Speedo inaccurate ?????

Hi guys,
Drove past an automatic radar "your speed is (whatever)" boxes today and it significantly disagreed with my speedo. my speedo read 70 the box read 64. 10% out !!!

I've just bought this old GQ y20 safari.
Could someone in the past have...
1/ put in the wrong instrument cluster?
2/ put in the wrong auto transmission?
3/ put in the wrong diffy?
4/ put in the wrong transfer case?
5/ put on the wrong tyres?
6/ All of the above?
From my basic understanding of the speedo I doubt if it would read high. Low perhaps, but not high.

Any comments please.

Thanks
Dave

I wouldnt trust the box thingy mate ive had the same type of thing before. best bet is use (if ya have1 or borrow) a GPS should set ya straight

speaking of gps has anyone had experence with hema gps or iphone vms gps

Quote:

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Originally Posted by CptClinac

Hi guys,
Drove past an automatic radar "your speed is (whatever)" boxes today and it significantly disagreed with my speedo. my speedo read 70 the box read 64. 10% out !!!

I've just bought this old GQ y20 safari.
Could someone in the past have...
1/ put in the wrong instrument cluster?
2/ put in the wrong auto transmission?
3/ put in the wrong diffy?
4/ put in the wrong transfer case?
5/ put on the wrong tyres?
6/ All of the above?
From my basic understanding of the speedo I doubt if it would read high. Low perhaps, but not high.

Any comments please.

Thanks
Dave

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Hi Dave, It may be the tyre size. There is a thread with a few links to tyre calculating sites. http://www.nissanpatrol.com.au/forum...onversion-Tool
Lets you calculate how much your speedo is out when you change tyre sizes

Quote:

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Originally Posted by growlers71gq

I wouldnt trust the box thingy mate ive had the same type of thing before. best bet is use (if ya have1 or borrow) a GPS should set ya straight

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I went past one of those things I was doing 100 and it said I was doing 14....... no joke

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Originally Posted by Ben-e-boy

I went past one of those things I was doing 100 and it said I was doing 14....... no joke

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That happens with 16" tyres!!!! LMFAO

There is a fudge factor built into speedos - commonly 5% to help us stay legal.

Change tyre diametre and things get interesting :-) I've checked mine against a few GPS units, and its out by the same as yours - Mav on 10Rs.

You can mentally adjust for it if you can be bothered - but beware swapping cars - The Cook's Camry is much closer to the mark with it's current boots.

Not sure of the actual percentage, but certainly all new vehicles sold in Australia MUST overstate speed - that is, the speedo tells you you're doing 100, when you're actually doing less. That legislation came into affect some years back - id say it's probably the same guidelines companies use who can adjust/recalibrate speedos, but that part is only an assumption ... based on logic, but when does that ever apply when it comes to legislation??

Mate you will find that the radar is probably only slightly inaccurate.
You may find tyres are wrong size, should be sticker in glovebox with recommended size.
The fellah who said doing 100 and radar 14 or something, these things look for vehicles speeding it had moved on looking for the next one. And when multiple lanes are there they scans alot, and alot of shadows created.
moving vehicles create shadows/blocking a reading at times for the next vechile and so you can see a funny display before it's locked in on actual speed or completely shadowed.
fairly accurate a great deal of time testing em before they are allowed on site.
but a warning only to guilt people into slowing, but sooner or later a bit further down the Rd a radar that does matter will be waiting for ya.
If ya cause an accident, their more likely to throw the book at ya instead of a lesser penalty as you had possibly been warned about going to fast, food for thought.

Quote:

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Originally Posted by CptClinac

Hi guys,
Drove past an automatic radar "your speed is (whatever)" boxes today and it significantly disagreed with my speedo. my speedo read 70 the box read 64. 10% out !!!

I've just bought this old GQ y20 safari.
Could someone in the past have...
1/ put in the wrong instrument cluster?
2/ put in the wrong auto transmission?
3/ put in the wrong diffy?
4/ put in the wrong transfer case?
5/ put on the wrong tyres?
6/ All of the above?
From my basic understanding of the speedo I doubt if it would read high. Low perhaps, but not high.

Any comments please.

Thanks
Dave

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you forgot option 7) Perfectly normal.

For about 30 years now ADR's require that a Speedo overeads by 0 to 10% of the actual speed plus 4 KPH. Speedos are not allowed to underead by even 1/10th of a KPH... so that means if your vehicle is doing 64 KPH the speedo must read between 64 and 74 KPH (IE actual speed or up to 10% of 64 plus 4)

Ex factory... most vehicles will be around 3 to 4 KPH under IE 100 KPH indicated is about 96 to 97 KPH actual.

If you want to look at it the other way... if your speedo says 100 KPH the vehicle must be doing more than 86 (approx) and not one iota above 100 KPH.

You can by different sized cogs for the gearbox speed sensor to calibrate the speedo if you wish (Nissan have 4 sizes each 1 tooth larger than the prev) OR you can use GPS derived speed

Quote:

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Originally Posted by Robo

Mate you will find that the radar is probably only slightly inaccurate.
You may find tyres are wrong size, should be sticker in glovebox with recommended size.
The fellah who said doing 100 and radar 14 or something, these things look for vehicles speeding it had moved on looking for the next one. And when multiple lanes are there they scans alot, and alot of shadows created.
moving vehicles create shadows/blocking a reading at times for the next vechile and so you can see a funny display before it's locked in on actual speed or completely shadowed.
fairly accurate a great deal of time testing em before they are allowed on site.
but a warning only to guilt people into slowing, but sooner or later a bit further down the Rd a radar that does matter will be waiting for ya.
If ya cause an accident, their more likely to throw the book at ya instead of a lesser penalty as you had possibly been warned about going to fast, food for thought.

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There wasnt any other cars on the road and it was in central queensland

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Originally Posted by Ben-e-boy

There wasnt any other cars on the road and it was in central queensland

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may also have been just a faulty display? maybe ment to say 104 and was missing the "0" so said 1 4?

Wonderful food for thought.
Do they fiddle the odometer too. This could be a wonderful source of road tax revenue ! ! ! !

I've got a handheld gps in the boat.
Will do that tomorrow & deliver my verdict.

Yesterday I passed 3 box things and they all clocked me 8-10% over.
A week ago when we bought the truck I'm sure I passed one that clocked us within 1%.

My old Terrano had various options of gearbox etc for various configurations of vehicle. Could be tricky to find which bit is wrong in the trans train.

Thanks for the thoughts guys.

Dave

Quote:

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Originally Posted by CptClinac

Wonderful food for thought.
Do they fiddle the odometer too. This could be a wonderful source of road tax revenue ! ! ! !

I've got a handheld gps in the boat.
Will do that tomorrow & deliver my verdict.

Yesterday I passed 3 box things and they all clocked me 8-10% over.
A week ago when we bought the truck I'm sure I passed one that clocked us within 1%.

My old Terrano had various options of gearbox etc for various configurations of vehicle. Could be tricky to find which bit is wrong in the trans train.

Thanks for the thoughts guys.

Dave

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When my ute was on 31's the speedo was out by about 10% (speedo was faster), with the 35's the speedo is now slower by about 5%. 33's should make it close to spot on

Did the GPS thing yesterday. Definitely 7 - 8% over. All tyres very worn. Will try with new tyres (correct size to the manual) and if req'd will change the pickoff gear to make better.

Thanks for the ideas.

From my electronics background I would suggest that the 100 kph with a radar box reading 14 was more likely to have lost the first digit. (maybe never installed!) so was trying to read 114kph.
?? Is there a group of 4x4 ers called "diesel heads" ?? :)

Thanks for the discussion
Dave.

Tyres corrected it a bit. Now only 5%.
Will investigate the pickoff gear dodaddy. Anyone have details on this bit?

Thanks
Dave

You can buy gears with a different amount of teeth from nissan.
double check these part numbers as they were from the net so might not be right.
32743-VB015 15 Teeth
32743-VB016 16 Teeth
32743-74P17 17 Teeth
32743-74P18 18 Teeth
But if it is a gq i am sure i read that you can adjust the speedo itself by 10 % either way i do remember pulling one apart and i think it was a little adjustable variable resistor on the back of it.
I had a rd28 i converted to td42 and my speedo was out by a mile i just put the rd28 gear on the td42 and it was fine.

Quote:

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Originally Posted by 97_gq_lwb

You can buy gears with a different amount of teeth from nissan.
double check these part numbers as they were from the net so might not be right.
32743-VB015 15 Teeth
32743-VB016 16 Teeth
32743-74P17 17 Teeth
32743-74P18 18 Teeth
But if it is a gq i am sure i read that you can adjust the speedo itself by 10 % either way i do remember pulling one apart and i think it was a little adjustable variable resistor on the back of it.
I had a rd28 i converted to td42 and my speedo was out by a mile i just put the rd28 gear on the td42 and it was fine.

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thats interesting. so where do they get the signal from? having a variable resistor, does that mean that they have an electric signal?

Yes electronic signal from the speedo sensor.

i had the same problem with my shorty i just egnoored it ahaha:P

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Originally Posted by Ben-e-boy

There wasnt any other cars on the road and it was in central queensland

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That explains it QLD.
Na just playing.
sounds broken.
I've placed these things out for the RTA and they are calibrated to be fairly accurate.
Thats why I wrote such info.
Just trying to help.
cheers

As someone has previously said, speedos in cars are designed to over read the actual speed based on the manufacturers suggested rims and tyres for the vehicle.

I bought a GU4 last October with 265/75R/16s and was astonished when my GPS and the speedo were in perfect agreement. I replaced those tyres with 265/70/R16s and on my journey today with my GPS found that my speedo is now about 7%/8% out and when I'm traveling at 108 kph according to the speedo I'm actually doing 100kph according to my GPS. The 265/70/R16s are Nissan's recommended tyre size according to the label in my glove box. What made the difference was tyre height.

speed difference will even change with tyre wear,

Tim

Update...
New, 'factory spec', highway tread tyres fitted.
pumped to 40PSI.
Speedo still ~5% high.
Gearbox take-off gear is next on my hit list.

Thanks for all the great info.

Dave.

Mine runs at exactly 10% over. Use a GPS quite regularly and the speedo overstates how fast I'm going. It doesn't bother me cause I know it's pretty unlikely I'll ever get pinged.

Chris

My speedo is 100% correct. Tested it with 3 seperate GPS units and the speedo always matches the GPS reading.
I think they should all have to be 100% correct. Everybody knows that they are deliberately overstated so they compensate for it by doing say 105 in a 100 zone. However their speedo may only be out by 3kms for all they know so they are speeding. If they were all 100% correct you would do 100 as it shows on the speedo.

You have a very unusual speedo, cobber. Vehicle speedos are rarely linear. It costs waaay too much to even attempt to make them that way. It just means you have lucked out with that 1 in 1000 instrument.

It is well nigh impossible to calibrate any driven sensor to be 100% accurate without huge dollars.
Tyre size, tyre wear, winter, summer, inflation pressure, road surface, vehicle load plus about a page of other variables will all affect the reading.
Even changing the brand of tyres in exactly the same case sizes will change the error. EG Cooper 33's are closer to 32's IE the circumference of a Cooper 33 is different to a Procomp is different to a BFG is different to a Mickey T etc.

I don't use my speedo at all and just use one of the GPS readouts. Works for some people but not others...

The whole issue is a technical one. Most if not all electronic speedo senders count number pulses at the dedicated "pole wheel" either at the prop shaft or driveshaft. Things which influence the pulses most are you've guessed it final drive ratio and tyres. The unpredictable variable is a tyre size as it is dynamic, it changes as tyre wears, the load imposed and its inflation pressure because all these factor influence the rolling radius which in turn influences how many times the tyre turns per distance. Number of turns is than read as impulses per unit of time aka frequency ....yadda, yadda you'll get a point.
The more impulses per distance the faster the speed reads out. As the tyre is wearing out, or is compressed by load and less/more inflation pressure the more impulses are read hence the speed is read faster even though the actual speed is less. So technically fitting brand new tyres which are e.g. 3 % bigger than worn out ones would cause a difference of 3% at indicated 100km/h so actual speed would be 103 km/h if it was exact/accurate when tyres are worn by 3 % as an example. This also influences odometers, fuel trip meters etc.
To combat/avoid this the deliberate error is factored in so the less read speed than actual speed never occurs.
This tyre dynamic characteristics can be actually advocated/used as an "el cheapo" tyre pressure monitoring on ABS/EBS equipped vehicles where control units are able to sense the difference in speed among wheels and deduct that a particular tyre is/might be deflating and warn a driver.
Cheers

Ok my mate drives a TJ wrangler with 33" claws I drive a troll with 33" mtz's he's auto I'm manual I think both came standard with 31's his speedo reads around 90km at 100km and mine 110km at 100km checked at the same time same road same gps?????


Tappin N Crappin

When you put larger tyres on it decreases your speedo. So 100km/h on the speedo is actually a bit higher than that. So yours sounds right but his seems like a strange one.

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.