ZR-1 Under or Over Steer

[scottfab]

This is a partial reprint of a discussion about under and over steer from my mail archive of 1995.

What I'd like to know (because I'm planning on some suspension freshening this winter) is how most of our cars steer.
This is a poll. Please do not guess. If your not sure don't vote.
If you're set up for autocross etc and have departures from spec for this purpose don't vote please.
Thanks.

From Finspeed@aol.com Fri Mar 31 00:26 EST 1995
Date: Fri, 31 Mar 1995 00:24:11 -0500
From: Finspeed@aol.com
To: zr1@firefox2.East.Sun.COM
Subject: Tech Question
Content-Type: text
Content-Length: 579
X-Lines: 15
Status: RO

Understeer or "push" or "tight" means that for a given steering input the car
turns less than it should or was expected. With respect to what the tires are
doing, a car that understeers has more traction at the rear than at the
front, thus the fronts will "break loose" first.

Oversteer or "loose" means that for a given steering input the car turns more
than it should or was expected. With respect to what the tires are doing, a
car that oversteers has more traction at the front than at the rear, thus the
rears will "break loose" first.

cYa
H. Halverson
finspeed@aol.com

[batchman]

Alignment and user input make an overwhelming difference to this question.

It has long been the habit of manufacturers to set all cars up to understeer (you see the accident) because that's what the public expects (can handle), as opposed to outright oversteer (you don't see the accident). That said C4s have a published alignment spec (positive camber? really???) that virtually ensures understeer under all but the most ham-footed throttle maneuvers.

The ZR-1 staggered tire configuration adds assurance of understeer commensurate to the added power as the increased rear tire footprint intends the front to lose traction first, or it would if the factory rear alignment wasn't just as baffling as the positive camber at the front.

I believe they learned these alignment settings from the C3 and when the committee met they chose crazy settings to protect their customers from themselves. Even the handling option Z51 is virtually undrivable in a performance sense at factory alignment settings. Once aligned sensibly, it is wonderfully neutral with under- or over-steer tractably available by user command.

All my humble opinion respectfully submitted,
- Jeff

[mike100]

Certainly the car can oversteer when powering a bit much out of a sweeping corner, but abrupt inputs on hairpin corners understeer pretty badly. I have experienced it worse on the LT5 cars as the lump up front weighs quite a bit more than the small block C4.

Seems to understeer worse when braking deep into the corner as well.

[XfireZ51]

Although the basic demeanor of the C4 appears as understeer, I always had the impression and some experience that it will snap around on you in a blink if not careful.

Jeff,

What are those specs for a more neutral handling characteristic.

[ZRXMAX]

A lot of variables make it an experiment at times. Their are times when I want it to oversteer and its difficult to get it to rotate. At other times is does want to come around so fast its hard to stop. Try drifting it on purpose sometime where you have room. It seems the less traction I have availible the easier it is to oversteer.

[batchman]

Although the basic demeanor of the C4 appears as understeer, I always had the impression and some experience that it will snap around on you in a blink if not careful.

Jeff,

What are those specs for a more neutral handling characteristic.

Don't mean to clutter Scott's thread but, Xfire there's a thread with some of my opinions post #33 or so:
http://www.zr1.net/forum/showthread.php?t=17235

That much got me to where I can tailor under- or over-steer by tire pressure. Yes, that's a variable too.

As mike100 points out user input makes a huge difference. The press types get their impressions on a skid pad where you slowly approach the limits of adhesion, about the only place you can be smooth enough to coax out the basic demeanor short of a race track. On the street in an emergency situation, or an autocross course (which is basically 30-90 seconds of cascaded emergency maneuvers) it is not so subtle. Shocking the tires at either end will wash that end out, and this is especially dependent on the tires themselves and the pavement, of course.

Cheers,
- Jeff

[scottfab]

Don't mean to clutter Scott's thread but, Xfire there's a thread with some of my opinions post #33 or so:
http://www.zr1.net/forum/showthread.php?t=17235

No foul. All opinions are welcome. This is not one of those other forums where if you have a differing opinion you're slammed.

That much got me to where I can tailor under- or over-steer by tire pressure. Yes, that's a variable too.

Good point......also age of tires and type of tire and whether they are all the same vendor, and sizes of tire, and driver weight, and body molding kits, and whether the road is banked or an outside curve and so many more. Lots to consider for many. I'm after the center condition. Mostly stock, what does every one feel on the average turn. Mine is just a little on the side of under steer but at times annoying on long sweepers. I will probably try for neutral after the work this winter.

As mike100 points out user input makes a huge difference. The press types get their impressions on a skid pad where you slowly approach the limits of adhesion, about the only place you can be smooth enough to coax out the basic demeanor short of a race track. On the street in an emergency situation, or an autocross course (which is basically 30-90 seconds of cascaded emergency maneuvers) it is not so subtle. Shocking the tires at either end will wash that end out, and this is especially dependent on the tires themselves and the pavement, of course.

Cheers,
- Jeff

I think the press goes for a baseline that can be used across different cars. It's valid. I agree user input is a factor but not much if the user is familiar with the equipment. First time drivers, sure.

There is an exit locally here on the north side of the 205 Interstate bride here between Oregon and Washington. It banks right then left to join state HWY 14 and then a straightaway. I hope to see what that feels like with neutral steering. The yellow "slow" sign says 25mph. It's a 55 easily and on a good day it's 65-70 in our cars. I'll report back next spring. http://www.corvetteactioncenter.com/forums/images/smilies/woot.gif

[lbszr]

With stock suspension, if the goal is to keep it balanced and smooth through a turn. I would have to go with understeer, from what I've seen on a road track.

I've changed springs now, but it still favors undesteer......until I corded the front 275s, so ended up with a square set up, fresh 315 hoorsier r on the front and 5 year old nt01 315 on the back.....it was great, fastest times so far and it oversteered consistantly, but I liked it.

So really it is a preference.

If you want to try a little more oversteer, VBP has a 26 mm bar for the back.

Or this adjustable rear bar, which is my next experiment. http://cartechstuff.blogspot.com/2013/01/sway-bars.html#!/2013/01/sway-bars.html

[Kevin]

i always prefer oversteer, that way I don't see the tree that kills me...

[batchman]

Oversteer prevents swearing. You say "Whee!" instead of Oh Shxx!