2001GU posted:

Thanx Flappa,
When talking about the legality of the 285's is this state dependant, I am in Vic? How ever if there is a need for lift the 265/75's sound ok. Lift will come much later on depending on $$$$$$.
Cheers
Andrew

Truckster (Vic) posted:

Legally in Vic you cant run them. Unless you get it engineered.

15mm bigger over OEM size is all you can go.

flappa posted:

AFAIK , in every state the max increase over standard (which I think is 265/70/R16) is 15mm.

My 265/75/R16 are in fact illegal by about 1 or 2mm. Close enough to say I cant be stuffed.

I think the 265/75/R16 are roughly . . . 32 inch

I think the 285/75/R16 are about 33 inch.

A lot of guys do it , and , I believe you can buy a new tyre placard from Nissan so that the 285/75/R16's are legal

Other then QLD , you can get bigger wheels certified by Engineers Cert , cost you a few hundred for the privledge.

rolande posted:

The placard from Nissan is for 265/75/16. Is for the cab chassis.

you can then run 15mm larger from that

Rolande

madCrow posted:

Hi 2001GU,
Yes there are legalities with just about everything you do that changes the specs of a vehicle, but you asked about suspention hieght. So I have assumed your interested in the effects of increased tyre size in relation to your truck & it's preformance.
There are a few things of importance or relavance that happens when you increase tyre size/diameter.
-Your going to need more thortle when your taking of in first gear in high range @ the lights.
-Making a steep descent in 1st gear low range you'll find you may require a touch on the brake pedal more often than you want.
Why? Your gear ratios have changed in relation to diameter to the wheels, there will be less torque at the wheels in every gear.

Because of the increased tyre diameter your brakes are forced to work a lot harder in case of an emergency stop, ie: when you have to slam the brakes on to avoid the roo or little child running across the street.

Even the vehicles speedo will be affected, for each tyre size increase it's about 12.5% change, so when your speedo says you are doing 100kph on the highway more than likely you'll be doing 112kph, hmmm... so when your doing 110 on your speedo your doing........ Start writing out cheques for the speeding fines.

Why do I say this, well I'm running tyre that are increased in size for my Patrol. The stock standard Tyre Size is 265/70R16. I run 265/75R16's, this is an increase of diameter of 35mm (with 285/75/16 tyres it's an increase of 63mm over the standard size). Braking is harder, so I have to be always very aware.
With this size tyre decents down steep slopes is still cool, I like to leave my feet of the brake, clutch & god forbid the accellorater & no I have not lowered my 1st & 2nd gear ratios
I have been thinking/pondering 285/75/16 tyres myself but the effects to the trucks overall performance will noticable. To keep it up to its current specs would require further cash expenditure on the gears, brakes, body suspension lift & speedo etc..
I'm very happy with the 265/75/16R's at the moment.
Anyway 2001GU I have not meant to waffle on, but with changing tyre size there's a hell of a lot more to consider than just body lift though that is very important as well. Now all you have to do is sit back ponder all that that you'll learn form this forum and decide do I want a 1 step tyre size increase or 2 step increase. Just enjoy & be happy.

madCrow

PS: I really low going down steep inclines, letting my truck do the work it was designed for.

Member - Phil G (SA) posted:

Madcrow,

Agree with most of what you say, but How does a bigger tyre make the braking worse? Its still the same vehicle mass being stopped by the same size brakes. Afterall, if you are stopping from say 60kph, the tyres are rotating a bit slower with bigger tyres. Its just that I've not noticed a difference in braking just from upsizing. Any other ideas?

And going from 265/70 to 285/75 is a 6.8% increase, not 12%.

Cheers
Phil
Also running 265/75!

madCrow posted:

Hi Phil,
I suppose it's a question of symantics, how much is noticable & to what degree it is noticable, the braking difference with tyre size.
I contacted a friend who is a mechanic who's specialty & passion is vehicles, I daren't ask him a question about diesal engines unless I'm prepared to sit & listen for many hours if not days to the answer. I wanted a more substanial answer to & reply to your question re: upsizing tyres & braking preformance.
The word I got thrown in my face was "Mechanical Advantage" is the reason, explanation for the increased work load on your/our brakes when the tyre size is increased.
It's the leaverage principle at play here.
You have a very tight nut on your bolt, you first try a 6 inche spanner, it hardly moves, then you try a 12 inche spanner, viola! it moves.
Why? the 6 inche doesn't exude as much power/stress on the nut as the 12 inche spanner. With the 12 inche there's more power being exerted on the nut, the only thing that has changed in the set-up is the radius length ie: the distance from the nut to the end of the spanner.
The same principle is appling to your tyres, the type of brake is not changed but the radius (& diameter) is changed to the outer rim of the tyre, so there's more stress on the brake.
Anyway the question of difference in braking from upsizing may not be all that noticeble at 60 kph, except in the fact that you pull to a stop now 6 inches (15.2cms) ahead. That 6 inches though can possibly mean the difference between life & death. (Again sorry if this sounds now heavy but hey that's reality)
When your off road this braking difference is negligable because of the speed one is driving at, but on black top where speeds increase sizably, the wieght of your vehicle (mine 2.6 ton unloaded, well over 3 when loaded) is massive, these added to the tyre size increase, affect your braking power & stopping distance, more speed, more stopping distance, bigger tyres, bigger stopping distance.
It's just a case of being aware of the worst case scenario & driving appropriatly.

madCrow

Member - Phil G (SA) posted:

Thanks for that MadCrow

Cheers
phil

govo posted:

Quote...Even the vehicles speedo will be affected, for each tyre size increase it's about 12.5% change, so when your speedo says you are doing 100kph on the highway more than likely you'll be doing 112kph, hmmm... so when your doing 110 on your speedo your doing........ Start writing out cheques for the speeding fines.

your wrong there madcow..i have 285x75 and speedo is spot on.

madCrow posted:

Hi govo,
You say "i have 285x75 and speedo is spot on".
That's excellent that your speedo is spot on now.
I assume that you have increased your tyre size from 265/70/16R, which can only say that your speedo was reading incorrectly with the factory fitted tyres.
Factory settings for speedos are usually under-rated, you think your doing 100 kph, actually you might be doing 95->97 approx.
My original comment was regarding the fact that an increase in diameter does influence a lot of different factors on your truck.
So anyway whether you realize it or not congratulations on fixing the problem. It's great what simple things can do!

PS larger tyre size will also last you longer, ie: 285/75/16 make less turns to the kilometre than 265/70/16R's. Double cool!

madCrow

at4x4 posted:

If your tyres dont rub, it means you can fit bigger ones. ;-)))

patrol freak nsw posted:

it means I lifted it 4" to stop rubbing

at4x4 posted:

I went 6", and they still rub ;-))))))))

govo posted:

Dave i have 285x75 and have had my 02 gu in area's where the suspenion is fully stretched and never experinced any rubbing and that is with standard suspension and no lift kit.

Truckster (Vic) posted:

yup, had ~7in suspension and 2in body and mine still rubbed.

patrol freak (NSW) posted:

Found springs not heavy enough for weight of car have now fixt problem hopefully