Thread: Speedo, Tyres and Correction

Originally Posted by trout1105

Personally adding MORE electronics to a D2 is Not a great idea, Using a GPS to get an idea of the difference between what is being displayed on the speedo and you actual speed and driving accordingly is a much simpler option to adding another electronic device

The only issue with this is that if you rely solely on the GPS for true speed reading, your vehicle could be technically unroadworthy if the speed difference is lower than indicated.
Of course that has it own implications.
The other thing that you have to also recalculate is the distances on the odometers too. So you'd need to keep another track of driven distances.
Out in the boondocks where fuel can be quite a way between stops, this can also have a bearing on calculations required between stops.

Nothing wrong with electronics if they're well designed.

To the OP!
Important to note that if you try to source cheaper than the HunterDi speedo corrector, you will almost likely fail.
Brother (owns a D2) has tried this .. on two occasions! .. just that type of person that doesn't learn the hard way .. anyhow ..
If you do decide to do it, just go with the HunterDi C6100.

Don't try a TD5 defender speedo corrector, nor should you try a Jaycar Speedo corrector(even tho it was 99% close to working).

Originally Posted by AK83

To the OP!
Important to note that if you try to source cheaper than the HunterDi speedo corrector, you will almost likely fail.
Brother (owns a D2) has tried this .. on two occasions! .. just that type of person that doesn't learn the hard way .. anyhow ..
If you do decide to do it, just go with the HunterDi C6100.

Don't try a TD5 defender speedo corrector, nor should you try a Jaycar Speedo corrector(even tho it was 99% close to working).

Just bought my 2nd Hunter-Di C6100 - first one was about $120 in 2014. This one $206 (delivered), but still good value in my book.

I normally travel at about 3-5k under the speed limit and quite often set the CC at that using the speed displayed on the GPS.
I haven't had a speeding ticket Ever using this procedure.
IF I ran standard size tyres the speedo would be accurate But I like to run a bit larger tyre, Not a 33in or 35in only a 31in But it does throw the speedo out that is why I use the GPS readout
Fitting an electronic speedo corrector would be just fine when the tyres are new But as they wear that adjustment would get out of whack anyway, The GPS seems to work all the time every time regardless of tyre diameter So for me personally it is the better option

You cant gain engineering approval with a GPS speedo - that was what the RTA engineers told me when I spoke to them. Its because it doesnt work in all conditions.

I'm not sure about the other units, but the Samras (Iceland) unit I have has 2 correction settings and based on that I was engineer approved to run 2 different tyre sizes.

I don't need any engineering approval here in WA as we don't have to go over the pits every year to renew our rego

Originally Posted by trout1105

Fitting an electronic speedo corrector would be just fine when the tyres are new But as they wear that adjustment would get out of whack anyway, The GPS seems to work all the time every time regardless of tyre diameter So for me personally it is the better option

Not true. If you are that anal about speed differential with partly worn tyres, the C6100 has almost infinite adjustment within the range, so a simple procedure to adjust. Only thing it doesn't have compared to the (no longer available?) Truspeed is 2 settings to cater for regularly swapping between 2 sets of tyres.

Originally Posted by gavinwibrow

Not true. If you are that anal about speed differential with partly worn tyres, the C6100 has almost infinite adjustment within the range, so a simple procedure to adjust. Only thing it doesn't have compared to the (no longer available?) Truspeed is 2 settings to cater for regularly swapping between 2 sets of tyres.

I'm not being "Anal" at all I just don't want a speeding ticket and I don't have to make Any adjustments to the GPS
I can Navigate with complete accuracy using the GPS systems on my boat So I cant see any problems relying on them in my trucks as well.

Whilst GPSes are generally accurate, they're not fool proof!
The only major issue is that you get complacent with their generally solid behaviour, and they let you down very unexpectedly.

Do you, or have you ever seen Andrew StPierre White's youtube videos? He had one recently on how GPS had let him down with respect to his mapping products!

And now I have a strange/weird/confusing story time to share.
Yesterday, the Yokohama G012's had driven me bonkers for the last time .. enough was enough and 20 or so punctures in the last 2 years .. I couldn't take any more. New tyre time.
Couldn't even bother topping up the tyre showing 17psi on the TPMS, just wanted it off the car!
The Yokos were not my choice, but they worked well.. good grip, etc. They had 5K klms, or less, so the previous owner reckons, and I reckon they still had a good 20K klms left in them, with the 60K klms I'd done.

So my experience with my D1 has only ever been on these 255/70 r16's. I noted early on, speedo was about spot on, maybe 1km/hr difference, showing over true speed(ie. at 95 indicated, GPSes showed 94-95).
I can't really remember the speedo being anything other than that factor difference, but the odometer was initially out by 8% when tyres new, full tread.
On my last trip, I did another confirmation log, and now it showed -5.4% difference, so that where odo showed 100klms, it'd actually done 105.4klms. ie. my fuel usage was always better in real terms than indicated.

So, yesterday, I ended up getting 245/75 r16's .. and was expecting a slight change in speedo accuracy, maybe more accurate even!
What I wasn't expecting tho was accuracy difference I now get .. backwards.
That is, 245/75 is theoretically larger diameter, so I was expecting the +1km/h showing on the speedo to come good and be about spot on, or maybe show -1km/hr at worst.
But, either the 245/75's or the 255/70's had variations to the theoretical specs, so what actually happened was that the 245/75's now show +2km/hr difference.
That is the 245's have supposedly under geared the driveline compared to the supposedly smaller 255/70's.

What totally threw me tho, was that after a quick test drive up the freeway, now the odometer difference has gone back up to 7% from the 5% I'd been getting for the past year and a bit.
GPS speeds were confirmed with two GPSes(OziAndroid and phone via GPS test) and distance via OziAdroid and mile marking posts.

ps. new tyres are a little better in every respect too!

@ Trout: the issue isn't about engineering approval, or yearly RW testing in itself. The issue is that if your speedo is showing less than actual, then it is unroadworthy. For your own usage in every day driving .. not a problem once you have a handle on it. Just keep in mind the differences, and you don't even need the GPS.
ADR is clear on this, and there is leeway for speedo display up to specific accuracies either way .. something like at 100k/h can't show less than 100, or more than 110 or something like that.
The issue is, if it ever came to it, insurance could be a problem, or if it came to selling the vehicle. If the RWC tester was hardline strict about it, or in the event of an accident .. could be used against you(which you just don't want to have hovering over you).