[godunovs65]

Originally Posted by Dawgz

I am not saying that alone will make the difference, i said every bit counts. So yes, lighter wheels, removing rear seats, passenger seat, lighter driver seat - all those will help every little bit. if you can shave off 40lbs (of the sunroof), that's even better.

If racing, undoubtedly, one must get the free carbon roof. My original question was to those who never race. Why do they choose the CF roof? Am I missing something obvious? So far, I hear it's only for looks, for extra headroom, and for resale value and desirability. All are valid reasons. Just don't apply to me. Maybe there are more reasons and one will be convincing enough to forgo the sunroof. I still have a few months until the allocation to change the configuration.

[godunovs65]

Originally Posted by Needsdecaf

Lol, you are WAY over analyzing this.

And I'm not even trying hard to do so. I have a lot of help. 6 pages now. That's 5 too many.

[G MONEY]

Originally Posted by godunovs65

The cf roof is for torsional rigidity. Weight saving is secondary. Losing the muffin top, on the other hand, should be the primary concern for many.

Lol. I hear that. January 2 we all start the diet

[Needsdecaf]

Originally Posted by godunovs65

The cf roof is for torsional rigidity. Weight saving is secondary. Losing the muffin top, on the other hand, should be the primary concern for many.

You keep saying this. Not even BMW says this in their internal product guide.

https://g80.bimmerpost.com/forums/at...8&d=1622934458

And in fact, there is an entire discussion on rigidity, and the CF roof is not mentioned at all.

[M3SQRD]

Originally Posted by Gottagofast

"According to the documentation, the weight saving is only 3.3lbs or 1.5kg"

Completely wrong.

That weight saving is compared to a regular aluminum roof. The sunroof adds about 30-40 pounds, to the worst possible place to add weight, the roof of a car.

You also can not spec M driver's package with a sunroof and are now hard limited to 155 MPH top speed as BMW deems the car unsafe to go faster because of the air pressure exerted on the glass top and all the movable parts.

Think about it, it's a zero cost option. The carbon roof is more expensive for them to make than a regular metal sunroof.

Exactly! You can’t forget the glass, motor, drive belt, etc. when selecting the $0 sunroof option.

However, I did love my e46 M3 Imola Red slick top with Imola Red leather with manually adjustable seats. Ordered my 240ix with slick top too.

If BMW still offered a non-sunroof slick top option, I wonder how that would affect CF vs sunroof vs Al slick top build rates?

[Mike02z]

All personal preference. Two reasons I went CF roof

1) room for my helmet
2) never used a sunroof on any car I’ve had it on

[BryanCO]

Originally Posted by godunovs65

And I'm not even trying hard to do so. I have a lot of help. 6 pages now. That's 5 too many.

The point Needsdecaf is making (maybe) is that, we can workshop the objective and subjective reasons for and against the CF roof and the sunroof. But, it’s a personal decision and you want a sunroof (not that there is anything wrong with that) so why the repeated discussion (that we are contributing to…).

[geko29]

Originally Posted by godunovs65

The cf roof is for torsional rigidity. Weight saving is secondary.

Not true. The roof panel is not part of the roof structure, and carries no torsional load. Which is good, because if you've ever seen the roof off the car, it's very thin and flexible as hell.

[godunovs65]

Originally Posted by Needsdecaf

You keep saying this. Not even BMW says this in their internal product guide.

https://g80.bimmerpost.com/forums/at...8&d=1622934458

And in fact, there is an entire discussion on rigidity, and the CF roof is not mentioned at all.

I read the guide, sure. A lot of people say "torsional rigidity" and the words "pressure resistance" must imply that.

Originally Posted by M3SQRD

Exactly! You can’t forget the glass, motor, drive belt, etc. when selecting the $0 sunroof option.

However, I did love my e46 M3 Imola Red slick top with Imola Red leather with manually adjustable seats. Ordered my 240ix with slick top too.

If BMW still offered a non-sunroof slick top option, I wonder how that would affect CF vs sunroof vs Al slick top build rates?

More people would still choose CF. It's just so expensive, why would one not get it for free? Unless, there are convincing reasons to choose otherwise.

Originally Posted by BryanCO

The point Needsdecaf is making (maybe) is that, we can workshop the objective and subjective reasons for and against the CF roof and the sunroof. But, it’s a personal decision and you want a sunroof (not that there is anything wrong with that) so why the repeated discussion (that we are contributing to…).

I dont' know. It's a rhetorical question. The best way to stop this is for everyone to stop replying. But it's very hard to stop replying. Oh well.

Originally Posted by geko29

Not true. The roof panel is not part of the roof structure, and carries no torsional load. Which is good, because if you've ever seen the roof off the car, it's very thin and flexible as hell.

Carbon fiber is thin, flexible, but stiff. Carbon fiber bicycles are the living proof of that. My full-carbon (frame, wheels, seatpost, saddle) bike is super light, stiff, yes smooth as butter. And carbon fiber used for bikes gets stiffer every iteration, yet rides becomes smoother. I can't explain that. Science, man. It's all science.

[FloridaM5]

Originally Posted by godunovs65

Carbon fiber is thin, flexible, but stiff. Carbon fiber bicycles are the living proof of that. My full-carbon (frame, wheels, seatpost, saddle) bike is super light, stiff, yes smooth as butter. And carbon fiber used for bikes gets stiffer every iteration, yet rides becomes smoother. I can't explain that. Science, man. It's all science.

I love science, especially physics.

I also love lamp.

[godunovs65]

Originally Posted by FloridaM5

I love science, especially physics.

I also love lamp.

Are "M" and "P" still in use?

[Needsdecaf]

Originally Posted by godunovs65

I read the guide, sure. A lot of people say "torsional rigidity" and the words "pressure resistance" must imply that.

Except that it doesn't. When they are talking about pressure resistance from the roof over a certain speed, it has to nothing to do with torsional rigidity. There is either too much pressure or negative pressure (suction) over that speed from AERO which is either pushing down on the sunroof or pulling up on it enough to compromise the seal.

Nothing to do with chassis' torsional rigidity. You're reading into this to fit your own conclusions. But those two things are not interchangable.

[geko29]

Originally Posted by godunovs65

Carbon fiber is thin, flexible, but stiff. Carbon fiber bicycles are the living proof of that. My full-carbon (frame, wheels, seatpost, saddle) bike is super light, stiff, yes smooth as butter. And carbon fiber used for bikes gets stiffer every iteration, yet rides becomes smoother. I can't explain that. Science, man. It's all science.

I don't disagree with any of this. But it doesn't change the fact that you're wrong about the roof panel being a structural member of the frame. There are three beefy crossmembers that carry all the torsional load, and then the roof panel is either spot-welded (for metal) or glued (for CF) at the edges.

If those crossmembers weren't there and there was a significant torsional load, the roof panel would bend upward into a curve, because it just isn't very rigid. The huge, flat, paper-thin roof panel is NOTHING like a small tube used for a bike that is designed to carry a structural load.

[godunovs65]

Originally Posted by Needsdecaf

Except that it doesn't. When they are talking about pressure resistance from the roof over a certain speed, it has to nothing to do with torsional rigidity. There is either too much pressure or negative pressure (suction) over that speed from AERO which is either pushing down on the sunroof or pulling up on it enough to compromise the seal.

Nothing to do with chassis' torsional rigidity. You're reading into this to fit your own conclusions. But those two things are not interchangable.

Makes sense. That's a reasonable explanation. Thanks! We can all agree, that a carbon roof is required for racing applications. Therefore, no functional benefit for those who are not racing, except perhaps the extra headroom for those 6'4"+

[godunovs65]

Originally Posted by geko29

I don't disagree with any of this. But it doesn't change the fact that you're wrong about the roof panel being a structural member of the frame. There are three beefy crossmembers that carry all the torsional load, and then the roof panel is either spot-welded (for metal) or glued (for CF) at the edges.

If those crossmembers weren't there and there was a significant torsional load, the roof panel would bend upward into a curve, because it just isn't very rigid. The huge, flat, paper-thin roof panel is NOTHING like a small tube used for a bike that is designed to carry a structural load.

Being wrong is a part of learning. The "Features" section on the M4 page says "Carbon fiber-reinforced-plastic roof". I missed the second dash. CF reinforces the plastic itself, not the roof of the car. I read it as the carbon fiber-reinforced plastic roof as though the plastic roof reinforces the car. Learned something new today. Thanks!

[geko29]

Originally Posted by godunovs65

Being wrong is a part of learning. The "Features" section on the M4 page says "Carbon fiber-reinforced-plastic roof". I missed the second dash. CF reinforces the plastic itself, not the roof of the car. I read it as the carbon fiber-reinforced plastic roof as though the plastic roof reinforces the car. Learned something new today. Thanks!

I can see how that could be confusing. Cheers!

[BryanCO]

Originally Posted by godunovs65

Makes sense. That's a reasonable explanation. Thanks! We can all agree, that a carbon roof is required for racing applications. Therefore, no functional benefit for those who are not racing, except perhaps the extra headroom for those 6'4"+

No. The CF roof is not required for anything. There are various benefits of the CF roof. This is a street car. Get the features you want. A sunroof, convertible, and many other features on these cars (including mine) makes the car more appealable to a broader audience but all result in cars further from the core M or enthusiast spec.

Originally Posted by godunovs65

Being wrong is a part of learning. The "Features" section on the M4 page says "Carbon fiber-reinforced-plastic roof". I missed the second dash. CF reinforces the plastic itself, not the roof of the car. I read it as the carbon fiber-reinforced plastic roof as though the plastic roof reinforces the car. Learned something new today. Thanks!

Look up how CF is made to understand the ‘plastic’ reference.

[chicagofan00]

For those curious, here is what the CF roof looks like on the M3 when you drop the headliner.

[godunovs65]

Originally Posted by chicagofan00

For those curious, here is what the CF roof looks like on the M3 when you drop the headliner.

Nice!!! Yes, I was definitely curious. Thanks for sharing. Are you turning your roof into a night sky?

[chicagofan00]

Originally Posted by godunovs65

Nice!!! Yes, I was definitely curious. Thanks for sharing. Are you turning your roof into a night sky?

Yes, I had the starlights installed back then and grabbed this photo when the installers were taking a break. No longer own the G80 though.

[eugenebmw]

For me, CF any day.

Reasons:

1: Extra room for helmet.
2: Keep my head warm in the Canadian winter lol.
3: Safety reason. I track my car at least one a month, sometime 2.

[godunovs65]

Originally Posted by eugenebmw

For me, CF any day.

Reasons:

1: Extra room for helmet.
2: Keep my head warm in the Canadian winter lol.
3: Safety reason. I track my car at least one a month, sometime 2.

Thanks! My head started to hurt when I read your reason #2. Even in Virginia I have to keep that screen closed in the winter. The glass is ice cold to touch. Interestingly enough, I don't track any cars and I want a metal roof for safety reasons too. Metal doesn't crack as eagerly as CF. Glass shatters though. A solid metal roof would be the safest probably.