e30 Cabrio Chasis Stiffening

[mr2peak]

If you really want to stiffen up the car, look at the Flying Miata butterfly brace for inspiration.

[decay]

We are each just sharing our own experience and what we learned from it. To me THATs what it's all about. Saying everyone is wrong but you....well...kinda ends the conversation....if we let it...but don't we cause it's too much fun :)

conversation really isn't going to continue a lot further when you say your opinion > my direct experience anyway, so go ahead and continue being wrong :)

you haven't told us anything about YOUR vert build, so i'm guessing one hasn't happened.

[squidrope]

I'm "guessing" that BMW wouldn't have put all that extra weight and expense into stiffening the vert chassis if they didn't need to. The roof ads tremendous strength to the chassis to say otherwise is just not true.

[allen_t]

Have the garagistic xbrace on my vert and it's been one of the best upgrades I've done.

[validius]

Have the garagistic xbrace on my vert and it's been one of the best upgrades I've done.

I bought a different brand but i agree, the lower X brace is a night & day difference.

[jeffnhiscars]

conversation really isn't going to continue a lot further when you say your opinion > my direct experience anyway, so go ahead and continue being wrong :)

you haven't told us anything about YOUR vert build, so i'm guessing one hasn't happened.

My "opinion" is based on my experience and If you haven't seen my Cabrio build thread, you only have to..oh..I dunno...lower your eyes 1/2" ;)

Having said that, I stand firm in my "opinion" that a piece of frp anchored at 4 points and with zero torsional reinforcement whatsoever will add anything noticeable (let alone anything measurable) to the stiffness of a Cabrio...beyond the placebo effect...in my opinion....which is based on my experience.:p

I'm good to agree to disagree. Seems you aren't...cause we are all wrong..except for one of us

[Ether-D]

I disagree to agree. Hard top makes a big difference. Jeff, I feel like you are usually reasonable about stuff like this. Why so stubborn this time?

[Ether-D]

Ahh, maybe I'm being stubborn. Anyway, it don't matter, it's just the Internet...

[validius]

I disagree to agree. Hard top makes a big difference. Jeff, I feel like you are usually reasonable about stuff like this. Why so stubborn this time?

Because a convertible with a hard top is just a worse coupe?

I'd like to stiffen up my car while keeping it open on top.

[Ether-D]

Because a convertible with a hard top is just a worse coupe?

I would state it this way:
In the summer a convertible with a hardtop is a worse coupe.
In the winter a convertible with a hardtop is a better convertible.

[jeffnhiscars]

I disagree to agree. Hard top makes a big difference. Jeff, I feel like you are usually reasonable about stuff like this. Why so stubborn this time?

I just have a different opinion on the subject is all after driving half of each year with a hardtop. Now I haven't had it on since I installed the konis or did the 5 speed swap but neither of those would stiffen the chassis. Keep in mind this is entir conversation is anecdotal (like a butt dyno) since no one has offered any science on the subject.

Trying to be as scientific as possible, I just don't see how a thin sheet of un reinforced frp will offset the twisting of a 3000lb flounder traveling at high speed and the stiffer that flounder gets, the less potential there is for that flimsy sheet of fiberglass to make a difference.

Think of it like this....the cars torques from all 4 corners and the mounting points of the roof are within that rectangle only much smaller. That means the leverage effect of the car twisting the roof has to overwhelm the roofs ability to "torque back" (yes I made that up) aka resist chassis flex.

To me it's physics. The roof is competely submissive to the chassis and has a very marginal ability to fight back given the forces involved....in my opinion :)

What if I'm right and ALL of YOU are wrong ;D

Any engineers or physicists out there ?

[validius]

Any engineers or physicists out there ?

Yes, i'm an ME. I don't have anywhere near enough data to come to any conclusion about the hard top except it almost certainly wont make the car worse.


A small amount of strength in that shell shape across the mounting points that the hard top attaches to could make allot of difference. Fiberglass is deceptively strong in tension. It is absolutely plausible that there could be a real benefit to a hard top but without data i cant say.

[Brezzi]

I would state it this way:
In the summer a convertible with a hardtop is a worse coupe.
In the winter a convertible with a hardtop is a better convertible.

100% the reason I need to buy a hardtop.

Even if the jury is out on adding any stiffening.

Personally I see both stances on the subject but I think it would add a little bit of stiffness. Not a lot but again no 1st hand experience.

[jeffnhiscars]

Yes, i'm an ME. I don't have anywhere near enough data to come to any conclusion about the hard top except it almost certainly wont make the car worse.


A small amount of strength in that shell shape across the mounting points that the hard top attaches to could make allot of difference. Fiberglass is deceptively strong in tension. It is absolutely plausible that there could be a real benefit to a hard top but without data i cant say.

That's really all I'm saying....it might and yes its plausible. That leaves enough room for me to be comfortably sceptical...as opposed to stubborn that it's not a foregone conclusion :)

Aren't we talking torsion not tension ?

[Ether-D]

I feel like we're talking torsion, tension, and compression. To me it's like a 2"x4"x12" cardboard box versus a 4"x4"x12" cardboard box. One is certainly easier to twist and bend.