repman

Being a first time corvette owner I have a few questions about the handling aspects of the car.

It is a 99 FRC - with a lingenfelter mini tub and has 275- 40 -17 up front and 335-30-18 in the rear it is currently running on BF Goodrich KDW tires ( plan on R compound for the track) suspension is c6-Zo6 shocks and springs , poly bushings , PFADT sway bars. It has a 6 point cage with removable door bars installed . new steering rack and really everything under the car is new.

I recently had the car aligned by a very reputable shop here in Atlanta (they always did my widebody Supra alignment to perfection)

The issue I am having is that the car seems twitchy on normal roads and higher speeds exacerbate this issue.

I am including a sheet of how the car was aligned and am asking if anyone has any input if this may be the source of my complaint and different settings might be in order to settle this old girl down thanks for any help

froggy47

A track car setup is by definition going to be twitchy on the street. Tracks (usually) don't have potholes, trolly/train tracks, manhole covers, heavy truck traffic depressions, utility tear up/patch up sections, etc.

Tires are (usually) not up to temp on the street, brake pads not heated.

Apples & oranges.



That alignment is more street than track IMO.

brkntrxn

With 275s up front, my Z06 was "twitchy" on the street. I fixed that by letting the tag expire. LOL.

Seriously, I did notice that my Vette is more "nervous" on the street than any other car I have ever owned. Especially with a somewhat wider tire on the front.

repman

Thanks for the input Froggy and breakin/traction I appreciate it.

travisnd

Poly bushings will do that on the street. Also, how low is the car? Most Vette owners lower the cars too much and the shocks can't work properly.

repman

It is aprox 1/2 into 3/4 of an inch lower than stock , I am sure I am getting full shock travel. Thanks

Bill Dearborn

Front toe out gives quicker turn in on corner entry but the car will be twitchy. If it has a little front toe in it will settle down quite nicely but it will not turn as smartly. You also need rear toe in to keep the car stable.

Looked at your toe settings. Are they in inches or degrees? The numbers look like degrees but the dimensions are shown as in. There is wide spread confusion whether toe in is shown as negative or positive, you can find it defined both ways on the net. I believe it is positive. Your sheet shows positive numbers for toe settings so I assume that means you have both front and rear toe in. If the readings are toe out Vs toe in then your car would really be twitchy.

I used to run my C5Z with 315/35/17s on 17x11 wheels on all 4 corners. On the street I ran stock C5Z wheels with stock size tires. Camber was set at -1.5 front with just a touch of toe in and -.8 in the rear with about .05 degrees of toe in. Car tracked straight and did not wander on the highway. It also got around the track quite well but probably not as well if I had another degree of negative camber in the front and toe out instead of the toe in.

The C5 has trailing throttle oversteer in corners and can feel very loose if you don't have your foot on the gas. In a corner you need to get on the throttle as quickly as possible to get the backend planted. When you do that it will charge through a corner.

Bill

repman

Thank you Bill , appreciate the advice.

sperkins

Yeah I'm with Bill. It looks to me like you have toe out both front and rear based on the posted numbers.
Let me know when you're ready to get serious with your setup. Pretty sure I can help you with that.

froggy47

I read it as toe in both ends, but it's really hard to know from that printout.

Toe out both ends would def make it hinky handling.

I run zero toe front (BIG TIRES) & toe in rear. Varies depending on track.

repman

I am ready to get serious if you have some alignment specs I will be getting coilovers in the next few weeks and a new alignment so I would appreciate the help with a tried and true set up

Thanks, Larry

repman

Thanks Froggy duly noted on the toe settings I will check with my alignment guy

Pfadt Racing

To back up what the folks above have said, the alignment spec sheet is a little ambiguous. If the car was Toed Out it will definitely feel twitchy, and the twitchyness will increase as the speed increases as well.

Here is a copy of our recommended alignment specs. We like to dial in just a touch of Toe In because it tends to tune in quite a bit of high speed stability. Everyone has different ideas of how to setup a track car, but these are a great place to start. Be sure to click the image for a larger printable version.

Let us know if you need anything else! sperkins definitely knows how to setup a club racer Corvette, his results at nationals last year speak for themselves!

repman

Thanks for the alignment specs I appreciate it .

I was going to go with the LG coilovers but with service like that I will go with the PFADT's now !

CHJ In Virginia

I just completed a major suspension mod with Pfadt bushings, coilovers and heavier sways. Their recommended street / track combo alignment specs worked great for me. Absolutely stable on the street and on track.

repman

Good to know thanks

Pfadt Racing

Thanks repman! When you're ready to make some upgrades be sure to give us a call. We will definitely set you in the right direction based on your needs.

TKOGTO

[QUOTE=Pfadt Racing;1580126464]To back up what the folks above have said, the alignment spec sheet is a little ambiguous. If the car was Toed Out it will definitely feel twitchy, and the twitchyness will increase as the speed increases as well.

Here is a copy of our recommended alignment specs. We like to dial in just a touch of Toe In because it tends to tune in quite a bit of high speed stability. Everyone has different ideas of how to setup a track car, but these are a great place to start. Be sure to click the image for a larger printable version.

Let us know if you need anything else! sperkins definitely knows how to setup a club racer Corvette, his results at nationals last year speak for themselves!


Looking @ the recommendations, I see the toe settings as negative. Is this toe in?

Pfadt Racing

There seems to be some confusion as to how Toe is measured on different machines. Our alignment guide calls for Toe IN, which our guide is described as a negative number. Make sure that if you take this alignment guide to an alignment tech that he understands that the negative numbers mean Toe IN.

This is also mentioned at the top of the guide for the sake of clarity.

Bill Dearborn

I wonder why after all the years the automobile has been around they can't standardize toe in as being positive or negative??? Seems like it would be pretty simple to have SAE define it as one or the other.

Bill