Speedo problems

[JoshA]

Just got my D40 and its reading 6kmh higher than it should be, and I am just using my Sat Nav to confirm the readings. WHen I wear out the tyres that it came with I will probably go with some higher profile tyres.

anybody have any suggestions as to how wide and how tall you can go on standard wheels??

 

[navarian]

I run 265/75/16 on mine.My speedo ran about 4 kmh higher,now 1kmh slower.
You might not want to go bigger in tires than this size on a standard rim or you could get rubbing on the inner guards or the front plastic bit under the bumper,if you have one.

 

[Old.Tony]

My speedo ran about 4 kmh higher,now 1kmh slower.

Don't forget that in order to remain roadworthy, your speedo must NEVER indicate a speed lower than it is travelling. It is allowed to indicate up to 10% over, but it is a zero tolerance for under reading.

That being said of course, they may never inspect it. It may only ever become an issue during a roadworthiness inspection, or accident investigation.

 

[bullwinkle]

Speedo problems are common right across the whole spectrum of registered vehicles in Australia. At highway speeds I usually drive at an indicated 5km greater than the posted limit in the Navara. My wife's 2007 Ford Territory also has a speedo which is about 4km/hr under.

 

[Bosshog]

Don't forget that in order to remain roadworthy, your speedo must NEVER indicate a speed lower than it is travelling. It is allowed to indicate up to 10% over, but it is a zero tolerance for under reading.

That being said of course, they may never inspect it. It may only ever become an issue during a roadworthiness inspection, or accident investigation.

I have spent far too much time on getting 265/75s certified for my D40. Anyway, Tony's not too far off the mark. ADR18/03 changed on 1 July 2006. All vehicles made after that date CANNOT indicate a lower speed than is actually being travelled. Furthermore, there is now NO upper limit on how much faster a speedo can read. As a result to ensure compliance vehicle manufacturers' default to around an average of 14% higher (so the engineer tells me). We're lucky with just 10% error, Hilux's are closer to 14% I gather.

Anyway I have to get my Speedo checked and recalibrated and the engineer 'has to observe' the tyres actually being fitted to the vehicle. What a load of rubbish to fit tyres that should have been standard fitment.

 

[navarian]

So if my vehicle was made in September 2005 and i run a different tyre size than the vehicle was made with and my speedo reads a couple of kmh's slower it is still roadworthy?Or would that only apply for a vehicle made then with the factory tyre size.

 

[Old.Tony]

Guys, if you're recalibrating your speedo, don't forget that it may be possible to use that kit from Jaycar, it's a plug-in on-the-fly-adjustable calibration tool for electronic speedos.

It's been mentioned in these forums before, can't remember where, I'll find the thing on Jaycar's site again: here is a direct link to the part in their Kits - Automotive section.

 

[Bosshog]

Guys, if you're recalibrating your speedo, don't forget that it may be possible to use that kit from Jaycar, it's a plug-in on-the-fly-adjustable calibration tool for electronic speedos.

It's been mentioned in these forums before, can't remember where, I'll find the thing on Jaycar's site again: here is a direct link to the part in their Kits - Automotive section.

Thanks Tony, however at $55 I'll pay another $15 to get an 'expert' to check and calibrate the speedo as they quoted me $70 for the job.

 

[Bosshog]

So if my vehicle was made in September 2005 and i run a different tyre size than the vehicle was made with and my speedo reads a couple of kmh's slower it is still roadworthy?Or would that only apply for a vehicle made then with the factory tyre size.

Navarian, I'll my new best friend - the engineer and then you'll have the experts answer rather than my opinion.

 

[Nomadic Navara]

All vehicles made after that date CANNOT indicate a lower speed than is actually being travelled. Furthermore, there is now NO upper limit on how much faster a speedo can read.

This is not correct. Go back to the link I posted in message 3 and see the correct limits specified in the ADR.

PeterD

 

[the_bluester]

If I read that correctly then most people have slightly mis interpreted it since the new ADR was introduced.

It must have been written by a bureaucrat, whoever it was seems fond of un needed complication, I would think that starting with the fact that zero must be equal to or less than the error and then that the error is allowed to be 0.1X the actual speed + 4KMH would be better put in plain terms that a speedo may display a higher speed than the actual road speed and that any error must be less then 10% of the actual speed plus 4kmh.

By my reading that would equate to 14% at 100KMH, more at lower speeds and less in a 110 zone or above.

Have to say that requiring that sort of accuracy and now without the older tolerance of + - 10% at speeds over 40KMH pretty much nixes any speedo not based on a pulse counter and stepper motor or a digital readut by definition. I am an ex tech and the older style electronic speedos are basically a multimeter, the sender on the box outputs pulses and a circuit in the dash integrates the pulses to produce a DC voltage proportional to the speed and the actual speedo was basically just a voltmeter. That is fine but analog meter movements are rated as a percentage of full scale deflection, to give an example, if you have a 10% meter movement on a 300KMH speedo, by definition the accuracy of the speedo would be plus or minus 30KMH at any given speed.

I personally dislike ANY speedo error and anything above a couple of kmh in a standard car irritates me. I want to KNOW how fast I am going, not roughly how fast I am going.

 

[Old.Tony]

That's why I *rely* on my GPS speed indication more than my instrumentation. Most GPS devices are accurate to within 1% and since they're calculating movement between two physical locations over a period of time with an accuracy of about a metre* (when there's no war on** ) the GPS devices are pretty good.

Notes:

* This was mentioned to me once by someone reasonably well versed in these devices. I have not confirmed this, although it seems reasonable. My old Navman was accurate to about 10 metres, you could see it on the screen when it was a little bit out. My new Pioneer in-dash system seems to know exactly where I am and shows me distinctly off the road when I am in my driveway - the sensor being about 3 metres from the road.

** During war time (which may include extensive military exercises), because some missiles and all military vehicles both manned and unmanned use GPS location instrumentation, the military once took bandwidth from the GPS satellites to ensure the accuracy of their location information, and back in the day, it rendered civilian GPS devices less accurate - you could pinpoint yourself to within 100m, but no guarantees. With more satellites going up, this may have changed - but I wouldn't count on it.

 

[Bosshog]

This is not correct. Go back to the link I posted in message 3 and see the correct limits specified in the ADR.

PeterD

Peter


Yeah I read the ADR Specs several days ago. Annex 3 clearly tells manufacturers what the tolerances are allowed and Bluster's rationale is correct - hence the 14% at 100km/h.

I can only go the advice the Engineer is providing me in order to certify the fitment of taller tyres. He tells me that since 1 July 2006 all new vehicles cannot have a speedo fitted which reads slower than the speed the vehicle is actually travelling at (e.g. - indicates 95 when actually doing 100). So (he says) manufacturers' default to speedo settings that indicate a speed that is well over what the vehicle is actually travelling at. They do this for one reason - to ensure all models comply regardless of whether you buy the poverty pack with smaller rims (i.e. greater speedo error) or the top of the line with larger alloys (speedo will be much closer to what the vehicle is actually travelling at).

That said, I intend getting a second opinion from the guys who are recalibrating my speedo - I'll ask the dumb questions and let you know what they say


Regardless, If I can't have an accurate speedo, I'd prefer a speedo that reads slightly fast as there is less chance of travelling over the limit that way.

Gus