Auto Power Industries/DSE/Tiger Cage

[Ron Sutton]

Sieg,

I thought I saw saw engineering numbers on this site after someone installed frame connectors. But, I don't have anything quantitative. I got to see a Pro/Stock car on GM's test equipment, simulating forces, to see where it flexed & didn't ... which was very helpful ... but nothing with stock bodied cars.

I know the frame connectors, when welded in, add a degree of stiffness. And when the roll bar utilizes braces from the main hoop ... under the cross bar ... attached to frame connector ... the roll bar is much better prepared to withstand roof impacts ... than compared to just welding plates to the sheet metal.

Running door bars at the correct height and effectively making this an 8-point roll bar is going to raise the level of safety while improving the torsional rigidity of the chassis quite a bit.

I just can't put a number on it.

[Sieg]

Thanks Ron.

[Ron Sutton]

I'd like to add ...

If i were installing a 4 or 6 point roll bar without door bars ... or a 4, 6 or 8 point roll bar with door bars ... but not a "roll cage" ... I would use 4130 Chromoly for ultimate strength ... and mount to as many frame structure points as I could.

[Track Junky]

Ron, I'll be using fiberglass doors for next season. Would love to chat about door bars.

[Ron Sutton]

Originally Posted by Track Junky

Ron, I'll be using fiberglass doors for next season. Would love to chat about door bars.

Gotcha. Do you have a roll bar now without door bars?

If yes, post some info on it ... brand, diameter, wall thickness, material, bolted or welded in ... and photos would help.

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A couple of quick tips:

a. You typically want it to connect to the main hoop at the bend, in line with the bar behind the seats. But this is just a starting point.

b. Ideally, you want to run the lower mount as far forward as you can, to create a wide "truss-like" footprint.

c. After you mock up some plastic sprinkler pipe at these two points ... we need to see if we run into "packaging problems."

d. We want to make SURE the door bars don't interfere with your ability to steer the hot rod. because seat height, door bar height & driver height all play a role ... i never know until we mock it up.

e. Often times, the bar is too close into the driver's seat (passenger too) and putting a bend in the door bar, with the curve "out" ... provides more driver cockpit room.

f. At the other end, we simply need to make sure it doesn't interfere with your feet or pedals.

g. Don't put a downward bend in it if you can avoid it. Especially in a track car. The improved strength & safety of having the bar at the right height outweighs the inconvenience of climbing over the bar.

h. I like to use 4130 Chromoly for door bars, regardless of what the main hoop is main of. Chromoly welds to mild steel just fine & the increased driver & passenger protection is worth the small difference in tubing cost.

i. I typically use the same size of tubing for the door bars as the main hoop ... 1-3/4" or 1-5/8". An exception would be if we need to go down 1/8 or 1/4" for clearance purposes. If you use 1-3/4" or 1-5/8" diameter Chromoly ... .083" wall is good. If you drop down to 1-1/2" diameter ... bump the wall thickness to .095"

When you post the info & photos we'll be able to discuss more.

[Simmo]

Hi Ron,

With reference to point g. - what are you're thought's on triangulating the downward bend a in this image? Seems like a good compromise strength/ergonomics.

BTW: Really been enjoying reading - and re-reading your posts!

[Ron Sutton]

For chassis strength, the triangulation of the door bar makes up for the bend & then some, making it stronger.

But often the door bar being lower doesn't offer as much side impact protection in a crash. I say "often", because it all depends on the height of the bar versus the people in the seats.

Ultimately, for safety, you want the door bar to prevent things ... cars, telephone poles, ends of concrete barriers, etc ... from coming in & hitting the driver or passenger in side impacts.

Stock Car style bars with uprights & 1/8" plate work best & Pro/Stock X-braces work well too, but both require people to "crawl in". For single down bar with braces, I prefer the structure & placement in this photo.