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Hey all, I know there was a post in the technical threads about steering components but this one is about how you think it will actually handle, like oversteer or understeer stuff like that wether it will rip around the corners or drift or just spin out. its been a while since pontiac made a true sports car. my buddy and I were talking about the miata and how well it handles hes a car freak like me and hes driven a miata on a track and he loved it. so who knows?
whats your predictions?
your expectations?
your hopes?
 

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All production cars have (steady state) understeer. No exceptions. It's just a matter of degree (actually degrees/g). You never see it printed in the CarMags.

I would think that the General is constantly comparing to competition, and knows the ins and outs of the Miata and probably the Honda as well.

What is people's opinions/expectations on the following areas (things that you would see in the Car and Driver or Road & Track or Motortrend data sheet)?

0-60mph:
1/4mi time/speed:
skidpad lateral g's:
60mph stopping distance:
80mph stopping distance:

Take a look on road and track's website for examples of a data sheet, or take a look at the one here for the Cadillac CTS-V

http://www.roadandtrack.com/assets/download/2252004154854.pdf
 

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Am sure the lawyers insist on understeer - the general has had some bad experiences with oversteering cars (Corvair) in the past.

Is not so much that American drivers are inexperienced, just that they expect to hit things with the front of the car, not the back.

Add in the fact that a basically understreering car is easier to drive and with big honking V-8s, oversteer is reachable with the right foot (part of the reason dealers discourage limited slip differentials even in the snow belt.

That said given a reasonable amount of torque, the fastest way around a long curve with a RWD is with enough oversteer to allow neutral or slightly reversed steering. That way there is a significant vector of tractive force toward the center of rotation (accelerating into the turn rather than out of it). In other words, with the tail out you a pushing the car towards where you want to be and not at an angle to it.

Now if the tail is out too far, this becomes counter productive and may induce unwanted rotation, the ideal seems about 15 degrees or enough so that with the nose pinned to the inside of the turn, the tail is about three feet out.

With a really stiff suspension you can carry the inside front tire over minor obstructions on the apex and shorten the turn slightly. Does tend to concern the corner workers the first few times you do it though. Later they may place small objects (cups, apples) a foot inside the apex just to see how high off the ground that wheel is.

However the art of the four wheel drift is not one taught in driver's ed and practicing on pulblic streets can result in expensive pieces of paper and unwanted public appearances.

As a consequence and to make it easy to determine fault in an accident (reconstruction may be difficult if two rear bumpers are interlocked), American cars are designed to be "stable" and understeer just as Ralph intended them to.

That said, I would expect 0-60 in the 7.5-8.0 range with 1/4 in 15.5-16.0 c.a. 90 mph for a n/a version expected to be sporting, faster with s/c. Lateral force and slalom speed will be a function of the tires but note that 245s were used on the 4000 lb CTS-V. I said before that would not want over a 215 in a street tire for something in the 2800 lb range.
 

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Maybe I'm stupid or something, but I've never understood the "understeer is safer" theory. In my experiences if I were taking an clover leaf on ramp for instance, a slight, progressive oversteer seems natural to me and countersteering to combat this is instinct. Understeer in the same situation however, always leaves me unsure if I'm over powering the front tires until too late. My reaction, and I'm sure most others tends to be sudden throttle lift, which always rotates the rear. I don't know, I've just always found this more dangerous.
 

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How many 4 wheel drive vehicles have actually been driven off-road? Statistics say less than 5%. So how many Solstice roadsters do you believe will be driven to there full potential?

When a car is subjected to side force, due to cross wind or the road's irregularities, understeer can resist the force and avoid the car being steered automatically, therefore the driver need not correct the steering frequently, so when running in straight line, the average consumer wants a little bit of understeer to make the car stable.

Understeer can be remedied by a slight reduction in throttle to transfer weight forward to the front wheels, aiding their traction and ability to negotiate the turn.

Oversteer generates higher cornering forces bring the required traction even closer to the limit of the rear wheels, and thus causing even more oversteer. The situation becomes worse until the rear wheels lose grip completely causing the car to spin and all directional control is lost. Quickly becoming a point of no return, so to speak. And harder for the average driver to control.

A well handling car should feel neutral with respect to over or understeer, with just a touch of oversteer in high speed maneuvers.
 

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Notice I said (steady-state) understeer. I did not talk about "transient" behavior.

BTW, even the Corvair had understeer (granted, it was awfully low but with a huge rear weight bias what does one expect). Most of the NASCARs, and all of the F1 and Indy cars have healthy doses of understeer because of the huge speed range those cars cover.

At Bondurant, the saying is "if the wheels is spinnin' you ain't winnin'". It may look spectactular, but driftin' is not the fastest way around a road course. There is, however, a big difference between a proper 4whl drift (which is taught at many race schools) and "driftin'".

There's a bunch of mathematical baggage that goes along with lower understeer, among these are increasing instability and a less damped yaw gradient, as well as increasing response time (I know that sounds wrong, but I assure you it is not). These things conspire to make controllability on a power limited car very difficult.

Case in point, several people running pre-2004 Honda S2000's found themselves with their hands full time and time again with the taillights swapping with the headlights under both AutoX and road racing conditions. According to one mag article, Honda made some changes to the rear suspension and the front and rear tires to improve this. They changed from 205/55 16Front-225/50 16Rear to 215/4517Front-245/4017Rear. The tire width difference (rear wider) is greater, and the aspect is lower for both - this usually means more understeer.

For RWD's that you can't smoke the rears at will, the name of the game is energy conservation, and the faster you go the more important it becomes. Setups for AutoX and Club Racing are significantly different, and I and other friends have found ourselves with hands full taking an AutoX setup to a road course - so if your experience is with AutoX the tendency will be to prefer lower understeer.

With increased speed, a low understeer car will approach uncontrollability (your wheel responsiveness gets quicker with increased speed).

Bottom line, understeer is required for a stable and controllable car in all conditions. Like anything, there is a correct amount that each car needs to feel natural and correct throught it's usable speed range, and it is definitely possible to have too much or too little. Some vehicles (not ground, aircraft) have 'oversteer' in pitch, yaw and roll, and it is physically impossible to control them without computer intervention (F-111, F16, F18 to name a few).

Again, two very good books on the subject:
"Race Car Vehicle Dynamics" by Milliken & Milliken and "Fundamentals of Vehicle Dynamics" by Gillespie

Darkhamr, you're not stupid. There is plenty of misguided info in and out of the industry when it comes to "understeer" and understanding what it means. It takes plenty of schooling, driving experience, and concentrated effort to understand and see in your head what is truly going on. If you're really interested, look up those books and have a read, some of the Milliken & Milliken book is very entertaining (especially the chapters about the Chapparals).

So, getting back on track (as I have digressed) we've got (N/A version, since that's the only official version of the car):

0-60mph: 7.5-8.0 sec
1/4mi time/speed: 15.5-16.0 sec @ 90MPH
skidpad lateral g's: Anybody's guess? (sure to be tire-related, the Detroit Auto Show pics have a very agressive looking Goodyear tire on them.)
60mph stopping distance: Anybody's guess?
80mph stopping distance: Anybody's guess?

Perhaps we can put this (if we have a consensus) in the technical section or have it put in the "specs" section as "anticipated performance specs".
 

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Funny you should mention the F-111 and F-16 since while at GD-FW (now LM TAS) I worked on advanced controls specifically full authority digital flight controls for the PDFCS and AFTI F-16 (which to a certain extent could fly sideways - made life "interesting" for chase planes but mean it hold the nose on target far longer than normal.

The term we used at the time was "unstable" which really meant to to go up, you dropped the tail rather than raising the nose (one reason the Falcon is not flown off carriers.

This is analogous to oversteer in turning where the tail goes out and I agree, too much oversteer makes a car uncontrollable by normal drivers ( a few years ago I recall being told you could not drift a Formula Atlantic. Could.) and slow. Just a wee bit now...

An understeering car is usually accompanied by enough caster to make the car want to go in a straight line. This is ideal for driving from New Orleans to Orlando after work which is essentially a right turn after about six hours and a bear left two hours later. Typical American driving.

On a superspeedway, neutral to slight understeer is the least exhausting on both driver and tires particularly in a state where aerodynamics are important.

However we are talking about autocrossing (or I thought we were) and the rules are different. Here the need it to negotiate and exit quite tight turns as rapidly as possible (sometimes I will trade entrance speed which I can kick off quickly with braking & which also transfers the weight to the front tires for exit speed which determines the time down the next chute).

As for underpowered cars, the force required to spin a typicl car once traction is broken is about 40 lbs. Even a mouse motor with RWD can swing if properly balanced. This is where a limited slip or locker is essential so that the car doesn't raise one rear leg and pixx rubber on the track instead of delivering tractive force.

Have already discussed "unladen understeer" so will not go into that again and the increased tire size on the Honda sounds more like marketting than tuning. If a car is really 50-50 and the fronts are not limited by the wheel well then the same size all around is where I'd start. (of course knowing where to deviate is important also but that is part of tuning. Must admit some amusement at the thought of a 245 non-race-tire (well maybe with a wear index of 40 or so) on a 2500 lbs car. Is one way to achieve understeer.

As to Bob's aunchient comment about sliding, tires develop maximum force at a 30-40% slip. This is not "spinning and smoking" but is not precisely going in a straight line either. One technique I recommend to people once their car is properly set up is to aim for the inside pylon.

When you are really going fast, the car feels like it is on ice and you are concious of all of the little squirmings going on at all four corners. Dick Turner's "Slow Hands" are essential and anything you do suddenly is wrong (is an interesting dichotomy - all of your reactions speed way up but adjustments are minute and often have no immediate effect. If you drop a wheel off the edge, the best thing to do is to think "oh-gee-whiz-I-dropped-a-wheel-off" by which time it is usually back on the track. Anything sudden is wrong.

If you have ever watched someone going really fast, it often looks deceptively slow until you start noticing the cars attitude and the almost gentle swaying motion that leaves it perfectly aligned for the next curve. A good driver can even carry on a conversation with a passenger while doing it.


So understeer or understeer is the question. Personally, I'll take neutral with the ability to induce some (not a lot) oversteer. Push is just another word for slow.
 

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solsticeman said:
skidpad lateral g's: Anybody's guess? (sure to be tire-related, the Detroit Auto Show pics have a very agressive looking Goodyear tire on them.)
I'll hazard a guess of 0.89 Gs.
 

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Actually the 30%-40% slip peak mu tires are or tend to be drag strip tires. Most AutoX and road race compound tires (esp hoosiers) actually peak lower (18-23%) in traction, with no lat slip angle. At slip angles above 1 deg or so, the peak traction happens at lower %longitudinal slip.

Or so the data looks, or I mean, I hear, anyways. Guys talk. Y'know. Ya hear things.

I think the best setups I've seen and/or driven are moderate-low understeer (steady state), with a predictable lateral cornering 'edge' (which the hoosiers are well known for), and decent throttle steer characterstics (throttle lift = more beta, judicial throttle application = 'plant the rear'). Cars set up like that are good to 'toss' into a corner, much like throwing a dart, and use small amounts of throttle to control the vehicle.

The Miata is actually nice to use throttle to control cornering attitude (beta). Honda S2000 (pre 2003) is also ok on it's production tires, but sometimes a bit hairy. The honda with the same size all four corners with hoosiers is a real bi*ch on an autoX course.

In traffic (meaning on a road course with 23 or so of your friends/opponents), the miata is very nice, but it's difficult to be elegant with the Honda.

The Corvette Z06 (2002) is a very fun car to drive on an autoX course, and also road courses. Since I can still afford a Solstice, you can deduce I managed not to collect the guardrail at any tracks when I was allowed to drive it (open course but not in traffic).

You know, Padgett, we may have crossed paths at some time in the past...

Any predictions (getting back to the thread topic) on Max Lat or braking (for if you ignore braking as a part of handling, you do so at your own peril).

Glancing at autosite.com:http://www.autosite.com/new/grabbag/perform/3760.asp
and
http://www.autosite.com/new/grabbag/perform/3811.asp

looks like around 0.88 g for the Miata, maybe a bit higher (0.89 average?) for the S2000

60-0 braking looks like 121 or so for MX-5, maybe 117 for the honda. I'm sure this is also very tire-related, these should be for the tires as provided by the manufacturer.

Maybe anticipate max lat around 0.88-0.93g?

Maybe anticipate brake performance equal to or better than miata? (120 or so feet 60-0?)

What else?
 

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im interested in chassis rigidity and how the stice will compare to its competitors.

which reminds me, all these car makers are claiming "35% increase in torsional rigidity...etc". does anyone know where to find hard data/numbers?
 

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Only way I know to get good ridgity in a roadster (35% better than what ? A Flexible Flyer ?) is with a cage and doubt that the stylists will go for that. OTOH it is a critical suspension component in many race cars & needs to be designed as such.

Of course if the Solstice really is close to 50/50 then transfer will not be that important and can be accomplished with braking.

BTW control of lateral slip is why I like rims wider than the tread and preferably at least as wide as the section. Deformation of the sidewall maintains the contact patch rather than lifting the inside.

Are a lot of factors involved and a 35 profile is less affected than a 60 but as long as you can keep the slip within limits there is nothing wrong with hanging the tail out a bit.

Really we are not talking about big differences here, too much under and you plow, too much over and you spin. Both are bad and slow.

That said I cannot think of a condition where understeer is desirable unless it is to mask a loose rear end and you wind up still going slow but with an easier ride. I prefer to discover the max from both ends then figure out how to "improve" (often with driving technique) the lesser.
 

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Padgett,

Rigidity in a roadster is a possible thing. Look at the old Lotus Elan 197something and earlier. Generally considered to be one of the "stiff body" roadsters, the big innovation was the big tunnel in the center (the one that displaces the driver and the passenger and makes it one of the most uncomfortable english cars to drive).

The current corvette convertible is pretty darn rigid, as well as the BMWZ4 and even the Honda S2000. Look inside the Miata and then look at the chassis pics of the Solstice from the Detroit auto show and you see the key to making a rigid roadster: the central tunnel. This is the key, and Mazda figured it out with the RX8 - that's how we take out a center pillar for the 2+2 door and still get a rigid body. The Nissan Maxima (the new one) also has a tunnel that goes through the entire body, into the back seat and seperates the rear passengers. That's how the Maxima can put the swiss-cheese longitudinal roof panels in and still get a rigid body.

The F-body had a center tunnel, but it's not as big, and it shows.

I'd expect decent rigidity in the Solstice. The chassis vehicle at the Detroit Auto Show looked like a mini-corvette through the middle, and I've driven the corvette convertible, so I would hope the solstice would approach this level of rigidity.

How stiff (natural frequencies) does everyone think the Solstice needs to be? I'll do some googling later to see if these are somewhere on the 'net for other vehicles for a sense check.
 

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Some data for the engineering geeks out there:

Audi TT 22Hz & 10KNm/deg, although this seems a bit high.http://www.sae.org/automag/globalview_10-99/01.htm
Edmonds.com was not as impressed with the Audi TT roadster's torsional stiffness, which makes me think they are overstating the rigidity. http://www.edmunds.com/reviews/roadtests/spin/44725/article.html

The germans/I mean Chrysler, is quoting a BU**3HIT number of 27.2Hz for the Chrysler Xfire - I don't believe it, 'cause I drove a hardtop crossfire at the local chry/dodge dealership (not impressed). They must be talking the body only number (without engine, suspension, etc.) and it's misleading because they didn't release a stiffness. Extradordinary claims require extraordinary evidence, and you too can have all this crap for $35,000-$50,000.
http://uk.us.biz.yahoo.com/prnews/040315/dem006_1.html

BMWZ3 17Hz & 7 KNm/deg, BMWZ4 19.5 Hz & 10 KNm/deg
http://www.unofficialbmw.com/images/01 E85 Complete Vehicle.pdf

Chevy SSR is 16Hz top up and 13.8 top down according to this article: http://www.sae.org/automag/globalvehicles/01-2003/1-111-1-10.pdf

Most sedans talk about being in the 25-30Hz range, and if I remember from somewhere, tube-frame race vehicles (NASCAR, F1, etc.) can be 40-50HZ and over 25 KNm/deg. I'm sure the Solstice is not going to be that good.

Corvette (2001): "...convertible’s first torsional frequency is 20hz. Coupes with the roof out are at 20.5hz and, with the roof on, jump to 22hz. The Z06 is a stout, 24hz. ..." http://www.idavette.net/hibz06/page2.htm

The SAAB 9-3 weighs in at 12.5 KNm/deg, http://www.autoweb.com.au/start_/showall_/id_SAA/doc_saa0310161/cms/news/newsarticle.html

The japanese manufacturers tend to not state a frequency or stiffness, just "XX% improved over the previous model with the new (insert your widget name here) technology". Can't find any Honda, Mazda, Nissan or Toyota numbers.

So, I'd think the Solstice would be approaching the Corvette, because it seems like the closest in structure.

So for comparison:

Audi TT Roadster (***cough, BS!, cough***) 22Hz ; 10 KNm/deg
Chrysler Xfire (***cough, BS!, cough***) 27.2Hz ; ?? KNm/deg
BMWZ3 17 Hz ; 7 KNm/deg
BMWZ4 19.5 Hz ; 10 KNm/deg
Corvette Convertible 20 Hz ; ?? KNm/deg
Corvette Coupe Top off 20.5 Hz ; ?? KNm/deg
Corvette Coupe Top on 22 Hz ; ?? KNm/deg
Corvette Z06 24 Hz ; ?? KNm/deg
Chevy SSR top up 16 Hz ; ?? KNm/deg
Chevy SSR top down 13.5 Hz ; ?? KNm/deg
SAAB 9-3 ??? Hz ; 12.5 KNm/deg
Honda S2000 ???Hz ; ?? KNm/deg
Mazda Miata ???Hz ; ?? KNm/deg
Solstice ???Hz ; ?? KNm/deg

WHEW!
 

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Discussion Starter #16
all i got to say is WOW guys, thin this all started with a simpled question and you guys took it to a whole new level. what i was really looking for is somthing like, "oh yeah when I exit off the 401 and go around the corner i dont wanna feel to much body roll of the tires sqeauling like a little pig" not geting into exact deciaml places on how much a F1 car turns in a corner. but I did learn a lot. and I do agree that with that long tunnel in the sosltice will make it a better handeling car. keep up the good work fellows. and i stil cant wait for that fithful day where I sit into this beauty and my hand falls on the shifter, I start the enigne a teach the road a new lesson on how to drive!:cool
 

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How bad can it be? It's small, relitivley light, RWD and looks so cool! As long as they hit their price target everyone will be happy I'm sure. It would be really hard to screw it up. I'm sure Pontiac engineers know a little something about how to make cars go around corners.

Can't wait:D
 
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