LSJU

Probably about 0%. Not being made of metal is generally a good thing, not a bad thing (though, weight aside it's a very small difference in practical terms).

I'm not sure what you mean by kinesthetic insulators. I think you mean that extra damping inherent in using a composite rather than homogenous spring material would reduce feel. That basically wouldn't happen. The difference in natural frequency of the leaf spring vs a coil spring is well outside of the range that would mater for ride and handling. Also, some extra internal damping means less for the shocks to do.

The lesser feel of the Corvette steering over the years probably starts with the wide front tires. All else being equal, narrow tires give you superior road feel. Changes in the road surface don't shift the center of contact patch pressure as much and you can run king pin angles that would cause front end jacking with wider tires. Of course the down side to narrow tires is a lack of ultimate grip thus a trade off between handling and numbers.

Now for a given level of performance and vehicle weight we can improve things by moving mass to the rear of the car. This is because when we want a balanced chassis going around a corner what we actually want is equal front and rear slip angles. Loosely speaking, if you size your tires such that their contact patch area is proportional to the weight on the axle you will get equal slip angles at both ends (that is very simplified). So where does that leave us? Well we want narrow front tires for handling feel but we want a lot of rubber overall for grip. Well move the weight to the back of the car and the narrower front tires can do more with less. Net result we have better feel without having to resort to wide tires for grip.

The other thing that has hurt the Corvette over the years (and helped Porsche) is the need for a rear LSD. To avoid the peg leg burnouts the Corvette has had various LSDs over the years. The problem with a normal, passive LSD is the diff is effectively causing understeer. Most people don't realize this but when the diff is "limiting" what it's actually doing is trying to slow down the faster wheel and speed up the slower wheel. Now think about that in context of going around a corner. The diff is trying to speed up the inside wheel and slow down the outside, exactly the opposite of what you want to happen. The more open the diff, the less the front wheels have to fight the understeer torque created by the rear LSD.

So Porsche also uses LSDs, why is it worse in the Corvette? Well again it comes down to weight distribution. Because the Porsche has more weight over the rear axle it needs less bias in it's passive LSDs to get the job done. That means the front wheels aren't fighting as much inherent understeer. Note that Porsche actually avoided using a LSD in some Cayman models. Contrary to what Clarkson thought, that was probably to improve handling (even if it meant under some circumstances you could do a peg leg).

With the new Corvette GM tries to address this issue. A computer controlled LSD can act like an open diff when you are off the power, a low bias LSD when you are partially on the power (or trying to go in the snow) and a full on locked diff when you are doing a jack rabbit start. The only thing that would really be better would be torque vectoring.

So GM is clearly working to fix some of the issues that hurt the handling of the Corvette. I suspect the new diff will really be the biggest factor since it will finally let the car have open diff handling when off the gas or even partially on the gas but more aggressive locking when needed. Improvements to the steering rack and even getting more weight to the back should also help.

JohnnyBahamas

Good stuff! I'm learning more and more.

By "kinesthetic insulator" I meant to suggest that from my observation, having handled these leaf springs in the past while swapping them in and out on my C5, that the material does not transmit vibration or sound well at all. Point, one day, as I was swapping in a Z06 front spring in an attempt to get more feel from the contact patch, it occurred to me that the spring material and suspension geometry was the problem. Just my intuition but with hands on information behind it.

An example, holding the spring in one hand, rapping it with a hammer in the other, and very little feeling is transferred to the holding hand through the spring. Or, put the spring to your ear and tap it with a hammer on the far end and... no ping makes it to your ear. With a metal spring, on the other hand, you'd feel and hear even the faintest touch.

So, by observations made sitting on the garage floor playing with these springs, my intuition has been that they are an insulator of information from the contact patch... and further note that these springs contact the lower control arms through a screw adjustable "refrigerator leg" with plastic on the bottom of the leg, I kid you not... so a large percentage of the kinesthetic information coming up from the contact patch through the lower control arm is lost when it fails to transfer across the spring to the frame. Not transferred to the driver.

Further, with the upper and lower control arms connected to the frame points through rubber bushings, a large percentage of the contact patch information is deadened by polymer, rubber, and fiber.

Point, IMHO, and it is humble, the entire design and material construction of the Corvette street suspension (street noted because GM does not race on this suspension) is a very poor transmitter of kinesthetic information from the contact patch TO the driver.

To feel the difference suspension design and material make, climb behind the wheel of a 911. Big metal coil spring in metal contact with the lower control arm and the metal frame point and a suspension designed to transfer information to the driver. Much more feeling to the driver. GM is SO close to having an INCREDIBLE machine in the Corvette except for this achilles heel of a suspension. It's just heart breaking. Seriously, heart breaking and I'm pissed at GM for doing it.





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Carrera GT

And if you hold a car tire to your ear and hit it (the tire, not the ear) with a hammer?

Your earlier post focused on tire aspects (sorry) and I think that's where the spring issue is resolved. The damper is a-whole-nother ball of wax in your ear.

TRAKCAR

:-)

TRAKCAR

Autoweek driving a C7 from Monterey to Michigan
http://www.autoweek.com/article/2013...NEWS/130829999

JohnnyBahamas

I do hope so. I love the torque, I love the price, and I the the country of manufacture so I want to be able to love the Corvette. I'm looking forward to a test drive in the C7.

trumperZ06

Good Video offering new information on engineering that improves the Vette's on track performance as well as making it more "customer friendly".

There is NOTHING wrong with the composite leaf spring suspension...

which enables the C6 Z06 to have neutral handling with proper alignment and tire selection.

Some guy's seem to blow this all out of proportion... given the proven track performance available.

We have yet to see the high performance ( Z06) "track version" of the new C7... which I expect will set new standards.

Quikag

Great first post, LSJU! Welcome to the board. You clearly have some good knowledge and understanding, so we'd love to keep you around here.

Speaking of tires, one of the points made in a few articles I've read on the C7 with going back to a very sticky supersport in SMALLER sizes (245 front, 285 rear, versus the Grand Sport) for the C7 is to help provide more nimble handling. That, in conjunction with the e-diff and a myraid of other improvements, is what apparently gives this C7 a very tossable and playful feel.

Admittedly, while the absolute limits of my ZR1 are quite high, I do agree that it feels fairly insulated and a bit ponderous (probably too strong of a word) with its responses to driver inputs. That said, going with my recent switch to poly bushings, a camber kit, and aggressive alignment went a lot way to provide much more immediate and direct response. Car feels much more nimble now.

Either way, this C7 seems to be an improvement in a lot of different areas to the C6.

LSJU

I think tactile would be a better term in this case. Kinesthetic implies knowledge of a position based on feel, you know the position of your arm without seeing it. Tactile would imply information transfer through touch. Dead steering would lack tactile feel.

Your observations about the spring's mechanical properties are spot on. The spring has very good internal damping as compared to a coil spring. Internal damping is a good thing in this case though the natural frequency of the coil and the leaf are high enough as to not really mater for ride control or road handling.

The "refrigerator" leg is also a non-concern. Think about it. The spring pushes down. So long as the length of that leg doesn't change under load how would it affect the transfer of forces from the suspension arm to the spring? The 911 uses a rubber bushing at the top of the strut in a similar way (the weight of the car rests on those rubber bushings).

The rubber bushing concern is legit. There is certainly a reason why true race cars don't use rubber suspension mounts. Even track prepped street cars typically will replace soft rubber bushings with harder poly bushings. However, it's worth noting that Porsche, on most of their cars, also uses rubber bushings. They are common on road cars because they aren't susceptible to dirt and wear like spherical rod ends. They are cost effective and help isolate road vibrations. Often, the compliance of the bushing is a designed in part of the suspension. A classic example is the Weissach axle used on earlier 911s. It depended on bushings that would deflect under lateral loads but not under vertical loads. I'm not sure to what extent the current 911s use rubber bushings as more than just pivot joints but the concept is standard in all but the most hard core road cars.

Basically there is nothing in the Corvette suspension that isn't state of the art for a road going sports car. The leaf spring is different but Carroll Smith seemed to think it was a better idea than coil springs. Coils are common on road cars because they are cheaper and most road cars don't have the packaging constraints GM had.

Any issues with Corvette handling can not be placed at the feet of the leaf vs coil springs. Yes, sometimes a Corvette will handle better when the factory shocks and springs are swapped for coils and aftermarket dampers. Then again many people do the same sort of swap with their Porsches. The big change is the dampers. The coils (or leaf) are changed so their rate is appropriate for the new dampers. The dampers are the real change, the spring is really a side show. It's just that it's different in the Corvette so, human nature what it is, we say teh difference in handling is due to the spring type. Interestingly, if you drive a Solstice I think you will find it feels a lot like a Corvette yet it runs on coils.

LSJU

Thanks!

Everything in your post seems to jive with what I've read. Sadly I haven't had a chance to drive any of the higher power Corvettes (or Porsches). The best I've been able to manage is the pathetic 400 hp C6. I was lucky that damned Honda minivan didn't beat me to the grocery store.

JohnnyBahamas

Excellent stuff! Yes, "tactile" is much better. Thank you.

Seriously, I appreciate having a prejudice pointed out logically and with ratiocination vs. the all too common alternative.

So, if all cars run on rubber tires, rubber bushings, and dampers, yet the difference isn't the suspension design and construction materials, what is it that gives less tactile delivery to one car versus another car? Honestly, can it fundamentally be tire aspect ratio? Again, my prejudgment is that it must be more than that or the fix would be so easy.

Is it simply that GM has been designing the Corvettes I've owned, a C5 coupe and a C6 Z06, to feel that way? Possibly to appeal to a larger target market?

I mean, at the end of the day the question remains, what is it that makes the difference?




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kosmo

whens the dam car coming out? Lets go drive one already.

trumperZ06

It certainly is NOT the composite leaf springs nor the set up !!!

So look elsewhere... rear engine location vs front, weight bias, tire selection, just to mention a few.

Maybe the difference isn't as dramatic as some would suggest. Try comparing a Vette to a 944 or 964, or any other front engine/rear wheel drive vehicle, instead of the 911.

There are inherent differences between the handling with front engine/mid engine/rear engine vehicles which need to be taken into account.

Quikag

I'm not going to pretend to be as well-versed as LSJU in this stuff, but I do remember reading a running change GM made to the '08 Vette was to machine some of the steering components and build them to tighter/stronger tolerances to get a 'better' steering feel. It worked and the difference was noticeable. However, it still wasn't or isn't as nice as a P-car.

I think the rest of the difference is the tire size, weight distribution, quality, design, and construction of the steering components and even moreso, the "programming" of everything. Tactile feel is what P-car goes for. GM may go for less tactile feel and more road isolation, so the steering wheel doesn't shake as you drive over road pebbles and other imperfections.

I think appealing to a larger market with the pre-C7 cars is a decent part of the equation. GM has catered to older people with the squishy seats and the isolated steering/ride because that is what the largest cross-section of their audience wanted. It seems with the C7, GM is trying to still cater to that audience, but is also able to cater to a sports car audience using technology and the enhancements and engineering designed and built into the C7. It seems GM is trying not to rely on old, lame excuses anymore for their shortcomings. That is refreshing.

LSJU

Actually I think the shortcomings of the C6 were not GM trying to appeal to older, less affluent (a relative term given even the base C6 price) buyers. I think GM plum screwed up. Lutz actually all but said some of this when he joined GM.

The C6 was clearly an extension of the C5 architecture. I'm not sure how many parts were actually carried over but some clearly were. For example the back side of the instrument cluster looks to be the same in both cars. Even though the gauge faces were changed I suspect much of the dash interior was retained.

The seats were probably either a cost cutting choice for GM or an issue of finding a seat that fit. For example, GM used some very nice seats in the Caddy CTS-V. Those seats were too wide to fit between the central tunnel and the outside frame rail of the car. Thus rather than simply buying a good, already designed seat from say Recaro, GM would have to commission them to make a new seat. That hurt the business case for a design change given the waning C6 sales. Mind you, the old seats were very comfortable for long drives, just not for the level of performance the Corvette could pull.

The interior was one of the last of the pre-Lutz interiors and he commented that by the time he joined GM it was tool late to really do much to fix it. Sadly, it wasn't any cheaper than the interior in the first gen Cayman. I know some will balk when I say that but once you look at the parts in isolation you see that the GM interior was made just as well, fit just as well, had just as much hard and soft plastic etc. There was one critical difference. Porsche got the styling right, GM didn't. I spent some time comparing the two a while back. What I realized was things like the panel gaps on the Porsche were no better. The dashes were both made of soft touch plastic. The switches in both felt about the same. The few hard plastic bits in both cars had about the same finish (metallic pained plastic) and when tapped sounded about the same.

So why do people say the C6 interior was so much worse? Easy, GM didn't do a good job styling the forward part of the dash. The doors were actually fine and about on par with the Cayman. The center dash was a failure. Take the radio and climate controls. They look like bog stock GM parts that would be used in the Cobalt. They weren't. They were bespoke and used only on the Corvette. So if you are going to make bespoke parts why make them LOOK like generic parts?! The center stack has a large seam that runs around the top between the soft touch dash and the stack. That seam looks large and as if GM couldn't fit things any better. It's actually about the same size as the Cayman's horizontal line and mechanically is there for the same reasons. Porsche made theirs look like a styling choice. GM made it look like an assembly necessity. Thus GM did spend the money. They just spent it poorly.

Finally, the steering wheel was a travesty. Not because it was mostly the same as the Cobalt wheel. Because it LOOKED the same. I've seen some refinished C6 wheels that look really good. One of the biggest gains is replacing the plasticy looking airbag cover with something (ANYTHING) that looks nicer and matches the grain of the rest of the interior. It was such a small thing but it would have gone so far to killing the 'cheap interior' comments.

Happily it appears that GM is largely (totally?) addressing these issues with the C7. They might still get the 'cheap' comments. Some will be perception. I mean if the finish and fit of a Seiko is just as good as a Omega I suspect a number of people will still say the Omega is better because of the name or perhaps because they like the styling of the Omega better regardless of the name.

Anyway, as for the question about differences in handling, it's really so many things.
Wide tires never helps and the Corvette was known for wide front tires. Little changes which GMs to be appreciating like reducing friction and slop in the steering make a big difference. Suspension geometry, not necessarily the check box of A arms vs struts (in theory the A arms should be better) but details like king pin angle, scrub radius, power steering tuning etc all can make a big difference.

Another thing that helps Porsche with cars like the Cayman is not always chasing the numbers. As I've mentioned things like narrower or even harder tires can have better feel but potentially less grip and slower lap times. Porsche can 'give a bit of performance' with most of their cars because they feel like they don't have to prove anything. Small trade offs that result in lesser numbers but perhaps better handling (Note that is a generalization). Certainly the front vs mid or rear engine makes a difference (I don't care if the Corvette motor is behind the front axle, in front of the driver = front engine). Porsche does have ultimate numbers cars but often they are rather single purpose (based on what I've read, looking for volunteers to throw me some keys to back my perception... anyone... ... ). Even the C6 seems to be rather civilized given it's level of performance but I suspect the car could feel better if GM was willing to give up some performance for better feel. Porsche normally does but still has some killer track cars to maintain street cred if you will. Of course it also helps when you have that rearward weight distribution (see my earlier post).

I think the Corvette has long had a numbers mentality but starting with the C5 GM started to see more than just numbers. Remember that the C4 pulled 1G on the skid pad in '85, the first street car to do so (insert volume car, major make etc disclaimers). The C5 was a major leap forward in that GM got a class leading, rigid chassis. The C6 addressed more issues and the C7 seems to be yet another step forward.

BTW, thanks all for the warm welcome!