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CSPTK
01-06-2004, 02:03 PM
I have a question about cages, and mods that actually work.

I have a Spec Miata (yeah, who doesnt!) that I'd like to stiffen a bit and I have a couple ideas.

Many people add a "Petty bar" from the main hoop near the drivers head, down to the base of the leading edge of the passenger door. Good proven design, 'nuff said. But I'd like to leave space for an occasional passenger seat.

I've also seen some cages built with a diagonal bar going from the main hoop near the drivers head, over to the top of the passenger a-pillar (along the roofline). Is this method effective in adding rigidity and tosional stiffness to the cage?

Also, I'm looking for thoughts to adding another bar going from the same point on the main hoop (near drivers head), diagonally down to the right rear, attaching near the top of the shock (tied into existing support).

These two ideas together seem, in theory to be ideal...but I'm not a cage builder....

Thoughts?

Thanks,

Tom
Finger Lakes Region

joeg
01-06-2004, 02:24 PM
I refer to the first bar as an "anti-intrusion" bar. It would keep things out of the driver's compartment if you are laying on your side. Will also offer a degree of stiffness (as would trianguating any are of the cage structure).

They are actually required by some sanctioning bodies.

The traditional"petty Bar" is probably going to offer more stiffening.

As long as the second bar you describe goes to a legal mounting point(not beyond the eight you are allowed), it will help also. Once again, triangulation is the key.

Cheers.

racer_tim
01-06-2004, 02:26 PM
Both of those work to add regidity. But you pay a price for the extra weight. I'd check how much weight you have to "play" with, then go from there.



------------------
Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html

Knestis
01-06-2004, 04:41 PM
I read an analysis a long time ago that suggested the roof diagonal that you describe can do a LOT for torsional rigidity.

I'm getting one as soon as the sunroof comes out - first thing in the transition from SSC to ITB.

K

gsbaker
01-06-2004, 05:27 PM
Originally posted by Knestis:
I read an analysis a long time ago that suggested the roof diagonal that you describe can do a LOT for torsional rigidity.
K

Yup, this would vastly increase the torsional rigidity. Even better would be two roof diagonals that formed an X, making the rigidity symmetrical, but that's probably overkill and not worth the added weight.

(I can still hear my old structures professor lecturing on bridge design and triangulation.)

Of course, the perfect setup would be 4 Petty bars on the inside, but you could never get in the car. http://Forums.ImprovedTouring.com/it/smile.gif

------------------
Gregg Baker, P.E.
Isaac, LLC
http://www.isaacdirect.com

kthomas
01-07-2004, 11:40 AM
That's weight up high. Probably do more harm than you'd ever notice benefits from. It ain't like you can adjust your remote reservior shocks to account for the extra stiffness!! Bwah Hah!!!!

Seriously, the guys up front aren't winning because of their superior cage- they're winning because they can drive. Now if you want to mod the cage to make it safer that's another discussion.

------------------
katman

CSPTK
01-07-2004, 01:34 PM
Originally posted by kthomas:
Seriously, the guys up front aren't winning because of their superior cage- they're winning because they can drive.

Gee, really?! Thanks for that great leap in insight. I never would'a figured that out...work on the driver, the nut behind the wheel, yada yada yada.



Now if you want to mod the cage to make it safer that's another discussion.
[/B]

Well, consider this "another discussion" (the original one for those playing along). I never mentioned that I wanted to stiffen the cage so it would "help me win", improve my driving, etc. You misunderstood my original post, sorry if it wasnt clear. Simple explanation: I am underweight now. I can add (more) balast and still add to the cage and still make weight....I was looking for insight as to cage design, not "driver improvement"...but thanks anyway.

Tom

whenry
01-07-2004, 02:08 PM
Since National decided to add 45# to the minimum weight of 1.6 SM to 2300# I was needing to add 32# myself. My research tells me that .095 tubing adds 1.44# per ft so you may not be able to add enough tubing to add the weight that you need.
I am adding several tubes that are low in the cage(one in trunk and one behind the seat) which will be about 15# and then "improve" my fire extinguisher and battery mounts to add the necessary pounds without resorting to ballast in the front passenger footwell. YMMV

ddewhurst
01-07-2004, 05:09 PM
Tom, within the following attachment is a cage feast for anyones eyes. If I was in your situation & had a substantial cage I would first check out the fastest cars (Herr Coello Dewey)cages. I would rather add weight to balance the car.

www.bimmerworld.com/cages/cagepics.htm (http://www.bimmerworld.com/cages/cagepics.htm)

Have Fun http://Forums.ImprovedTouring.com/it/wink.gif
David

kthomas
01-08-2004, 04:40 PM
Originally posted by CSPTK:
Well, consider this "another discussion" (the original one for those playing along). I never mentioned that I wanted to stiffen the cage so it would "help me win", improve my driving, etc. You misunderstood my original post, sorry if it wasnt clear. Simple explanation: I am underweight now. I can add (more) balast and still add to the cage and still make weight....I was looking for insight as to cage design, not "driver improvement"...but thanks anyway.

Tom



Duh, my mistake. Your original post said you had a spec miata you "wanted to stiffen". I don't know why I didn't take that to be you needed to add weight. Use ballast, it will be lower than cage parts.

------------------
katman

grjones1
01-10-2004, 01:22 PM
[quote]Originally posted by CSPTK:
Thoughts?

Tom,
If you don't already have them and if the Mazda accommodates them, consider adding vertical base plates to the car's frame rails up from the cage's base plates on the floor - adds safety, puts the weight low, helps rigidity, and it's legal.
GRJ

chuck baader
01-10-2004, 07:57 PM
One thing to remember when adding bars..straight bars carry loads, bent bars are springs. That said, if you triangulate, do not run any bars from the center of one to the center of another. They shourld be from mounting gusset or tube intersection to gusset. As was said, one of the best ways is to take advantage of the 100in2 rule and use "L" shaped plates to mount the tubes to the floor. Then add triangulation from those points. The only problem is that the driver gets into the way of a really good cage http://Forums.ImprovedTouring.com/it/smile.gif Chuck

badal
01-13-2004, 08:29 AM
Chip Herr's car has a copy of a Mitch Piper cage. He has a Petty bar, but it is mounted with huge rod ends, so it can be removed. This is one way to do it if you want room for an occasional passenger seat.

Knestis
01-13-2004, 10:25 AM
Speaking of, has anyone else seen the Piper cages that don't have parallel bars from the main hoop back to the rear of the cars - only an 'X'?

Are any of those cars logbooked for SCCA club racing?

K

Grumpy
01-13-2004, 10:31 AM
I have seen them and don't like them. I held a National Tech license at the time, but was locally overruled and logbooks were issued.

My contention is that at the point of the X there is ONLY ONE BAR.

Gussets at the X would help the situation. I would not sign the logbook. I would pass it to someone who thought it was legal.

This needs to have an "official" ruling.

The diagram in the GCR "suggests" the X bars as optional.

Additionally

6. Bracing:
The main roll hoop shall have two braces extending to the rear
attaching to the frame or chassis. Braces shall be attached as
near as possible to the top of the main hoop not more than six (6)
inches below the top and at an included angle of at least thirty
(30) degrees.

IT SAYS TWO BRACES.

in an X one brace does not connect the main hoop to the frame or the chassis.

Additionally With the picture of the roll cage for SS/IT it states:


IMPROVED TOURING DIAGONAL
Tube A-D of B-C is required
Note: Tubes A-F and/or B-E
are acceptable extra tubes
in addition to the
required tube.

Tubes AF and BE are the tubes that would form the X supports, and are clearly marked as acceptable EXTRA tubes.

I rest my case.

[This message has been edited by Grumpy (edited January 13, 2004).]

Knestis
01-13-2004, 02:41 PM
I was thinking of you, Grumpy as I typed that. I don't remember if you were in on the conversation that I had with someone at one of the NASA HC races last year or if they just mentioned what you had said.

I think they are a really bad idea, FWIW, the cross-section of the structure being approximately the area of one tube at its narrowest point.

K

Speed Raycer
01-13-2004, 06:55 PM
I built a cage with a guy (1st I'd ever done)and we did the single rear X (We had other supports running to the middle of the X from the main hoop). After personally slamming into a wall with the rear pass side, I could see the benifit of the design... but that was the only one. If it had been a rear collision... or any collision other than a direct hit on the wheel area, I believe that the cage may have been compromised.

The X is a great addition to the standard support braces, but not a replacement.

bldn10
01-14-2004, 12:18 PM
This is a little off-topic but for the sake of conversation let's turn the discussion around for a moment. Safety aside, does all this extreme stiffening really make a car quicker? If so, how much? Hypothetically, take a well-built ITS car that does a 1:43 at Road Atlanta w/ a decent cage - all else being exactly equal, how much quicker could it be w/ the most elaborate triangulated super-stiffening cage? Then, assume you can adjust the suspension if necessary - quicker still? I'm asking if all the talk about stiffening cages (for speed) isn't perhaps overblown.

chuck baader
01-14-2004, 12:32 PM
O.K., for the sake of discussion...without empirical testing we really don't know. However, the cages we are allowed to run in IT make tuning the suspension extremely difficult at best. What we are really doing is tuning the chassis flex with springs and shocks to make the car turn, etc. Personal experience from my Solo 1 days with a bolt in cage and now with a full weld in, springs are much softer now that the chassis is stiffer. Still we need, not only for handling but also for safety, to be able to tie the front shock towers to the cage and triangulate the front end. I'm not shure that would drop lap times, but I'm positive it would increase the integrity of the driver compartment. Chuck

Geo
01-14-2004, 10:31 PM
Originally posted by bldn10:
This is a little off-topic but for the sake of conversation let's turn the discussion around for a moment. Safety aside, does all this extreme stiffening really make a car quicker? If so, how much? Hypothetically, take a well-built ITS car that does a 1:43 at Road Atlanta w/ a decent cage - all else being exactly equal, how much quicker could it be w/ the most elaborate triangulated super-stiffening cage? Then, assume you can adjust the suspension if necessary - quicker still? I'm asking if all the talk about stiffening cages (for speed) isn't perhaps overblown.

The purpose of stiffening the chassis is to make the suspension respond as it is supposed to. With a flexi-flier, you can do all you like to tune the suspension, and many times it won't do what you want/expect.

The Sentra SE-R is a great example. We are running 450/400 springs and the car is just on the understeer side of neutral. But, it had a bolt-in cage (currently being replaced and the car upgraded to EP). I also drove a road version at Summit Point Jeff Curcuit that rotated more than any SE-R I'd ever driven and that was with 450/275 springs. The rest of the suspension was pretty much the same. The difference is, the car is so flexible, the chassis has a spring rate below the 400 (essentially) that we were running.

Flexible chassis do weird things. That is why race car designers work so hard on rigidity. Does this make your car faster? Well, if you have a clue about chassis tuning, you should be more consistently faster.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

Scooter
01-15-2004, 09:47 PM
------
Many people add a "Petty bar" from the main hoop near the drivers head, down to the base of the leading edge of the passenger door. Good proven design, 'nuff said. But I'd like to leave space for an occasional passenger seat.
-------

I added a Petty bar to my cage, as well as a horizontal bar behind the dash. That noticably stiffened the car.

On the other hand, IMHO, I don't understand how a cage like this http://www.bimmerworld.com/E36%20cage/Mar2804.jpg could possibly be necessary when you can't attach the front strut towers, or really even the firewall, to the cage.

But I'm not out there winning the ARRC. So what do I know?

joeg
01-16-2004, 08:25 AM
On the other hand, IMHO, I don't understand how a cage like this http://www.bimmerworld.com/E36%20cage/Mar2804.jpg could possibly be necessary when you can't attach the front strut towers, or really even the firewall, to the cage.

Perhaps he got a deal on tubing.

[/B][/QUOTE]

Knestis
01-16-2004, 10:09 AM
I got a nasty surprise one day driving an ITB Rabbit home from a race in Portland. It had an Autopower bolt-in and I had absentmindedly wrapped my hand around the A-pillar tube as we tooled along on I-5. We hit an exposed expansion joint and my fingers were pinched between the cage and A-pillar as the gap went from more than 1/2" to less than a finger thickness.

That's one brand of "not stiff" and the one that is addressed by adding a Petty bar here or a dash bar there.

On the other hand, the difference between a basic, six-point, welded-in cage and Stiff (big S) is a whole 'nother deal.

Geo was spot-on about a car actually having 5 springs - the fifth being a big, poorly damped, combination torsion bar/leaf spring that we call the chassis. It has a rate and a frequency just like the coils that we buy for each corner and, if its torsional rate is low enough, that becomes the movement in the entire system. As suspension spring rates get higher - and some IT cars are very high - the 5th spring comes into play earlier and earlier. Importantly, notice that I said 'undamped.'

Part of the point of my wacky door bars is to triangulate the HUGE bay imposed by the hole in the 2-door Golf shell intended to let people in and out of the back seat.

http://www.it2.evaluand.com/gti/images/cage08.jpg

I would anticipated that, particularly with a modern front-drive car, the connection between the strut towers and the firewall is probably pretty good (relatively speaking): The connection between the front and rear suspension is not so there is a lot to be gained in terms of stiffness, in the back of the car. The structures that appear in the back of cars on which real engineering money gets spent (ETCC, BTCC come to mind) reinforces this belief in my mind.

It's a great exercise to model rollcage structures in your kitchen. Use those bamboo skewers from the grocery and a hot glue gun, mocking up cages in something like 2"=1' (so a 12" stick gets you 6' of rollcage pipe). Don't fuss over the joints, instead just poking each end in a blob of hot goo. Let it cool and twist away...

It becomes apparent VERY quickly what additional elements add stiffness and (qualitatively) how much.

I used to do a slightly more complex version of this activity with my junior high engineering class students. Their task was to design a spaceframe for a touring car, which we then tested for tosional stiffness (you'd be impressed with the numbers) and crash tested into a cinderblock wall.

http://www.it2.evaluand.com/images/m3chassis2.jpg

Have fun and don't put hot glue on your hand.

K

Speed Raycer
08-14-2005, 09:42 AM
Originally posted by [email protected] 13 2004, 01:41 PM
I think they are a really bad idea, FWIW, the cross-section of the structure being approximately the area of one tube at its narrowest point.

K

600


Was just reviewing the GCR last night about the 7th/8th point rules and came across a blurb stating that the X is allowed in addition to rear braces. It was in one of the drawings showing the 8th points and giving the A-E discriptions (GCR's out in the shop or I'd give you the section #s)

{EDIT} Whoops... thats what I get for not tossing old copies of the GCR out! I just looked through the PDF file and the wording has been removed.
{/EDIT}

zracre
08-14-2005, 10:11 AM
Back in the mid 90's i tested an auto power cage (bolt in) at road atlanta...I had a wheel depart the car (4 bolts on LR hub not secured properly *NOTE: when driving other peoples cars, tech them carefully) and went into the grass at t3 backwards with the trailing arm acting like a pogo stick. the car flipped landing RR corner first then alternating LF RR for 4 rotations. the cage was very ugly and i had always said "i would hate to crash this thing". The cage held up and I was uninjured. Inspection showed that the cage bent down 1 inch in the RR corner and about 2 inches on the LF corner. They are stronger than you may think and alot of engineering goes into them. I think the biggest danger to us as racers are the other things flying around the cockpit in a bad wreck. More injuries could be avoided if all the fancy things we put in the cockpit are bolted down more securely.

charrbq
08-15-2005, 03:48 PM
Originally posted by [email protected] 14 2005, 02:11 PM
Back in the mid 90's i tested an auto power cage (bolt in) at road atlanta...I had a wheel depart the car (4 bolts on LR hub not secured properly *NOTE: when driving other peoples cars, tech them carefully) and went into the grass at t3 backwards with the trailing arm acting like a pogo stick. the car flipped landing RR corner first then alternating LF RR for 4 rotations. the cage was very ugly and i had always said "i would hate to crash this thing". The cage held up and I was uninjured. Inspection showed that the cage bent down 1 inch in the RR corner and about 2 inches on the LF corner. They are stronger than you may think and alot of engineering goes into them. I think the biggest danger to us as racers are the other things flying around the cockpit in a bad wreck. More injuries could be avoided if all the fancy things we put in the cockpit are bolted down more securely.

58360

Ditto what you said, Evan. I watched an SS Mitsubishi tumble down the hill from under the at Atlanta several years ago. The cars fire extinguisher came loose, and detonated making it an omni-directional missile that crashed through the rear window. I was really surprised that the SCCA didn't immediately require a different type of security for them, or at least make fire systems mandatory in all cars. Imagine what would've happened if the driver's body had taken the blow the rear window did. :o

lateapex911
08-15-2005, 05:39 PM
Hey...time to put out "Blue Sky" thinking caps on...

The new IT cage rules require certain tubes be present, and that they be of certain sizes, depending on the race weight of the car. All well and good.

The new "option" the rules offer is that you can add as many bars within the stucture as you want, and they may be of any size you desire....

SO...........if I wanted to make the lightest cage possible, I would use the required tubing in the required areas, but I would be inclined to use alternative sizes for the rest.

What could I do and not get slapped with a protest that could stick..(under appeal)??

ANY size, right? How about aluminum tubes bolted in with turnbuckles?? Does the method need to remain the same for optional stuff?? Lots of pre "any size bar rule" cars used smaller bars as gussets, but called them "handles" to avoid the wrath of the tech inspector.

What else??

Speed Raycer
08-15-2005, 09:44 PM
Originally posted by [email protected] 15 2005, 04:39 PM

ANY size, right? How about aluminum tubes bolted in with turnbuckles?? Does the method need to remain the same for optional stuff??
What else??

58443


As long as that material meets the material specs (which I believe is specifically outlined as DOM or 4130) and the attachment point is welded 360 degrees and meets the AWS standard.

I'm thinking aluminum tubing and turnbuckles might not pass the test ;)

lateapex911
08-16-2005, 04:53 PM
Hmmm..I should have read that bit more completely.

But...it would be really cool if we could add stuff in that manner, LOL.

I do want to do a camera mount that way.

Wreckerboy
08-17-2005, 03:48 PM
ddewhurst wrote:

... within the following attachment is a cage feast for anyones eyes. If I was in your situation & had a substantial cage I would first check out the fastest cars (Herr Coello Dewey)cages. I would rather add weight to balance the car.

www.bimmerworld.com/cages/cagepics.htm

They certainly were, and thanks for the link. Very informative. Slightly OT, but one caption mentions how the seat mounts are attached to the cage, which seems like a sound idea, but how does that happen without going beyond the allowed 8 points? It looks to me like the inner points of the seat mounts would be cage attachment points nine and ten. Or is this a rules nerd thing that I'm missing?

Thansk in advance for the education

ITANorm
08-17-2005, 05:02 PM
8 points are the limit on chassis attachments. If the seat is only attached to the cage, it doesn't count.

Wreckerboy
08-18-2005, 08:39 AM
Perhaps I wasn't clear enough - in the pictures provided it appears that the mounts for the seat are attached to cage on the driver's left side of the cage and to the transmission tunnel on the inside (driver's right) side. Would those be two extra points of attachment, or are am I missing something?

Speed Raycer
08-18-2005, 11:57 AM
Originally posted by [email protected] 18 2005, 07:39 AM
Perhaps I wasn't clear enough - in the pictures provided it appears that the mounts for the seat are attached to cage on the driver's left side of the cage and to the transmission tunnel on the inside (driver's right) side. Would those be two extra points of attachment, or are am I missing something?

58583


Not legal in IT... that site is full of great ideas... just not all of them legal in our class.

Goofy rules (surprise) would rather us bolt to the 20 ga. floorpan.

Dick Elliott
08-18-2005, 01:35 PM
Those pictures show two of the worse window net set up I've ever seen on a race car since SCCA outlawed bungie cords. Look like they were installed after the 5 min whistle in the hot pits.