08 4.8 GRX (275/65R17 to 285/70R17?)

[Stefan]

Ek kon nog nie my Patrol hoog genoeg in die lug kry vir die skid-plate nie, maar die Bashplate pas soos 'n droom nadat ek van die voorste gaate effens geruim het.

Baie posetiewe opmerkings oor die Bashplate gekry! Fantastiese werk Peter.

[CarloG]

I think I have done my PHD in research on M/T tyres of late. I've also got a 4.8 GRX and am looking for a set of M/T tyres for trips etc.

These seem to be the issues:

1 - Diamater variance from OEM
2 - Rim size: current 8JJ

There seems to be some thought that you should not increase the diameter by more than 3% from the OEM without putting strain on couplings, gearbox and brakes. The LA Sport patrol which has been featured in the last few leisure wheels had 305/70/17 tyres in those pics in the dunes. Thats a diameter thats 8.11% MORE than the OEM of 275/65/17. They have changed tyres to 285/70/17's which are 4.99% larger in diameter. This size to me is the best size as it will also give a lift of 41mm from OEM. Thats as much as putting a suspension on. The rim size range on this tyre is 7.5" - 9" which means that a 285 section tyre will be in the middle of the standard 8JJ rim in a 4.8 patrol. The 305 section (and a 295 section) tyre requires a minmum rim of 8". Too narrow a rim (like an 8" rim on a 305 section tyre) will allow lots a sidewall flex when fast cornering on roads. Too narrow a rim will result in a harsh ride and deflation wont work as well.

I spoke to the guys that installed the rims for the 305 section tyres (they put 9" wide rims on for those wide tyres) and he said that they had to shim the rims as they interfere with a weld on the Patrols' hub. bot a bog though and each of those rims cost about R1200.

There are two great websites to do the calculations that I have summarised in the attachment below.

http://www.carbibles.com/tyre_bible_pg4.html
http://www.1010tires.com



After all this my conlusion as to tyre size is:

285/70/17 is the best compromise on size as:
- The increased diamater seems manageable from other posts I've read (even though its more than the recomended 3%)
- It's required rim size of 7.5" - 9" means that the standard 8" is neitehr too large nor to small.
- there seem to be quite a few makes that make this tyre. BFG, MAXXIS, Cooper, Firestone & Goodyear. There are others but these makes are on my shortlist.

QUESTION: Has anyone tried the Firestone or Cooper M/T. In some reviews that I found on the net the firestones performed really well.

[CarloG]

Dont ask how I got that table like that.

[G-MAN]

CarloG, a 275/65/17 tyre circumference is 789.3mm and a 285/70/17 tyre is 830.8mm.So its 41.5mm bigger which gives you a 20.75mm lift not 41...! Jy moes geluister het in wiskunde!

[Peter Connan]

Hi Carlo

There is another factor influenced by rim width: the sidewall bulge. The wider the rim is, the more of the sidewall is exposed to damge from rocks and sticks. Even so, what you propose should be fine, although I would personally have preferred 285/75/16's if I had a 4.8.

[Tinus lotz]

i agree with Piet the 16inch is a better idea because more rubber works better i have had =- 10 sets of bf tires on my 4x4 and bakkies but the km2 are yster tires only one set in my fleet at the moment but falling in love more every day my best km was on my kzte bakkie 15000 on 31 10.5 all terrains they work for me if you need them let me know and i will make a plan
the 4.8 will be better on the sand for pulling boats with bigger wheels and power is not a problem

[Kagiso II]

16-inch rims.jpg (138.01 KiB) Viewed 2390 times

[CarloG]

CarloG, a 275/65/17 tyre circumference is 789.3mm and a 285/70/17 tyre is 830.8mm.So its 41.5mm bigger which gives you a 20.75mm lift not 41...! Jy moes geluister het in wiskunde!

I was listening - just to the wrong things!

[G-MAN]