# 2 door's rigidity/body strength vs. 4 door



## yafayu (Aug 17, 2005)

*couple rigidity/body strength vs. sedan*

Hi, i know the new 3 is out for a while but should i wait for 2 door couple to release? i really don't care the looking, but for the money should i pay less get a 4 door and upgrade to sport package, rather than pay more money just for sporty look?

and anyone know what have better rigidity and more stiffness of body construction between coupe and sedan?


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## jeff330i (Feb 2, 2002)

sedans are much more rigid because they have pillars between the front and rear doors which the coupe lacks. Its like two extra braces so there is less "twist" on the body during hard maneuvering. There were torsional numbers for the coupe and sedan with and without folding rear seats (which also make it more flexible) posted on this bored sometime back if you do a search.

Just imagine all those times you can just open the back door instead of folding the front seat down and diving in the little hole will more than make up for the "unsporty" look. get a sedan :thumbup:


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## yafayu (Aug 17, 2005)

so is sedan more likely to used on track racing than a coupe? but is sedan heavier than coupe tho?


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## Malibubimmer (Sep 28, 2005)

yafayu said:


> Hi, i know the new 3 is out for a while but should i wait for 2 door couple to release? i really don't care the looking, but for the money should i pay less get a 4 door and upgrade to sport package, rather than pay more money just for sporty look?
> 
> and anyone know what have better rigidity and more stiffness of body construction between couple and sedan?


Forgive my curiosity, but are you an Anglophone or a Francophone? Or was your native tongue something else?


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## yafayu (Aug 17, 2005)

English is not my mother tongue


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## jeff330i (Feb 2, 2002)

yafayu said:


> so is sedan more likely to used on track racing than a coupe? but is sedan heavier than coupe tho?


yeah they are. Unless it's an M3.


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## andy_thomas (Oct 7, 2002)

jeff330i said:


> sedans are much more rigid because they have pillars between the front and rear doors which the coupe lacks.


Just out of interest, what would you call the big pillar between the front door and rear window of the coupe? The one with the seatbelt upper mounting on it? Looks like a B-pillar to me 

Coupes have fold-down rear seats as standard. According to BMW NA, they are slightly stiffer than the 4-door equipped with fold-down rear seats, but not as stiff as the sedan without this option.


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## jeff330i (Feb 2, 2002)

andy_thomas said:


> Just out of interest, what would you call the big pillar between the front door and rear window of the coupe? The one with the seatbelt upper mounting on it? Looks like a B-pillar to me


it is a B pillar, but look where it's placed, and compare it to where the sedan's B pillar is.


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## jeff330i (Feb 2, 2002)

ok i mustered up the time to do a search for yall:
You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.

Sedan (w/o folding seats)	18000Nm/deg of torsion
Sedan (w/folding seats)	13000Nm
Sport wagon (w/folding seats)	14000Nm
Coupe (w/folding seats)	12500Nm
Convertible	10500Nm

Not that a coupe is a twisty-toy, but the sedan is still 44% more rigid in the non-folding seat setup, and 4% stiffer than the coupe in the folding seat setup.


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## Malibubimmer (Sep 28, 2005)

jeff330i said:


> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats)	18000Nm/deg of torsion
> ...


Thanks for the info. Can you give us the values for the E63 and E64 (645Ci/650i)?


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## EdCT (Mar 14, 2002)

jeff330i said:


> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats)	18000Nm/deg of torsion
> ...


Interestingly, the Z4 slots in there at 14,500 (I think), pretty good for a 'vert. :thumbup:

Ed


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## SLang (Dec 1, 2003)

> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats) 18000Nm/deg of torsion
> ...


I know the original post was not racing or track related necessarily, but if you're going to base a track car decision on this, here are some things to consider:

The info in the quote would imply that the only real reason the sedan is stiffer than the coupe is because of the panel welded in when the car is not equipped with folding seats. This can be easily accomodated by welding a panel into the coupe chassis. After all, 4% difference from coupe to sedan is not going to be a lap-time breaker.

Also, remember that the coupe DOES have a B pillar. It just isn't quite as big and does not have a door attached to the backside.

Many like the larger door opening of the coupe for egress in case of an accident or emergency. It's easier to get out of a coupe than a sedan, especially with a cage installed.

Some like the fact that the sedan's B-pillar is right by your head, because it offers additional protection in case of side impact. Interestingly, some do NOT like the sedan's B-pillar location because it's just another place to hit your head in an incident.

In the end, the chassis are comparable when the panel is welded in. Although my last race car was a sedan, the next one will be a coupe, as I like the larger opening for egress.


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## tim330i (Dec 18, 2001)

yafayu said:


> so is sedan more likely to used on track racing than a coupe? but is sedan heavier than coupe tho?


 I don't think the stock chassis flex number matter much when it comes to building a race car because of the roll cage. Most 'serious' levels of racing allow for suspension point tie-in to the cage so the chassis in terms of flex is very different

Thanks to DTMPower for the pics -
http://www.dtmpower.net/pictures/ptg2005/DSC_2154.jpg
http://www.dtmpower.net/pictures/ptg2005/DSC_2146.jpg

For the coupe/sedan weight as far as I know the sedan is lighter...but again it doesn't really matter when it comes to racing.

Tim


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## andy_thomas (Oct 7, 2002)

jeff330i said:


> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats)	18000Nm/deg of torsion
> ...


Ah, I remembered seeing those numbers, but got the coupe and 4-door the wrong way around (12,500/13,000). Thanks for the heads-up.


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## Magna (Jan 4, 2002)

jeff330i said:


> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats)	18000Nm/deg of torsion
> ...


Hi Jeff, Are those figures for the E90 or E46?


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## andy_thomas (Oct 7, 2002)

Magna said:


> Hi Jeff, Are those figures for the E90 or E46?


I'm not Jeff, but I can tell you those are the figures quoted for the E46.

The E90 is supposed to be 25% stiffer, according to the British marketing puff. Even if we take the stiffest E46 (the 4-door) and apply that improvement, that's still only 22,500 Nm/deg. The Saab 9-3 from 2003 is allegedly better than that, but all comers are comprehensively blown away by the Alfa 159, whose makers claim nearly 32,000 Nm/deg.


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## Rowag (Nov 12, 2004)

jeff330i said:


> ok i mustered up the time to do a search for yall:
> You can see that the coupe with folding seats is NOT as rigid as the sedan with folding seats.
> 
> Sedan (w/o folding seats)	18000Nm/deg of torsion
> ...


 Those numbers are for E46s, right? The E90 (sedan and sport wagon only at the moment) should be even more rigid.

Also, the E46 coupes were sold without the folding seats as standard for a few years, so depending on the model year you're looking at there may be other options available.


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## Watchdog (Jan 23, 2005)

When I attended the BMW Canada Driver Training I asked a question related to this.

I asked the instructor, if there was a handling difference between the coupe and sedan. He said yes there was, left a pause to keep everyone hanging and then went on to say that when they race and BMW asks which 3 Series they want, they always ask for the sedan because it's stiffer due to the B pillars.

He didn't specify folding or non-folding seats, but seeing the above figures I assume they would go with non-folding seats.

Interesting that in Canada we get folding seats as standard now. I think for the E36 it was an option, but now it's standard here, well at least for the 325 and 330, not sure about the 323.


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## BlackChrome (Nov 16, 2003)

Rowag said:


> Also, the E46 coupes were sold without the folding seats as standard for a few years, so depending on the model year you're looking at there may be other options available.


Really? I don't recall Coupes being sold without the fold down seats. Heck, even they have been standard on the M3 Coupes. :dunno:


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## andy_thomas (Oct 7, 2002)

Rowag said:


> Also, the E46 coupes were sold without the folding seats as standard for a few years, so depending on the model year you're looking at there may be other options available.


My 2004 ETK doesn't list a solid rear seat back for any E46/2 in any market. Are you sure?


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## Rowag (Nov 12, 2004)

andy_thomas said:


> My 2004 ETK doesn't list a solid rear seat back for any E46/2 in any market. Are you sure?


 Hmm... I'm not 100% certain. Perhaps it was the '04 or '05 330i's that came standard with the folding rear seats? I'm pretty sure that some model came with them standard at some point, but I'm not certain whether it was the sedan or the coupe.

I remember thinking "that really sucks for people that want the rigidity", though now that I think about it it may have been the sunroof (which was standard on the latest E46 coupes).


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## Moderato (Nov 24, 2003)

Are we talking about a daily driver BMW or an all-out race car?  Get which ever car you think looks better or will suit your needs better.


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