Roll cage questions

I din't make any assumptions other than a generic steel density. I answered with good, factual, and representative numbers and without getting into full engineering analysis - I added a number of listed tubes just because i thought some might find it interesting. either 1.5 095 or 1.75 080 is a fully legal tube size per SCCA 2699# and under.

Luckily the club doesn't allow crazy tubing sizes. you'll note the thinnest allowed wall is 0.080" - likely to avoid the under-thought engineering shenanigans you suggest I'm proposing.

most cage failures I've seen have been related to the weldments, and I've seen too many - so a good fabricator is the key to a safe cage, the allowed tubing sizes are ALL adequate for the task when built correctly.
 
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Taking the car to the shop this week to get the cage put in. Weighed the car tonight and it's 2480 with me in it. That's with stock driver's seat, automatic transmission, stock wheels, stock gas tank, stock exhaust, stock suspension, and lots of extra pieces on the stock motor. Have to add back in some weight for a lower front fascia & splitter, thicker sway bars, and other misc stuff. I figure subtract maybe 50 lbs from the 2480 to 2430. ITCS weight is 2630.

The cage in the current tub has 61' of tubing. Using 1.5" x .095 tubing that weighs around 87 lbs. I'm thinking it'll be another 20-30' of tubing to have all the additional stuff I want done. 90' of tubing is 129 lbs. Looks like I should have enough head room to do whatever I want to the cage.

Thanks for all the info. I'll take some pics when I get it back.

David
 
DavidM said:
Taking the car to the shop this week to get the cage put in. Weighed the car tonight and it's 2480 with me in it. That's with stock driver's seat, automatic transmission, stock wheels, stock gas tank, stock exhaust, stock suspension, and lots of extra pieces on the stock motor. Have to add back in some weight for a lower front fascia & splitter, thicker sway bars, and other misc stuff. I figure subtract maybe 50 lbs from the 2480 to 2430. ITCS weight is 2630.

The cage in the current tub has 61' of tubing. Using 1.5" x .095 tubing that weighs around 87 lbs. I'm thinking it'll be another 20-30' of tubing to have all the additional stuff I want done. 90' of tubing is 129 lbs. Looks like I should have enough head room to do whatever I want to the cage.

Thanks for all the info. I'll take some pics when I get it back.

David
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David - just for sake of reference, what do you think you weigh?
 
I'm a skinny bastard at 165. That was shown by the scales. Car was 2315 without me. I'm rounding some. Think it was actually like 2482 with me.

David
 
DavidM said:
I'm a skinny bastard at 165. That was shown by the scales. Car was 2315 without me. I'm rounding some. Think it was actually like 2482 with me.

David
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Hmmm... I would love to know what the car weighs with the manual trans and all the extras stripped out. I've been thinking of trying to find a coupe to move into; have always heard they're considerably lighter, and by your calcs that sounds like the case. My hatch was 2680 with me in it last year; I was right around 250 (in driver's gear) at that time, and with ~60' of 1.75x0.095 tubing it sounds like there is about 100 lbs of cage in the car. That means the car started at around 2330. If you're right, and there is another 50 lbs or so to come out of yours, that means the coupe is a good 60-70 lbs lighter than the hatch.

OTOH, if I just got serious about getting the lead out (of the driver) and dropped those last 25 or so lbs of lard, and then could find another 10-15 lbs to come out of the car, I would be right there anyway...
 
The hatch was aproximately 100 lbs. heavier than the coupe, If I remember correctly from back in the day, when I built mine. You should be able to build a hatch easily to the minimum weight. Might even have better f/r weight distribution. The drawback is that that weight is high up, and I think the coupe has slightly better aero numbers.
 
Dropped the car off at the shop yesterday and chatted with the guy who will be building the cage for a while. I also looked at a cage they had just finished. He was saying they typically put the top door bar about 1/2 to 2/3 up the door. I've seen other people's cars with the door bars at a similar height. The current cage has the top door bar at the very top of the door.

I kinda like having the door bar higher as there's no way something could hit the door without hitting the cage. It does mean that I have to crawl in and out the window. The front of cars are typically low to the ground, though, and in a T-bone lower door bars would work fine. It might make getting in and out a little easier.

Thoughts?

For the most part I was thinking the same thing as the cage builder. The door bars were the only piece that was a little different.

David
 
noses on modern cars are a bit higher than on older sportscars. even miatas have a pretty high beak. top bar ~2/3 should be good, egress is important, too. If you have to add weight, a 3rd bar along the door bottom is a good addition. tie it to the other door bars with verticals for a really strong "door"
 
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