GQ on road speedo variances

[JimboGQ]

Hi guys, this is my first time on a forum, not sure if this is the first time this question has been asked but I have 285/75/16's on a GQ 4.2 carby and at 100km will my speedo be out and if so roughly by how much? I drive on the freeways at 95km and all cars fly past me but I don't want to risk going over the speed limit as in WA the coppers have cameras everywhere over and have numerous fines (have a heavy right foot which I need to lighten)? Any advice would be greatly appreciated.
Cheers, Jimmy

[rkinsey]

Hi Jimmy,

I would have the speedo calibrated as there could be several reasons why your speedo could be out. I did a search on google and came up with these guys http://www.ahgwa.com.au/Duncan_Nissa...ts.php?dept=32

Cheers,

Rob

[DX grunt]

Hi Jimmy.

Welcome to the forum. From memory, there's a place called Australian Instrument Services (AIS) in Perth somewhere, that re-calibrates speedos.

Take care out there.

Ross
DX grunt

Edit: May be Allied Instrument Services or Aust Instr Svcs. can't remember.

[Bigrig]

Hey Jimmy

same goes for me - have a set of 285/75/16's and when I sit behind my mates brand new BT50 with him on 100, I am only doing about 94 (ish) ... not sure of WA, but in QLD now it is illegal to have ANY level of over speed calibration on the speedo itself (there was an ADR that allowed for up to 10% either way originally, but this has now been canned for the new guidelines) - i.e. not only can you get done for speeding, but if you mention you were only doing 100 to the boys in blue, they can order a mechanical and ping you for the over estimation on the speedo calibration also ... definitely worth just taking it to one of the joints mentioned above for peace of mind - if they are anything like here in QLD, they will under calibrate by about 2-3% (i.e. when you are sitting on 100, you'll actually be doing about 98 etc).

Good luck with it ... they are cracking down on this everywhere by the sounds of things ...

[JimboGQ]

Thanks guys for the replies and definately will get it looked at.

Cheers again, Jimmy

[kopyme]

Hey Jimmy,

Just to let you know that Marks 4wd does a speedo calibration electronic box to fix the problem too.

[JimboGQ]

Thank's kopyme I have just ordered a calibration box as it will be quicker for me to order online and fit on a Sunday than getting time off work. I was going to get the old girl calibrated over the Christmas break but this will work out a lot better. Cheers again to all the above for their imput.

Jimmy

[sweet_gq]

I have the same problem, I run 285/75/16's...

Lined up my speedo, odometre against my GPS and found about a 5% variance. I haven't worried about the marks adaptor. Just keep it in mind when travelling.

B

[Finly Owner]

Try this to explain tyre v speedo

http://www.exploroz.com/Vehicle/Tyres/SizeCalc.aspx

[tkn]

All cars have "error" between speedo reading and actual speed. If the error is about 5% or less, then best to live with it. If you can't, then buy tyres with 5% larger rolling diameter - you can check this by putting a white spot on your current tyre and mark the ground, then the vehicle forward until the tyre rotates 360 degrees and measure the distance travelled. Your proposed new tyre should be 5% more - don't take all said in tyre brochures as gospel. The travelled distance does not have to be millimetre perfect, an error of say 3mm in 2.4 metres will be negligible.
You say you have a "lead foot" - use a bit of reverse phsychology on yourself, leave the speedo as it is and you will find that you will drive to 100Km shown on the speedo (or a bit over), keeping you within the speed limit.