Dock,
That is very interesting. I absolutely agree that putting the rear seat backs down will move the car's CG forward ever so slightly, but I wouldn't have thought it would be as much as .1%. I am not being facetious (quite serious as a matter of fact). I routinely calculate CG's for structural purposes in the design of buildings for earthquake and the design of steel and concrete members and really didn't think that the up down attitude of the seats would make a measurable difference. I took mine out altogether so I guess every little bit helps.
That makes a very good argument for leaving the front spare in place. Although its removal lightens the car, it also will create more rear bias.
In calculating the front rear bias, the equation P/A +/- Mgc/I +/- Mwc/I is used. To make a point and look at this very simplistically,

• P=weight of car
• A=Area (but in this case the number of wheels)
• Mg=Moment due to gravity. This equates to the car's weight times the distance between the fore/aft CG location and the 1/2 wheelbase dimension.
• c=1/2 wheelbase
• I=4 times 1/2 wheelbase squared (don't ask)
• Mw=Moment due to wind while traveling. This would be the wind pressure psf times the frontal area times the vertical dimensional difference between the frontal area centroid and the CG of the car

Now, in a worst case situation, you are traveling at speed with full wind force acting on the front of the car. Multiply/add the terms together and the weight bias result is very interesting.

Disclaimer:
This rudimentary disertation neglects any effects of downforce and uplift due to aerodynamic spoilers and other aids.

Sorry guys, I got carried away.................

 

dkc_gt2,

Go to www.optimabattery.com .

Regarding spare tire in relation to being crash worthy. What about the GT2? I have seen the front's disassembled on both cars. There is a special crash construction to either side of the spare wheel hole. It is my understanding this is what makes the car crash worthy. As for the above pic, the car is well dented but the front does not appear to be crushed in at all. It must have not taken a direct front impact as it is my understanding the front is designed to crumble (up to the point of the fuel tank) while absorbing energy.

 

LMAO...well I guess if you don't consider going down an 15 foot embankment on your top then smashing into the ground head first a direct impact I am confused. Granted this was after it hit the **** end of the embankment at 80+ then flip three times. The windshield and both air bags were deployed. I will try to find a better picture. I am still finding battery acid on anything that I still have from that. Through my contacts it has always been verfied including the several service blurbs in the body service repair manuals that the spare is used in conjunction with the crush zones. I looked long and hard into this after the wreck when wanting to upgrade.

 

Stephen,

I am looking at the pic. Sorry, but I have seen direct hit frontal impacts....this is not what occured. It appears it hit or glanced passanger front side and went over with most of the contact occuring on the top one third of the car. The crush zone in the front middle do not appear to have taken a direct frontal hit.

Yesterday, there were pics on the web of Lady Dianna's car after the accident. That was an example of a direct front hit. Since the discuession was about the "spare tire" and the crash worthy aspects in relation, I can only assume you are taking about this type of impact.

 

Um, Chad I was in the car when it went the embankment. It hit rear first then flipped three times and went down the embankment on its nose. You can assume you know what happened and I urge you to call public records and pull the police report. I was driving it when the accident occurred. Unless you were there you have no idea what happened. As I said it hit **** first then flipped then slid down the embankment hitting head first. I really wish not to debate this with you. I was in the car!

 

Granted I didn't hit a phone pole head on, but I can sure you the front end was moved back enough that it crushed the gas tank, the spare and moved the dash back. That was not caused by the rear impact. The rear shoved the 1/4s in to the doors 3 inches and the tranny through the front diff. Broke every control arm and did over 52K in damage to the body only. This was not including the engine and suspension.

 

In order to earn a crash worthiness endorsement from the NHSTA or DOT (not sure which has jurisdiction), I would tend to think that cars are required to be crash tested as they are intended for use by the public otherwise the test would be worthless. This type of testing is common in the engineering community (i.e.: test in accordance with intended usage). If the TT is meant to have a spare (which it obviously is) I would have to assume it was crash tested that way. Similarly, I would have to assume the GT2 was also crash tested without the tire. There is no debate that cars have crumple zones to absorb collision energy. Since the spare is a relatively stiff element, I would have to assume the engineers accounted for its presence in the deisgn of the crumple zones.
Just my $0.07. (Inflation..)

 

KPV,

I agree! Now see if you can determine if there is any difference in the crumple zone of the turbo and the GT2. The high strengh steel in both cars begins right before the fuel tank.

Stephen.

We agree. You did not take a direct frontal hit, you took a very hard glancing hit approximately where the hood line starts. I also agree, my point is made and I do not intend to make my point any further with you either. People can investigate and come up with their own conclusions. It is nice for them to have different opinions to look at.

 

Stephen...

Is that your 993 TT in the accident?

 

Yes, it was. I was coming home after giving a local Tech session and a car cut another car off on the highway as he entered. I was in a split lane that the other lanes merged in to. The guy jumps right out in front of me out of no where. I had two choices. Hit him at 80MPH from behind and run the risk of sending him across the highway into on coming traffic or trust my abilities. I hit the grass median and went around him only to have the left rear tire go down. I got back up on the highway and the rear end was everywhere so I pushed into the throttle to settle her down. As the rear started to stop moving so much the tire came off rim and sent me **** first across the highway and into the embankment. I hit the rear hard enough that is pushed the 1/4s in the door, shattered the turbos in half, split the cats and ripped them off of the car. Broke the nose of the tranny, all the mounts and sent the drive shaft through the front dif. As the car came up on the embankment it caught and flipped three times when finally it stopped it slide down from the top of the embankment on the top smashing in to the ditch. Heck of a ride. When the **** snapped I simply let go of the wheel and hunkered down into the seat. I knew I was in for a ride. Never was really hurt. When I hit the ditch the impact left my shoulder to the bottom of my neck yellow for days from the belt. The seat was moved 8 inches up from the floor where it buckled and pulled in towards the pillar towards the seat belt. The windshield also smacked me in the head. They never could find the guy that caused the wreck.

I loved that car. 540HP and still was working on it. Full MODE suspension, GTII tranny, allthe goodies. Too bad. But I ended up in the 01 so I have nothing to complain about

 

Dock,

Forgive me but your numbers add up to 110%

I assume you mean 38.5/61.5.

Point well taken about lightening front end. When I first read your post and saw 48.5% up front, I figured losing the spare would not mean too much. But it really is bias toward the rear. I guess someone has to figure out how to lighten the butt.

 

An exhaust helps lighten the butt since the OEM is soooo heavy!!

 

What kind of weight savings can you get?

 

Wow Stephen...Pretty luck to even escape a horrific crash like that. I never did think of Porsches are very safe cars, but the more I hear about people surviving high speed accidents...they are indeed very safe automobiles.

I still love those 993TTs...

 

The Fabspeeds are around 30 lbs, so that's about a 25 lb savings in the rear. The RUF and europipe weigh about the same as stock, so no weight loss on those.