Thread: Speedo, Tyres and Correction

Originally Posted by trout1105

At 100kph on the speedo in my D2a I am actually travelling at 108kph at the moment on 245/70/16 Mickey Thompson ATZ p3's, Which is under the 100/110 limit so the truck IS roadworthy

.....

I think you better double read up on the ADRs!

If you have 100 indicated and doing 108 actual .. you're way beyond unroadworthy!

ADRs say you can't have a speedo indicating less than actual, and the leeway for underestimating is 10% +4km/h
ie. at 100 actual road speed, you're speedo can show you 114k/h and still be roadworthy.
and at 60k/h road speed, you're leeway is 70k/h on the display.
But there is zero leeway for showing you less than actual. Fine of display = actual tho.

I should have kept the link I found last night to post .. but that's what I read.
If I can locate it via my browser history, I'll post it.

But prior to '06 or something I think, it was +or- 10% or something, but they changed it.
I'm guessing that all the Jap bushbasher types, were way over doing it with their seriously huge wheel/tyre mods and the authorities got tired of it all.

Well, I was seriously waaayyy off wasn't I.

Thanks to all replies it has been an most informative read.

I had another look at the Nanocom and I must have seen it earlier and forgot, I actually have a multiplication factor in there, so that is probably why I'm getting a reasonably acurate speed on the Nanocom. I don't think I will be investing in a correction device and will most likely go down in tyre size when the time comes to renew. I believe that a 245/70/16 will be kinder to the drive on the old girl and I'll sacrifice about an inch and a half in diameter for a smidgen extra width. Also it will be easier to live with the speedo error of bugger all (about 1-2%).

Thanks again and as I have said before this place is a fantastic resource.

Originally Posted by ChookD2

Well, I was seriously waaayyy off wasn't I.

Thanks to all replies it has been an most informative read.

I had another look at the Nanocom and I must have seen it earlier and forgot, I actually have a multiplication factor in there, so that is probably why I'm getting a reasonably acurate speed on the Nanocom. I don't think I will be investing in a correction device and will most likely go down in tyre size when the time comes to renew. I believe that a 245/70/16 will be kinder to the drive on the old girl and I'll sacrifice about an inch and a half in diameter for a smidgen extra width. Also it will be easier to live with the speedo error of bugger all (about 1-2%).

Thanks again and as I have said before this place is a fantastic resource.

I am running 245/70/16's and my speedo is out 8kph at 100kph
Apparently my D2a is unroadworthy at 8kph over what the speedo is saying, Maybe I should mention that to all the people I see broken down or bogged in my travels

Apologies to Trout .. my bad, should have read the entire article and not skimmed past the gory details.

The latest ADR applies to vehicles built after 1 Jul 2006. I thought it applied across the board.

The way the rule is applied can be a bit confusing in the format of the wording:

In the case of vehicles of categories M and N:

0≤ (V1–V2) ≤ 0.1V2 + 6 km/h

V1 = indicated speed on display; V2 = actual road speed.

ADR 1803 word doc link:

Originally Posted by trout1105

.....
Apparently my D2a is unroadworthy at 8kph over what the speedo is saying, .....

Nah! .... tell them your Navara is, the D2a is less likely to bog, and is pre 2006 so roadworthy!

Sorry for the confusion, once again my bad .. I shouldn't speed read late at night and confuse 'yas all.(trying to decipher the math made it even doubly harder on my reduced late night grey matter capacity!)

Oh, and the 4km/h allowance was for L1 and L2 vehicles(moped type motorbikes, basically) N and M vehicles = just about all cars and trucks.

ps. on a semi related side note: the new rules seem to be taken directly from the Euro specs, and they seem to be dated 2003, so maybe in the Eurozone your D2a could be considered unroadworthy.
Maybe when you pass these broken down/bogged persons, explain to them that if you were somewhere in Europe your D2 could be considered unroadworthy.

Originally Posted by ChookD2

..............

I am assuming that the Nanocom is working off wheel speed rather than final drive speed from transmission. If this is the case, then is there any way to have that signal read by the speedo, as opposed to where ever the signal is coming from now, and that would eliminate the need for any other "device" to correct the speedo no matter what size tyre you are running.

As I said, I know nothing of these systems and how they interact so there is probably a simple answer as to why this cannot be done. But then again we are a collective of intuitive, innovative and inventive individuals so maybe there is someone who can work it out.

When you change tyres, the ABS sensors don't change. They read the number of rotations of the hub. The speedo system is set up for the factory tyre size.

Taller tyres = more distance covered per rotation. Speedo under-reads.
Lower profile tyres = less distance per rotation. Speedo over-reads.

For calculating distance/fuel consumption or range, simply figure out (using whatever means floats your boat) what the inaccuracies are in your system, and allow for them in your future driving. Do the same again if you change tyre brands/sizes.

Simples!

P.S. In nearly a half-century of car ownership, I have never had anyone (outside of a dyno) do a speedo accuracy check, for a RWC or anything else.

[QUOTE

.S]. In nearly a half-century of car ownership, I have never had anyone (outside of a dyno) do a speedo accuracy check, for a RWC or anything else.

[/QUOTE]

Me neither, All this unroadworthy nonsense because of an inaccurate speedo is But a storm in a teacup

Maybe, but I’d rather have the vehicle built well and certified as required. I get the impression that I’m one of the few.

There is absolutely Nothing wrong with the build of my D2a and I am very fussy about its maintenance But I have No interest in altering the electronics by adding a non genuine part just to have my speedo read 100% accurate when it doesn't make any difference whatsoever to the truck reliability and performance.
From what I have read these speedo correctors actually can cause the speedo to fail anyway.
I have spent about $20k on my D2a getting it up to scratch over the last few years of ownership So I'm not stingy, I just cant see the point or any value in doing the speedo mod.