[poopoo head]

Hi, I posted this topic in the Autocross section of this forum but didn't get too many replies, although they were very good ones:
http://www.focaljet.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=8;t=002007
So I am posting the topic here to see if anyone can help out? Is this allowed? Sorry if it isn't? Here it is...
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Hi, just wondering, which body shell type of the Focus is the most rigid?

I used to think somehow that the sedan would be most rigid since it has a B pillar right in the middle of a large opening, as opposed to a ZX3 which has a larger opening for the single door. The ZX5 also has a B pillar exactly like the sedan to divide the opening into 2 smaller ones and so buttress the roof and the floor, but it has a larger cavity in the rear where the sedan has a smaller cavity. Not to mention that the rear hatch makes a large vertical opening compared to the opening of the sedan (which shape of opening would compromise less of the structure?)

But after reading many things on such topics, people say that 2 doors are more rigid than 4 doors. I suppose that even though the 2 door has a larger door opening, the portion aft of the door opening is a fixed metal piece and so would more than compensate for the larger opening. Does the hatch latch or trunk latch make the car more rigid when the hatch or trunk are closed?

I drive a '02 ZX5 and when I corner, I can hear creaks coming from the driver's side area (door?). Another question... does a door actually help the structure of a car? For example, if i removed a door, would the car be less rigid? The door connects the front of the car to the B pillar or rear of the car with some hinges and a door lock mechanism...I suppose that door lock mechanisms can be very strong...but was it designed to aid the rigidity?

How about a sunroof? Does this really make any difference in the rigidity? Did any Focus ever have a sunroof? Does the roof rack of the wagon help its structure?

So is this the order in decreasing stiffness of chassis (not suspension tuning, which could be the exact same for the first three types?):
1. ZX3
2. Sedan
3. ZX5
4. Wagon (entirely different rear suspension that does not have 'control blade'??)

Which one is lightest (not including the wagon)?
A door is quite heavy, even if it is a smaller rear door. There are door lock mechanisms, power windows, (side impact beams only in the front doors?), but the ZX3 does have a fixed metal area instead of the rear door...and this is heavy, too? The front door of the ZX3 is also very heavy compared to the front door of the four door versions?

All of this probably won't make a difference in the real world, but it is interesting to know?

So... the SVT 2 door would be more rigid than any of these shells...if they have somehow added extra welds to it or something else?

 

[Vegeta]

I dont know about the chassis but yes sunroofs do redudce the stiffness of the chassis cause your cutting a hole in one of the biggest pieces of metal on the car and where the sunroof goes there is usually a brace but that is removed to make room. Also it adds weight but I have a sunroof in my zx3 and i wouldnt have it any other way. Especially on the many nice days we have in Fl.

 

[focalBlur]

I would say sedan would be the most rigid

why you ask

b/c the sedan has a trunk
the way the trunk is area is made it acts like a rear strut tower brace, the rear shelf behind the rear seats is all metal, making the rear of the car very stiff

all other body style lack the extra "brace" and IMO this would mean the are less rigid

as far as doors go, yes they help if they are closed, when they are closed it completes the structure of the car

sunroof - it makes very very little difference if it is closed and factory installed, and even when it's open it's not that large of a change
as far as a brace being remove, i dont think so, any braces that would have been there would only be there for rollover protection, something that cant be removed, so really you are just replacing sheet metal with glass, and only adding a little weight

i also found this on the web about a ZX3

http://www.racecar.co.uk/roadtest/focus.html
page 3

The other contributing factor to the good structural integrity and handling is a very stiff bodyshell. Ford say the big number is 14,500Nm/degree of twist. The Porsche 911 Carrera boasts 16,500Nm/degree and the BMW Z3 Coupe 16,400 Nm/degree, so for a family car with a big hatch in its rear, the Focus is very stiff indeed. This is particularly impressive when you learn that its body structure is also the lightest in class. Kerb weight of the 1.6 litre five-door Focus is just 1,077kg. Incidentally there is a 12-year corrosion warranty on its galvanised shell.

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[ 04-09-2003, 01:29 AM: Message edited by: focalBlur ]

 

[MichaelXi]

Honestly, you shouldn't "Cross-Post".
I think your answers lie in your original thread in Auto-X.

I understand the desire for more info however.

 

[Roger Eastman]

I think the wagon is being overlooked here. If you look at the real world crash statistics (those compiled based on actual accident/crash reports), the wagon does fairly well; the ZX3 not so good, and the sedan the worst of all. See data at www.highwaysafety.org. They have not picked up data for the ZX5 yet.

If the wagon were not more structurally rigid, why would it hold up better in all different sorts of accidents ?

 

[flat 4]

One explanation as to why the wagon fairs better in real world crashes might lie in the same vain as why Volvo wagons fair so well in crashes.
OLD / SLOW PEOPLE DRIVE THEM!!!
I am not saying the Volvo's aren't safe, hell they are a damn safe car, but Volvos and Foci wagons dont have 19 year old idiots driving them 78 mph in a 30 zone hitting a cement barrier.
An interesting set of data would be looking at the crash results by car style and age of driver at the time of the crash. You could then see the severity of the 20 something crash in a ZX3 vs. a 55 year old driving / crashing a ZX3 and how much damage was done to each car.
4 out.

 

[Roger Eastman]

I believe the data is normalized for things like that so that it is directly comparable. Otherwise, how do you explain that the Focus sedan does much worse than the ZX3 ?

 

[sh0velman]

i think relating crash tests directly to chassis rigidity is a foolish activity.

i belive this guy is more worried about its performance effects, not how bad he'll be hurt in a wreck. heh.

 

[poopoo head]

yes, 'heh', 'this guy' is more interested in performance effects. But I do care about how badly I might get hurt in a wreck.

The wagon probably fares better in crash tests because of its additional length in the rear. About the other tests coming from all sides, then, I don't know how the extra length would affect it, but the roof that is longer must be reinforced somehow more than the other Focus.

And crash tests subject a car to forces that are different than the forces that going over a bump or turning around a corner subject a car to. So bumpers see different forces than, say, a suspension mount and so safety stats would not neccessarily reflect handling characteristics? Even though in this case, the flex differences would be minute enough to not affect lap times or something?

So why even talk about this topic? Good question, I don't know why.

[ 04-10-2003, 01:15 PM: Message edited by: poopoo head ]

 

[Roger Eastman]

Just a last word on the subject: I was not talking about crash tests; I was talking about data obtained from actual accidents. I believe that the data that I mentioned would be directly related to the overall rigidity of the body, as these actual accidents are stressing the vehicle in all kinds of positions and situations. The actual accident/crash data shows that the wagon must be the most rigid of the 3 body styles, otherwise it would not consistently perform better than the sedan or 3 - door.

Furthermore, from a handling point of view, the wagon would probably prove to handle better, as it has the best weight distribution, and it has progressive rear springs. Also, the wagon outperforms the other Foci models in having the best aerodynamic characteristics, i.e., the lowest coefficient of drag.

 

[hatched]

But isn't the wagon the heviest of all Foci?

 

[01sportwagon]

Here are some posts from the past on this topic:

http://www.focaljet.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=010378#000000

http://www.focaljet.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=012228#000000

In fact, the first one is a post that I started a year ago (almost to the day). The only things I can see missing are the numbers… it’s the numbers that we are after.

In this post, focalBlur listed the ZX3 as being over 14,000 Nm/deg in torsional rigidity (stiffness). Does anyone else have access to this type of data?

The least tortionaly rigid shape is a plane (sheet of paper), but it would be easy to slap some wheels on the side and use it for transprotation. The most torsionaly rigid shape is a sphere. And because a sphere doesn’t have a door, we can’t drive it. So, we have to compromise. Now a round cylinder is torsionaly stiffer then a boxed tube, but again we have to compromise. That is how we end up with shoebox looking things with wheels and doors.

The weight of the car also has an effect because the momentum is greater and will transfer that energy to the structure. Therefore, the different versions of the same model would react differently and have different torsional values. But the manufacture could add reinforcements to compensate for the added weight and the resulting version (read: Wagon) could be stiffer even though it is heavier. This is why we need the numbers.

 

[Roger Eastman]

I purchased a new 2001 Street Ed Sedan; the invoice showed the shipping weight at 2508#. I later purchased a new 2002 ZTW Wagon; the invoice shipping weight is 2683#.

I believe the original premise posted by the starter of this thread, that the wagon rear suspension is entirely different, is not correct. All the Foci rear suspensions are similar, the most noted difference on the wagon being progressive rate springs and diagonally mounted shocks rather than vertically mounted shocks.

 

[MichaelXi]

Originally posted by Roger Eastman:
I believe the original premise posted by the starter of this thread, that the wagon rear suspension is entirely different, is not correct. All the Foci rear suspensions are similar, the most noted difference on the wagon being progressive rate springs and diagonally mounted shocks rather than vertically mounted shocks.

<font size="2" face="Verdana, Arial">That makes for a HELLUVA Difference!

I like the wagon, and it can be a decent handler, but it IS Very Different.

 

[MichaelXi]

Originally posted by Roger Eastman:
I think the wagon is being overlooked here. If you look at the real world crash statistics (those compiled based on actual accident/crash reports), the wagon does fairly well; the ZX3 not so good, and the sedan the worst of all. See data at www.highwaysafety.org. They have not picked up data for the ZX5 yet.

If the wagon were not more structurally rigid, why would it hold up better in all different sorts of accidents ?

<font size="2" face="Verdana, Arial">I looked for a few and didn't find the Data. Are they talking Repair Costs or Passenger Safety in the info you're talking about?
I know nothing of their compiled data, but I DO know a Focus Impact Crash FIRSTHAND.
I hit a Concrete Pillar that supports an Overpass that was set in a Concrete Drainage Ditch at approx. 45MPH at roughly a 35-40 degree angle w/ the Left Front.
The car was "Technically Totaled", (Though another 'Jetter now drives it in "Like New Condition"), but I got out w/o ANY Injury, save a sore shoulderblade from the jar of the impact.
I Witnessed News footage of a sedan traveling at roughly 70MPH when it rear-ended a trooper's car that was parked on the shoulder.
The 70-ish year old man and his 30-something daughter were only mildly injured, and emerged from the debris-strewn wreckage in fine shape.
Out of MANY reported Crashes here among our community, James Hock is the ONLY 'Jetter I know of who has been Fatally injured in a Focus, and his circumstances are unclear.
All evidence indicates to ME that the Focus is a HELLUVA car to be in IF you have a Crash.

 

[blackbird]

If you want to see how the Focus really stands up in real world accidents and how strong the body shell is, check out the following web site:

http://www-nass.nhtsa.dot.gov/BIN/NASSCASELIST.EXE/SETFILTER

This is the site for searching the case files the NHTSA keeps on auto accidents. If you want to see what happens to the cars involved in crashes, there's pictures of the vehicles as well as full accident reports including information such as the cause of death for fatality accidents, the circumstances that caused the crash, vehicle component failures, etc.