Speedo inaccurate ?????

Thanks for this thread, but unfortunately it mainly covers the simpler problem of the spedo reading higher than the actual ground speed.

I have hit the unfortunate problem of the sped reading less than the ground speed. After some tests with the local service manager there are the interesting results:

GPS reading: 84 Km/h ; (note: 2 different branded GPS units were used)
Spedo reading : 80 km/h
Onboard Nissan computer system: 76 km/h ; ( read via dealers laptop)

The computer and spedo readings are within the so called Nissan tolerance, 4-5 Km/h. The computer reading is supposed to be actual vehicle speed but that is 8km/h slower than that recorded by the GPS units.

Wheels and tyres as per Nissan specs:
I have original Nissan alloy rims as pew: 8JJ17 alloy wheels with 275/65R17 tyres
Tyres at rated pressure.

No load in vehicle, only driver and passenger.


SO far the main comment has been well the spedo and computer are in order as they are 4 km/h different.

Any solutions to this one would help. The police have this zero tolerance attitude.

Just go By your GPS as they are 99.9% accurate.. This is all I use and it never lets me down :-))

Have you tried this adjustment

http://www.nissanpatrol.com.au/forum...edo-adjustment

I have 285X75X16 tyres, put in a 15 tooth cog at the gear box and the speedo is dead on with the three GPS units I have. On longer trips I generally drive by the tacho, 2000 rpm is peak torque and just on 95 kph, I get the best fuel economy here.

97_gq_lwb: Thanks for that.
I will add it to the other piece about changing the cog on the sensor in the gear box whne I next talk to the service manager.
Perhaps Nissan might actually come up with similar/some solution as well !!

TimE:
Driving long distances using the torque approach is nothing new. When you pull loads it is the best approach anyway. Power peaks higher and is only worth bothering with when you have to pass a couple of B-doubles or a road train.

At present i am getting about with the GPS sitting on the dash. The solution to the problem, I have left with the service people and Nissan so far. I am really feeling positive they have a solution :rolleyes:

Just to put it out there, ADR rules state a speedo needs to be only 10% accurate, even brand new cars today can legally have a 10% variance in speedo reading and still e legal and within manufacture specs. ignore the speedo and use the gps or mentally adjust. This is just one of those things you will never be able to fix as it is just how it is.

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Originally Posted by johno90

Just to put it out there, ADR rules state a speedo needs to be only 10% accurate, even brand new cars today can legally have a 10% variance in speedo reading and still e legal and within manufacture specs. ignore the speedo and use the gps or mentally adjust. This is just one of those things you will never be able to fix as it is just how it is.

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This is true however it would be interesting to see case law done in regards to speeding fines you can have +/- 10% in speed variance

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Originally Posted by oncedisturbed

This is true however it would be interesting to see case law done in regards to speeding fines you can have +/- 10% in speed variance

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Actually that is wrong, it is not +/- 10%.

The subject has been done to death on this forum but to save the searching... ADR's since about 5 years ago require that speedos cannot underead at all. IE 0 tolerance.

Speedos are allowed to overread by up to 10% plus 4 KPH. Most manuf will have the speedo set so it overreads even with the largest size tyre as per the placard.

Therefore if you are driving to your speedo you cannot be speeding. If you change your tyre size or ratios then the onus is on you as the person who modified the vehicle to adjust the speedo or wear the consequences.

Were this may be true, we did a check through some some speed cams v council speed cams v gps on 4 different vehicles with different spped check units . The vehicles were all stock and the variance in speed ranged between +/- upto 7kmph in difference. Average was at 80 kmph with readings ranging from 76-84 kmph.

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Originally Posted by the evil twin

Actually that is wrong, it is not +/- 10%.

The subject has been done to death on this forum but to save the searching... ADR's since about 25 years ago require that speedos cannot underead at all. IE 0 tolerance.

Speedos are allowed to overread by up to 10% plus 4 KPH. Most manuf will have the speedo set so it overreads even with the largest size tyre as per the placard.

Therefore if you are driving to your speedo you cannot be speeding. If you change your tyre size or ratios then the onus is on you as the person who modified the vehicle to adjust the speedo or wear the consequences.

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If thats the case then why in every training ive been to say 10% either way, manafacturers themself even state that varient in manuals.