Benton

John and George...
I think you two have different definitions of head tubes. John is referrring to the arch connecting the top of the two a-pillar tubes, and George is referring to the tube connecting at the node of the X and harness bar to the middle of the front bar (between top of a and b pillars). Correct?

I notched the tubes with a cheapo hole saw notcher from ebay. Not the fastest, but it worked.

Adam Richman

George, I went out to the garage to look at the 944 and saw what you meant. I hadn't remembered the a-pillar bend starting that far back. You are worried about your size? Heck, I think a tube laying the way I described would only work for Plastic Man Going back to comprimises, I know you don't like the nascar-style door protection but there would be a value - because the tubes run out, it provides a much larger opening to exit from my way of looking at it. Trade-offs ...

On your concern of the seat allowing your body to contact the tubes, that's my concern as well. I hate to say it but I doubt there is really any distance we can put them that would completely remove that possibility. Its almost worth considering the wrist leashes even in a closed cockpit car. I know that in my wreck, my left arm was slammed into the doorbar and I had a distinct sense that it was coming in towards me (and on later inspection, this was exactly what happened). So, I know for myself, the big concern is being driven into the tubes as they are driven into me. I do think you are very wise to have that lengthwise tube from the main hoop to the front tube - the RX7 in particular seems very well suited to punch in that gap (would think 944/924s too actually).

Red, I thought John was just pointing out other variants of the same concept applied in different locations. ??

fatbillybob

"I'd rather not trust "DOT" strengthening at 150 mph." Well car was designed for 150mph so the oems never thought of that? Also you do have apiller tubes in fact 2 for them. Three, what are you trying to protect in your car in that part of a rollover...your knees? rollhoop is what does the main job. Take a look at the cage design in a radical SR3. Sloping to the dash tube nothing like a jeep cage.

"just repeating what you have read on message boards" Doh low blow...hey I've got a tube bender too just like you...

"you didn't look at the pictures much" How about looking at my picture. My "x" pic is different from yours. It will follow the seat outline from head to toe. Yours starts at your harnessbars which I assume is about shoulder level or less if HANS equiped

Anway, I'll go hide in my cavenow. REember my name when I finish my cage you can bash me right here on Rennlist.

Geo

fbb, don't sweat it. I really think discussions such as these are really worthwhile. Learning about cages is sometimes very difficult. There are so many ways to construct them (most of them bad BTW) and so few texts dedicated to the subject.

Benton

Dude, chill out. No need to get an attitude about it. You critiqued my cage, can I not critique what you say? The X in your picture is not exactly synonymous with what you described, so before you go bashing me, proofread what you said. The beltline to the harness bar is approximately 15 degrees downward.

About the OEM deal, sorry, but I'm not following you on that. A 928 is a GT; it wasn't built with the race track in mind. Nor was any other production car for that matter, as it is not practical to build a full-blown roll cage in a production vehicle. "Adequate" comes to mind when I think of crash testing. I don't want "adequate" protection from crash testing when I'm going through turn 12 at Road Atlanta near 100 mph. Just look at, say, a BMW M3 GTR. Originally, the M3 was designed by BMW to meet crash standards. Does that mean BMW should not implement a-pillar protection into the GTR? I'll leave that as a rhetorical question...

George,
I tested out the opening today, and I think I can get out fine. Going back to what I said originally, though, is that I wouldn't be able to get out safely if my seat had a halo. I'll take a picture tomorrow of the opening and see what you guys think. I'm really on the fence as to whether I should delete it. I can't make it closer to the dash, as the dash wouldn't fit in if I did that.

Benton

Another question... should I add a tube from the base of the main hoop to the base of the front tube like Adam describes?

Geo

Hard for me to say. I looked at your first photos and it's hard for me to tell how much room there is between the rocker and the middle of the X. It looks like you won't need it, but I can't quite tell. I have it in mine. But my X was higher than most due to the mounting points.

Dave in Chicago

All these X-Door-Bar installs are making me jealous. I had to be a bit more conservative and compromise as the car still goes to the office most days in between events. Maybe I'll add the other bar in the future...

But life is full of compromises then, isn't it?

Benton

That's a really nice car, Dave. I've always loved the F-stock 968's.

RedlineMan

Re: "Head Tubes"

As in header, as in windshield header, as in the top of the windshield. As opposed to a central roof intrusion bar, seen in my VW cage to meet the ice racing rules.

Geo. I think you are refering to this type of side brace creating another fulcrum at this point?



That could be. I look at it this way; I have substantially shortened the longest unsupported length of tubing on the whole cage. This must be good. It also does not effect ingress/egress, vision, or anything else, and adds head containment. These are also "halo-friendly." It also supports the area right over the driver's head, which should be the focus, not over his knees.

I feel these bars do a lot of good without negatively effecting any aspect of LIVING with the thing day-to-day. The 944T they are in is quite easy to get in and out of for very large me or the slightly shorter but older and less flexible owner.

Adam Richman

John, in the above picture, the side brace you have pictured is bent, I am curious as to your decision to do this. Was this out of a concern/desire to have it join pysically at a junction point on the bottom of the A-pillar tube or was it just to give the driver's head/seat more clearance or were you working w/ a main hoop that wasn't put in w/ this consideration at the onset? It strikes me that the bend, for the purpose of the bar, _somewhat_ takes away from its effectiveness (not that its not much more effective than nothing being there).

RedlineMan

Re; Door bars;

I have always built my cages with sill tubes to protect as Geo is thinking about.

4 is the sill tube.




Makes a really great foundation for everything that you would like to be strong to "grow" from. Tree roots if you will.

Geo

Yes, those are the tubes I'm referring to. I would assume the pro teams have done the calculations on the effects of these tubes, but you never know. But as to your point, I'm not so sure they effectively shorten the tube. This is not meant as an argument, but rather a discussion/concern. Take a pencil and secure one end and place a force on the other end. To a certain extent it will give and flex. Introduce a hard point to the middle of it and will it be more likely to snap or to hold? I think the answer is "it depends" but I'm admittedly not a professional engineer. I know we have some here and am a bit disappointed none of them entered the discussion.

As for adding support over the head or the knees as you say, we can disagree there about the effect. I simply say if you support the top of the a-pillar those side tubes are less likely to collapse around the driver's head.

BTW, I went to the site the Aston-Marton photos were from and actually found quite a lot of BTCC, ETCC and other big-time pro teams supporting the a-pillars in this way (as well as the tubes we were talking about above).

DK

Re: low front tube: 'knee buster', mine was done under the factory cross tube, and once braced and secured, removed the factory cross tube (it's not even close to a valid roll-bar spec obviously)

Pics are big, so just hit the links...

http://www.eaglesledge.com/images/Or...PIA39B%7E1.JPG

http://www.eaglesledge.com/images/Or...PIA39B%7E1.JPG

'79 Euro +/-
'80 SC +/-
www.eaglesledge.com

Dave in Chicago

Thanks Mark. I like the 968 too. Now I just need to work on making the car much faster, driver much faster, or both