the GPS speed with the speed being recorded by the ECU. (using the Torque app) The readings are surprisingly close but as you say the speedo is well out.

You are allowed a 10% error in the speedo reading either way. They normally over-read to save folk getting caught for speeding.
 
G
#5 ·
lookskyward1 said:
I believe the speedometer on all Navaras are all the same.

I have compared the GPS speed with the speed being recorded by the ECU. (using the Torque app) The readings are surprisingly close but as you say the speedo is well out.

You are allowed a 10% error in the speedo reading either way. They normally under-read to save folk getting caught for speeding.
Click to expand...
It is not only Nav or Nissan… every car has about 5-10% error speedo reading but not either way, only under-read is allowed by official low.
 
#7 ·
Thanks for the replies. The end result of the speedo being roughly 7% out, is that my truck hasn't done 80,000 miles at all, but only 74,400! on the flip side, I use my truck for work and get paid mileage, so with the smaller standard wheels, I am 7% better off for it. Don't tell HMRC, or that's another thing they will stamp on.... :(
 
#9 ·
nexsuperne said:
Thanks for the replies. The end result of the speedo being roughly 7% out, is that my truck hasn't done 80,000 miles at all, but only 74,400!
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Not really, as I said, the speedo may be out but the ECU is recording the speed really close to GPS speed. Nice thought though. :pirate:
 
#11 ·
Think its so you cant "accidently" speed
possibly? Maybe? Or am I just chatting what im shoveling?
 
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#13 ·
lookskyward1 said:
nexsuperne said:
Thanks for the replies. The end result of the speedo being roughly 7% out, is that my truck hasn't done 80,000 miles at all, but only 74,400!
Click to expand...
Not really, as I said, the speedo may be out but the ECU is recording the speed really close to GPS speed. Nice thought though. :pirate:
Click to expand...

I think the mileage is wrong as well, if I have the sat nav on and it says 15 miles on the sat nav it will be over 16 miles on the truck, so I am with nexsuperne on this one!
 
#14 ·
I get over error on the YD25, but on the TD25 the speedo is dead on (when approaching a certain toll gate there is a speed camera which displays your speed just as a reminder).
 
#15 ·
The speedo (U.K.) vehicles over reads by an average 8% up to 10% is allowed legally. So at lower speeds it wouldn't be as noticeable i.e. 30mph would show on speedo as 32.4mph

At 70mph the speedo would show 75.6mph and at 100mph the speedo would read 108mph

As far as i know, it's mainly to cover any legal matters that are speed related, bear in mind the readings are set with factory wheels and tyres in mind.

Increasing the overall tyre/wheel diameter will make the speedo reading more realistic but, will effect fuel economy.

If the tyre/wheel diameter is altered too far (bigger) the speedo will under read. :thumbright:
 
B
#16 ·
Arguably it doesn't effect fuel economy as much as the odd reads less with bigger wheels. When I put 33's on my l200, it was a 10% increase in circumference, therefore my odd would show 10% fewer miles on the same journey as before. At fill up I'd add the 10% back on before doing mmy figures.

I'm not saying which if either figure is accurate, but at least I was comparing like for like. Actual drop in may wasn't that bad.
 
#17 ·
B16mts said:
Arguably it doesn't effect fuel economy as much as the odd reads less with bigger wheels. When I put 33's on my hairdresser wagon, it was a 10% increase in circumference, therefore my odd would show 10% fewer miles on the same journey as before. At fill up I'd add the 10% back on before doing mmy figures.

I'm not saying which if either figure is accurate, but at least I was comparing like for like. Actual drop in may wasn't that bad.
Click to expand...
I had big tyres on mine last year and fuel economy was abysmal, put normal tyres back on and fuel economy went back up.

Definitely made a difference in my case, there's a thread on here somewhere about it :wink:
 
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