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Toughening up a 4wd for driving on corrugated roads

February 28, 2020 — BarryK

Outback dirt roads in Australia are famous for their bone-shaking corrugations. I posted about this awhile back:


I will be upgrading to a 4wd soon, with the intention of being able to handle these roads, and also to drive on soft sand tracks. So, I read with interest any experiences and information about toughening-up the vehicle appropriately.

A few days ago, I came across a Facebook post by Benno. Benno took off into the Red Centre of Australia in his new Jimny 4wd, driving 10,000km, 2,000km of those on corrugated roads.

Now that is fascinating. I have done a couple hundred km, and it felt like my car was shaking to bits. Okay, it was only a road car, Holden Barina, with suspension only designed for smooth roads.

This is Benno's Facebook post:

This is a photo Benno posted. The trailer is custom, with tyre-width to match the car, and the original tyres off the Jimny:


Quoting Benno:

The trailer had my bed in it plus battery and charging for the solar panel. Chairs and table and my chemical toilet plus 2 more jerry cans. The trailers tare is about 140kg. I estimate that I pushed it to the 350kg limit with a tow-ball loading of about 40kg. I fitted the tyres I took of the Jimny onto the trailer. The suspension on the Jimny gave up the ghost after 2000km of corrugated road, but I got into Coober Pedy. Found out that TG just released the 40mm lift kit which I had sent the closest installer which was in Alice Springs. Also did my 10k service in Alice Springs. The people in Alice Springs sure know what they do. I can only recommend it. My Jimny is automatic, and if you set it on cruise control, it just goes. Towing the trailer was no issue I would even say that the trailer stabilises the car on corrugated roads. There is always a surprise around the corner, but the Jimny has mastered them all in its stride. From bulldust holes that could have swallowed a truck to cattle grids that had a 10cm step up invisible potholes (more like open-cut mines) to rocks on the road, you would never believe they fit under your car. And whenever you were flying over the corrugation and court yourself thinking, "This is actually not too bad" then this was precisely the point to get ready for the next surprise. But all in all, I would do it again in a heartbeat. 

I posted a reply:

When you say that the suspension "gave up the ghost", what actually happened to it? 
Benno replied:
When you travel over corrugated roads for extended periods, the oil in the shocks heats up, and cavitation can cause the oil to foam, in which case the oil in the shock absorber loses its viscosity and simply stops doing its job. Because of the weight in the back and the tow-ball loading, the shocks collapsed, and I was riding the rubber bumpers. This occurred going around a corner and just given me one more of my unforgettable memories. The back dropped by about 10cm, enough for my trailer chain to hit the road. Suzuki Australia offered to replace the shock, but I decided to upgrade. The original shocks are not built for this kind of work, so if you choose to drive on corrugated roads you probably can do it with very little weight in the back, then I think you will be ok. If you intend to do some overlanding, you have to do some modifications. 1st Tyres, 2nd Bullbar, 3rd Spotlights and shocks. And if you want to put your Jerry cans somewhere, you need a roof rack. After all that you learn to travel light. You know the weight of everything you put into your car. Then comes the point when you simply give up because of all the necessities the better half requires and get a trailer, which I find is the way to go. If you get a trailer, make sure it fits the profile of the Jimny as wind resistance is the most significant factor when travelling. So keep your speed to 100 or less and watch what you put on the roof rack. 
Fascinating! I am beginning to understand why so many serious 4wd'ers do a lift, of at least 40mm. Superior shock absorbers, with longer travel are put in, and most people also go for fatter tyres.

I also recently posted about live-axle and IFS (Independent Front Suspension) in 4wd's:

The "old school" front live-axle is superior if you want to do a lift. The problem with IFS, as I understand it, is that a lift will increase the angle of the CV joints, greatly increasing their wear rate.

Then there is the question of legality, and possibly voiding the vehicle warranty. To find out about legaility in Australia, this is a great page:

...that page is written for WA, where I live. Basically, the vehicle height must be increased no more than 50mm (2 inches). Ah, that explains something -- many new Jimny owners are going for an ARB or Tough Dog (TG) 40mm lift kit, with a tyre size of 215/75R15, up from the stock 195/80R15.

The "195" and "215" figures are the tyre width, going to some online tables, I see that the tyre height is increased from 693mm (27.28 inches) to 704mm (27.7 inches), a difference of 11mm.

That tyre size jump will increase the vehicle height by half of that, in other words, 5.5mm.

So, the ARB or TG 40mm lift, with those 215/75R15 tyres, will increase the vehicle height by 45.5mm, which is legal. Very interesting! 

Rereading Benno's posts, it seems to me that what actually failed was the coils. The sudden drop of 4 inches would happen if the coil springs broke. The Jimny has coil springs front and rear. Certainly if the shock absorbers were no longer doing their job, or less so, that would have put enormous stresses onto the coil springs. The effect of the trailer would be to tend to keep the vehicle body steady, further stressing the coils. So one thing lead to another.

Which does make me think, a Jimny without a trailer and not to much weight in the rear, would probably be OK. Well, Benno did say that.  

Tags: nomad