Any real benefit to installing a roll bar on M1009 ??

[tim292stro]

2.409# per foot x 32 =77.08 so, yes! My 75# guess was off the cuff but now it's calculated. Is 4 sticks and estimate?

For a K5 Blazer (M1009) I can see using more than 4 "sticks", especially if you want to retain the rear seat... One 12-16' stick would be your main "hoop" in the B-pillar, one 5-6' stick would be a diagonal in the hoop (not even meeting the minimum structural needs IMHO though) - two crossing in an "X" would be better, but would complicate getting in the rear seat by flipping the front seat(s) forward. That would only cover roof-crushing and side-to-side "racking" in the b-pillar area, wouldn't touch front-to-back racking, and wouldn't protect any back seat passengers. IMHO the initial polygon shape of the cage is easy and doesn't require much steel, but making it strong enough not to become a hazard (I have this awful fear of amputation/crushing by my own safety device construction), takes about as much steel if not more than the initial shape.

Side-to-side racking in a house "polygon" - it's "shear failure" without a break:

 

[mdeamicis]

For a K5 Blazer (M1009) I can see using more than 4 "sticks", especially if you want to retain the rear seat... One 12-16' stick would be your main "hoop" in the B-pillar, one 5-6' stick would be a diagonal in the hoop (not even meeting the minimum structural needs IMHO though) - two crossing in an "X" would be better, but would complicate getting in the rear seat by flipping the front seat(s) forward. That would only cover roof-crushing and side-to-side "racking" in the b-pillar area, wouldn't touch front-to-back racking, and wouldn't protect any back seat passengers. IMHO the initial polygon shape of the cage is easy and doesn't require much steel, but making it strong enough not to become a hazard (I have this awful fear of amputation/crushing by my own safety device construction), takes about as much steel if not more than the initial shape.

Do you think it is possible/practical, to build a cage that allows retention of the rear seat and does not make it a nightmare to get in and out of the rear seat via the normal method? And while still being reasonably strong to protect in the event of the accidental rolls and falls of every day wheeling?

I ask because this is exactly what I want to do. I am not planning to run balls out high speed desert runs nor competition rock crawling. But I do know how to wheel and have a talent for finding those off camber situations. I need a good cage to keep[ my family safe off the trail but my rig is a daily driver. And my days include riunning the kids to school and back home.

 

[tim292stro]

Yes, I do think it's practical/possible to build a cage that works for a daily driver. My above post was more to indicate it was going to cost more than 4-sticks of tube

Just a rough sketch, the orange bars go to the floor in the rear - this should be made removable. The green bars are behind the rear seat.


The red bars and blue bars are behind the front seats, and the red bars are removable.


A top view - green, orange, and blue bars are from the above pictures, The purple bars in the top picture are pressed against the roof, and running down the A-pillars.

The side-view, again the orange, green, and blue bars are from the above inside pictures. The red bar across the front door should be removable.


The removable bars make it more useful as as daily driver when out, and add structure when in.

 

[mdeamicis]

Thanks. That is **** stout.

 

[tim292stro]

Again, it's a rough sketch. Keep in mind that everything that isn't triangle shaped (the strongest shape in geometry) can deform in an event. Note that without any triangular reinforcement in the windshield area, the top edge of the windshield could be pushed inwards. This would impart a lot of force on the rest of the body, expanding either the head or foot-space in the front row. In my opinion the front row is the weakest portion of the cage design, where the bottom of the front door meets the bottom of the front fender doesn't have any structure below it. This is very hard to "fix" without eating up passenger volume - but some additional truss-work on the firewall and another bar passing under the front row sets to tie that corner into the bottom of the front row's primary hoop can fix that - it just may complicate driver's pedal location...

From the last side view, the orange and red bars are there to prevent the forward or rearward rotation of the primary hoops behind the rear and front row seating respectively. If you were to not have those bars installed in a roll over, the structure could be compromised and you could be pinned by bent steel if it folded onto a seat/row.

Keeping at least 4 triangles in a single plane, with two adjacent triangles to each triangle, keeps the plane from racking from just about any compressing angle on the same plane.

 

[tim292stro]

Found these on Flickr, from someone named Nick Anderson:

His story is that of the less than a slow roll... obviously. Look how much of the factory structure got compromised:




[EDIT:] This accident is also a good opportunity to see the front row cab structure at its weakest - note that where the front doors meets the rear fender bent, as did the b-pillar backwards at the top of the "bed-box". The back of the cab actually overrode the rear top also. This give allowed the A-pillar to fold back, taking the front edge of the roof down towards the dashboard.

If you could swing a pair of bars that went from the body mounts behind the front row seats, up to the top center of the windshield, this kind of collapse could be mitigated. The flip side is that by making the body more rigid, it will transfer more of the crash energy to the occupants, so extra padding, and shock mounting your seats would help, but this also complicates things. If you allow more movement to slow the transfer of crash energy, you need to have more space for that movement to occur, so this means the constraints on your cage design are much more severe. [/EDIT]

 

[olly hondro]

Yes, the A-pillar structure did not survive. I will focus there.Good info, thanks.