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Unibody durability off road #4974762 01/10/19 04:15 AM
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avacado11 Offline OP
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I always see videos or pictures of off road capable trucks/SUVs being ran hard in the dunes or charging thru ruts on dirt trails.

My friend drives down dirt roads and hits ruts hard in his stock Wrangler JK like a baja truck without long travel suspension. I would never drive my Subaru down a trail like that, I don’t want to break or bend any suspension components.

So does body construction effect how durable a vehicle can hold up to abuse like that? Running into ruts, having suspension bottom out or come close to hitting the bump stops.

Would having body on frame be more durable or would the extra weight do more harm than good to the suspension? Does it even matter for stuff like that? I understand rock climbing where the frame is under constant stress but for super bumpy roads...would it matter from a durability standpoint. Say something like a Jeep Grand Cherokee vs a Chevy Silverado 1500


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Re: Unibody durability off road [Re: avacado11] #4974763 01/10/19 04:35 AM
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Shannow Offline
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That's been on my mind lately too.

My wife's Captiva is super stiffer in the body than my Colorado (In can see the movement in the box on the bed through the rear view mittor), and I've soend a few hours under the Captiva today and really like how the box unibody is put together and stresses transferred through it (plus can transport a single bed and mattress with the rear seats folded down.

On damp dirt roads, especially clay, the Captiva feels really quite torsionally rigid, with the suspension doing it's job, and the unibody being the platform for it all....in my 80s and 90s with 70s and 80s unibodies, chassis flex made suspension tuning hit and miss. My parent's R16 at 380,000km cracked the windscreen one day when I pushed it into a roundabout hard...the box flexed enough to stress the glass.

Wife's Captiva, I stuck the floor jack under the front subframe at the suspension pickup point, and with the tyre less than half inch off the concrete, the other side "slid" in as the suspension relaxed, and the tyre adopted a cambered position...there was nearly no load on it...that car is stiff.

Subarus and Captivas with a couple of inches of lift do well around here on the trails and the slippery stuff, ground clearance being the major issue, and decent tyres in sizes that fit (Toyo Open Country on wifes, jagged that one).

Not good at rock ledges, with no low range...but themed 80s subarus with low range did pretty good.

Unsure how well they last before they start busting windscreens like Ma and Pa's old Renault...but bush bashers need work/repairs typically anyway.


If it's the truth....it can handle the pressure !!!
Re: Unibody durability off road [Re: avacado11] #4974765 01/10/19 04:48 AM
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Silk Online Content
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Here's a bit of a comparo...they all have a chassis except the Pajero which is a unit body and full independent suspension. About 6 minutes in check out the Pajero compared to the Prado.



1987 BMW R65 - Penrite VTwin 20-50
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1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.
Re: Unibody durability off road [Re: avacado11] #4974767 01/10/19 05:05 AM
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Shannow Offline
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And a little suby brummy



If it's the truth....it can handle the pressure !!!
Re: Unibody durability off road [Re: avacado11] #4974774 01/10/19 05:18 AM
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You still have some...they all rusted away in 3 years here.


1987 BMW R65 - Penrite VTwin 20-50
2005 Nissan Expert - 5W-30 Castrol Edge
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.
Re: Unibody durability off road [Re: Silk] #4974777 01/10/19 05:32 AM
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Shannow Offline
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Yeah, there's even a couple those older ones with the "power bulge" in either side of the bonnet around here.

edit...1988, a friend had one of those "power bulge wagons"...when we used to drive long distances, he jammed a jandal down beside the accelerator as a rudimentary cruise control.

Last edited by Shannow; 01/10/19 05:34 AM.

If it's the truth....it can handle the pressure !!!
Re: Unibody durability off road [Re: avacado11] #4974791 01/10/19 06:18 AM
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Here’s the way I think of it... you either have something so solid it has no give at all, like a really stiff unibody, or you have something that has some give, like a body on frame.

In the case of a stiff unibody, it’s great for on road handling. But stiff isn’t always good. Think like a piece of steel. It only has so much give before it breaks or bends permanently.

Now the body on frame. It’s got some more give to it, more springy. Kinda like a leaf spring. It can tweak a bit and return back to normal.

Now, what I’m describing here are very vague generalities. There are unibody vehicles that off-road great (Jeep Cherokee), and there are BOF vehicles that would fold in half off road.

Last edited by Skippy722; 01/10/19 06:18 AM. Reason: Fat thumbs

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Re: Unibody durability off road [Re: avacado11] #4974845 01/10/19 08:06 AM
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Chris142 Offline
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Your friend drives like a fool. You can bend axles,frame etc from driving like that. " As fast as necessary, as slow as possible".

Some times you may need to get up a little speed to get over an obstacle. But dont be smashing over things constantly.


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Re: Unibody durability off road [Re: avacado11] #4974895 01/10/19 09:08 AM
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maxdustington Offline
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I have a feeling constant abuse and high miles will fatigue a unibody, more because it is glued together. Steel has an infinite fatigue life so in theory as long as you stay under the fatigue limit you should be good.

However, I know that if you plan take a air cooled Beetle off road it is recommended that you install a cage to reinforce the unibody. I'm sure that one is welded together.


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Re: Unibody durability off road [Re: avacado11] #4974900 01/10/19 09:10 AM
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^^^ this ^^^


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Re: Unibody durability off road [Re: avacado11] #4974930 01/10/19 09:47 AM
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Originally Posted by avacado11

My friend drives down dirt roads and hits ruts hard in his stock Wrangler JK like a baja truck without long travel suspension. I would never drive my Subaru down a trail like that, I don’t want to break or bend any suspension components.



There's no reason you can't drive down that trail in your Subie, just don't do it like you're racing in the Baja 1000. Easing over things isn't going to hurt anything but if you find yourself doing it very much a unibody might not be your best choice. Keeping a vehicle stock and avoiding underbody contact will keep you pretty safe, if it's going to drag don't do it. Find a new line or stack rocks.


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Re: Unibody durability off road [Re: avacado11] #4975099 01/10/19 12:58 PM
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The unibody Pajero didn't do too bad for what it is, and it was weird seeing that Prado without all the luxury stuff, as it's sold in the US as a Lexus. I know, Top Gear but it's a Range Rover being at least used for something else but a mall/soccer cruiser.


Re: Unibody durability off road [Re: avacado11] #4975207 01/10/19 02:51 PM
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madRiver Online Content
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The 1984-200? Jeep Cherokee was unibody and a sought after off roader. They seem to last.

Re: Unibody durability off road [Re: AZjeff] #4975251 01/10/19 03:49 PM
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Originally Posted by AZjeff
There's no reason you can't drive down that trail in your Subie, just don't do it like you're racing in the Baja 1000. Easing over things isn't going to hurt anything but if you find yourself doing it very much a unibody might not be your best choice. Keeping a vehicle stock and avoiding underbody contact will keep you pretty safe, if it's going to drag don't do it. Find a new line or stack rocks.
But they drive fast on rough roads during the commercials! It's AWD right? That means it should be unstoppable and never break, because it is a Subaru after all.


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Re: Unibody durability off road [Re: Skippy722] #4975321 01/10/19 05:08 PM
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avacado11 Offline OP
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Originally Posted by Skippy722
Here’s the way I think of it... you either have something so solid it has no give at all, like a really stiff unibody, or you have something that has some give, like a body on frame.

In the case of a stiff unibody, it’s great for on road handling. But stiff isn’t always good. Think like a piece of steel. It only has so much give before it breaks or bends permanently.

Now the body on frame. It’s got some more give to it, more springy. Kinda like a leaf spring. It can tweak a bit and return back to normal.

Now, what I’m describing here are very vague generalities. There are unibody vehicles that off-road great (Jeep Cherokee), and there are BOF vehicles that would fold in half off road.


if both vehicles hit a rut that bottoms out a suspension, which body construction would have a higher threshold in general? A unibody designed with off road in mind(ex. Grand Cherokee that’s trailrated) or a Half ton BOF with off road HD suspension(Silverado z71).

Would a 3/4 ton or 1 ton hold up any better with a even stiffer frame or would that work against it? What about fancy suspensions like Chevy Zr2 or Ford Raptor. I’m assuming that stuff is just for comfort. But would a well designed IFS be a weak point compared to a solid axle?

Last edited by avacado11; 01/10/19 05:12 PM.

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