Thread: Any Suggestion on Off Road Modification for Disco 4

Originally Posted by LRD414

Interesting. The conclusion of that article is ........

"So for tyres and sand driving, tyre pressure dominates all other factors to the extent that other factors mostly don't matter. There may be some other factors at play but they are dwarfed by the effect of pressure. Reduce pressure until you float on top. Any tyre will work."

<EDIT: supports Gordon's point above, except ignores consideration of vulnerability.>

Thus you can counteract the extra weight of the D4 with lower tyre pressure and then take full advantage of the extra torque and traction control.

Scott

Mate where he says tyre pressure dominates over any other factor he is referring to the factors of width versus height not vehicle weight. And in the real world using contact recording a 31 in high profile achieves a considerably longer and greater volume contact area than a fat 31 low profile.

Cheers

.....probably off topic, but backing up the truck a few posts to where Tombie left off, when comparing torque to weight ratio's, don't forget to factor in the torque multiplication from the overall gearing ratio's as Tombie was reflecting in his table. The Defender has much lower gearing and hence much higher torque at the wheels. Combined with lighter weight gives it the advantage on a torque (at wheels) to weight ratio. Comparing engine torque to weight without factoring in gearing has little meaning (unless comparing two vehicles with the same gearing set up like different engines in the same vehicle).

But as I said getting off topic.

Originally Posted by BobD

The D4 is definitely not useless in mud or sand. Might I suggest that you get hold of Gordon's book from the GOE web site and read it carefully.


My D4 has done thousands of km of sand driving. It is what we have most of in WA! The sand has had no effect on the suspension and I have no idea who would have propagated such a ridiculous statement. It is amazing what "experts" that have never seen a D4 can say!

Sorry, mate. I never mean to D4 is useless in mud, but mud /LT tyre is better than pirelli scorpion atr tyre 255/50R20 that I have now. I had done off training and knew D4 got the capacity to off-road condition. Some how, my AT let me down that I could not stop on downhill mud road, crash into another Nissan patrol.Most of vehicles with Lt tyre escaped without problem, but driving in the dark on 1st trip wan't helping.

Then, change a good mud tyre is priority if I want more off road. The noise likely be an issue if I do lot more on road. Also costly to get all gears equipped, some mates rather get a fully equipped LC80 from 10-15k than upgrade D4 will cost more. Thanks all opinions shared.

Originally Posted by DiscoDB

The Defender has much lower gearing and hence much higher torque at the wheels. Combined with lighter weight gives it the advantage on a torque (at wheels) to weight ratio.

True to an extent - but the torque to weight figure already accounts for the difference in weights, and one doesn't generally do sand driving in low 1st!

Cheers,

Gordon

Originally Posted by Drizzle

Theoretically, it's the same size footprint...

Why Wide Tyres Don't Help In Sand | outbackjoe

"Why Wide Tyres Don't Help In Sand"

It's funny that he doesn't actually say that at all, 'cause that comment is out of context.

He starts off by tying to eliminate variables to get things down to the basics of pressure and contact area. But then his article actually acknowledges that there are a shed load of variable that make it hard to compare apples to apples outside the world of theory.

However, there is a big paragraph that reads to me like it contradicts his article title....."A wider tyre will need to flex less to achieve the same footprint of a narrower tyre. This means a wider tyre may be able to run at a lower pressure when compared to a narrower tyre, as the narrow tyre will deform more and so increase the risk of pinching the tyre tread between the rim and the ground. In this case a wider tyre may offer a slight advantage since it can be run at lower pressure, however for a typically weighted car, extreme minimum tyre pressure is determined by the minimum pressure required to keep the tyre bead seated rather than the rim impacting the tyre. So a wide tyre may not offer any benefit." The only negative he points to there is the chance of losing the tyre off the rim at extremely low pressure.

Sounds to me he's saying a wider tyre can achieve a larger contact area easier (safer in the real world) than taller ones, as long as you don't drop too far. Does that mean that the skinny tall tyres are well out of the race by then?

He does say width definitely isn't a negative ..... so what happens if you have wide tyres that are tall?

Anybody confused? .... LOL!!! :-/

Haha. Yes clear as mud isn't it. You can go too wide in sand. I have seen vehicles with very wide tyres that simply are poor in sand....the silly but clearly understood example is picturing a log being rolled in sand versus a tall thin tyre...log has a considerable build up of a sand wedge along its length that needs to be fought against and overcome all the time.

A taller tyre will be able to deform a lot and still have more meat than a wide very low profile at road pressure so I don't agree with his comments.

Cheers

Originally Posted by ozscott

Haha. Yes clear as mud isn't it. You can go too wide in sand. I have seen vehicles with very wide tyres that simply are poor in sand....the silly but clearly understood example is picturing a log being rolled in sand versus a tall thin tyre...log has a considerable build up of a sand wedge along its length that needs to be fought against and overcome all the time.

A taller tyre will be able to deform a lot and still have more meat than a wide very low profile at road pressure so I don't agree with his comments.

Cheers

Yeah, I've heard the log analogy too but he's refuting that theory. I think he's saying if you have excessive build-up (regardless of width), some of the variables are wrong, like the tyre pressure for the weight of your vehicle for example.

I guess it's all about getting the balance right in all the factors to match the conditions to get the right amount of contact patch......without risking tyre damage.

I think he's clear in what he means .... he's just muddied the water a bit trying to talk about all the contributing factors.

My 285/60/18s seem to work pretty well in soft sand ..... about to be re-tested in a few weeks time on Moreton Is. :-)

I guess in practical terms, the physical limitations of your vehicle will play a major part. For example ..... the old LC the Police use on Moreton Is is basic, not too heavy and has the ability to run small wheels with skinny tyres at pretty low pressures. However, a 3 ton, 3.0l D4 can only get 18" wheels, so getting the extra contact patch from much taller, 'skinny' tyres is limited without modifying the car illegally. So I guess you have to go wider to spread the pressure.

Mate those big tyres on the 18's would be fine I reckon...60 percent of 285 nominal is a good margin. I have just come back from Moreton...great fun.

Cheers