EarthCruiser
Adventurer
FUSO EarthCruiser Dual Cab
Mitsu Fuso Camper examples
- Thread starter haven
- Start date
FUSO EarthCruiser Dual Cab
Never understood why people think a very flexible frame is "good" or "cool". It is the JOB of the springs, coils, dampers, airbags or leaves to articulate and move and sway to keep the load relatively level and the tires in contact with the ground.
Contrast this with a modern family sedan or minivan or SUV.... There is NO reason IMO to have a super flexy frame when you can easily design a proper suspension to accomplish the same goal.
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SkiFreak
Crazy Person
I totally agree.
pugslyyy
Expedition Vehicle Engineer Guy
There plenty of good reasons. Believe it or not, the engineers didn't design them that way just to irritate you and your sense of what is right.
It's all about coming up with a design that strikes the right balance of cost, weight, durability, carrying capacity, comfort, etc. A very rigid frame carries a big weight penalty, which increases cost to operate (and can impact an automakers overall fleet mpg rating).
The problem is it does'nt work in off road situations, constant uncontrolled flexing and it will eventually break.
It's just a cheap and easy way to mass produce a chassis.
Buckstopper
Adventurer
I suspect that engineers designing heavy truck frames face a geometry problem that was solved with frame flex. Look at the previously posted photos of my truck in the mogul field and imagine the amount of lift and suspension flex that would required to allow a rig with a completely rigid frame to keep tire contact. That much lift would elevate the center of gravity to the point where the heavy payload of a large truck would make it top heavy and unstable on the road or otherwise. Flex in the suspension works for a light vehicle but not a truck.
Ideally you would have a frame rigid to the point that the suspension bottomed out and then the frame flexed. This would force the suspension to do most of the work but you would still have tire contact at extreme articulation. I think the Fuso does a pretty good job of this but the engineers have to design for the maximum payload. The right answer with a camper is to adjust the suspension to the payload since that weight should be fairly constant. The caution is that once you do that you can't go over that new maximum payload.
My truck weighed 10,400 lbs as set up for Expo. That is conciderably under the 14,050 rating so the suspension isn't flexing the way it should. Under static conditions in my shop I couldn't get the suspension to bottom out and the frame was already flexing. I believe that the Australian approach of parabolic springs or coil overs is the right direction with these trucks. It's only money!
Buckstopper
Ideally you would have a frame rigid to the point that the suspension bottomed out and then the frame flexed. This would force the suspension to do most of the work but you would still have tire contact at extreme articulation. I think the Fuso does a pretty good job of this but the engineers have to design for the maximum payload. The right answer with a camper is to adjust the suspension to the payload since that weight should be fairly constant. The caution is that once you do that you can't go over that new maximum payload.
My truck weighed 10,400 lbs as set up for Expo. That is conciderably under the 14,050 rating so the suspension isn't flexing the way it should. Under static conditions in my shop I couldn't get the suspension to bottom out and the frame was already flexing. I believe that the Australian approach of parabolic springs or coil overs is the right direction with these trucks. It's only money!
Buckstopper
ben2go
Adventurer
I guess but our troops rock and roll the some of the same frames offroad and they seem to hold up well.Also logging trucks live offroad and they seem to hold up.I think they're designed to flex.They probably select specific steel mix to make frames out of so they can flex a lot before they start breaking down.I'm no engineer.I'm just speculating about how trucks are used and the nearly 100 years they have be in production and started life offroad.
Overland Hadley
on a journey
My take on it is that it flexes so it does not break.
This is the way bridges and skyscrapers are built, both have an incredible amount of flexibility.
Of course repeated over flexing will cause stress and fatigue. And I have no idea at what point a Fuso frame is over flexed.
This is the way bridges and skyscrapers are built, both have an incredible amount of flexibility.
Of course repeated over flexing will cause stress and fatigue. And I have no idea at what point a Fuso frame is over flexed.
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gait
Explorer
its not just "twist".
Before I bought and converted the Mitsi I observed lots of trucks of all sizes in motion. Scariest was a large garbage truck, two rear axles, at 50km/h over a string of bumps. The middle of the chassis was bending at least 150mm (6in) up and down (total movement 300mm). More noticeable in the gap between the top of the garbage container and the rear top of the cab. I was driving alongside for quite a while.
Trailers for articulated trucks may have a curve when empty. Flat when loaded. They flex longitudinally.
The Mitsi also bends longitudinally. Not so much as the garbage truck as its shorter. But bend significantly it does.
Sideways is constrained by the ladder. Twist is partly constrained by the ladder.
Twist is exacerbated in the Mitsi due to the narrow chassis. An outcome of dual rear wheels.
Start with a wider chassis that only has to accommodate single wheels and twist is more easily constrained. The balance between axle and chassis movement is very different. Deeper chassis rails reduces bend.
Possibly part of what makes the Iveco attractive given its new availability in Aus. Its been done before with the Oka, which has some basis in the old forward control landrover. And long leaf springs (we are perhaps using parabolic as there isn't the space for longer springs). I haven't looked too closely at Unimog and similar but suspect the chassis is wide and deep.
Before I bought and converted the Mitsi I observed lots of trucks of all sizes in motion. Scariest was a large garbage truck, two rear axles, at 50km/h over a string of bumps. The middle of the chassis was bending at least 150mm (6in) up and down (total movement 300mm). More noticeable in the gap between the top of the garbage container and the rear top of the cab. I was driving alongside for quite a while.
Trailers for articulated trucks may have a curve when empty. Flat when loaded. They flex longitudinally.
The Mitsi also bends longitudinally. Not so much as the garbage truck as its shorter. But bend significantly it does.
Sideways is constrained by the ladder. Twist is partly constrained by the ladder.
Twist is exacerbated in the Mitsi due to the narrow chassis. An outcome of dual rear wheels.
Start with a wider chassis that only has to accommodate single wheels and twist is more easily constrained. The balance between axle and chassis movement is very different. Deeper chassis rails reduces bend.
Possibly part of what makes the Iveco attractive given its new availability in Aus. Its been done before with the Oka, which has some basis in the old forward control landrover. And long leaf springs (we are perhaps using parabolic as there isn't the space for longer springs). I haven't looked too closely at Unimog and similar but suspect the chassis is wide and deep.
charlieaarons
Explorer
The unimog U500 has a straight frame, members are 9mm thick. Plus, there is a 7mm reinforcement in the front third. Despite that, it twists when "crossed up, quite a bit. A unibody would be impossible. There is no series (present on all models) rear body and the cab is carbon fiber - very little steel, and it tilts forwards.
Frame flexing comes with the territory in medium and heavy trucks due to body-on-frame construction.
Charlie
ben2go
Adventurer
I believe the front is stiffened up so it doesn't spit out the drive train when it gets flex up.
