20' wheels - Speedo recalibration?

[finnbe]

Hey. I am thinking of putting some 20 inch wheels on my stock VX (stock 15inch). I have been told by many people that you can legally only go up two inches in size in my case that would be 17 inch wheels.

The question I have is that if I do upsize to 20 inch wheels, what would I need to do to my car so that it would be roadworthy?

Would I need a speedo recalibration?

What about suspension, etc?

I basically need to get it 100% roadworthy so my insurance company will pay out if anything were to happen.

Any suggestions/comments would be much appreciated.

Thanks, Benjamin

[arrow224]

In WA, the wheel size + 2" rule still applies, however I am not sure in other states.

You would only need to have your speedo recalibrated if the overall diameter of the wheel + tyre is larger/smaller than what your current diameter of wheel + tyre is.

[| evaN |]

Dunno where your from but in vic, your only allowed to increase the width of the wheels by only 1inch. eg if your stock wheels are 6.5inch wide, then SS wheels which are 8inch i think are illegal. Pretty sure its hard to find 20s that are under 8inches wide.
Then you've got to make sure the offset is right, the tyres are the right width, the right profile, the right load rating etc..
Pretty much if any of those are off then your car is illegal = no money when you crash if the insurance company is tight.

[1991_Vn2nV]

Dunno where your from but in vic, your only allowed to increase the width of the wheels by only 1inch. eg if your stock wheels are 6.5inch wide, then SS wheels which are 8inch i think are illegal. Pretty sure its hard to find 20s that are under 8inches wide.
Then you've got to make sure the offset is right, the tyres are the right width, the right profile, the right load rating etc..
Pretty much if any of those are off then your car is illegal = no money when you crash if the insurance company is tight.

That is incorrect mate in part.

VSI8 from Vic Roads states that:

The width of any replacement rim must not be more than 25mm greater than the widest wheel specified for that model or vehicle series

Therefore its not what sized rim came on your car stock, but the largest rim used for that model i.e. largest rim any VT had from factory. So the SS rim would be included which means you can go an inch wider than that, even if you have an exec.

[Doctor Bob]

yes the speedo will need to be recalibrated, it is a simple process, to a certain extent.
anyone with a Tech2 can program the PPK to correct it with one limitation, the factory tool (Tech2) can only go as high as 7500 PPK, in your case this may allow enough adjustment. as you havent changed the diff ratio.
if the figure needed is higher than this you will need to take a different approach using some specialised software to program it.

Rob

[1991_Vn2nV]

In WA, the wheel size + 2" rule still applies, however I am not sure in other states.

You would only need to have your speedo recalibrated if the overall diameter of the wheel + tyre is larger/smaller than what your current diameter of wheel + tyre is.

Incorrect. This no longer applies in WA, it ONLY applies in SA and maybe NT.

Legislation for WA can be found here mate:
Vehicle publications

WA refers you to DOTARS National Code of Practice for Light Vehicle Construction and Modification (NCOP). Relevant information is found in NCOP11 (NCOP11 Section LS Suspension and steering 3 Feb 2006) which can be found on this page:
National Code of Practice for Light Vehicle Construction and Modification (NCOP)

If you still don't believe me I would like to see legislation from WA that states otherwise

[arrow224]

Incorrect. This no longer applies in WA, it ONLY applies in SA and maybe NT.

Legislation for WA can be found here mate:
Vehicle publications

WA refers you to DOTARS National Code of Practice for Light Vehicle Construction and Modification (NCOP). Relevant information is found in NCOP11 (NCOP11 Section LS Suspension and steering 3 Feb 2006) which can be found on this page:
National Code of Practice for Light Vehicle Construction and Modification (NCOP)

If you still don't believe me I would like to see legislation from WA that states otherwise

I stand corrected. Last time I followed this issue, WA had the rule. Seems not now though.

[Troy711]

Tire size calculator

[azzfox]

yes the speedo will need to be recalibrated, it is a simple process, to a certain extent.
anyone with a Tech2 can program the PPK to correct it with one limitation, the factory tool (Tech2) can only go as high as 7500 PPK, in your case this may allow enough adjustment. as you havent changed the diff ratio.
if the figure needed is higher than this you will need to take a different approach using some specialised software to program it.

Rob

I know it can be easily changed for people who have an eprom programmer and running the 'memcal socket install' mod for VN-VR? But just a Q while were on the subject.. How do you calculate the Pulses/Km according to tyre diameter and diff ratio? Is there a program for this or do you have to do it with pen and paper somehow?

[Doctor Bob]

I know it can be easily changed for people who have an eprom programmer and running the 'memcal socket install' mod for VN-VR? But just a Q while were on the subject.. How do you calculate the Pulses/Km according to tyre diameter and diff ratio? Is there a program for this or do you have to do it with pen and paper somehow?

its nothing to do with the memcal thing, its the instrument cluster needs to be programmed.
the PPK needed can be calculated using the current PPK figure, indicated speed & actual speed.

if the wheels have been changed use this Current PPK / (Indicated Speed / Actual Speed) = New PPK
if the diff ratio has been changed use this Current PPK / Original Ratio * New Ratio = New PPK

[azzfox]

its nothing to do with the memcal thing, its the instrument cluster needs to be programmed.

But you can change the PPK in the tune. I came across it while playing around in TunerPro.

[| evaN |]

That is incorrect mate in part.

VSI8 from Vic Roads states that:



Therefore its not what sized rim came on your car stock, but the largest rim used for that model i.e. largest rim any VT had from factory. So the SS rim would be included which means you can go an inch wider than that, even if you have an exec.

My bad. I always assumed that it was for every lower model because you always see defect threads and how that person wants to get their 20inch wheels engineered and ****. The way i was thinking was that because they had an exec, 225/30/20 would be ok, where as 245/35/20 would only suit calais.
So if its the largest size across the whole model, what are these threads about then, why are they getting defected lol

[old_fella]

id say they are getting defected because the tyre diameter is to large i tihnk it can only be 15mm larger and with 20 inch wheels you would need a very low profile tyre to keep it with in that

[Doctor Bob]

But you can change the PPK in the tune. I came across it while playing around in TunerPro.

yes but this has no bearing on the speedo, this is only used for internal calculations in the ECM.
also there are differences from VN-VS & VT onwards, the early ones cannot be programmed, Vt & onwards can be adjusted by programming.

Rob

[greenfoam]

My bad. I always assumed that it was for every lower model because you always see defect threads and how that person wants to get their 20inch wheels engineered and ****. The way i was thinking was that because they had an exec, 225/30/20 would be ok, where as 245/35/20 would only suit calais.
So if its the largest size across the whole model, what are these threads about then, why are they getting defected lol

The Victorian guide is probably no longer relevant anyway as we are all supposed to be following the federal guides now

[azzfox]

yes but this has no bearing on the speedo, this is only used for internal calculations in the ECM.
also there are differences from VN-VS & VT onwards, the early ones cannot be programmed, Vt & onwards can be adjusted by programming.

Rob

ah ok, all clear now

[jules]

The Victorian guide is probably no longer relevant anyway as we are all supposed to be following the federal guides now

it's always the state guide that matters. the federal guide is a model for the states to follow. they may or may not do so.

That is incorrect mate in part.

VSI8 from Vic Roads states that:

The width of any replacement rim must not be more than 25mm greater than the widest wheel specified for that model or vehicle series

Therefore its not what sized rim came on your car stock, but the largest rim used for that model i.e. largest rim any VT had from factory. So the SS rim would be included which means you can go an inch wider than that, even if you have an exec.

does the SS have different brakes or suspension though? if it does, they may argue the larger wheels were only ever certified with the whole 'package'. it's a bit unclear though.