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Discussion Starter #1 (Edited)
Very nice, very expensive, nice article:

Lamborghini Aventador Roadster, ready for takeoff: Motoramic Drives | Motoramic - Yahoo! Autos

but getting down to the removable top, this was interesting:

"And when it came to the carbon fiber convertible roof, Lamborghini freely admits sacrificing some ease-of-use for beauty: “We told the designer, you can do whatever you want – it just has to look the best,” says Stephan Winkelmann, Automobili Lamborghini’s elegant chief executive.

The result? No bulky folding hardtop or shapeless cloth pup tent to break up those suggestive body lines. Instead, two glossy, ridge-backed panels of carbon fiber, weighing just 13.2 pounds each, pop into the roof -- and take up nearly the entire under-hood cargo space when not in use. Storing or fitting the roof takes some practice and steady hands. Owners will want to keep a sharp eye out for sudden thundershowers."

:lol:

Well....at least we didn't spend $450k+ AND be fighting with a removable targa.

What could have been......I think Pontiac would have redesigned the targa top into 2 pieces that would have fit in the trunk after a year or two more coupe production.
 

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I've wondered why GM didn't opt for T tops for the coupe because I would think they could have been designed to be stacked in the back of the car when removed.

Anyone know if the addition of a permanent member between rear and front window areas would have constituted an officially different body model and required complete recertification and crash testing? That's one reason I thought might have prevented what would otherwise seem a preferable course to the rather odd set up we ended up with a top that you can take off with nowhere to put it.

Of course I would also have liked a roof that increased torsional stiffness the way the Aventadors apparently does! I was never sure that was even posible with a removable panel until I saw that article. Too bad GM missed a bet.
 

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Discussion Starter #3
Well, Hopefully the thought of Ttops would have never entered their minds....I just can't get past that being a 70'/80's thing. A targa that comes off in half would be the preference. And that increased safety and stiffness cost the car in weight to the tune of 110 pounds. Seeing as we don't have a top speed of more than 200mph I would have hoped that the top redesign really would come with little or any added weight.
 

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Know what you mean about T tops, I just regret the missed opportunity to up to double the stiffness of the chassis for no significant cost by making it a real coupe!
 

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Know what you mean about T tops, I just regret the missed opportunity to up to double the stiffness of the chassis for no significant cost by making it a real coupe!
I think double is a bit over-estimating.


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I think double is a bit over-estimating.


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I could understand how you might think that, but see this on the BMW Z4 sports car:

Scoring 14,500Nm/degree in BMW’s torsional stiffness test, the M Roadster is pretty stiff for an open car, and despite its wide 225/45 and 255/40 rubber on 8.0J and 9.0J x 18-inch alloys rubber, scuttle shake on poor roads in minimal. Even so, it does not come close to the Coupé’s impressive 32,000 Nm/degree, which is more than double the Roadster’s rigidity.
(BMW Z4 M Coupé - PistonHeads)

Anyone have a torsional stiffness figure for our favourite 'flexible flyers'?
Ah, wait, I found an old thread on this http://www.solsticeforum.com/forum/f26/strutural-feel-rigidity-flex-stiffness-body-roll-ect-5388/

The Solstice is apparently 8,000 Nm/degree or half as stiff as the convertible BMW. No wonder the factory found out they needed special kits to keep the rear suspension under control when they went racing! Mind you that thread quotes lower figures for the BMW than the pistonheads article did too.

DDM may have something to add although I seem to recall asking Dave if they had actual torsion measurements regarding their Backbone and I think they just had some measure of droop indicating effect, but not a conventional value in Nm/deg. of twist.
 

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DDM may have something to add although I seem to recall asking Dave if they had actual torsion measurements regarding their Backbone and I think they just had some measure of droop indicating effect, but not a conventional value in Nm/deg. of twist.
I believe you're right...
 

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I could understand how you might think that, but see this on the BMW Z4 sports car:



(BMW Z4 M Coupé - PistonHeads)

Anyone have a torsional stiffness figure for our favourite 'flexible flyers'?
Ah, wait, I found an old thread on this http://www.solsticeforum.com/forum/f26/strutural-feel-rigidity-flex-stiffness-body-roll-ect-5388/

The Solstice is apparently 8,000 Nm/degree or half as stiff as the convertible BMW. No wonder the factory found out they needed special kits to keep the rear suspension under control when they went racing! Mind you that thread quotes lower figures for the BMW than the pistonheads article did too.

DDM may have something to add although I seem to recall asking Dave if they had actual torsion measurements regarding their Backbone and I think they just had some measure of droop indicating effect, but not a conventional value in Nm/deg. of twist.
It would appear from Solsticeman's post that its almost impossible to accurately compare car "stiffness" from one car to another given all the variables.

I'm not arguing that a coupe wouldn't be stiffer. I'm just saying I doubt it would double the perceived stiffness of the car.

I do also believe that Dave found the weak link in the car with the tunnel brace. GM was on course to make those updates to the car to stiffen it up. The pro beam is a perfect example. They just ran out of time. :(


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I'm not arguing that a coupe wouldn't be stiffer. I'm just saying I doubt it would double the perceived stiffness of the car.
Not sure I follow.

The BMW convert was already stiffer than the Solstice and converting it to a proper coupe more than doubled the stiffness. Why wouldn't doing the same thing to the Solstice result in at least that much improvement?

And not sure what you mean by 'perceived' stiffness. We are talking about measured numbers, not seat of the pants impressions.

The figures in my quotation were from BMW and presumably can be regarded as gospel; I'm not sure where the poster in that thread I dredged up got his figures.
 

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The BMW convert was already stiffer than the Solstice and converting it to a proper coupe more than doubled the stiffness. Why wouldn't doing the same thing to the Solstice result in at least that much improvement?

And not sure what you mean by 'perceived' stiffness. We are talking about measured numbers, not seat of the pants impressions.

The figures in my quotation were from BMW and presumably can be regarded as gospel; I'm not sure where the poster in that thread I dredged up got his figures.
If you read that post more carefully, I think you'll see those figures were JUST examples for comparison. NOT actual figures for those cars. So the BMW may - or may not - be stiffer than the Sol.
 

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If you read that post more carefully, I think you'll see those figures were JUST examples for comparison. NOT actual figures for those cars. So the BMW may - or may not - be stiffer than the Sol.
You are right. I don't think there is much doubt that the Solstice will be less stiff than the BMW though - that car is better than most.

I wonder if we have any factory guys that have actual figures - I searched and couldn't find any.
 

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Interesting.

I get into arguments with guys that race old MGs. My MGA has a very sturdy frame, further reinforced by a careful roll bar installation and is a pretty stiff platform. The MGB guys have a unibody made up of welded together stampings which gives you a decently stiff chassis that can quickly deteriorate when the rocker panels rot and people bodge them and don't repair properly, resulting in extreme cases where you can't open both doors at once and expect to be able to close them again.

The MGB owners somehow manage to ignore the second part, about how bad it can get with any rust and assume they all have pristine mint cars that are as stiff as when they left the factory.

I guess we don't need to worry about rust as much on the Solstice, but I have a vision of some junior engineer analyzing the torsional stiffness of the original design, putting his stamp on it as being 'good enough' and then having to eat his words when the factory first sponsored solo competition and found out that his calculations had been garbage and the chassis flexed far to much for a competition setting.

They probably made him design the rear suspension kit (elaborate and expensive) to fix that and probably sent him off to shred the original figures on the stock chassis, never to be released to the public.

IIRC the Miata is also bad in this respect - at least the first guys fitting Ford V8s to them found that they twisted all over the place.
 

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Discussion Starter #14
You are right. I don't think there is much doubt that the Solstice will be less stiff than the BMW though - that car is better than most.

I wonder if we have any factory guys that have actual figures - I searched and couldn't find any.
The Sol has done well on road coarses at sanctioned events. If you want that there are cages out there for it. Our car seems to handle pretty darn well having the backbone, probeam and LV brace installed. I want the car to stay light.

Just line that BMW up for me on a nice straight 1/4 mile......
 

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Just line that BMW up for me on a nice straight 1/4 mile......
I'll save you the humiliation -

Solstice GXP 1/4 mile around high 13s
Z4M 1/4 = 13.2 or so.

I don' really care that much about 1/4 mile times anyway, I am much more interested in how the cars handle on a winding road.
 

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Discussion Starter #16
I'll save you the humiliation -

Solstice GXP 1/4 mile around high 13s
Z4M 1/4 = 13.2 or so.

I don' really care that much about 1/4 mile times anyway, I am much more interested in how the cars handle on a winding road.
I do hope that you are comparing a 2009 Z4 to a Solstice? A 2013 model is what I expect you are looking at, because as I recall the '09 z4 was unimpressive.

No matter, with the tune and IC I will beat 13.2, so sorry about the beemer. It was how much more $$$ again?

I like winding roads for fun, not serious cornering, you need to go to a course for that. Car is fun enough as it is, wouldn't want to be pushing things too hard if not on a course.
 

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Tons more dollars for sure.

I compared the Z4M to the GXP. You could also compare the regular Z4 to the NA, though I have no idea what the result would show. The BMW is heavier but more powerful (and stiffer of course...;)

I just snagged a 1/4 mile figure from a road test. What are you doing with the GMPP tune? I've never seen a legitimate sub 13.0 time with that.

In any case, clearly yours and my priorities are a little different. The fact that I am a racer doesn't mean that I drive on the road in an unsafe fashion, just that I have a great appreciation for handling on the street.

I test drove the Z4M (convert, as I couldn't find a coupe for sale) and it is faster in a straight line than a GXP with GMPP tune (what I own now) and a heck of a lot of fun in the curves. It is the only German car that has ever impressed me enough to consider owning one.

But having said that, the fact that the Solstice is much less rigid than the Z4 doesn't really matter that mush. I set to improving matters and with ZOK bars at both ends, a Probeam, Backbone and LV front brace, I'd say that the handling is now as good as the Z4M (I stress M because the suspensions etting were different than on the regular Z4) and in fact the Solstice does the job with much less drama. The feel of the car has been substantially changed by those mods.

With the deep set instruments on the Solstice, very hard to read in full sun, I tend to drive by feel when on open winding roads with no traffic. I was doing that in the BC interior in a large constant radius end in the road when my wife asked how fast I was going. I said probably around 130 kph (80 mph). I looked down and without feeling at all hung out, the car was comfortably doing 160 kph (100 mph).

The point of my posts in this thread wasn't that the BMW was in any way better than the Solstice. While it is clearly better outfitted (look at the interior) faster and better handling in stock form, the Solstice can be made to match it for far less money than the BMW costs. The point was simply that GM missed a bet when they failed to make the coupe as stiff as they easily could have done because it would have been a worthwhile job in terms of result. At least for the maybe 1% of owners that knew the difference or cared about that sort of thing.

If you want to watch an enjoyable clip from Top Gear comparing the Z4M with the Boxster S, take a look at this (I really, really wish the Pontiac guys had offered a stock GXP with their uprated suspension package and the GMPP tune, stock, so that the mags would have road tested it - I think it would have kicked ass!)

 

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Discussion Starter #18
It definitely would have been nice if the mags. had the chance to test drive ANY Sol GXP with GMPP and perhaps the aftermarket handling goodies. I honestly don't know what they felt like driving a stock GXP since our car came with the tune and all the DDM items. I'm sure if I ever took it all off I'd be disappointed going backward....spoiled so to speak.

I didn't write anything about sub 13 1/4 mile runs. I just stated I would beat a 13.2 run (which leaves us with 13.1 or 13.0 flat).:thumbs:

And I can't prove my statement as I don't have a track slip. But it would be fun to find out. There may be another member on here that has a track time though, this is pretty basic for our cars to have a GMPP tune and aftermarket IC, nothing else.......

I'm not finding the Z4M though, I looked up the Z4 for '09 and for '13 and grabbed their upgraded units (based on price) as follows:

09 list is $52475, '13 is $65,095 and both years are sdrive 35i's? whatever that means?

both are inline 3.0 6's that are twin turbo (or so cars.com says)!!! And yet here are the specs, not real impressive if you ask me (given 3 liters and TT's):

Horsepower 300 @ 5,800 rpm 335 @ 5,900 rpm
Torque 300 @ 1,400 rpm 332 @ 1,500 rpm

The cars weigh in the range of 4-500lbs more than our cars around 3k pounds. Both are running 225's front, 255's rear.
 

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The Z4M I was after (and am talking about) is the original version (E85) which has an 8000 rpm red line, no turbos and 330 bhp. Also an exhaust note any Kappa owner would kill for. The later E89 series that was reintroduced in 2009 has a twin turbo engine that dropped 200 cc and only produced about the same power as the earlier nonturbo. Not what you or I would call progress!

The early engine can take low boost turbo (it is fairly high compression) and produce around 500 + bhp with various turbo kits (or the sky is the limit with a fat wallet - claims of 800 -0 1000 bhp abound).
 
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