Unibody durability off road

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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
 
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.
 
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.
 
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.
 
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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.
 
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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.
 
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.
 
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.
 
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.
 
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.
 
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?
 
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Originally Posted by AZjeff
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.


I have eased my way thru some ditches with my outback, points where the car was on opposite corners. It was cool to see but I know it's not good for the unibody. The alignment was still good and no creaks/rattles, but I'm always afraid to blow a ball joint or control arm from hitting a rut too hard, or worse bending the suspension mount points. I can fix scraping with a lift and and skid plates.

I don't off road my Subaru that much anymore after a ball joint went from hitting a 6" deep rut at 10 mph. But my next car will have to be more durable off road. Wranglers are nice but I'd want something more civilized
 
Originally Posted by avacado11
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?


The BOF, in general, will "survive" a hit like that better than a unibody. As for suspension, it depends what you're doing. Bombing down a fire trail, out in the desert or something like that? I'll take IFS. Rock crawling? Solid axle. I've always wanted a pre runner... crawling slowly over rocks doesn't appeal to me. I want to do 110mph flying over stuff lol
 
Originally Posted by Skippy722
Originally Posted by avacado11
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?


The BOF, in general, will "survive" a hit like that better than a unibody. As for suspension, it depends what you're doing. Bombing down a fire trail, out in the desert or something like that? I'll take IFS. Rock crawling? Solid axle. I've always wanted a pre runner... crawling slowly over rocks doesn't appeal to me. I want to do 110mph flying over stuff lol



The unibody Mitsubishi Montero/Pajero has participated in the Dakar rally among other for many years. Not exactly crawling.
 
Originally Posted by nthach
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.




I hope Land Rover paid TG well for that ad...I mean episode.

That said, the RR's are decent off road, really good considering what they are. Putting aside the shilling for LR, it is a cool video.
 
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