I've run my '98 vert in a couple of auto-x's now and I get understeer under hard braking entering corners. It's a pace car model with Z-51 suspension, plus it's been lowered, has Hotchkis sway bars, modified shock travel, Michellin Pilot Sports 285/35-ZR18 on the front and 345/30-ZR19's on the rear, stock brakes. I'd prefer to have slight oversteer. Is there anything I can do to tweek the handling to my preferences? Or is the answer, "Learn to drive better!"???

Thanks!

 

Typically a smaller front bar or a larger rear bar will do it..

I'll assume you want to keep your Hot. sway bar set up..

With your tire / wheel sizes and lowering, you have a lot of variables to consider..

How do you know the car isn't riding on the bump stops in the front during your auto-cross runs? I'd be willing to bet it probably is, which of course will instantly cause the balance of the car to go out the window, and probably make the front end push even more than it normally would.

You may have better results raising the car up a bit. If you are really serious go with a coil-over setup, so you can pick the spring rates front-to-rear..

 

Beautiful car, I should have bought it when I had the chance. Congrats!

I saw your post mentioning the Z51 & was wondering if that was something Specter Werks added to the car when they built it?

Reason I ask, every 1998 Pace Car came off the line with the base suspension. Couldn't get Z51 from the factory on them.

Just wondering......

 

Call me at the office to discuss your car. I would like to get your information and keep in touch with you. Congrad's on the car...it was one of our favorites. I can help you tune the car for auto-X.

248 583-9559

Jeff

www.spectergtr.com

 

Also...

Raise front --- lower rear
Brake lightly thru corners
Bigger/stickier front tires
Smaller/harder rear tires
Front downforce
Lighter front end


With the braking situation you describe, adding front brake calipers to the rear will introduce more a rear brake bias, which sounds like what you want.

 

 

Re: Z-51 question -- I have to claim a certain level of ignorance here. I'm not as familiar as you with the history and evolution of various features. But the Z-51 suspension is what I was told by the seller, and confirmed by Specter Werkes, as well as an article in May 1999 Road & Track featuring this car. So I believe Specter Werkes made the Z-51 conversion as part of thier build. Actually, I see that Jeff Nowicki of Specter Werkes posted a reply to this thread. JEFF -- Can you confirm the Z-51?

Did you pass up buying it new? . . . Or from a previous owner? It's definately a fun car to drive, and it's very unique -- Gets lots of comments, anywhere from little kids all the way to little old white-haired ladies.

 

I'm not giving you a hard time here - honest.

But if you've only got a couple of events under your belt, then the most likely cause of your corner-entry understeer is excessive corner-entry speed.

90% of the "handling problems" you'll encounter in your first season or two of autocrossing will be driver induced. Driving in competition, especially in autocrosses, and doubly especially with a car whose limits are as high as the C5, is an unnatural act. It's a learned skill. You are asking your brain and body to react to things it has never experienced before, and the actions you need to take, you've never done before. So it's going to take a little time to develop those skills.

Of course, every red blooded male figures he came out of the womb the reincarnation of Ayrton Senna - myself included. It's really easy to try and pin the blame for the evil habits of the car on the setup, the tires, the weather, the course.....

But if you want to be truely successful, you need to actively NOT muck with the car for a while, and learn to drive.

Happily, you're in a good vehicle for learning. The C5, especially the Z06, is an incredible autocross car. I've never driven a car that was so easy to drive so fast. My own car asks a lot more of a driver.

The next event you're at, try slowing down at corner entry to the point where the understeer goes away, and concentate on getting back on the gas as early as possible. I'll bet dollars to doughnuts you drop seconds off your time.

Good luck!

DG
------------------
http://www.atimotorsports.com
http://farnorthracing.com
http://streetmodified.org/books.html

 

from F-Body Europe
http://fbodyeurope.org/board/viewtopic.php?t=5568

If you have to ask "what is understeer / oversteer?", it’s quite simple: if you approach a fast bend in the road, turn the wheel, but the car just plough straight on into a ditch, then you suffer from understeer. If you leave the same bend spinning backwards into the ditch, then you suffer from oversteer. Of course oversteer can easily be provoked when there is an idiot at the wheel, so don’t always blame the car.

For those of you who understand your car’s dynamics well enough not to make the typical beginner’s mistakes that will upset the handling, here is a list of changes that will guide you to tune your suspension to a neutral-steer for superior high-performance handling.

DECREASE UNDERSTEER..... CORRECTION.....DECREASE OVERSTEER

higher pressure........................tire pressure - front......................lower pressure

larger contact area....................tire section - front...............smaller contact area

more negative.........................wheel camber - front.......................more positive

softer.................................. ..........springs - front................................... ......stiffer

thinner (softer).............................swa y bar - front.........................thicker (stiffer)

larger.................................. .........spoiler - front................................... ....smaller

lower pressure.........................tire pressure - rear.....................higher pressure

smaller contact area.................tire section - rear..................larger contact area

more positive.........................wheel camber - rear......................more negative

stiffer................................. ...........springs - rear.................................... .....softer

thicker (stiffer).............................sw ay bar - rear.........................thinner (softer)

smaller................................. .........spoiler - rear.................................... ....larger

weight bias rearward................weight distribution..............weight bias forward

A few words of warning: if you are unsure about what you are doing, rather get help from an experienced person. Make your changes in small increments and first test the result in an open area where you can do little harm (like at one of our slaloms). Rather tune towards neutral-understeer, since an oversteering car is quite a dangerous beast that needs a fast hand to catch it. Have fun.

 

Thanks DG! That anwers the question I posed at the end of my initial post . . . "Do I just need to learn to drive?" . . . Sounds like that's more the case right now than any issue with the car. Gotta go get a big hammer and adjust that loose nut behind the steering wheel!

 

Thanks Lancer033 for the further detail in adjusting a car's handling. Sounds like I need to work on driver adjustment before monkeying with the car set up.

 

Whether the car has the base suspension or the Z51, the handling should be very neutral assuming you are not doing anything weird with it. As DanC5 mentions above, that neutrality can be thrown out the window when you start screwing around with tire sizes/pressures and most certainly the lowering aspect. The Vette is an extremely well behaved beast with either of the stock setups but when you lower it, you reduce the amount of travel to the bumpstops. If the car is lowered more than a half inch, under hard cornering you can use up all that space and hit the bumpstops at which point you no longer have a suspension. The result is instant understeer.

Most of the guys here lower their cars for looks, not performance. If you want to lower it more than a half inch, you have to increase the spring rates so that hard cornering will not use up the given amount of travel. I would start there.

Autocrossing is a very difficult place to try and learn how to handle a car. You just don't get enough laps for practice. I suggest you try a HPDE at a track near you. You will learn more in one weekend than you will in 5 years of autocrossing. Then if you prefer, you can go back to autocrossing with a whole new outlook.

 

There's an easy way to check this.

Get 4 zip ties (wire ties). Jack up the car, and put a zip tie around each shock shaft (if you still have OEM shocks, you'll have to detatch the top of the shock shaft and slide the dust cover off to get at the shock shaft)

Then slide the zip tie down until it contacts the shock body, and reassemble the car. You now have a "maximum shock travel indicator" as the shock body will push the zip tie up on the shock shaft. (on the Penskes and Bilsteins we sell, we provide a rubber O ring on the shock shaft for just this purpose)

Go out, do your runs, and then pull the shock and see where the zip tie is sitting.If it is smashed into the bumpstop, then the car is bottoming out and either needs to be raised, needs more spring rate, or needs a shorter bumpstop.

I don't agree.

Driving on a track - especially with a car whose limits are as high as a C5 - means you are physically moving a whole lot faster, and that means that the penalties for overreaching are much higher. The natural tendency is going to be to drive within the driver's comfort zone, when what needs to happen is to get the driver uncomfortable and teach him to get confortable with being uncomfortable.

Adding to the problem is that road race courses, with their (typically) fast corners and long straights, reward cars with big horsepower, and the C5 has big power. You can drive a C5 like a total monkey on most road courses and still turn in decent lap times, so you won't get a good handle on how well you're really doing, unless there happens to be a real hot shoe out there in a car with similar power.

So typically, spending time at track days teaches you to underdrive the car very consistantly.

Autocrosses, on the other hand, don't reward power nearly as much, and they really, REALLY punish driving errors, or timidity. At the highest levels, like at SCCA ProSolo, you need to be driving at 100% pretty much on every single corner, or you're going to lose (ESPECIALLY in a class that is so talent-heavy as Super Stock, the home of the nearly-unmodified Z06)

But the *physical* punishment for overreaching on an autocross course is far less. Pretty much the worst that can happen is some flatspotted tires and a bruised ego. Hell, as far as I'm concerned, if you don't spin the car every once and a while, you're not pushing hard enough.

The biggest problem with autocrossing, as mentioned, is lack of seat time. A lot of smaller, local-level events will often allow "fun runs" after an event is complete - do them. There are travelling driving schools out there that rent lots and do comprehensive training (like the Evolution school, you can find it on Google, tell Jean Kinser I sent you) If you get to know some of the local hotshoes, you can often find out about private test'n'tune events where you can drive to your heart's content. And you always have the option of just attending as many events as possible - I know in Detroit that there's an event pretty much every weekend from May-Sep.

Autocrossers are a friendly bunch too, so you can often get a hotshoe to ride along with you (or give you a ride in his car) and get feedback on how well you're doing.

I've seen a lot of top-level autocrossers cross over to road racing, and I've seen a lot of road racers and track-day guys try autocrossing. Good autocrossers tend to be excellent qualifiers and run really fast lap times for the equipment they have - compared to an autocross, a road race track happens in slow motion. They also typically lack a lot of "race craft" skills, especially passing and making a marginal car last a whole race (autocrossers tend to be hard on equipment) so it's not like an autocrosser is some sort of Godlike UberDriver.

But road racers and track-day guys typically don't adapt well to autocrossing - the skill set is just so different to what they are used to.

There are exceptions, but the guys who are successful at both (guys like John Heinricy and Scotty Bob White) *practice* both, and develop the appropriate skillset doing the actual sport in question.

Lemme put it this way - if you want to play pro tennis, you don't practice by playing badminton and hope the skills cross over. Yes, both sports use rackets and nets, both sports are outwardly similar, but the skills actually used during the sport are completely different. Nothing in badminton will teach you how to return a 120 MPH serve. Nothing in road racing will teach you how to best get through a 5-cone, 70 MPH slalom with the tail dancing the whole way. And nothing in autocross will teach you how to outbrake Scotty and get past him at Turn 1 at Laguna Seca.

DG

 

I've never autocrossed.
That said........ to combat understeer you might try pushing harder into the turn. This may be counter-intuitive but it does work, sometime.

 

Well, I say it's the tires. Yes, we all need to learn how to drive with the stuff we have before we start modding the stuff (my FRC is still running stock hardware except for wheels&tires). BUT, you've got a 60mm differential between the front and rear tire sizes, stock is only 30mm. And the stock setup is designed to understeer.

So, this means you really need to drive "conservatively" into the areas of the course that you will understeer, and don't expect to get any throttle oversteer with those enormous meats you've got out back.

I'm running 275f/315r and my car goes towards understeer, but not too bad. The only time I can get the car to slide the rears is coming out of a really tight corner. If the corner is open just a little bit, then I get a throttle understeer that I can control fairly nicely to the outside cone on the exit gate.

Also, I've had very little success with trail braking in my car into a corner. That might be due to bad technique, little experience, whatever, but that's my experience.

Finally, I definitely agree with NOT doing a track event [i]for the purpose of learning how to autocross.[/b] Track events are great fun, but what you learn there will minimally (if at all) transition to an autocross event.

HTH, and have a good one,
Mike

 

I've also autocrossed and I guess this issue is just a matter of opinion. To me, doing 5 or 8, 60 second laps in a day, you will need at least 20 events to get the seat time you get in one weekend at a track event. You will never learn how to drift a sweeper or trail brake without years of autocrossing. Yes there's more time between most of the turns but that's where you enjoy the benefits of a Vette over a Miata. Yes, you are rewarded for horsepower. That's one of the reasons we bought Vettes instead of Miatas. I also think that it is ludicrous to compare roadracing to autocrossing as badminton is to tennis. I guess I should have stated that it was JMHO.

 

But there's more to learning how to do something than just raw seat time - you also need constructive feedback (from some mechanism) to give you some indication of what you are doing right and what you are doing wrong.

After all, if you just keep doing the same thing over and over and over again, you're never going to improve, right?

At most track day events, you get a large variation in the quality of the cars and the drivers, and little to no formal mechanism to try and eliminate the car factor from the equation. Plus, the nature of the event is that big power is going to go faster. A C5 is pretty much always going to hand a Miata its hat on most road courses, unless the Miata driver is spectacular, and the C5 driver can't drive sheep. For all intents and purposes, the question of who is going to be faster than whom is decided by the cars they bring to the event.

This means there is little in the way of motivation to get an individual driver to really push the limits (especially when the penalty for overstepping the limit can be a car in the wall) and more importantly, little in the way of example of just how fast the car is capable of really going in talented hands.

So yes, you're getting more seat time, but the rate of driver improvement per minute of seat time is low - certainly not ZERO - but low.

Now in the autocross environment, you are almost always running in direct competition against drivers in similar cars, prepared similarily. Every single time you go out on course, you get a time and (more importantly) a ranking against people with cars that should be running the exact same times if they were driven by "perfect" drivers. And there's usually a good representation across the talent range, especially in classes like Super Stock, where the combination of high ultimate performance and little need to wrench on the car brought to the party by the C5 Z06 attracts a LOT of talent - if you can win a National level SCCA autocross event in SS, you have really accomplished something of note.

As such, you get direct feedback about just how well you are *driving* every single time you turn a wheel in anger. And if the talent pool at the event is sufficiantly deep, you are going to get a graphic lesson in just how fast your car can go, because Joe Hotshoe, driving an *identical* car, is going to put quite a bit of daylight between you and he.

Autocross does a very good job of removing the car from the equation, especially in Stock classes.

(Oddly enough, once the talent pool gets deep enough to where the top 10 guys are more or less equally fast, the emphasis then switches to car preparation, and small differences in car potential start to become the telling points on who wins on any given day. But that's a long way away from your first couple of events)

With all that feedback, there is a very large motivator to push harder, go faster, flirt with the limit, and go beyond your personal comfort zone - and THAT is when the real development really starts. It's AMAZING just how fast things start coming to you when you start to push your limits and try new things - and with there being very little at stake for overstepping those limits save some tire smoke and some punted cones, fear plays a much smaller part in the process.

Actually, I learned how to trail brake by about my 7th or 8th event. I learned the importance of getting on the gas early - earlier than I had ever thought possible - at about the same time. I have a very distinct memory of learning that I could catch the rear end from coming around by adding throttle (to send weight rearward) at like my third or fourth event.

In fact, I'd say I picked up a new driving technique, or measurably improved an old one, at every single event I've ever attended. there is NO motivator better than "I need to go faster than I am if I am going to win" The best way to improve is to compete.

I've been autocrossing seriously since 1997. I've been autocrossing professionally (as professionally as can be done at least ) since 1998 - yeah, I was a quick study (took Rookie of the Year too ) and it is a phenominal way of teaching people how to drive fast, and doing so very quickly.

Have a look at the SCCA National schedule (National Tours and ProSolo) on the SCCA website, and if one comes close by wherever you are, go out and spend a day watching. If the sight of Eric Strelneiks or Danny Popp or Matthew Braun or Gary Thomason dancing a Z06 around that course doesn't move you to tears by the sheer beauty of what they are doing... then you ain't a real Corvette guy.

And let me tell you.... My own weapon is a Street Modified Eagle Talon. It's a blunt instrament of a car; big power, big grip, just a brutal rocketship and a very difficult car to drive. You guys that have C5s, especially the Z06, you are so lucky - you have the best sportscar that GM ever made, and an absolutely spectacular autocrosser. The car has zero bad habits, and lots of good ones. I can think of no better car in which to develop into a top-rank autocrosser (assuming you have the talent and desire)

I work for ATI PE. We make and sell all kinds of go-fast C5 parts that I'd be tickled pink so see you guys use (I did most of the engineering and design, and I'm really proud of the stuff we've done) But I'd rather see you learn to drive the car you have right now, and really learn how to wring a good time out of it, and THEN come see us for the go-fast goodies, because in the long run, you'll be all the more faster (and happier) for doing that.

DG

 

TalonDG, I agree with a lot of what you're saying. I want to bring up a point Carroll Smith made about debriefs. A debrief allows you to analyze what just happened, and it needs to be done quickly, otherwise the lessons are lost. In an autocross, that debrief can happen after just a minute, and there SHOULD be lots of stuff to go over. While I'm drawn by big tracks, I'd rather do my learning between the cones where mistakes only cost seconds and cones.

 

Don't misunderstand me, taking my car to the local track is a blast. It's also expensive, $250+ for that weekend. Plus, comparing track events to autocrosses is like apples to oranges: both are fruit, and both are very tasty, and both come in several varieties.

But, they're not the same, and that's not a bad thing. When I'm on course, it's not being timed, so I run probably around 7-8 10ths, just having fun. Am I the fastest? Who knows? I don't get passed by many people, but the local experts hand me my head every time. Do I care? No, because I'm not willing to risk my car to keep them behind me.

Now, autocross? I run at 10/10ths of my ability, and when I step over that line some poor cone takes the punishment, not me, my car, or my wallet.

Have a good one,
Mike

 

I did the SCCA autocross thing from 91 through 95. I've also done the NHRA thing and the WERA and AMA thing. I did very well in all of them thank you. I just prefer the track thing over the cone thing. A LOT more exciting to me. But that's personal preference. There's no right way or wrong way. I guess I like the exhileration of putting the gonads on the line and doing things with the car that you just can't do in a parking lot. There are certainly things you can do at an autocross that you don't do on a track. The "art" of autocrossing is definitely different than the "art" of tracking. One is a Picasso and the other is a Monet. Both exciting in their own way to their respective owners.

Thanks for the input