Posting pics of Roll Bar attaching base

[Albert]

Thanks for the input guys

[breakaway500]

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[Albert]

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[jlwhorf]

Also, wing nuts might not be the best either.

[962porsche]

you guys are just wrong ! funny as hell but wrong LOL !

I'm sure that is just a mock-up ?
but that is not a good way to install a main roll hoop . you want the hoop to be all one piece to welded foot plates . from the foot plates you then can bolt the plates to the chassis . using a grade 10 bolt for that would be best but you could use a grade 8 depending on the size of the bolts them selfs . with a backing plate on the under side of the floor or chassis rail .

you can use slip joints and bolts for other roll tubing joints on a roll bar or cages but they should never for a main hoop .

if you were to use a slip joint for another section you would want to use 4 bolts at each joint with two bolts going thru one end of each tubing .

[brucesallen]

the luggage carrier is a sufficient roll bar. At least it is metal.

[dinoracer]

Al

I think you're on the right track. After seeing these pics, and reading your PMs:

1- I like this approach better than the fancy weldments on your Corvette pictures

2- Close tolerance fit is best between main hoop OD and foot tube ID, but holding the dim between the hoop legs will be tough. Plan on a horizontal member at shoulder harness height, and a second cross bar right above the two pockets, to hold the dimension between the two legs

3-Two grade eight bolts each side to hold in place

4-Of course still need two legs going back, fixing them to something solid also

5- The hoop uprights must bottom on the plates , not be held up by the bolts

Tom

[962porsche]

the chief of tech is giving his ok for doing this and it is totally his call as I have nothing to do with tech with comscc .
how ever I build bar and cages for a living and it got me to do some testing of this type of design as it is described . keeping me up until 3:30 AM doing so .

I took the measurements from a MGB in my shop now and using 1.75 dom .140 wall tubing and built a bar with rear legs on CAD to the spec given and to the high of the clothe top .
butting the main roll hoops legs until they bottom out is only one out of 6 regular force loads a roll bar could and will see in a crash .
the big thing that is missing is triangulation in the structure . by running a harness bar then running another bar parallel say 5 to 6" up from the bottom of the legs only makes a box . this will work ok kind of for a side impact but in a roll the force is placed on the upper part of the roll bar . 2400 lbs of force is all it took to start to bend the main hoop . a simple test for this is to take a cardboard box and cut the two ends off . the box folds right up flat .
running a diagonal bar from the top of the hoop on the left side to the lower hoop on the right side did help some .
but because of the hight and width of the main hoop on a MGB it was not much better with the problem being the lower legs and what your looking to do with slip joints there . it makes the diagonal bar to parallel to do it's job as it should .
on a MGB you have battery boxes at the rear behind the seats . there is very little mounting area for the rear legs and it's only to thin sheet metal or you have the inner wheel houses . the wheel houses are better but not good if your looking to get the needed triangulation out of the rear legs of the bar .

I then built a dubble slip joint out of the tube that would be used for a bar of your cars weight . drilling holes 4" apart and clocked at 90 degrees from each other using grade 8 hardware . I then placed them between the two puling towers of my frame bench and . they pulled apart by the gauge on the towers at about 17 thousand LBS .


what it all comes down to is there are reasons why roll bar CO. and people like my self do not build bars and cages with slip joints on the main hoops for a reason .

if all this it to pass a broom stick test I would rethink playing with a main roll hoop to do so .
a better way is to drop your seating lower in the car . you can buy a race seat and a simple bracket remove 4 bolts and swap out the seats . a racing seat is 1st safer for you and it will let you feel what the car is doing under your ass and it will hold you in place unlike the seats of a MGB will do .
but it's the call if COMSCC's tech like I said I only build cages for a living .

[Albert]

Thanks for your thoughts on this topic as I have expressed to you in our personal conversations as well.

I do intend to use a Kirkey aluminum racing seat as several folks from the MG Motor Sports forum that I also belong to have suggested. I will also be using a diagonal brace to triangulate the roll bar structure . As far as the location points being inappropriate for mounting the rear supports, these locations have been used by MG racers for many years and to my knowledge have never amounted to a weak point in the roll over protection on the MGB. Auto Power brand, one of the nation's best roll bar manufactures as well a Peco, Safety Devices and several other brands that I have seen over the years all use the back shelf area that I am planning to use as their preferred location points.

Rather than being a weak area area the fact that the horizontal shelf meets the rear bulkhead at this point makes this location a logical locating point. If you look below the floor from the exterior on the MGB you mention you will also notice the angle braces that MG have welded into the monocoque structure. The strength of the rear shelf/bulkhead area of the MGB has long been recognized as one of its principal reasons for the overall strength of the car.

I am further planning to run a forward diagonal bar from the horizontal harness bar which will fasten to the transmission tunnel just rear of the console. This is another very strong area due to the arched construction of the tunnel/cabin floor area.

All mounting points would have substantial backing plates like the ones that Auto Power provides as well. And all mounting hardware will be grade 8 or better.

You can be sure, considering its my body in the car, that I will be constructing a bar that will meet or exceed what is required.

Actually, except that the bar mounting I'm proposing is removable, the overall structure is not unlike the Miata bar on your Facebook page that you suggested I look at.

While this is an "evolving" plan I very much respect your input and those of the MG Motorsports community.

As far as your comments that a racing seat "will give me better feel of what's happening under my ass" as you say, I have a pretty good idea of what a race car feels like in that part of my body both in my experience running with COM where I had all second place finishes and one first in class (in the wet at Bridgehampton) and from my experience driving an SCCA Sport Renault, Formula Ford, X 1/9 and my SSC prepared Honda Civiv SI.

Again, thanks for your thoughts. And as says at MG, "Safety Fast!"

[962porsche]

just because I build cages in no way means I also don't install other makers bars and cages too .
the reason why they have the rear legs mounting to the sheet metal and not to the inner wheel houses on the MGB's is because if the top and how it folds and unfolds .
when your dealing with a street car you have to make certain compromises so the best way is some times not a option .
if you have to have a mounting point go to say the sheet metal of a floor instead of say the top of a rocker it in no way would be as strong as it will be to a welded plate on a rocker then it would be as a sandwich plate with sheet metal .
building and repairing race cars I have seen sandwich plate tear the sheet metal of floors .

it states right in the SCCA along with every other rule book I looked in from racing sanctioning body that the main roll hoop be constructed all of one piece to welded foot plates with no seams and cut outs .


COMSCC has no rules for building a bar or cage . all they tell you is in some classes you have to have one .
so you could in theory build one out of exhaust tubing to meet the rules .
with enough cross bracing and tubing you could even make a exhaust tubing roll cage safe to a point .


with a spec Miata seat sitting on 3/16 plate in a MGB and the top up I have a good 6" of clearance to the rail of the top frame . the only problem is the steering wheel of the 1968 MGB is like a bus so I would get a small wheel .
I'm 6'2" tall and a 20 degree lay back seat would give me more head room .
so why would you need to alter the autopower bar ?
I have never had to do this for my customers I have installed the io-port bars into there MGB's all I have had to do is drop the seat height by swapping out seats to a racing one . then by doing so you also get all the other pluses a racing seat give you .

this is all totally pointless as it seams you got the ok from the COM's tech all I'm saying is as a builder and installer I would not do what your thinking of with a main roll hoop . so have at it your going to safe !