[AndrieK]

This could all be interesting for guys with utes. How do they measure the back, particularly as I don't think there is any standard for tray height?

I don't think the suspension data is required for NA category vehicles as part of the RVD however, it seems like Nissan does provide data for utes with factory fitted tubs.

There's no suspension information for UY61 as it was only ever sold in AUS as a CabChassis.

Road Vehicle Descriptor (RVD1)

rvcs.infrastructure.gov.au

I've seen ride height specifications in some of the ESM's previously. I'll see if I can dig that up.

 

[jackbyo]

I'm not aware of any regulations or guidelines that dictate rim size changes. As long as the tyre size is within limits and the wheel has sufficient clearance to brake / suspension components there should be no issue. On a later model Y61 (post S4), I believe this pretty much limits you to a 16" wheel anyway.

You are allowed a maximum track increase of 25mm on the front axle (50mm on the rear of a Y60/Y61 because it's a solid rear axle), so you can change your wheel offset by 12.5mm assuming the tyre still sits inside the wheel arch and does not interfere with any suspension components.

yes I think you’re right. Not sure why I thought 15” rims weren’t legal (when changing from factory 17”s).
I had read somewhere that it’s to do with the load rating, and a sufficiently rated tyre for the GUs weight isn’t available in 15”. I never bothered to check as 16” has been a great size.

wheel track you’re correct too. I believe a lot of people do -25, but from my understanding the -13 is the most offset that’s legal. Tbh I wouldn’t want my turning circle any wider and it looks good with the -13s anyway.

 

[AndrieK]

yes I think you’re right. Not sure why I thought 15” rims weren’t legal (when changing from factory 17”s).
I had read somewhere that it’s to do with the load rating, and a sufficiently rated tyre for the GUs weight isn’t available in 15”. I never bothered to check as 16” has been a great size.

wheel track you’re correct too. I believe a lot of people do -25, but from my understanding the -13 is the most offset that’s legal. Tbh I wouldn’t want my turning circle any wider and it looks good with the -13s anyway.

Yes of course! I should've added that both the selected wheel and tyre needs to be suitable for the vehicle's mass.

I'm sure I've read on here of people who fitted 15" wheels on early model GU's, but maybe it was GQ's not GU's...? Either way, I think back in the day, people wanted to move from 16's down to 15's because of the availability of tyres in remote areas. Then everyone (me included) wanted to go from 17's to 16's for the same reason. But it seems nowadays that even 17's are more freely available because a lot of vehicles used for outback travel have 17's as standard. It's now the 18/19/20" crowds that want to go down to 17's.

I've mentioned it before. I currently have 16" OE steelies with 33" M/T's on them. If I had to do it again I probably would've stuck with the 17" alloys and just fitted 33" M/T's. For my type of off-road driving I don't think the 1/2" extra sidewall would've made a noticeable difference and the 17" alloys weigh considerably less than the 16" steelies.

 

[Benny Jahmin]

Can some explain from an engineering perspective why 50mm is the maximum track increase allowable?

 

[AndrieK]

Can some explain from an engineering perspective why 50mm is the maximum track increase allowable?

25mm, not 50mm... Unless if you plan on running different offsets front and rear.

The 25mm value is something that some bureaucrat sucked out of his thumb, but the idea is to try and limit the impact it has on steering geometry changes. Changing the wheel offset changes the scrub radius.

 

[Benny Jahmin]

25mm, not 50mm... Unless if you plan on running different offsets front and rear.

The 25mm value is something that some bureaucrat sucked out of his thumb, but the idea is to try and limit the impact it has on steering geometry changes. Changing the wheel offset changes the scrub radius.

25mm per side or overall wheel track?

Most people say its to do with wheel bearing load but that doesnt make sense to me. I was also suggested on a solid axle its to do with beam strength of the axle housing.
After my recent binge reading on steering geometry scrub radius seemed like the only handling aspect that would be adversely affected my increased wheel track. However an increase in tyre diameter will require an increase in wheel offset to keep scrub radius where the oem wanted it.

 

[AndrieK]

"Track" is measured from contact patch centre to contact patch centre, i.e. overall, not from the centreline of the vehicle.

VSI 8 on the Vicroads website says:
The maximum allowable track increase is:

• in the case of a front axle — 25mm
• in the case of a rear axle with independent suspension — 25mm
• in the case of other rear axles — 50 mm; and
• in the case of a motor vehicle manufactured with a combination of front wheel drive, McPherson strut front suspension and negative scrub radius steering geometry, no increase in wheel track is permitted unless specifed by the vehicle manufacturer
• in the case of a motor vehicle tted with a diagonally split braking system (i.e. one front wheel and opposite rear wheel on same hydraulic circuit), no change in the wheel track dimension is permitted
  

I suppose the VSB's and NCOP's are written and inacted in isolation, so track changes do not necessarily consider a wheel diameter size change at the same time. So if you stick to a combination of the 12.5mm offset and 7% tyre rule, the impact on steering geometry is considered to be within a safe margin. If you go beyond that, the complete suspension and steerig system should be re-evaluated and signed off by an engineer.

https://www.vicroads.vic.gov.au/-/media/files/documents/safety-and-road-rules/vsinumber8guidetomodificationsformotorvehicles.ashx?la=en&hash=ADC5076B9F3DA0D047319217ECDEDEB1

 

[Benny Jahmin]

Sorry to the OP for getting off track but this is why things get so confusing.
This is the document i get when googling track increase https://www.rms.nsw.gov.au/document...FjAAegQIAxAC&usg=AOvVaw1I6d24ZpNLB3MfLxJpyhLR

It says 50mm increase for 4wd vehicles. Doesnt specify front or rear. Or even independant vs solid axle suspension.
It does say if the axle is from another vehicle it can only be increased by 12.5mm each side. Or 25mm track increase. So i guess GU diffs under a GQ can only go to a 0 offset rim.

 

[AndrieK]

One of the joys of living in a Federation of states that can't agree on Jack ****...

Ozzie, Ozzie, Ozzie, Oi, Oi, Oi!!! 🇦🇺