RSR fiberglass = safe?

[jamesjedi]

When the car is lightened with F/G RSR panels, most of the weight comes off the front (I think). Does this not make the car more unstable during high speed track driving? And, are there safety concerns if car is crashed?

[air-cool-me]

if you have an SC and bumper pads i think the weight it about the same.

im pretty sure if you did take more weight off the front you would add understeer.

i dont know if added understeer would be called "unstable"

as far as crash protection.. this topic was just touched on in another post...

i dont think it would matter much in a life or death crash... but then again there are alot of factors..

i cant seem to find that post right now.

[Tspringer]

My RSR bodied car will have substantial roll cage intrusion into the front compartment that significantly strenghens the entire structure. It also has a splitter and larger front air dam that will increase downforce at the front of the car. The RSR flares also allow much wider front tires.

So.... yes it will weigh far less, but it will also be far stronger and generate a great deal more front grip.

It will also be safer in a crash.

RSR front panels on an otherwise stock car? Well.... the wheels would look awful silly

[911pcars]

The rear also benefits from LW body parts (deck lid and rear bumper).

Add'l downforce and added tire contact (provided by larger wheel openings) offset any weight distribution effect. See history of Porsche racing to verify.

Metal deforms and dissipates crash forces during a collision. Because composite parts are more brittle or much more ductile, there is little/no energy absorption. Because of this, there is some safety concern. Race cars with or w/o composite panels usually have a roll cage embeded within the chassis for this purpose.

When discussing "big egg" vs "little egg" theories, one must weigh accident avoidance (better braking and manueverability, keeping the shiny side up, etc.) along with survivability (unavoidable crunch). There is no black and white answer despite conversations with SUV owners.

Sherwood

[jamesjedi]

Thanks for replies!

"RSR bodied car will have substantial roll cage intrusion into the front compartment that significantly strengthens the entire structure"

In reference to the above....I want my car to still be street-able..not a daily driver though. With this in mind, what kind of cage should be used to provide structural strength? I don't like the idea of NASCR cage.

[Jack Olsen]

There's nothing more dangerous about the RSR body style than any other body style (RS, Carrera, whatever). And while it's true that fiberglass does absorb less energy than sheet metal, in a high-speed impact it's not the exterior skin that's going to be doing the bulk of the work. Sheet metal and bumpers will add to the overall cumulative crash-worthiness of a car, but the unibody is still where the vast majority of the energy goes. I'd say a fiberglass-bodied car with an intact steel unibody is not significantly more dangerous to drive than a sheet-metal bodied car. The helpfulness of external pieces will be easier to see in low-speed impacts.

[island911]

Originally posted by Jack Olsen
There's nothing more dangerous about the RSR body style than any other body style (RS, Carrera, whatever). And while it's true that fiberglass does absorb less energy than sheet metal, in a high-speed impact it's not the exterior skin that's going to be doing the bulk of the work. Sheet metal and bumpers will add to the overall cumulative crash-worthiness of a car, but the unibody is still where the vast majority of the energy goes. I'd say a fiberglass-bodied car with an intact steel unibody is not significantly more dangerous to drive than a sheet-metal bodied car. The helpfulness of external pieces will be easier to see in low-speed impacts.

Say what!?

ah ....yeah ....You guys with f/g bumper covers just keep on telling yourselves it's all okay. . .none of that OE engineering matters, in a bad crash.

Energy absorption-- It really is all simple physics. The longer the decelleration, the better. (lower loads). The more deformable material you have the more energy you can absorb. (toughness)

While f/g bumbers can be made strong (and tough) the bumper covers designed to shave the pounds are not among them. Taking off the OE bumpers leave you with ~5" less structure to slow the car.

And yet, people will take off the engineered, energy absorbing bumpers (removing that weight down low --tell themselves how smart they are. Then, weld in a heavy rollcage --tell themselves how smart they are, again.)

Hey, how much do helmets weigh? . . .make one out of papier-mâché and reallize the weight savings ... your head handles all the impact anyway.

[Bill Verburg]

When the car is lightened with F/G RSR panels, most of the weight comes off the front (I think). Does this not make the car more unstable during high speed track driving

It lowers the absolute weight and more importantly lowers the polar moment of the car. This allows the car to rotate in either pitch or yaw more easily. If that is your def. of unstable then yes, it is more unstable.

And, are there safety concerns if car is crashed?

Yes, you have lost some of your crumple zone, and no a full cage doesn't compensate.

Old really strong race cars w/o crumple zones are death traps. Think 50's style Indy cars. They hit something and the human driving it is the deformable structure.

Modern cars, both street and race are designed w/ soft and detachable parts that absorb and carry away energy, allowing the driver to deal w/ lower g forces.

If you do this type of thing make an informed decision and live w/ it.

[jamesjedi]

Thanks to all who replied...some very informative insight. Here is some food for thought... I was wondering how many fatal accidents with F/G bodies would still be fatal if the body was all steel. Chances are (and I am guessing), that they would still be fatal. Deceleration is the killer. Drving fast=dangerous. There is only so much that a 20+ year old design can do for safety.

[Jack Olsen]

Originally posted by island911
And yet, people will take off the engineered, energy absorbing bumpers...

'Say what,' indeed.

Randy's recent thread on crash safety didn't turn up anything like this. And absent some actual data, I'd say that the impact bumpers on a 911 are probably there for a very simple reason, and it ain't got nuthin' to do with a crumple zone. More likely that it has everything to do with the Insurance Industry's hard-lobbied-for low-mph bumper impact standards. And in spite of a lot of consumer advocates working hard to make cars safer in that era, the bumper standard was put in place for what President Nixon then described to Lee Iacocca and Henry Ford II as "parking lot damage," which was costing insurers $13 per year per car in minor claims (constituting something like 30% of the cost of insurance pay-outs).

Porsche (and all other car manufacturers) did not suddenly decide to get safe in the early seventies when they modified the bumpers. They were told they couldn't sell cars here if they didn't meet the new standards (some were state and some were federal, some 2.5-mph and some 5-mph).

I wish that the mandate to Porsche's engineers was 'guys, why don't you think up something really safe for the cars this year,' but I think a much more likely scenario would be the company telling them to 'engineer' a bumper that met the new low-impact standard, was as inexpensive as possible to implement, and to get it done in time for the 1974 model year.

[island911]

Originally posted by Jack Olsen
'Say what,' indeed.

Randy's recent thread on crash safety didn't turn up anything like this. And absent some actual data, I'd say that the impact bumpers on a 911 are probably there for a very simple reason, and it ain't got nuthin' to do with a crumple zone. More likely that it has everything to do with the Insurance Industry's hard-lobbied-for low-mph bumper impact standards. . . .

hmmm, I don't think that I posted on Randys thread.

A few points:

The structure built to sustain a 5mph hit, with ZERO damage, is sure to add significantly to the energy absoption in a faster hit. (it's not as if, after 5mph, that structure is null)

The "shock tubes" which the OE bumper is mounted on, are NOT simple springs. They are dampers. As such they provide a velocity dependent response. That is, the faster you try to compress them, the harder they become. This means they will work in tandum w/ a collapsing primary structure, absorbing energy throughout the event.

The OE bumpers also are a rigid member, which will distibute a hit along its length. Pushed back far enough, the end, thru its internal bumper structure, will contact a tire (another great energy absorber) The back side of the bumper will start loading a large patch of primary structure.

Porsche had been a leader in safety implemantations . . and not just for "parking-lot safety."

btw, Bumper which can not sustain a bump, are called façades.

[Jack Olsen]

Originally posted by island911
The structure built to sustain a 5mph hit, with ZERO damage, is sure to add significantly to the energy absoption in a faster hit. (it's not as if, after 5mph, that structure is null)

I started out by saying that sheet metal and bumpers will add to the overall cumulative crash-worthiness of a car. But then, 500 pounds of nuts and bolts in the trunk will absorb a lot of energy, too. I haven't seen any data on Porsche's bumpers that tells us exactly how much the bumpers add to the car's scrash-worthiness. In my own experience of hitting a wall with fiberglass bumpers, I was surprised at how well the unibody absorbed the energy. I don't think bumpers would have significantly reduced the damage, but that's speculation.

Originally posted by island911
Porsche had been a leader in safety implemantations . . and not just for "parking-lot safety."

The new bumpers were added exactly when they were federally mandated for the low-mph laws. Again, absent data, the timing points to this being less of a case of bold safety engineering than it was plain old business necessity. Then as now, if Porsche can't sell cars in the U.S., Porsche goes broke.

I think we'd both like to see good data on what the bumpers actually do, and I think we'd both be interested in knowing what the actual design goals were back in 1972-3. Absent that, we can't do much more than speculate.

[Lothar]

Weren't the bumper regulations of the late 70's referred to as the "5 mph bumper"? I'm generally not too worried about the 5 mph collisions. I do get concerned about the 105 mph meeting with immovable objects.

Per Jack O's comment, I would think that the front fenders and the tub would discipate far more crash energy than the bumper structure. That said, I would imagine that the removal of any deformable structure would compromise safety to some degree.

[island911]

Originally posted by Lothar
. . . I do get concerned about the 105 mph meeting with immovable objects.
. ...

well, yeah ... in that case, you won't be any less dead, w/ the engineered bumpers doing their work, than w/o. Your corpse may look a bit better. But thats just speculation too.

Has anyone seen that "Speed" (?) DVD, were they crash test an F1 ? . . the one were that little "bumper cone" up front makes all the difference in decelleration g's, and crash survivability.

Though, maybe they put that cone there just for potential pit-row contact. Afterall, pit-row demands all sorts of safety protocal. And, If you can't drive in pit-row, you cant win races. ...

[randywebb]

One thing we can agree on: the big, '74-on bumpers will "take" 5 mph "off" of your crash -- a 50 mph crash would be ike a 45 mph crash.

Maybe they do more. But, I'll bet we never find that out.

BTW, I found a guy in Germany who might be willing to look at whatever crash analyses whoever the Germany safety agency is puts out -- maybe.

[island911]

Originally posted by randywebb
.. , '74-on bumpers will "take" 5 mph "off" of your crash --. ..Maybe they do more. . ...

Maybe!?

See, now I just dont get how you guys can come to this.

Porsche has not limited their crash testing to 5mph. . ...the design of the bumper function surely does not end at 5mph!

To conclude that the bumpers were to provide ONLY the first 5mph of crash protection is a bit past the pale. For example, as stated earlier; the bumper (if pushed far enough) has structure to make contact w/ the tire. (energy absorption beyond 5mph) (and protects the cooler)

When I look at the engineering of the 74-on bumper, I see much more thinking than simple "parking lot" concerns. ...But if thats what anti-bumperites have to tell themselves....

[randywebb]

"Porsche has not limited their crash testing to 5mph. . ...the design of the bumper function surely does not end at 5mph!"

- C'mon! You're an engineer -- show me the data. Your thoughts are fine - but they are non-quantitative. I have nothing better, that's why I said "maybe.'

Want to substitute something else for "surely" above -- like:
'it is reasonable to suppose'
'suggests that'
even 'indicates' might work, but is really too strong

[island911]

Originally posted by air-cool-me
.. this topic was just touched on in another post...
...
i cant seem to find that post right now.

I just found that here.

. . .some good post there.

[Vonzipper]

I purchased my F/G bumpers today, cant wait to get them installed, am I worried about crashing, not as much as the statement below

I think I'm more concerned about the back of the car passing the front

IMHO, In a low speed impact the 5mph bumper will help over the F/G, However, In a higher speeds crash the bumper will be meaningless, Thank god for that Porsche tub


I stepped in something and cant seem to get it off my shoe

[dd74]

Originally posted by Vonzipper
...am I worried about crashing, NO...

But you should be worried about someone crashing into you...

The fact is both Island and Jack are correct. Many written accounts have mentioned the '74 bumper style as a "5 mph" bumper, owing such to a federal safety mandate. After a couple children melted inside a Pinto that exploded after being rear-ended, much changed within the U.S. as to safety. New windshields, safety belts, rubber bumper guards and such, became de rigeur.

However, far be it from Porsche to do an American thing, and throw something on up on their car bodies as did The Big Three. I've seen the results of those dampers after a rear-end collision, and yes, they compress very nicely just like a Coors can to the Belushi's forehead in "Animal House." I was hit at a greater speed than 5 mph by 3,000+ pounds of Volvo station wagon, and sustained minimal enough damage so that I could drive myself home. The Volvo was totaled. That says something about the engineering of the bumpers, particularly the rear bumper. The thick bumper pads take the initial absorption, the aluminum bumper dissipates additional energy, while simultaneously the dampers compress with the onslaught of what energy is left.

So you have, at least in the rear, three safety devices at your disposal. From an engineering pov, along with the three safety devices within the rear bumper, speaks well of Porsche's design. I think, as well, the word "simultaneous" speaks volumes of that same engineering, as within the bumper, a process of safety has been designed.

On that same note, Bill V., Randy, Jack and others have mentioned the necessity of f/g bumpers as vital to weight savings. This is true mostly because the bumpers are the end of the car, and with the 911, the more weight you concentrate from the wheels inward toward the driver, the better the car will handle. That's just simple physics.

Now, as to whether you want to take your chances with f/g in the city, either at 5 mph or 105 is a choice that truly relies little on any bumper scheme. I tend to err on the side of safety when driving on the street, because it sometimes seems no other drivers err in the same way with their driving. If your car is seeing more track than street, then the f/g bumpers is a no-brainer.