[vet 180]

watermouse wrote:

Tyres are only ever flat on the bottom. Just roll the flat side to the top...

Thanks for your suggestion, 1DYX. I wasn't trying to be dismissive and, to be honest, that is probably the option I will end up with when replacing the current ones.

I personally feel the 235/85's are just a fraction to big to live with daily from a liability and legal standpoint but I would have no qualms having a weekend set of tyres this large. My quest has been to find the largest, narrowest 16" tyre with an unloaded diameter of less than 800.
For 235/85 the calcs say 806 but some tyres such as the MickeyT ATZ P3 are stated as 812, another at 810. Others are as small as 806.
There seems to be a lack of tyres approaching 800mm in the 235 or 245 width in both 15 and 16 inch. 255's are practically non existent. 265 is getting too wide.

With the stock tyres on there is a piddling 215mm under the diff. Air down for off road and I have as much diff clearance as a Jimny. It stands to reason that an equally loaded 800mm tyre will give more or less a 25mm height increase on a loaded 750mm tyre.

Tbh I think your overthinking it (we have all been there!) A 235/85 on the correct sized stock looking rims will be far less cop bait than a really aggressive 245/70 MT on wide rims poking outside the guards.

[Zook_Fan]

1. Get one of the tyres that are 806mm
2. Do skids until you have reduced the diameter by 6mm
3. Enjoy your new tyres that are 800mm
4. ????
5. Profit

[Gwagensteve]

It's not quite that simple. Legal size is based on the manufacturers stated dimensions, not the on-the-car size. It does not take tyre wear into account.

[watermouse]

vet 180 wrote:

Tbh I think your overthinking it

Totally.


This from the SA Gov Transport website https://www.sa.gov.au/topics/transport-travel-and-motoring/motoring/vehicles-and-registration/vehicle-standards-and-modifications/wheels-and-tyres

Quote:

Tyres

The overall diameter of a wheel and tyre fitted to a vehicle must not be more than 15 mm greater than the largest tyre size listed on the tyre placard and not more than 15 mm less than the smallest tyre size listed on the placard.

No mention of 4wds being exempt or different


This in the NCOP (and I apologise if this has been discussed in this thread before. 31 pages TL:DR)

Quote:

The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not
be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle
manufacturer for that model.
The overall diameter of any tyre fitted to:
 4WD passenger vehicles specifically designed for off-road use (typically MC ADR
category). All wheel drive (AWD) vehicles including those AWD vehicles that may be
certified as MC ADR category, (also commonly known as soft roaders) are not
included in this category;
 4WD goods vehicles and their 2WD equivalents if the chassis and running gear are
essentially the same as the 4WD version (N ADR category); or
 any medium weight goods vehicle (NA2, NB ADR category).
Must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the
vehicle manufacturer for that vehicle.

Bit of a conflict there. I don't know if SA adheres to the NCOP.

[Zook_Fan]

Gwagensteve wrote:

It's not quite that simple. Legal size is based on the manufacturers stated dimensions, not the on-the-car size. It does not take tyre wear into account.

Yes I know this but all of the options raised are illegal in SA which still recognise the 15mm greater size rule. Seems silly to over analyse the heights given by the tyre manufacturers, which aren't always correct anyway, between brands of a tyre that is already illegal.

[watermouse]

FWIW, we had a nice lady (with serious 4wding credential) from a reputable insurance broker talk at a recent club meeting about 4wd insurance. They offer tailored 4wd policy with Allianz that specifically permits combined lift up to 100mm without an engineers certificate. That is a combination of tyres, suspension and body lift.
This would seem at odds with local regulations but consistent with the NCOP VSB14. Technically I have had illegal tyres and lift on both my Jimny and GV and there are plenty of dodgy looking 4wds getting around without harrasment which would suggest no-one really cares, much.
So while we may have the most restrictive legislation we also probably have the most lax enforcement of it.

I agree with you, zook_fan, that if my new tyres are only 3mm (edit: I mean 6) over the maximum 50mm increase I don't think even a half reasonable cop would care let alone be informed enough to ping it. If it looks ok it probably is.

[alien]

no one cares until you have a fatal crash - then, if the mods can be blamed, your compulsory 3rd party is null and void and you face manslaughter charges.

ie: Tyres too big affected your brakes, and with factory sized tyres you could have stopped in time to avoid the crash.

[henno]

alien wrote:

ie: Tyres too big affected your brakes, and with factory sized tyres you could have stopped in time to avoid the crash.

Yes, but this needs to be proven. If you hit a car that pulled out on you at an intersection and smash into them at 60kph, then the 8mm of extra diameter wouldn't do a damn thing and your insurance will have to cover you. Sure, they might use it to try and muscle out of their contractual obligations but they need to PROVE the modification directly caused (or failed to prevent) the crash.

[christover1]

Small tyres with portals is the future

[Gwagensteve]

Only if the government changes the rules on overall lift and no more than 1/3 change in suspension (compression) travel.

Personally, I don't want an undertyred, excessively tall car.

[alien]

henno wrote:

alien wrote:

ie: Tyres too big affected your brakes, and with factory sized tyres you could have stopped in time to avoid the crash.

Yes, but this needs to be proven. If you hit a car that pulled out on you at an intersection and smash into them at 60kph, then the 8mm of extra diameter wouldn't do a damn thing and your insurance will have to cover you. Sure, they might use it to try and muscle out of their contractual obligations but they need to PROVE the modification directly caused (or failed to prevent) the crash.

Hence "if the mods can be blamed" - I don't think i've ever heard of it happening, however the engineer who did my car was/is one of transports forensic investigators and he did say that on many occasions it was clear that modifications contributed to the crashes, and that while it wouldn't hold up in court there were instances where he believed a fatality would have been avoided if things were done properly / not done at all.

[got_bar_work]

Thats it. Most cars could get away with no lift if u could run bigget tires on road its much easier to add some bigger brakes and hydro assist then to mess with suspension geometry. Plenty of people drive around the states on 39"plus tires with out a problem.
I think wheel bearings being affected is a bit of a joke . Its going to shorten there life but its not going to make them instantly fail. I wouldnt care if i had to do them every 10-20 k to keep them happy. Mud normally kills them first anyway. U wouldnt run a 37 on zook diffs but i would have no problem driving on lux diffs with brake upgrade.

[vet 180]

christover1 wrote:

Big tyres with portals is the future

Fixed.

No point running petals on small tyres. The benefits in gearing and stress taken off the axles is just too big to ignore

[shiv]

Are there any 17" rims that suit WT SJ70? i was wondering if the 235/85/17R would go for a dailey driver size?

[Gwagensteve]

Is that a real size? Never heard of it- what tyres are available in that size?

[watermouse]

Gwagensteve wrote:

Is that a real size?

computer says yes. But not common by the looks of things.

shiv wrote:

I was wondering if the 235/85/17R would go for a dailey driver size?

33inch daily. Hmmm.

Choose gearing for your tyre size and anything can be a daily.

[shiv]

I found that size on a chart i didnt follow through on the tyres available.

Seems after having a look they only come as a radial spare example, https://tiresize.com/tires/Goodyear/Rad ... -85R17.htm

Are there any draw backs on using spares?

Back to researching more options

Edit: I have diff and tcase gearing so currently 32s sit on 3800 revs @ 100

[Gwagensteve]

They aren't intended for anything other than sporadic temporary use. They're nowhere near as durable as a normal tyre.

Yes 17" rims are available for a Sierra.

33 10.5 km2 or 255 85 16 are both in that ballpark.

Steve.

[shiv]

Thanks steve, ill look into that

[got_bar_work]

Or 255/80 r17

[Gwagensteve]

One thing to watch with 17's (like 16's) is high load ratings. Many of those taller/narrower 16's are for USDM pickups and heavy "suv's" and will have titanic load ratings.

That makes for a heavy tyre, added to the already heavier 17" rim, neither of which are ideal for a Sierra.

I like to use Petersens guide for rim diameter- the maximum useful rim diameter for off road use is not more than 1/2 the tyre height.
15"= 30" tyre
16"= 32" tyre
17= 34" tyre

This is to retain sufficient conformability and therefore traction off road.

[shiv]

Cheers, ill probably stick with km2 33/10.5/15 but was hoping for a skinnier option.

34s would be ideal for my gearing but i require guard work before i can go any bigger then 33s

[got_bar_work]

Just found that dick cepek extream country come in 255/85r16

[rustyzook]

shiv wrote:

Cheers, ill probably stick with km2 33/10.5/15 but was hoping for a skinnier option.

34s would be ideal for my gearing but i require guard work before i can go any bigger then 33s

KM2s are a really good tyre shiv. I'm happy with mine! If you want skinny simex make a 34x9.5. Or at least they used to.

[got_bar_work]

Gwagensteve wrote:

One thing to watch with 17's (like 16's) is high load ratings. Many of those taller/narrower 16's are for USDM pickups and heavy "suv's" and will have titanic load ratings.

That makes for a heavy tyre, added to the already heavier 17" rim, neither of which are ideal for a Sierra.

I like to use Petersens guide for rim diameter- the maximum useful rim diameter for off road use is not more than 1/2 the tyre height.
15"= 30" tyre
16"= 32" tyre
17= 34" tyre

This is to retain sufficient conformability and therefore traction off road.

Wish they would put this in the adr's. 18in rims with tiney tires on new cars are a joke

[Gwagensteve]

I agree (for offroad use) but nobody uses their cars offroad anymore.

[shandy92]

Just a bit of a heads up, just had to get rid of my maxxis treps (31") because they caused a really strange vibration that resinated and made a loud bearing like noise. All shops that i took it to said wheel bearings, i did them and made no difference. They were slightly scolloped tho.

[rustyzook]

I got rid of mine to, they became quite hard and wouldn't stay seated at low pressures and howled on the tar. When I changed them I noticed 80% of the vibration in my steering wheel and gear sick disappeared. It also drives straight at 110.

[DiscoS]

Sorry if somebody's already asked about this, but I'm looking at a few choices for me new tyres:

KO2
ST MAX
STT PRO

any first hand accounts with these on a sierra (coily)?

And been told thinner sidewalls are desirable for sierras but I don't know if I buy into that one.

[alien]

I ran the original STT and it was a good tyre, but to be honest my BFG KM2 were better, my General Grabber SRL better than those on non-sloppy surfaces, and my Kumho KL71 better again on absolutely everything, other than wet roads (the SRLs win that one).

IMO if you're after an AT-ish tyre and can afford coopers, get the Gerneral Grabber SRLs (depending on the size you're after).