Tyre size

[timbo2410]

Hi all, got the Y61 3.0L manual 5 speed and have done a 2 inch lift. Hit the beach with a set of desert duelers AT 275 x 65 r17's. I was slightly underwhelmed by performance to be honest. Tyres were at 18psi and dropped them to 15. Of course 15 was better than 18 but am still quite deflated (haha) at performance. Now all the tyre experts where I live, have suggested going to a larger tyre and rim (of course they would). Anybody in the real world done this and can pass on your comments please? I realise going larger will affect economy and at present i'm around the 11L to 13L per 100km's. I dont tow anything and have no plans to. I do most of my off roading on sand with the occasional trek into the bush with rock and mud. So pass on any helpful experiences you have had please :-)

[Rossco]

Hey mate, just to be clear what are you underwhelmed with exactly. Power, traction, handling ? . .

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[timbo2410]

flotation is probably the biggest issue ... at 15 psi yes there was a lot of sidewall bagging but not a lot of ground support. Not a real chance of making owns own tracks that's for sure. Handling ?? I don't rag it along the beach .. I'm fine with 3rd gear low at 2100 rpm and am not looking for max speed by any standards. Traction ?? plenty of traction no problem there at all .. no just looking for a possible lower resistance than what I have .. does that make sense?

[the evil twin]

For Sand you want max flotation and min rolling resistance.

Whilst everyone refers to it as 'bagging out' what you are indeed after is the longest, narrowest footprint you can ideally get.
Think dozer tracks rather than dozer blade

That means a larger dia tyre (longer footprint, less rolling resistance) is much more desirable than a wider tyre (wider footprint, more rolling resistance)
Sure as the pressure drops the tyre bags out sideways (nothing you can do about that) but the main deal is that the footprint also gets longer, much longer.

All of which is why, for years and years, large dia cheese cutters have been the tyre of choice for military, exploration, telstra etc etc

[timbo2410]

I agree totally. Hence the interest in finding out if there are any patrol 3.0 drivers who have gone for a larger tyre and what the affects are on engine and economy as it is effectively gearing up

[the evil twin]

I agree totally. Hence the interest in finding out if there are any patrol 3.0 drivers who have gone for a larger tyre and what the affects are on engine and economy as it is effectively gearing up

I ran 33 inch Cooper, Kuhmo and Desert Dueller on my 3.0 CRD the whole time I had it.
Best on the sandy tracks and softer beaches was probably the duellers.

Rule of thumb is if you go up 5 to 10% in tyre size you will affect all other things by a similar amount IE fuel will go from 11 to 12 ish lph, speedo will chnage from 100 to 95 etc etc.

If you don't change the diff ratios (again rule of thumb is one ratio step for every two inch tyre dia) you will usually find in the off road situations 1 gear ratio lower with larger tyres is best (remembering the Patrol gearing order is L1, L2, H1, L3, H2, L4, H3 etc)

On the soft stuff if the vehicle is lugging stop and see how much of a "bow wave" of sand is built up in front of the front tyres... if it is more than 25 to 50mm the pressure is too high.
By Bow Wave I mean the amount of sand being pushed up in front of the tyre on top of the undisturbed sand not how far the tyre has sunk in overall.

Finally, 3.0 litre donks hate falling off the front of the torque curve IE dropping below about 1600 RPM, they will be much happier and responsive if you travel around at 2,000 or so.
If you drop much lower the buggers will stall out if you hit any harder going... over 2000 they will power on much more easily.

[timbo2410]

Yep ive noticed that anything under 2000 when under load and there is a noticable drop in power .. the duelers do seem to have plenty of grip but i do think the smaller diametre tyre may just be the cause .. i was concerned that if i went slightly larger then it may be a bit better on sand but terrible in all other aspects.

[timbo2410]

I was also interested in knowing if there are any benefits of a larger snorkel diametre. Ive got a standard safari snorkel and intercooler. The 3 inch exhaust has helped tremendously so i was thinking about the intake side ..

[nipagu7]

do you have dawes and needle valves and egr delete , these help somewhat with more power at lower rpm. the snorkel and pipe are good , next would be a larger intercooler with fan underneath it as the intercooler does not work till about 80 kph when you get enough air flow across it , so when doing slow heavy work, ie; sand, an upgraded intercooler would noticeably help . if that is not enough after that you would be looking at a reflash or chip. all of these can help with fuel economy , if you can control your right foot. also it will never be a torque monster , you need to keep the revs up ( i find above about 2250 is best as it spins up quicker/easier when it start to labour in the sand. also, i've only ever used high range on sand , i've got the snorkel, pipe, dawes and needle valves and same size tyres as you but standard intercooler and no reflash/chip. i would not bother with larger tyres untill you have the power to turn them .

[timbo2410]

I have a dawes and needle valve ready to install but just didnt really know how to do it. I have a boost, egt gauge and catch can fitted so thats done ... i dont know of anybody local who can help with the install of the valves though