Quick, need thoughts/opinions on sand rail cage

I posted this in my build thread but my sawzazall finger is getting twitchy and I need to decide what to do.

Just about done with all fabrication mock up and I have to make a choice. The red bars (top) are the existing roof bars. When in the seat with helmet on, I have clearance but if I lean forward the helmet will impact about where the yellow circle is, kinda too close for comfort and proably wont pass the 2" rule. My thought is to cut the top bars out and then reinforce the fore and aft hoops with the green bars. This is autox only so rules wise it will suffice but before I start cutting Im open to other theories.

So, you're basically going to convert your "cage" into a roll bar. The windshield frame won't have significant strength, I'm not sure those new front bars are going to do anything worthwhile since they're going straight to the point where the frame will bend anyhow. If you want them to help, put them higher up. It's still not going to do much though.

The rear portion should be pretty good.

Keith Tanner wrote: So, you're basically going to convert your "cage" into a roll bar. The windshield frame won't have significant strength, I'm not sure those new front bars are going to do anything worthwhile since they're going straight to the point where the frame will bend anyhow. The rear portion should be pretty good though.

Essentially correct Keith.
Yeah, I don't like the front, there's no real good way to brace it that doesn't get in the way of ingress/egress but Im open to suggestions if there's a better way. I guess going higher up on the "window" frame might do something. Might just look stupid and do nothing though. At that point actually the windshield frame is pointless so maybe I cut it off down to the steering wheel mount and be done with it (close to the inspiration vehicle but with a more useable roll bar)

If you cut the front hoop off, you will lose torsional rigidity. Why not cut the top bars out and replace them with bars that are set further to the outside of the hoops? I never understood why you would want a bar directly over your head.

Don49 wrote: If you cut the front hoop off, you will lose torsional rigidity. Why not cut the top bars out and replace them with bars that are set further to the outside of the hoops? I never understood why you would want a bar directly over your head.

I had considered it but the vehicle is too narrow, there is no part of the hoop that's really not overhead. I agree with you on not having bars over the top of my head. I could move them both toward the center a bit more but Im not even sure that corrects the issue enough.

Cut off the red, the windshield and the steering support. Use the top 6-8" of the windshield (for the bends) to replace the steering support. Run bars from the horizontal white part (where you have green hitting the rear hoop) to the base of the steering mount (at the top of the side rail). Run two tubes from you beam outer edges to the center of the steering support above your feet.

yeah, I'd be worried about addition chassis flex with those two bars gone. Since they appear to be one piece all the way to the rear bulkhead of the car, they appear to be a fairly significant part of the substructure.... is there a way to "move" them as suggested?

nocones wrote: Use the top 6-8" of the windshield (for the bends) to replace the steering support. Run bars from the horizontal white part (where you have green hitting the rear hoop) to the base of the steering mount (at the top of the side rail). Run two tubes from you beam outer edges to the center of the steering support above your feet.

I was just looking at that possibility since the squared off corners that would be left would be less than ideal. Unfortunately everything angles in to the top so the top part of that bar is not wide enough to move down and be a new steering support.

mndsm wrote: yeah, I'd be worried about addition chassis flex with those two bars gone. Since they appear to be one piece all the way to the rear bulkhead of the car, they appear to be a fairly significant part of the substructure.... is there a way to "move" them as suggested?

'fraid not. As I noted above its too narrow to move them in or out and find a part where they wouldn't make contact. Their current location is probably as good as it gets as they are not directly above my head but set inboard a bit so technically if my helmet did hit it would glance off the side.

I actually went back out and played with seat location and such and I think I'll be ok. Gonna leave the bars in place for now I guess it's not ideal but short of bending up a new frame (quite a trick with no bender) I don't think there's a lot of room for improvement.

Another angle for those who are noodling on this.

What about cutting your red bars out and welding them back in swapped end for end, so the bend is in the front?

oldopelguy wrote: What about cutting your red bars out and welding them back in swapped end for end, so the bend is in the front?

Then they would be too low in the back. My helmeted head tucks right in that spot with just enough space around it, kinda like they designed it that way, probably because they did :)

Not sure how this would work with your rule set, but what about tying the windshield frame to the roll bar with Caterham style tubes? They use a sort of cross brace modified X on the inside, and bowed outward tubes out on the corners. You might have to modify the particulars for your chassis, but here one is to give you an idea.

That picture is hilarious. Big beefy roll cage connected to spaghetti.

As flat as the caterham bars are, he'd bounce his helmet off those waaaay too quick.

mndsm wrote: As flat as the caterham bars are, he'd bounce his helmet off those waaaay too quick.

Yep I think they'd just exaggerate the issue. Although I see what he's getting at, if the 2 bars up top were arranged in an X then there'd be a nice open space for me NOT to hit as I move forward.

At this point I'm waffling between just leave it as is, or remove everything forward of the rear hoop and just make sure the rear is beefed up enough to make a good roll bar. Remember this is not going off road anymore it will be a ground scraping autocrosser with very little chance of rolling.

I'd sure add some serious triangulation crossbracing to the top of the front area, between the torsion tube/shock mounts and the base-of-windshield bar. I think you'll really need the torsional stiffness. Personally, I like your green bars, too - maybe a bit bigger on the rear ones i. e. higher on the roll bar to closer to the front, while still allowing easy in/out. I'd add a diagonal bar to the main rear roll hoop, too - triangles are good things!

My solution was to notch the seat so it sits VERY low in my frame.

Pedals are adjustable

Cut the windshield tubes and section in another six inches to raise it up.

Move both red bars inward a-la T-Tops? Looses some torsional, but might help. Alternately, and much more awkwardly, going out along the radius of the corner bends?

wheelsmithy wrote: Move both red bars inward a-la T-Tops? Looses some torsional, but might help. Alternately, and much more awkwardly, going out along the radius of the corner bends?

Discussed above, too narrow, no matter which direction you move them they are still a potential head bashing hazzard.

Woody, I think sectioning in tube on that front hoop makes a questionably weak structure even weaker, at that point I might as well go with plan A and just remove all the forward stuff and just go with only a roll hoop in the rear.

JThw8 wrote: Woody, I think sectioning in tube on that front hoop makes a questionably weak structure even weaker, at that point I might as well go with plan A and just remove all the forward stuff and just go with only a roll hoop in the rear.

Add some sleeves inside the tubes.

The seats in my rail are flat bottomed and bolted to the floor. I can't get any lower than that. If I were you, that would be my first area to look into. Leaning the seat back a little may also be the easiest solution to your problem. If that doesn't work, I would cut the vertical bars for the front hoop and add in a few inches.

Can you lean far enough forward to hit your helmet on the tubes when belted in? When in your normal sitting position is the top of your helmet at least 2" from the TOP of the cage? If the answers are no and yes respectively I would get some cortizone cream for your sawzall finger.

bgkast wrote: Can you lean far enough forward to hit your helmet on the tubes when belted in? When in your normal sitting position is the top of your helmet at least 2" from the TOP of the cage? If the answers are no and yes respectively I would get some cortizone cream for your sawzall finger.

Strapped in probably not (belts not installed at this point). 1.5" clearance, not 2"

ncjay wrote: The seats in my rail are flat bottomed and bolted to the floor. I can't get any lower than that. If I were you, that would be my first area to look into. Leaning the seat back a little may also be the easiest solution to your problem. If that doesn't work, I would cut the vertical bars for the front hoop and add in a few inches.

Mine are flat bolted to the floor as well. My floor sits on top of the tubing, I may need to sink the seats down into the tubing to get the extra inch or so I need. Laying the seat back would involve the same level of cutting stuff out and reworking as sinking them into the floor so either way I guess. Still just tempted to cut the whole mess forward of the rear hoop out. The design all along was to make a 2 seat formula Vee, those dont have full cages either. It would also drop my CG by a little bit.