CF roof - possible Group Buy

[Mallard]

if it was only a skin opposed to a structural dependant peice then price may also work out better, as thickness/material needed would be ultimately less.

although procees and manufacture will still be the same roundabouts if its made of 6 layers or 10

[316i compact]

Originally Posted by DustenT

You will need to cut out the majority of the floor to make the 323ti floor pan work. Basically you cut out the 318ti part, then weld in the 323ti pan. Cali-ti on this forum was looking at doing the same thing, but it was too much fabrication involved so I think he scrapped the idea.

If you look on realoem.com you can see that the rear sections of the 323ti are completely different than the 318ti. Just an FYI.

Thanks for the info, i didnt know that the floorpan was different. You saved me from a lot of trouble. I searched in realoem several times about the part. I noticed that the only different part between 318ti and 323ti was the plastic cover under the floor mat, where the tools are. I thought the battery was located there in the 323ti, is it or not? (off topic)

EDIT: i am talking about the part no.5 on the diagram

[L84THSKY]

How does the battery fit in part# 5?

Originally Posted by 316i compact

EDIT: i am talking about the part no.5 on the diagram

[316i compact]

Originally Posted by L84THSKY

How does the battery fit in part# 5?

The whole rear assembly of the 323ti and 318ti is almost the same. From the whole bodywork and vehicle trim there are only few differences.
According to realoem the only different part number from that diagram you posted is the No.5. In the 318ti it is called "Support car tools" while in the 323ti the realoem calls it "LIFTING JACK STORAGE PARTITION". Obviously it has sth to do with the battery.
Secondly, the only differences in the rear structure is that the 318ti is missing the part 15 , and the parts 19 and 20 from the second diagram(which are the battery holders, i could do without them).
I think you could do the battery swap with only the part No.5 needed, "LIFTING JACK STORAGE PARTITION", just finding a way for the battery not to move.


EDIT: Please someone make another thread concerning the battery transfer at the back and take all these posts there.

[robcarync]

anyway, just to further explain myself regarding moments of inertia and what not

moments of inertia is a tendancy for an object to roate about its centroid/center of mass...

if you do a carbon fiber roof, the center of mass would still be in the center, but you would have a weight distribution of more weight on the front and back and less in the middle, which would create a 'baton' effect...like when you throw a baton in the air and spins forever...

http://youtube.com/watch?v=WtlzxEYpK_o

it seems to me following this logic that a cf roof would increase the tendancy for the car to spin out in cornering...

it seems the better option would be a carbon fiber hood and to take out a tool kit and a spare tire/someting else from the hatch area to keep the weight distribution closer to the center.

[zboot]

Originally Posted by robcarync

anyway, just to further explain myself regarding moments of inertia and what not

moments of inertia is a tendancy for an object to roate about its centroid/center of mass...

if you do a carbon fiber roof, the center of mass would still be in the center, but you would have a weight distribution of more weight on the front and back and less in the middle, which would create a 'baton' effect...like when you throw a baton in the air and spins forever...

http://youtube.com/watch?v=WtlzxEYpK_o

it seems to me following this logic that a cf roof would increase the tendancy for the car to spin out in cornering...

it seems the better option would be a carbon fiber hood and to take out a tool kit and a spare tire/someting else from the hatch area to keep the weight distribution closer to the center.

Actually, it will not cause that effect. If our axis of rotation is colocated with the car's center of mass, then any weight located there will have no effect on the rotational inertia. The car's moment of inertia about axes that are either colocated with the center of mass, or parallel to it, will remain unchanged.

If you remember, moment of inertia is calculated based on how far mass is located from axes of rotation. If mass is located at the rotation point, it's distance will be zero and thus have no effect. So changing the effective mass located at the rotation point will not change the moment of inertia about that point. It wouldn't matter whether you had the stock roof, carbon fiber roof, or lead roof, the moment of inertia will stay the same.

[slammed_ti]

if i really wanted to save that much weight in my car i would just go on a diet and lose 15 pounds before i ever spent the money to put a carbonfiber roof on

[robcarync]

yeah i understand the concept of the 'point' of rotation...but applied in real life, a roof's weight is not applied over one single dimensionless point with a distance of zero, it occurs over an area covering the point of rotation.

so i guess a carbon fiber roof would still be reducing the moment of inertia and not increasing it but, it seems removing the weight closer would not be as benefitial as removing the weight that is farther away.

thats just what i was thinking though...im still just an engineering student trying to make sense/apply what i learn in a class room

[zboot]

Originally Posted by robcarync

yeah i understand the concept of the 'point' of rotation...but applied in real life, a roof's weight is not applied over one single dimensionless point with a distance of zero, it occurs over an area covering the point of rotation.

so i guess a carbon fiber roof would still be reducing the moment of inertia and not increasing it but, it seems removing the weight closer would not be as benefitial as removing the weight that is farther away.

thats just what i was thinking though...im still just an engineering student trying to make sense/apply what i learn in a class room

You don't see the benefit because all you are concerned about is the rotational inertia. There is also the translational inertia of the car as well. Imagine having a lead roof vs the regular roof on your car. . . just how fast could you go w/o modding the engine? So, while you rotational inertia may not decrease too much (though it will since the CF roof will be of less mass than the stock roof), you will see a bigger change in your engine's ability to move the car, especially at the lower rpms.

You also forget the point is to maintain or enhance the look of the car. If the only point was to remove weight from the car. . . then yes, there are definitely easier (and zero cost) ways that would have greater effects. . .

BTW, what are you majoring in? I pretty much just finished a BS/MS in electrical engineering. . . and probably will start on a PhD sometime this fall.

[robcarync]

mechanical engineering....im in my sophomore year so all i have actually completed is statics at the moment...working on solid mechanics and dynamics right now. and some other general education requirements.

sweet thanks for the explanation. it makes sense. although removing weight in any way whether it be removing tools/cf hood/cf roof woud still result in a better ability to move the car with the engine.

and yes for looks too. good point.

once again im not trying to criticize anyone for wanting to do this....the topic just kind of peaked my curiosity when it reminded me of some statics stuff. twas a nice informative conversation!

[3DGE]

Would it not be cheaper to just get a calif top rather then CF replacement?

[cosmos schwarz]

all this natter, am i the only person who thinks a cf roof would look cool as. if it did change the driving characteristics of the car, alter your driving style for christs sake. you add weight/subs to the rear of the car, you brake more before turn in. you lower your car, you can be harsher on the steering wheel, and so on.

[zboot]

Originally Posted by robcarync

mechanical engineering....im in my sophomore year so all i have actually completed is statics at the moment...working on solid mechanics and dynamics right now. and some other general education requirements.

once again im not trying to criticize anyone for wanting to do this....the topic just kind of peaked my curiosity when it reminded me of some statics stuff. twas a nice informative conversation!

Hey, good luck with the ME stuff. My dad did his PhD in ME and all through high school has been trying to convert me over. I think he still feels he has a chance lol. Anyway, don't worry about your response seeming critical. The point of this discussion is to bring out issues with the idea of a CF roof and to see what other people thought. This entire forum wouldn't be as interesting if there wasn't some back and forth every once in a while.

[HuGo]

LMFAO @ this thread! How did i miss this?

So what happen, did you buy it? Your willing to spend 2,000 for a roof? What if you cant do the work yourself? You gotta pay another $500 plus dollars to have it installed (thats if any body shop would even touch it). Why dont you just get the total of ~$3,000 and buy a DASC? You'll go much faster than a CF roof. You can also buy a CF hood and hatch, lose weight, remove the back seat, and remove the spair tire and still would be cheaper.

Originally Posted by DustenT

This is the most ridiculous idea I've ever heard.

+ a gillion.

I dont know whats worse, CF roof or lambo doors?

[HuGo]

Instead of putting "no way!" you should have put, F NO!
LoL.