sill bars

do sill bar have to round tubing ?
can they be square tubing ?
with the cage built on them

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!

That is a grey area. I've done that and personally have no issues with it if the sqaure tubing is of proper thickness and size . It needs to be welded in quite well on the ends and stitched along the sill.

Mark B ????

No I won't pass square tubing, and the rules are not intended to allow square tubing. Square tubing has a farily wide variation in strength depending on the angle across the the tube's cross section at which the load is applied, and the collapse of the tubing is more unpredictable as even small variations in applied load angle will significantly change the loading of the material. Round tubing has the same strength and collapse properties for loads coming in at all angles around the tube.

So, square tubing is really not appropriate for general field fabricated roll cages; it migth be OK in an engineered cage but even the engineered solutions don't use square tubing that I know of. The rectangular tubing used in applications like NASCAR are really the frames, not the cage.

Ed, remind me again, what are you werkin' on? If it is a pickup, then we need to get together and work on how the cage gets supported and the cab and frame and cage get tied together.

i'm working on a fox body (1990) mustang
i want to run a sill bar at floor level from front wheel well to rear bulk head (kick plate)
then build the cage up from there.

round is fine but the square would fit the car tighter.

i don't plan to start on the cage until this winter or early spring
i'm planning to run rally wv this summer

when do you plan to be up this way ?

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!

Do both! Problem solved!

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Grant Hughes

Like Grant said....install the square tubes to reinforce the frame, and then the regular sill bar in the cage. If the new frame reinforcements are 1/8" thick wall, and the box size is large enough, then it will be similar to a box on the floor on which the cage is mounted, with one side missing. It just needs to be welded into the body 100% around where the cage mounts. And we'll have to look at the width of the box where the cage mounts; if it is too wide, it might collapse with a hit on the roof, and would need some added reinforcement there.

Went through your neck of the woods last week in the usual hurry and am going through again this week (exact day is TBD). That seat has a 1992 FIA sticker so I am not sure you want it...but it's yours if you do. It won't pass NRS tech without a 1999 sticker so it would be OK for runnin' around or non-NRS use.

my thought was to use 2x2 or 2x3 .095 wall square tubing as the sill bar
then weld the cage from there.

or drill holes large enough for the main hoop and a pillar bars to pass through the square tube and then weld it to the bottom as well as the top of the square tube

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!

.095 makes sense for the reinforcing tubes; no need to have 1/8" for that. It is probably easier to just plate over that area of the reinforcing tube and tie in the area. Maybe I'll stop by and we can figure it out. We'll be going back and forth to KY several times in the next month.

my other thought was to 1/8 plate where the cage would be welded to the square tube
its all still in the planning phase right now

i miss the bolt a cage in and go days!

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!

My thoughts exactly and run the plating down the side and onto the floor and lap up onto the B pillar a bit perhaps. 2 right angles of 1/8" might do it; depends on the shape of the area.

Yep, a lot more work. We have become so much smarter....or something.

we got some time to work it out
make it strong and safe

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!