Pipes

Me -- first year driving the Corvette, participated in only 4 autocrosses, no other race experience (read Skip Barber's "Going Faster").

Vette -- 2000 Hardtop with Bilstien Shocks and GY F1 GS-D3s, aligned to factory settings 6 mos ago.

Commute -- Over 2000 ft mountain pass (Hwy 9 in Santa Cruz, CA).

To see how much gas mileage I could get for my commute, I've taken to driving down the mountian in neutral. Without trail braking and, of course, without exit acceleration, the car 'feels' like it plows the corner (just a little). The wear pattern seems to bear this out as the fronts have worn out before the rears. Also, both the fronts and the rears have worn the outsides first (I plan on increasing the camber soon).

I've noticed that with just a bit of throttle in the turns, the C5 feels more neutral, more surefooted, without the feeling as though the front tires are plowing the turn.

Can anyone help me understand why this is so? Can the car be setup so that it feels neutral in neutral?

Curious,
Eric W.

carpe dm

:eek: :bb :nono: This is a very dangerous stunt; I wouldn't recommend you continue this activity. :skep:

wwashing

:iagree: :nono: :leaving:

JakeL

FWIW, that my hurt more than it helps. I don't know if the LS1 does it, but many modern EFI cars will turn off the injectors completely when coasting down a hill, since the drivetrain is keeping the engine moving - as long as you don't touch the throttle. By taking the car out of gear and making it idle, it has to inject at least *some* fuel.

John Ames told me this too. Just seems to be the balance of the C5's spring/bar setups from the factory.

Little more front camber might do it, and maybe move your battery to the rear to change the weight distribution a bit. Overall, I think it's just sorta how C5's "feel"

my $0.02, and you *might* have gotten your money's worth ;)

-Jake

BlackZ06

First, I agree with the others, don't descend Hwy 9 (or 17) in neutral, keep the car in gear when it is moving on the road.

The car cannot be set up to feel "neutral in neutral" and you shouldn't want it that way.

The car IS set up to do exactly what you are experiencing .... it has very mild understeer dialed into it if you are "coasting" through a corner.

The change in the cars handling from understeer to "neutral" when you give it some gas is because as you throttle up the car, the weight distribution changes.

Coasting, the car has about even weight distribution front to rear. When you turn, the front tires are having to do most of the work to turn the car. The rear wheels are essentially just trying to "track along behind".

When you give the car some throttle in the corner the front wheels have somewhat less weight on them, and the rear wheels pick up that weight. The rear end is now more firmly planted, and assists the car in rotating through the corner. If you REALLY get on the gas, you will cause the car to oversteer, and if you don't know what you are doing the tail will swap with the front and you will have the ride of a lifetime, especially on a road like Hwy 9.

Take some classes in car handling, or read a book like "Speed Secrets" (Ross Bentley) to gain a really good understanding of over/under steer and how your driving method contributes/mitigates these characteristics.

Hope this helps,

Steve

Cobra4B

I'm ignorant about the coasting thing... why is it bad to coast down the hill in neutral :confused:

BlackZ06

Cobra4B,

You asked "why is it bad to coast down the hill in neutral"

There are several reasons you want to keep the car in gear ....

1) You can use the throttle to change the cars handling through a corner, if you're in neutral, you can't do that.

2) Going downhill the engine braking (an earlier poster corrrectly pointed out that on our LSx engines the fuel injectors are off if you're in gear and off the throttle) assists in slowing the car without over heating the brakes

3) If you need to make an emergency manuever, you have the instantaneous availability of engine power ... if you're in neutral, you've gotta get the car back in gear while trying to manuever out of the emergency ... that split second could make all the difference ...

4) In that emergency, you not only have to get into gear, but you need to bring the engine speed up to the appropriate road speed ... let's say you're coasting at 35 mph and you pop the car into 3rd gear, let out the clutch, and turn at the same time ... the massive engine braking (engine at idle speed ... wheeels turning much faster) can, and probably will, cause the car to loose traction at the rear, spinning you if you are turning at that moment.

So, bottom line, keep the car in gear essentially all the time. Really you should (with a manual) only be in neutral while at a stop light or other prolonged stop.

Keep it shiny side up ....

Steve

Cobra4B

Gotcha, just for safety reasons... I thought there was some kind of mechanical problem to be had by doing this.

Soldiervette

HUmmm? :confused:

FlamerF1

Ive noticed this too, I was racing this kid in a Soap Box Derby car and; oops sorry I forgot the "no racing posts" forum policy, my bad. :bb

ndirishr1

"Just for safety"??? At least you won't coast down very many hills in Indiana! You'll have to find one first.

OldSStroker

You don't really change the front/rear weight distribution very much with mild acceleration, but you do ask the rear tires to provide froward thrust when you accelerate even a little, so according to "Traction Circle" theory, the lateral thrust (cornering force) decreases slightly because you haven't changed slip angle, and the car "loosens up" a little. The more gas you give it, the more this should happen until you reach the point Steve mentioned.

Remember the larger rear tires have the potential to generate more lateral (or longitudinal) force than the fronts. Yeah, the car was designed to be driven, especially though a corner.

Reading about handling/driving is useful, but more so is taking a driving school from Barber or Bondaraunt, etc. especially one using their cars.

[Modified by OldSStroker, 1:41 PM 2/8/2004]


[Modified by OldSStroker, 1:42 PM 2/8/2004]

CrazyMagMan

:lol: True, oh so true!!

Pipes

Thanks Stephen Barnes for the answer to my questions.

For the soap box derby racer from flat land Florida, starting from a 15 mph coast, I easily exceed 60 mph, plenty fast for this road.

As for the fuel injection speculation, the vettes computer reports approx 10% improvement in mileage when coasting in neutral over coasting in gear. However, the vettes computer mpg isn't all that accurate. So, I need to drive a tank in gear and out of gear and see how they compare. As mentioned, no fuel is less than a little fuel (besides the bad habit that I've developed and the wear and tear on the brakes).

Since it's unlikely that I'll spend the thousands of dollars it costs to attend a professional driving school, I'm wondering if joining the SCCA for about $100 and getting their training would be equivalent?

Eric W

BlackZ06

Pipes,

There are some cheaper (and one could argue better) alternatives to the Bondurant/Barber type schools.

The BMW club has an excellent HPDS (High Performance Driving School) program. Don't have a BMW ?? No problemooooo....

They don't require a BMW be in your stable to join the club. $35.00 per year, and you get a great magazine (Roundel) and the opportunity to attend their HPDS and CCC (Car Control Clinic) classes. The Golden Gate Chapter has a "BMW first" policy for their registration in classes, but the LA Chapter has a "1st come 1st serve policy". The $35.00 makes you a member of the National club, so you can attend events put on by any chapter, and the LA chapter does at least one school a year at Laguna Seca, about a 45 minute drive for you. They charge in the region of $500.00 for a two day school, and you have an instructor in the car with you whenever you are on the track. They require a helmet, and if your car is a convertible, a roll bar. They do have loaner helmets for I believe $10.00 for the 2 days.

There are also private groups such as Driving Concepts ( http://www.drivingconcepts.com ) that offer similar classes at about the same price and don't have a preference for type of vehicle.

One of the great advantages we have here in Northern California is an abundance of GREAT tracks (Laguna Seca, Sears Point, and Thunderhill - Buttonwillow and Willow Springs to the south) and these classes give you a chance to put your car through the famous turns like the Corkscrew at Laguna Seca and the Carousel at Sears Point.

Please feel free to email me if you'd like more info on these possibilities.

I envy your commute, sure beats sitting in the stop and go traffic on 101 down the Peninsula every day ... even if you have to stop, you get a great view .... I'm looking at a sound wall and billboards when I'm stopped .... :cuss

Have fun out there ....

Steve

BlackZ06

OldSStroker,

You're right about the Traction Circle theory, but I suspect that what is happening here is more weight transfer and its effect on tire adhesion, rather than that the tire is near its traction limit.

The theory addresses when the tire is asked to provide 100 percent, or more, of its traction ability. If, let's say, the tire is using 95 percent of its traction ability to corner and I now try to add 20 percent acceleration, the tire (or driver) will have to make some compromise as you can't get 115 percent traction. However, the original post implies that the driver is only using, say, 60 percent of the tires traction while cornering. His adding another, say, 20 percent acceleration does not overdraw the tires "traction account".

Throttle steering is mostly weight transfer and its impact on the tire's "total traction account". A lightly loaded tire has a lower total traction ability than a tire that is heavily loaded. It is the old pencil eraser theory. Try lightly pressing on an eraser and moving it across a surface. It will resist, but far less resistance than if I put a lot of weight on the eraser and then try to move it.

Even though it may not seem like it, you are moving hundreds of pounds of weight to the rear with even gentle acceleration.

Try this sometime (preferably not where you might hit something !!) .... Accelerate HARD in a straight line and while accelerating, turn the steering wheel .... you will have massive understeer ..... and if you suddenly lift off the throttle with the steering wheel still turned .... massive oversteer (possibly to the point of spinning). It is the shifting vehicle weight that is dramatically changing the tires slip angles.

The traction circle is great for understanding that a tire has a limited amount of grip available, and that limit can be split between varying amounts of lateral forces acting in different directions. The theory does not account for the fact that you can change that limit via weight transfer .... both for good (throttle steering) and bad (sudden hard braking during cornering).

Maybe you're saying the same thing I am .... I just had to clarify the effect of weight transfer and how it affects the Traction Circle.

Sounds like you've enjoyed your car at "the limit" ..... which is exactly what Chevy intended !!! :D

Safe times at the track,

Steve

OldSStroker

No offense intended, Steve. We just look at things a little differently... or maybe we just explain them differently.

My $.02

Jon

PS: I wish we had a preview function here. It would help on spelling/grammar check.


[Modified by OldSStroker, 12:24 AM 2/9/2004]


[Modified by OldSStroker, 12:26 AM 2/9/2004]


[Modified by OldSStroker, 12:51 AM 2/9/2004]

BlackZ06

Jon,

In reference to ...

I agree to a point. You are changing the front tire loading dramatically, which changes the lateral force, BUT other things are going on: under hard acceleration, the limited slip diff tries to assure equal torque to each rear tire which tends to push the car straight ahead in spite of any lateral forces from the front. When you lift, you now have differential action available again, and you have an existing front slip angle (which you determined by the steering angle you cranked in) which, as load increases rapidly, causes lots of lateral force at the front just because of the increase in normal force (load) on the fronts, which could be about 325 lbs. at 1 g longitudinal acceleration. Combining this with the loss of straight line thrust from the "locked" rear end and voila'...spin city!

While the Corvette's limited slip diff may contribute slightly to the fact that the car tends to understeer under hard acceleration, this phenomena will work with any car .... front wheel drive, rear wheel drive (limited slip or standard diff), even 4 wheel drive.

At a car control clinic I've attended, they lay oout the following cones (as seen from above:

+ + + +

+ + + +




+ + + +

+ + + +

The two rows of cones are about 100 feet apart. The driver is asked to get his car driving in a circle so that they can maintain a constant throttle and steering input and the car is driving through the two lanes (the lanes are quite wide) as a part of the circle.

+ + + +

+ + + +


+ +

+ + + +

+ + + +


Now, the two added cones shown above are pointed out to the driver. These cones are outside the circle the driver is following. The driver is informed that they must now drive so that they include the outside cones (effectively driving in an ellipse) WITHOUT CHANGING THE ANGLE OF THE STEERING WHEEL currently used to drive the circle.

Again, front wheel drive, rear wheel drive, whatever, the driver can do what seems to be impossible by using weight transfer to throttle steer the car. As they come through the upper line of cones they have to accelerate to understeer the car. It will "straighten out" somewhat and drive out toward the outer cone on the right. Once they come up to the cone, they come off the accelarator and the car will oversteer around the cone. As the car comes around they get back on the throttle and "steer" the car toward and through the (in my picture) lower row of cones.

====================

Also, I'm not following your math. Look at the body movement in a Corvette that is accelerating or cornering hard. It takes hundreds of pounds of force to move the body that much. See how far your front end comes up when you hit the loud pedal and then try lifting the nose that much in your driveway. It is far more than the 60 pounds your math implies. If you look at this picture .....

<img src=" http://www.bearhead.com/IMG_9683.JPG " border=0>


There is no way you can get your Corvette to lean that far over without many hundreds of pounds of force ... A 200 pound driver sitting in the car created no where near the lean you are seeing in this picture. All of that force is going into the tires.

Keep her shiny side up ... and a spell check ... preview function would be GREAT ....

Hey, fun to debate "real world" versus "theory" ... huh ?? :cheers:

Steve




[Modified by BlackZ06, 7:25 AM 2/9/2004]

vetterdstr

I should start looking for that real "quite" C5 coming over the hill then huh??

VR :jester

Pipes

Steve S,

The C5 in netural is plenty quite! I've marred the car by adding deer warning whistles, but the dang critters just didn't hear me coming until I was right up on 'em. :eek: :cheers: