PurpleLion

I have been told by a very authoritative source that the manufacturers of all of the current mid engine cars tune their cars to exhibit understeer instead of being neutral.

This is not terribly surprising given that the manufacturers typically wish to limit their liability exposure.

Also, automotive tests and reviews seem to bear this out. The C7 is often shown to beat the current crop of mid engine sports cars with better lap times, higher skid-pad lateral acceleration numbers, etc. But, with a little bit of thought, it is obvious that the C7 beating these theoretically superior cars makes NO SENSE! We all know that the mid engine layout is superior as far as ultimate road holding performance is concerned! There is a reason that F1 cars and Indy cars, which previously used a front engine platform, have long ago switched to mid engine layouts. So then, how can the FE C7 beat these cars? The answer is simply because the mid engine car's suspensions are not tuned for neutral handling at the limit. Instead, they are tuned to understeer which prevents them from attaining their highest possible performance numbers. Probably, if they were tuned to neutral handling, they would exhibit much higher performance numbers.

This is exactly the case with the new C8. GM told us that they went to a mid engine layout because they had reached the limit of what could be achieved with the C7's FE layout. Yet, this rational seems to be belied by the fact that the C7 seems to be faster than the C8

I submit that, in fact, the C8 is inherently faster than the C7, but, the C8 has been tuned to understeer whereas the C7 has been tuned to be much more neutral handling at the limit. Thus, the C7, in stock form, can be marginally faster than the C8 in some conditions.

C8Jake

outstanding report

BeastBoy

I think you should seek a more informed source. All current mid engine cars do not have “excessive” understeer.

PurpleLion

Ferrari is the possible exception.

But, apparently the McLarens do, which is the one marque that I would have expected to be neutral.

For the record, perhaps excessive is too strong, I guess that I will change my post. Regardless, I think that my main point is valid re the C7 vs the C8.

Lashedup

Porsche has done nice stuff with the 911 as well.

In the end I think the track guys are looking for a better balance towards neutral but still understeer initially. I think continued refinement of the C8 will yield closer results in the future.

thill444

Agreed and I bet you dollars to donuts the C8 GS/Z06 variants will be more track tuned and less prone to understeer. They will have a few more years with the platform and more time to tweak the suspension and tuning.

Honestly, most people don't and won't care if the car understeers, they probably prefer it since most cars will never leave the street and will be garage queens (no rain, no snow, no redline, no racing).

BIG Dave

Anyone we might know?

JerryU

The title is a bit deceptive but your first sentence is probably correct, it's designed in to most.

Quoting Tadge Juechter:
In a video he said: “he came from a Porsche family and was pleased they were able to overcome the inherent Oversteer of the early Porsche’s!”

In a C8 quote in Super Chevy Mag Interview: “We knew all of the bugaboos that other brands had to discover and correct over a period of many generations. … We were always sensitive to the car's rear mass with the mid-engine placement. We had to do it right the first time. There were many little details we had to design into this chassis to correct that, but the driving experience is amazing. “
(Note: The “bugaboos” and "generations" reference is obviously referring to Porsche who took decades to make that rear heavy car into a good handler!)

Also it took 2 years of carefully following the issue of “Why No Center Air Dam” in my early, September 2013 built C7 Z51 to find it was because it was making the car oversteer slightly at high speed when GM requires slight Understeer!

1. In an October 2, 2013 article about C7 aero, "Like a Knife" by John Bednarchik, GM's Chief Aerodynamicist, said it’s for high speed stability. I read that article when it was published. He gave no details.
2. A GM marketing exec, mentioned the reason was to allow more air to reach the rear brakes. However, I searched forum comments and found this statement that same marketing exec told a forum member in May 23, 2013 when he asked him at Sebring about a possible C7 center air dam, quoting that post: “He further explained no that due to the different way the Z51 package diverts the air,” The poster indicated he was puzzled with the answer! Like Bednarchik no details and made me continue to look for the "real answer."
3. Tadge at the April 2014 Bash said the center air dam on the Z51 is deleted to balance the lift characteristics.
4. Tadge in a 2015 Z06 intro video said it was not used because it was causing high speed Oversteer and they require some Understeer. Having a modified 1967 Cotvair I knew all about Oversteer and Ralf Nader's book. I'm sure GM did not want to discuss the issue or give Nader a reason to write another book full of part truths and falsehoods!
5. Tadge in a 2016 forum post said they carefully control “pitch moment” to provide neutral handling biased to Understeer.

Bottom Line
Once you learned how to deal with Oversteer it was fun! However if going to fast for a turn, turning the steering wheel as the average Vette owner would in an Understeering car will get it quickly facing in the opposite direction! Have a split second to turn the wheel corrctly. Having a modified Corvair did a number of things to reduce Oversteer in that 60% rear weight car. Porsche's of the era were similar. Quoting Juechter above,"There were many little details we had to design into this chassis to correct that." There are also a number of things that can be done to get it to Oversteer for those that prefer. Expect folks who Autocross will find those!

Not sure GM will deliver a car that Oversteers, but just like Tracking alignment settings for a C7 are outside GM specs, how Tarckers set their car's up is ther business!

The HACK

JFC.

I really wish you guys would just take the time to take some track schools and truly understand what understeer and oversteer is, before you come here spouting uneducated posts about understeer.

There are different types of understeer, and different degrees of understeer. You can understeer into a turn at corner entry, you can understeer coming out of a turn at corner exit. You can also understeer and oversteer at both phases of a turn. You can also have a chassis that is prone to understeer MORE or understeer LESS. You can have a chassis that is perfectly neutral at corner entry, and as you throttle in the car understeers OR oversteers towards corner exit at a certain level of power in a RWD car. You can have a chassis that understeers badly into a turn, then as you come out of turn and apply throttle, it continues to understeer MOAR, or you can have a chassis that is perfectly neutral upon corner entry, neutral upon corner exit, and neutral all throughout. All these different phases and levels of understeer all can have a desired effect or adverse effect. It all depends on how sever the understeer is, where and when it's occurring, and how you go about fixing it while on track.

One of THE best chassis I've ever driven was a Lotus Exige 240S. It really is insanely good. If you go into a turn way WAY too hot, and crank the steering wheel like you're an amateur, the car goes into an understeering state to save you. If you mash throttle upon corner exit WAAAAAY too early, the car understeers to save you. If you nail your corner entry just right, the front end responds to your input instantaneously, and as long as you're not attempting to "drift" the car, it will carry speed through the turn and exit the turn with incredible grace and agility. IF, and only if, you apply throttle too early, it will naturally understeer. But progressively feed into the throttle like how you're suppose to drive a car fast on track? Do it just right and you'll get a nice, near 4 wheel power slide with just the right amount of wheel slip angle. It is magical when done right, and you can induce understeer OR oversteer at will. The chassis is so short and nimble that a flick of the hand on the steering wheel, you can immediately reduce understeer or invoke oversteer.

Does it "understeer" at the limit? Depending on how you approach the turn. That, is a fantastically tuned, well balanced mid engine car. That is what induces cargasms for skilled and expert drivers, when the car does EXACTLY what you ask it to do.

They don't build cars like that anymore, of course.

But there are cars that understeers badly into a turn, and badly out of a turn. Poorly set-up front wheel drive cars are like that. This is an example of a car that understeers into and out of a turn:


Notice how hard the tires are begging for mercy here? Yes this car UNDERSTEERS. Badly. This is a stock first gen Veloster Turbo.

Most RWD sports cars with decent 50/50 weight ratio would typically understeer too, at the exit of corners as you power down if it's set up to understeer. I.e. much narrower front tire vs. rear tire, thicker front swaybar, etc.


This is my Z4 M Coupe on stock suspension and camber, with stock stagger (aftermarket tires). This has minimum amount of understeer in most turns, some moderate understeer in the tightest of turns towards the end of the run. There's a HUGE difference between the Veloster Turbo and the BMW, even though they both "understeer." The Veloster Turbo understeers everywhere, all the time, and basically can not power out of a turn to save itself. The BMW understeers a little on some of the turns, but is easily correctable, and mostly the bulk of the understeer happens at the slowest corner basically designed to make a car understeer.

WORLD OF DIFFERENCE.

Now, if a car naturally understeers in most turns, yes you can potentially tune out some of those understeer tendencies. Although the maddening understeering characteristics of the Veloster Turbo came mostly because it's a turbo charged front wheel drive (i.e. the same axle turns AND drives the car). I'd basically have to give up rear grip to make the Veloster Turbo more neutral (it could still be a hoot to drive though). But on the BMW? All I did was make some pressure changes and it dialed out the understeer from run 1 to run 3 (run 4 was just me elfin' around). But to make a generalized statement that "all mid engine cars understeer" without understanding the actual degree of understeer AND when it understeers shows little understanding of actual vehicle dynamics.

Like I said, it's a huge difference between, say, a car that goes into a turn perfectly neutral, comes out of turns a little understeer-y if you apply the throttle too early. It's the nature of the beast. A car like this is easy to drive fast. A car that understeers into a turn, then understeers MORE coming out of a turn, is very hard to drive fast, as when it's most crucial that you apply power, the car is only slowing down more due to understeer.

I'm not chassis expert, but judging from the few videos available of the C8 on track, the C8 base Z51 chassis as it stands, does not have enough grip up front. So it CAN understeer into a corner if you come in too hot (any car will understeer into a corner if you come in too hot), but it seems to understeer rather than go neutral once you transition from brake to turn, then to throttle, which is the ideal setup. And it has a tendency to continue to understeer if you apply throttle coming out of turns, but not badly. It only seems to understeer badly if you understeer into a turn first and try to correct it via throttle*. When driven properly, it appears to only have mild understeer coming OUT of some turns, as long as you don't try to play hero and mash the throttle. But it is definitely not as neutral or tail happy as the C7, and definitely not as balanced as some of the Porsches I've seen and driven, and no where nearly as magical as the Lotus Exige 240S that I judge ALL cars by with handling.

*p.s.: Using moar throttle isn't always the preferred way to correct understeer, but it seems the "fun" way for most journalists. I can see why a car setup to understeer more when you go "MOAR THROTTLE!" can be off-putting to some. It's not the fun way to go around turns. But for the majority of mere mortals buying the C8, it IS the safe way. But it's not likely to win over any automotive journalists that's for sure.

JerryU

You have said that before and I considered your suggestion! Admit my SCCA info is from college where a friend built and drove a Lotus Super 7. We'd spend time between classes on the backboard drawing cornering paths etc. That was before I bought and modified my '67 Corvair! Also have a neighbor and good friend who is older than me and raced a Triumph in collage when Rodger Penske was also racing SCCA, albeit in another class! We've discussed his racing experiences. When he retired he built a Triumph similar to what he raced but turned out to be 98 point car that he trailers to shows. So he built two more! I like pics so these are some of my neighbor when he started the first and after he installed a lift to store the others! When I retired 20 years ago I built a Street Rod!

I decided to add to my library and bought a recently published 550 page ~$100 text considered the handling bible by a number of very knowledge folks! As expected it has a lot of math like the Kinematics book I used in college (pictured with it below! But I like Math so it's fun to follow!) As one book reviewer noted, no need to follow his equation derivations as the pictures he develops with them provide a clear understanding of the issues! I have only digested 2 of the 11 chapters in this 550 page text. Enough to define reasons some race cars use reverse Akerman, my initial objective. Before my C8 arrives I have hopefully been able to cover the other 9 chapters!

Suggest you might consider GM attorneys are going to allow a car to have Oversteer as it's set up from the factory! Cars are a hobby but very familiar with class action lawsuits and "lawyers for injured people!"


Already accept that my simple vector sum model for forces on a contact patch is far from useful! Forces are not uniform and vary within the patch with braking, lateral acceleration and is not a simple vector sum with combined loads. Guiggianni's figures and graphs developed from his rigorous math models are excellent!


Friend and neighbors' Triumphs restored when he retired! Raced SCCA when in college at the same time as when Rodger Penske was doing the same - in another class! I built a ProStreet Rod when I tried 20 years ago!!



Buidt a Street Rod When I Reired. Today, Mostly Goes to Shows!

PurpleLion

Jerry, if I remember correctly, those Triumphs were known to be roll over Kings!!!

I went to school near Lime Rock and, if I remember correctly, I think that I saw at least one that did! I think a TR3.

JerryU

^^
My friend talks about racing at Lime Rock. I'll ask when I see him. Big car show in town on Saturday where I'll have mine, he'll visit but he's mostly been going to bigger shows in Amelia island etc. Recall he rigged the overdrive so it was easy to engage!

He drives the Red Triumph and had balancing issues with the engine he hopped up with Mikuni motorcycle cabs. I'm much more familiar with the modifying the 850 Holly double pumper I have on the 502 cid engine in my street rod!

PurpleLion

Yes, and I think that it would be really great if you would take a reading comprehension course!

My statement was that "the manufacturers of all of the current mid engine cars tune their cars to exhibit understeer instead of being neutral". I am not sure how that statement evidences a lack of understanding of what constitutes "understeer".

Perhaps you require a more detailed explanation: Mid engine cars (rear mid engine for those of you who bought the BS re front mid engine) have anywhere from 55% to 65% of their weight on their rear wheels. This means that, all things being equal, a mid engine car will always oversteer at the limit of adhesion (exhibit a higher rear slip angle). Please note "all things being equal" means that the same tires are being used at the front and the rear, same tire pressures, same spring rates, shocks, anti-roll bars, ...etc.

Since "oversteer" is an anathema as far as corporate lawyers are concerned, most manufacturers tune their cars, i.e. ensure that all things are NOT equal, such that "oversteer" is replaced with "understeer". This is typically accomplished by using smaller tires in the front, more front roll resistance, ...etc.

Yes, braking transfers weight to the front tires while accelerating transfers weight to the rear tires either of which change the instantaneous relative front to rear slip angles. Regardless, the overriding tendency of a mid engine car will be to oversteer.

JazzVA

Isn't the basic solution here to add more rear swaybar in order to make the car more neutral? Is it that simple? Or must the suspension also be retuned to allow for the change in bar? I am planning on autocrossing my car and doing an occasional track day (time attack) and believe that would improve the balance. Am I wrong on this?

Bill Dearborn

The main reason most people got in trouble with the Porsche wasn't its steering response it was the natural inclination to lift their foot off the throttle when feeling like they were going to fast into a corner. As soon as they lifted off the throttle around they went. I doubt you saw much Oversteer when the drivers just maintained their throttle input thus didn't transfer weight off the rear onto the front right at the wrong time. An understeering car will reduce the amount of understeer when the foot comes off the throttle and will turn in better. Even a stock C5/C6 setup with street alignment will exhibit a strong trailing throttle understeer in a turn. It is strong enough to scare the crap out of you the first time it happens. Once you keep your foot on the throttle the car will squirt through a corner and the driver has the ability to change the car's yaw rate by making short lifts and pulses on the throttle. It isn't about burying your foot on the go pedal and making the rear tires spin with the rear end sliding out like a drifter does since that is the slow way around a corner. Watch the guys that turn the fast laps. The backends of the cars are pretty much glued to the track with no sliding/smoking.

Bill

PurpleLion

Adding a stiffer rear swaybar will reduce understeer, but, it will also reduce the ultimate cornering ability of the suspension. On the other hand, using a softer front swaybar, will also reduce understeer while increasing the suspension's ultimate cornering ability. Same holds true for using a wider front tire or lowering the front of the car.

Reciprocal

That's what a rear sway bar does is transfer weight to the front, and this car has a fundamental rear weight bias. But the best performance investment you could make is to let Rick Malone at Spring Mountain teach you how to drive it.

JerryU

I agree, as you say backing off the throttle when you were near an apex using max available grip created engine braking. Using that old tire patch model you have a fixed force available by the tires and the lateral "g" force is reduced when engine braking occurred. That reduced lateral grip when you were on the "edge" meant you were sliding off the road- rear first. That was the basic issue with '65 and later Corvairs (not the swing axle 1960 through 1964.)

BUT if going fast enough the rear was going to slide and you could attempt to correct with proper steering but had little time. My '67 with the OEM HD springs, shocks, sway bar also had a quick steering box ratio option, not all that commo in the day. That helped as you had very little time to react. I also went with Plus1 14 inch tires and performance low profile tires.

The other issue with the 60% rear weight Corvair for the average driver was GM recommend 16 psi front tire pressure to reduce tire grip and promote Understeer. Many did not follow that recommendation. Then folks used the more natural understeering cars steering reaction to a skid and not the correct reverse. Turn the wheel like it was an understeering car and if you were lucky you'd spin on the road and were just be facing the other way! Actually only had a fraction on a second to try to correct properly. If going too fast nothing helped!

As Tadge said in forum post discussing the C7, they design for neutral handling at high speed with a bias to Understeer. When racing, the tire loads get more complex. Still have 9 more chapters to see if I can get a better understanding!

2cnd Chance

Notice a number of manufacturers have included rear-steering to help handle the oversteer. This might be part of a Z06 ZR1 package.

RKCRLR

I saw the picture of "How to Make Your Car Handle". I have that book somewhere (unless I gave it away). It introduced me to the importance of roll centers with respect to the car's communication with the driver. I also have Carroll Smith's series which have great practical information. I should re-read them sometime.