jaydubya

Eric - those pictures are GREAT! Your cage is very similar to what I was envisioning - minus the connection to the rear shock towers, which is illegal for my class. Do you happen to have higher-res photos? If so and you wouldn't mind sharing them, please email them to me, jeff dot weiss at utah dot edu.

A lot of the pictures in the pdf came from the tcdesignfab web page.

Cheers,

Jeff

Skip Wolfe

Do a search and you will find a couple good discussions about cage design - one with some FEA analysis that is pretty good. Also, are you running full steel doors? Keep in mind if you are going to gut your doors with NASA then you need door bars that protrude into the gutted door such as NASCAR style door bars or the pyramid based bars such as the 997 Cup cars have. I personally like the pyramid cross bars with the taco gusset as in the Cup cars.

jaydubya

Hi Skip - doors will remain steel and will not be gutted. I will use RSA style door panels.

"pyramid based bars" - do you mean the X bars with gussets where they cross?

Geo

What I mean is that the main hoop is being shown attaching about 3-4" in front of the plane of the front of the rear seat. Where the floor pan stops and the sheet metal rises about a foot to form the front of the rear seat. I'd attach (I did on my cage) the main hoop in this same plane (move the attachment back about 3-4" from what is being shown).

Yes, I meant the last set from the pdf. Easy access should be low on your list. Strength and stiffness should be high on your list. When you bend tubes you make them weaker. Sure they are reinforced, but I'd personally (again, I did) go with straight tubes in the X or NASCAR bars. The FEA that was done certainly changed my mind about NASCAR bars. They are much stronger than I thought, although the analysis including a direct perpendicular hit. I don't recall if it included a hit at an angle.

The "first set of door bars" where the first ones fully shown in the pdf document.

Geo

"Pyramid bars" are shaped like a pyramid laid on its side. It's an X that is not in a flat plane, but extends outward into the door cavity. It's sort of a hybrid X/NASCAR style.

JPhillips-998

They are primarily a BMW shop they work on a couple of 996/997 cup cars but will build cages for the plebs like us old 911/944 guys too. I haven't received my quote for the S2 but I'm hoping they go easy on me b/c I have never seen such nice work. The cages are finished to a level that matches exterior paint, welds are all 360* and perfect. They gave me great advice on bar placement/how/why/what each bar does. Got a good lessen on energy dissipation.

The owner runs the Rolex series

jaydubya

Gotcha - thanks!

Point taken. Given that the doors will stay intact, I'll probably go with an X.

bgiere

Here is Mark McMahan's site: http://www.rollcageguy.com/

He does Nonamakers and some other Rolex cars...Just had him do a cage for the 944 and it is perfecto! There are some decent 911 cage pics there.

jaydubya

Thanks Brant!

Jeff

jaydubya

Any advice for tubing diameter and thickness? The shop is suggesting 1.75" diameter by 0.095" thick, which seems to meet requirements for PCA, SCCA, etc.

Geo

That's stronger and lighter than 1.5 x 0.120". However, you cannot make quite as tight a bend with it either (r=5.25" vs. r=4.5"). Like most things there are trade-offs.

JoeMag

If you are going to have steel doors with door bars still in tact, just flat X across door opening. Not pyramid one (which probably would not fit). It's strongest and lightest. Like Earlyapexes.

jaydubya

Sounds good, will stick with the X.

Seems like they knew the proper tubing to use, that's a good sign...

joseph mitro

i don't like the "knee bar" in any cage. it's way too low and is a potential threat to your lower body. in my BMW 325 (and most BMW racecars I've seen including the ones at tcdesignfab.com) the knee bar is replaced by a dash bar going behind the dash. i mounted this successfully in my car but i don't know how it would work in a 911

lighter by how much and stronger by what definition? i have 1.5" by 0.120" and i think with proper cage design and gusseting, "stronger" is a relative term

kurt M

1.50 X 0.95 is 1.426 per foot. 114 pounds per 80 feet
1.75 X.095 is 1.679 per foot. 134 pounds per 80 feet
1.50 X .120 is 1.769 per foot. 141 pounds per 80 feet
1.75 X.120 is 2.089 per foot. 167 pounds per 80 feet
i like to think in 80 foot batches as this makes the real weight savings or weight cost more relatable.

The thought is that 1.75 X .095 dia tubing is stronger pound per pound than 1.5 X .120 is in the fact that it has a larger cross section and is a geometrically better shape. If space is not a factor and you have to use 1.5 X .120 or better then 1.75 X.095 might be used to make a slightly lighter cage that will be slightly stronger too, all other things being the same. As you see the weight delta between 1.5X.120 and 1.75X.095 in an 80 foot batch is only 7 pounds.