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Torsional stiffness is all about handling, so its benefit would be in preventing an accident. If cars collide torsional stiffness isn't much of a factor, There are lots of reviews for the safest cars on the internet, and I didn't find a Porsche on any of the lists that I viewed. Below is just one of many, but it is one of the most comprehensive. https://elmersautobody.com/safest-ca...auto-accident/
Not at all, BTW i am not a professional engineer just a retired Project Manager from the commercial construction industry.
My view is based only on comparing the c8 front crash structure to what i observed on my past 2010 Subaru Legacy (one of only 4 cars to achieve top safety pick that year) as well as my e60 m5 (a high performer in euro NACAP) when i had a chance to observe once the complete engine and sub-frame were dropped and front fascia removed.
The c8 has much more room for up front for controlled energy absorption via calculated collapse of space frame members prior to any hard parts (engine) or gas tanks adding constraints.
not to mention much beefier than Legacy and even the e60 m5 (which has good euro NACAP structural performance**) thus expect crash performance on c8 to be maintained to higher speeds than insurance institute testing.
**for the BMW e60 5-series: "Front impact The body proved to be strong, showing only minor distortion of the passenger cell. The driver’s door could be opened almost normally after the crash. Intrusion at the footwell was minimal and control of the pedals was good. The restraint system includes dual stage non-tethered airbags for the driver and passenger, driver seat belt with dual pre-tensioner and a single pre-tensioner for the passenger belt. Both are combined with load limiters. A deformable element designed for higher energy impacts and positioned at the top of the steering column completes the system. Despite a good deal of design effort in the knee impact area, there remains some risk of injury for the driver and passenger knees."
from the link with 63 cutaway pictures:
Last edited by bertram928; 07-29-2019 at 03:49 PM.
glad i reserved my c8 on the chev.com configurator the morning after reveal, I may get it by my wife's birthday in her team colors, one of the first deliveries my dealer assured me
Last edited by bertram928; 07-29-2019 at 03:57 PM.
So we have an article that first test production is almost sold out for the C8, and it's come down to how safe is it in a car accident?? If that's all the critics have to discuss says something. Like mentioned, worried about safety get something else. A bumper of an SUV staring level with your head isn't gonna end well. Buy a Range Rover or Mercedes GLS.
Glad to see some more in depth tech discussions on here rather than my car is better DMC. I think this is as exciting as hell and the most significant thing to come out of Detroit in a generation. Like USA Woman’s Soccer and Men’s Hockey I’m crossing my fingers GM can pull this off with flying colors. We can do world class all day long when we want to.
The Euro NACAP is a more severe test than that which define US crash standards and testing as evidenced by 2017 Mustang, which did well in US testing but not NACAP
euroncap.com
Last edited by bertram928; 07-29-2019 at 03:51 PM.
This is great news! Who wouldn't be happy if the market got flooded by tens of thousands of sub $70k, 500hp, midengine V8 sports-cars? I say, let them rain! Other sports car makers, roll up your sleeves, and make yours lighter, sportier, and even cheaper still. Markets are beautiful.
Porsche sells out every GT3 they can make when it comes out, with ADM’s that almost reach the cars MSRP. If you can even get one.
If they were “dreaming of such success” they’d release a sub $60K 911. Instead I imagine they’ll settle for being far more profitable than GM without having to release a Trax.
If really concerned about being safest on the road, you're better off driving something other than any sports car when you're looking eye level at someone else's bumper.
Yes. I’m safety paranoid, but I’d prefer a sports car that I choose to get (thus take the “risk” on) be as rigid and well constructed as possible. I.e, if I get a sports car, 40k makes me a lot more comfortable than 16K, which is now not rigid AND a sports car.
Originally Posted by fast1
But the 718 Boxster has a 19,000Nm/degree torsional stiffness number which is significantly higher than the C7. The 718 Cayman set the sportscar benchmark for structural stiffness, with an incredible 40,100Nm/degree.
Yep. 40K+K for both the 991 and Cayman show how much Porsche invests in structures. To me that’s worth more than the HP advantage Vettes get. Who wants their fast car to feel worn out and dilapidated during normal ownership (anyone driven a high mileage used Vette lately? Common issue).
Originally Posted by Nm2far
Neither the C7 (and I assume C8) or 911’s get crash tested. For a reason. Want safe get a Volvo
I don’t follow that logic. I wear my seatbelt because it helps. I’d like a sports car that is built like a vault. Because it helps.
Originally Posted by 2slow2speed
BTW: Are you correlating torsional stiffness to accident survival rates? Just because the chassis structure has high torsional stiffness doesn't mean that it can dissipate energy from the point of impact away from the passengers sitting in the vehicle.
I know they don’t necessarily directly correlate. But A: I have a loot more faith in VAG’s ability to dissipate energy than GM, who risked people’s lives to save pennies on ignitions, and who has more “warning/danger” signals on cars on NHTSA’s website, where they’d fold into themselves. I know they’ve come a long way since then, but still gives me pause.
And B: I see torsional rigidity as a signal as to how they constructed and built cars where you can’t see. I.e underlying quality. And I do think the overall strength of a chassis comes in handy if the chassis is put to a true stress test.
But also, this explains why Vettes don’t age well, and feel “flappy” after a while. An owner in this thread stated his C7 felt like a different (loosened up) car after tracking it a handful of times. This explains why.
Originally Posted by ZDan
Less than I would have guessed, but what makes you say it is "horrendous"? How much do you think you NEED? IMO, as long as the first mode is 20 Hz or so, that's plenty stiff enough for a very high-performance production car and there's very little if any to be gained from going stiffer than that as it's a factor of 10 or more over suspension natural frequencies.
I seriously doubt you would be able to feel the difference between 15kN/deg and 20kN/deg, at least at street car or street/track compromise spring rates...
C8 is stiffer than C7 despite being more "bolted-joint" intensive. I believe they went to bolted joints to avoid totaling cars from them barely bottoming out and cracking an aluminum weldment with no way to repair/replace the damaged portion. For sure it is possible to design bolted joints that are plenty stiff. Likely to be a weight penalty vs. welded though...
Stiffness is NOT the same as strength, or crashworthiness! In fact it is possible to be *too* stiff for safety, you definitely want the structure to have crumple zones.
Worth noting that some German cars with exceptional stiffness have had issues with primary structures cracking and failing over time...
And sometimes you pay more and still have structural failures, despite higher chassis stiffness...
So would I. It's too bad they've stuck with this design since the C3, with the only exception being the rather grotesque-looking C5 hardtop/Z06...
So even the coupe Corvettes are essentially roadsters/convertibles. Compared to other convertibles, they are in the ballpark for stiffness. C8 will apparently be stiffer than the 992 convertible.
EDIT: Somehow i forgot that the C6 Z06/ZR1 did have a fixed roof! Which allowed it to be about the same stiffness (slightly stiffer) but *lighter-weight* vs. base and GS coupes. They kinda skipped this approach for the C7 and went with more power over lighter-weight for the Z06. Doh...
FWIW I am an aerospace structural engineer, and have designed and/or analyzed structures for space, air, and road vehicles. Lately I've been working on a bonded carbon fiber spectrograph for the biggest telescope ever built by humans. ~2600 lb., 13' x 3' x 4', first mode > 50 Hz. Now that is stiff! For good reason...
IMO sports cars don't need to have bank-vault levels of rigidity to be good at what they do. There's a point of diminishing returns on chassis stiffness for sports cars, and honestly I think even my 987.2 Cayman is already beyond it. It feels much stiffer than my BRZ. But it's 250 lb. heavier BRZ is nearly as fast at slower tracks (did 1:23.1 at Thompson in the BRZ last Friday, vs. 1:22.7 in the Cayman the next day in similar conditions). I would be willing to trade some of the Cayman's stiffness for less weight...
All that said I have always been more a fan of fixed-roof sports cars over roadsters/convertibles, partly due to more efficient structure with greater stiffness/weight.
Who knows, maybe the Z06 or ZR1 version of the C8 will have a fixed roof?
See above for the crashworthiness factor. Also, rigidity is one of many reasons I avoid verts. They feel more flexy and and don’t hold up as well over time (more rattles and worn out feeling).
I call it “horrendous” because 14,000 (C7) is pathetic for a high performance car especially. Seriously, fine one new car less rigid. It may be impossible. Do you want one of the LEAST rigid new cars?
Imo diminishing returns is vastly above that. Hence why Vettes tend to feel prematurely worn out, especially when driven hard. I like as stiff a platform as possible. The 991’s extremely strong 40K is great, but I’d take even more if I could. Also to note, your 987 doesn’t have a 500 HP engine with the torque a C8 produces. Guaranteed 40K mile C8’s that have been driven as intended, with the chassis being put to task will be as softened and loosened up as predecessors.
Think about supercars that have 40-50K+ nm/deg of stiffness. They’re touted to have that because you get what you pay for and they’re guaranteeing you can drive the cars hard, and they’ll stay strong. Not to mention, stiffness correlates with performance more often than not. The better the C8 performs and how close it gets to supercars will in fact dictate just how much it’s far weaker rigidity will hamper it in the long run.
I would be really curious to know what a solid roof C8 would attain in rigidity. Hopefully at the very least over 25K.
07-29-2019, 02:32 PM
BRZ is nearly as fast at slower tracks (did 1:23.1 at Thompson in the BRZ last Friday, vs. 1:22.7 in the Cayman the next day in similar conditions). I would be willing to trade some of the Cayman's stiffness for less weight...