[Gussyb]

Hi everyone,
I was wondering what the biggest legal wheel height and width is a NT sierra/drover. Also how much work is required to fit a WT diff in and would that increase my legal track width.
Cheers

[sideways]

Where are you?

[Gussyb]

sideways wrote:

Where are you?

Sorry I should have mentioned that. I’m in Queensland

[Gwagensteve]

If your car is a “normal” passenger variant, 215 75 15 on the standard rim.
If your car is a commercial variant placarded for 16” rims these ran a taller tyre, so you have more options up to just over ~30” tall.

If you are concerned about staying legal pay careful attention to maximum permitted rim width. Sierras run 16x 4.5” or 15x5.5” rims.

Most people do not seek legal approval for swapping in WT axles as it’s basically an undetectable modification but it does require fabrication and theoretically engineering/mod plate approval. All the spring perches on the WT axles need to be moved inboards to match the narrower spring spacing of the NT chassis.

It will increase track width around 80mm.

[Gussyb]

Gwagensteve wrote:

If your car is a “normal” passenger variant, 215 75 15 on the standard rim.
If your car is a commercial variant placarded for 16” rims these ran a taller tyre, so you have more options up to just over ~30” tall.

If you are concerned about staying legal pay careful attention to maximum permitted rim width. Sierras run 16x 4.5” or 15x5.5” rims.

Most people do not seek legal approval for swapping in WT axles as it’s basically an undetectable modification but it does require fabrication and theoretically engineering/mod plate approval. All the spring perches on the WT axles need to be moved inboards to match the narrower spring spacing of the NT chassis.

It will increase track width around 80mm.

Yep mine is plated for 16” rims. I’ve tried to find info online about how much wider I can make my tires but there is almost no info online about it.

[Gwagensteve]

https://www.tmr.qld.gov.au/-/media/Safe ... .pdf?la=en

Section 4.2. This is a copy of VSB14 from the QLD transport website.

Maximum legal rim width is 1.5x the widest rim for your vehicle. As commercial sierras are not dual placarded (ie for 15 and 16” rims) you’re at 4.5”x1.5= 6.75”. To be strictly legal you’d need a 6.5” rim.

Track width can only increase 50mm, that will be a bigger challenge as a 4.5” 10p rim doesn’t give you much scope. A zero offset 6” rim would be ok.

[Gussyb]

currently im looking at some 30"x7.5" tires and I was wondering if a 2 inch lift will be suitable without body trimming or if I should go up to a 3 inch lift.

[Gwagensteve]

Suspension lift has nothing to do with tyre clearance. What size is 30x7.5? Is that a conversion of a P metric size?

[Gwagensteve]

You may need a bit of seam hammering and maybe a small bump stop spacer in the front.

[Brenno]

I had 245/75/16 plated which are under the limit for those that came with 16" rims from factory.

[Beery]

This is off topic, but how relevent is the tyre size the car came with if the axles have been swapped? I'm sure there's more to it, but i was under the impression engineerable tyre size has a lot to do with what axles are under the car.

As far as i know, no wide track sierra came out with 16" rims(?) So i thought, technically, you would be limited to 215/75/15 if you swapped over to wide track axles.

Obviously your car passed brenno, was this ever mentioned? Or can you give any more insight? I'm aware narrow track and wide track axles are very similiar apart from width, so an engineer may be happy to pass either based on 16"rim cars, but i'm a bit curious.

[Gussyb]

Gwagensteve wrote:

Suspension lift has nothing to do with tyre clearance. What size is 30x7.5? Is that a conversion of a P metric size?

Sorry i must have mistyped. The ones im looking at are 30x9.5R15. I'm just assuming that 9.5 means inches but I'm not good with metric tire sizings and prefer to read them as imperial sizes

[Brenno]

Beery wrote:

This is off topic, but how relevent is the tyre size the car came with if the axles have been swapped? I'm sure there's more to it, but i was under the impression engineerable tyre size has a lot to do with what axles are under the car.

As far as i know, no wide track sierra came out with 16" rims(?) So i thought, technically, you would be limited to 215/75/15 if you swapped over to wide track axles.

Obviously your car passed brenno, was this ever mentioned? Or can you give any more insight? I'm aware narrow track and wide track axles are very similiar apart from width, so an engineer may be happy to pass either based on 16"rim cars, but i'm a bit curious.

Engineer was happy to do it on WT axles as they are the same strength and brake wise and all that mattered what the tyre placard which I got from a dash swap by chance. Wasn't looked at in any more depth than needed.

30x9.5x15 will be under the legal limit.

[Gussyb]

Brenno wrote:

Engineer was happy to do it on WT axles as they are the same strength and brake wise and all that mattered what the tyre placard which I got from a dash swap by chance. Wasn't looked at in any more depth than needed.

30x9.5x15 will be under the legal limit.

Thanks for the info. Will I be able to run 30x9.5x15 on NT axles or will I need to swap WT axles into my car to make it legal.
Also where can I get my hands on a WT tyre placard if I don't want to do a dash swap

[Gwagensteve]

It will be legal on NT axles however, if you want to keep the car absolutely legal you will have to ensure the tyres can’t contact the body, chassis/springs or anything else except the road surface, you’re not increasing track width more than 25mm per side and your speedo is corrected.

You’ll need to run 6” rims around 0 offset which will be a challenge around the front shock mount. WT axles do help with this.

[sideways]

I ran 30x9.5s on my nt, no scrub with a little bumpstop spacing and trimmed down bumper mounts. From memory the rims were 15x7 -6 offset or thereabouts. I didn't touch the firewall.

[Gwagensteve]

Beery wrote:

This is off topic, but how relevent is the tyre size the car came with if the axles have been swapped? I'm sure there's more to it, but i was under the impression engineerable tyre size has a lot to do with what axles are under the car.

As far as i know, no wide track sierra came out with 16" rims(?) So i thought, technically, you would be limited to 215/75/15 if you swapped over to wide track axles.

Obviously your car passed brenno, was this ever mentioned? Or can you give any more insight? I'm aware narrow track and wide track axles are very similiar apart from width, so an engineer may be happy to pass either based on 16"rim cars, but i'm a bit curious.

Sorry Beery, I missed this.

VSB14 is specific that the rim and tyre options permitted are linked to the axles from the donor vehicle, so, for example, if you put landcruiser axles under your Sierra you could run a 34" tyre legally (assuming other parameters can be met like overall height, tyre clearance etc)

You're correct that there was never a 16" placarded WT and that, strictly speaking, means you're back down to 215's if you swap to WT axles, however, there is a good argument that the 16" placard can be carried out on the grounds that the brakes, wheel bearings, GVM etc are all identical. I believe 15" placarded sierras have been engineered with 31's on that basis, but I don't know if it's 100% compliant with VSB14.

[sideways]

Gwagensteve wrote:

Beery wrote:

This is off topic, but how relevent is the tyre size the car came with if the axles have been swapped? I'm sure there's more to it, but i was under the impression engineerable tyre size has a lot to do with what axles are under the car.

As far as i know, no wide track sierra came out with 16" rims(?) So i thought, technically, you would be limited to 215/75/15 if you swapped over to wide track axles.

Obviously your car passed brenno, was this ever mentioned? Or can you give any more insight? I'm aware narrow track and wide track axles are very similiar apart from width, so an engineer may be happy to pass either based on 16"rim cars, but i'm a bit curious.

Sorry Beery, I missed this.

VSB14 is specific that the rim and tyre options permitted are linked to the axles from the donor vehicle, so, for example, if you put landcruiser axles under your Sierra you could run a 34" tyre legally (assuming other parameters can be met like overall height, tyre clearance etc)

You're correct that there was never a 16" placarded WT and that, strictly speaking, means you're back down to 215's if you swap to WT axles, however, there is a good argument that the 16" placard can be carried out on the grounds that the brakes, wheel bearings, GVM etc are all identical. I believe 15" placarded sierras have been engineered with 31's on that basis, but I don't know if it's 100% compliant with VSB14.

Widetrack Marutis had F78-15, they're 27.8" tall. https://www.indiamart.com/proddetail/f7 ... 90373.html

[Beery]

Gwagensteve wrote:

Sorry Beery, I missed this.

VSB14 is specific that the rim and tyre options permitted are linked to the axles from the donor vehicle, so, for example, if you put landcruiser axles under your Sierra you could run a 34" tyre legally (assuming other parameters can be met like overall height, tyre clearance etc)

You're correct that there was never a 16" placarded WT and that, strictly speaking, means you're back down to 215's if you swap to WT axles, however, there is a good argument that the 16" placard can be carried out on the grounds that the brakes, wheel bearings, GVM etc are all identical. I believe 15" placarded sierras have been engineered with 31's on that basis, but I don't know if it's 100% compliant with VSB14.

No stress.

That makes sense.

Just brainstorming here, but I wonder how silly you can get with housings, wheel bearing, spindle, brake assemblies etc. As in, I wonder if doing a Suzuki based "hybrid" axle (housing, third member) with wheel bearings, brakes, king pins (basically from the swivel hubs out I guess) from another axle designed for a much larger tyre was possible. in theory a larger tyre (above 31inch) could be legal, but would maintain ground clearance, keep width sensible, work well within the confines of the chassis/engine and add as minimal weight as possible. I'm sure there's probably issues with housing strength (and a million other things) and too many unknowns that would just go into the too hard basket for an engineer to even bother thinking about, but... maybe.

It's possible to engineer some very substantial modifications on all types of cars, but it seems no one, no matter the car can ever get enough tyre on it while being legal. jeez I'd love a solution for that.

[Gwagensteve]

Agreed Beery. Something like my hybrid rear axle that’s running 60 series cruiser hubs should get me a legal 34” tyre (or bigger- people seem to be engineering big tyres on 79’s which run the same wheel bearing. Housing strength should be more about the GVM of the vehicle.

The front is more of an issue regarding kingpins, knuckle strength etc.

[Beery]

I've had a look over a 79 that was engineered on 37's. The rear housing was a fully fabricated thing, mainly for gvm, coil conversion and track correction reasons, but yes, still used factory wheel bearings. The front was completely standard as far as I could tell. I don't know the ins and outs of how it's done, this was pre-rego and I think they end up with a different set of ADR's to comply with.

Also NSW, which is a bit different regarding tyre size to other states i think (i'm aware of an engineer who is happy to go over the "50mm limit" of other states here - 35's on cruisers and patrols for example, and word on the street is he's working on a way to get 37's done) but the kit for 79's is legal Australia wide.