Speedo calibration and Tyre calculations

[sw20r]

Hi All,

Looking at getting my speedo calibrated by do I need to provide them any info?

Here's my old vs new setup

195/50/15 - 576mm Diameter , 1809.56mm Circumference
235/35/19 - 647mm Diameter , 2032.92mm Circumference

When driving and going through those speedo/safety checks the car appears to be at 72kms, when in a 60km zone. So I assume this has throw it out of 12kms.. But would I also need to find out the gear ratios etc to make this proper?

[PlacentaJuan]

i think you just need to know by what percentage your speedo is out.

if it is out by the same percentage at 100km/h and 120km/h then it can be easy fixed, and you can even buy a kit from jaycar that you can build and adjust yourself.

if you speedo is out by 12kms throughout the whole range then i think you will need to get someone professional to fix it.

[TA-022]

if its 12km the whole way .... it would read 12kms at rest.

you need the percentage like Placeta said.. then ya can do the Jaycar fix to tweak.



If that safety radar is around try a few speeds. note like 30-40-50-60 and so on up to the speed limit (so ur not done) and this should be enough to start ya calculations on what percentage your out.

[sw20r]

Hmm does it matter if the speedo drive is mechanical? or does it hook up to the dash?

ohhhhh just had a look at it! and it seems scary.. :| wouldnt know howto put that together

[CrUZida]

FYI what you have done is illegal.

You have increased the tyre height by more than the legal limit (15mm)

[PlacentaJuan]

oh yea if its mechanical speedo i dont think a jaycar kit will fix it1!

[Officer Doofy]

Hi All,

Looking at getting my speedo calibrated by do I need to provide them any info?

Here's my old vs new setup

195/50/15 - 576mm Diameter , 1809.56mm Circumference
235/35/19 - 647mm Diameter , 2032.92mm Circumference

When driving and going through those speedo/safety checks the car appears to be at 72kms, when in a 60km zone. So I assume this has throw it out of 12kms.. But would I also need to find out the gear ratios etc to make this proper?

11% out according to this
http://www.reanimotion.com/ToyMods/Tyre-Wheel_Calc.htm

[hybrid_turbo]

FYI what you have done is illegal.

You have increased the tyre height by more than the legal limit (15mm)

i didnt think it was done by tyres.. 15mm is jack shit all

[CrUZida]

Yes, 15mm is fuck all.

But that is 15mm larger than the largest tyre the car came with.

[RONA]

FYI what you have done is illegal.

You have increased the tyre height by more than the legal limit (15mm)

Correct linky for proof +/-15mm is the law

http://www.rta.nsw.gov.au/registrati...vsi09_rev4.pdf

Minor changes to wheels
Wheels up to 26mm wider than the largest optional wheel recommended by the vehicle manufacturer for the
vehicle can be fitted without the need to notify the RTA.
The outside diameter of the wheel and tyre combination must be no more than 15mm over the largest diameter
wheel and tyre combination specified for the vehicle and not more than 15mm below the smallest diameter wheel
and tyre combination specified for the vehicle.

[CrUZida]

Hmm, NCOP says +15/-10, but until that is inforce in NSW, the RTA one will override it.

[jonra23]

If is a mechanical speedo Castlemaine rod shop used to supply a small step/down unit to fit in the speedo drive cable to adjust. Generaly don't recomend there stuff but it is the only place I have seen that supplies a bolt in solution.

regards
jon

[Sigmeister]

If it is mechanical, take the speedo to a gauge place and have them adjust the magnets on the gauge.

If you have the percentage or any details it should be no problem for them.

[wilbo666]

If it is mechanical, take the speedo to a gauge place and have them adjust the magnets on the gauge.

If you have the percentage or any details it should be no problem for them.

That won't fix the odometer, or the trip meter tho...

Cheers
Wilbo

[Rogue]

There is a great tyre size calculator on the bottom of this page,will tell you how much your speedo will change too

http://www.mkiv.com/techarticles/index.html