3 Discoveries, 3 different tyre brands and 17,000 outback km's. Who won? (long post)

Great report pawky.
You have pointed out what is important on gravel roads,the need to air down and slow down on corrugations,especialy with low profile tyres.
Drive a 100km or so at 110kmh on a corrugated gravel road an feel how hot the tyres get,you cant hold your hand on them;););););).
Andrew

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Originally Posted by Eevo

the problem with going fast over corrugations is that you reduce steering and braking. i'm not really sure how to explain why.

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My theory is at higher speeds the tyres have minimal contact with the dirt at the low points of the corrugations. Your driving more over the top of them. So going by that train of thought your suspension would actually be covering less distance at speed compared to low speeds, however the velocity of the shock movement at higher speeds would obviously be higher. Would be and interesting thing to film with a high speed camera to see whats happening at various speeds

Its been done... I'll have a look on Youtube..

Andy: Airing down is a catch 22 - theres so many variables... And with low profile can do more damage than good... And with high profile can induce heat and flex failures...

It all is a balancing act :cool:

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Originally Posted by BSM

"You never really get fast enough to smooth out the bumps."

I've had conflicting theories about this approach to driving coruugations. On the one hand, there can definitely be a particular speed at which the ride smooths out. I assume it's a point where the frequency of the corrugations matches some sort of harmonic frequency of the springs and dampers of the suspension resulting in the cabin getting a nice smooth ride.

What I've been wondering though is if at that same speed, the dampers are getting a total hammering and thus are prone to overheating and blowing a relief valve..

If that is true then then the alternative theory of driving slower, and putting up with the discomfort in the cabin is actually better on the car overall.

What do you think?

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Rather the replaceable suspension than the entire vehicle shaken to pieces.

Hours of corrugations are extremely taxing on the vehicle and the occupants..

Usually - slightly lower tyre pressure and around 80-90km in a coil sprung vehicle tends to settle it down.

In a D4 you can really push that higher - although the safety of it is questionable... I have had the D4 and Camper well into triple digits on corrugations.... I dont recommend people try it...

At 80-90 the vehicle is 'skimming' the top portion of the corrugations giving enough control for most situations whilst avoiding the jarring of the lower portion...

I have been on a track though where the spacing was 300mm - nothing you can do there improves the ride...

So the KM2 was the only tyre to not be staked or get a flat. (Suspension failure destroying a tyre is hardly the fault of the tyre).

This mirrors my trip... I had no KM2 failures on my 2012 16,000km trip to the Kimberley, and I did a lot more gravel roads than this report.

:cool:

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Originally Posted by Tombie

...I have been on a track though where the spacing was 300mm - nothing you can do there improves the ride...

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Sounds like the corrugations caused by the harmonics of the trucks that use the Peninsula Development "Road" on the way to The Tip.

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Originally Posted by scarry

That is an excellent report:)

My BFG's on the D4 are way worse than your pic,i should actually post up a pic,but don't want to hijack the thread.

They had already done 20k,the damage i put down to a lot of k's at high speed on very rocky roads,combined with pressures that were probably a bit higher than they should have been.

I also find them an excellent tyre,apart from this issue,which is well documented.

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Our KM2s on our D4 are almost shagged after only 20,000ks, I put ours down to always towing and rough gravel roads, I've always kept an eye on pressures, but I have to confess I don't always lower the pressures once we get to a gravel road, rather I'll wait till I get to camp, so having road pressure for a couple of hundred Ks on each trip(42 rear 38 front) probably did help.

Never had this issue on the D2 and we had 2 sets both were 50,000ks plus before going to our last set just before we sold the car and why we went with the KM2s for the D4, sadly not going to get anywhere near 50,000ks with this set.

Baz.