When I traded the guy for the Z06 wheels, I let my Falkens go with the old wheels. Even though my old tires were 4 years old, they had very few miles..... and they tracked perfectly.

Enter into the picture (almost new) BF Goodrich TA KDW with 90% tread life still remaining.

Same exact size all the way around (17X9.5) and same tire pressure (30 psi all the way around) Now ~ I drive down the intersate and the tires track perfectly.... straight as an arrow........now go on secondary road with speed limit of 50 mph. Car feels like it wants to dart left and right.

Suggestions?
Is the toe in just enough on the edge that the new tires can't handle it? Too much? Not enough?

Handling Guru's unite...... I need your expert opinions.....
~ Purp

 

Purp, a couple of things come to mind...

The sidewalls on the KDW's are much stiffer than the Falken's. Your car will feel much more responsive on turn-in and on transiton. That's the good news. The tradeoff is that they will feel more darty than a regular softer sidewall tire. The secondary roads likely have a more pronounced crown to them and would exacerbate the tracking issue. Now if I'm not mistaken, actual C5 rims (vs. C5 lookalikes with a C4 offset) have more offset and therefore a narrower track than stock 56mm 9 1/2" C4 wheel. (for eg. a ZR1 11" rear wheel has a 36mm offset and would widen the track by roughly 3/4" over a 56mm offset 9 1/2")

As for moderate toe IN, it would suppress the darting. Toe out would really exaggerate the problem. I would limit the toe "out" to zero. If you are generally NOT on a road course I would run ~ 1/16" in per side. Same or slightly more in the rear. (+3/32" in, per side)





[Modified by h rocks, 10:13 PM 6/11/2003]

 

what he said... i had the same problem as a few others i know. 1/16" total toe in fixed the problem for all of us. this is not optimal for auto x though. but for a street driven car its fine.

 

H Rocks is correct about the toe in/out issue. I've played around with my settings quite a bit and 1/8th" total toe out in front makes it darty on grooved or crowned surfaces.

 

h rocks ~ that explains it. I don't race the Vette and will only be doing road trips. It sounds like 1/16" toe-in is the ticket. Thanks for the excellent feedback. Time to visit the alignment shop. :yesnod:

~ Purp

 

:cheers: Stan

As I have said previously, your car looks great

I have played with tire pressures to solve some of what you are describing.

I used to Listen to NASCAR broadcasters talk about add a pound, loose a pound and say YEAH!!!

But when I went to the heavier sway bars I found out what they were talking about. The composition and strength/flex of the tire walls can have the same impact as the change in sway bars. Your new tires may require a different pressure.

The average driver might not notice the difference, but then we know you aren't the "average driver" :D :D

Just a thought :rolleyes:

your friend


[Modified by jackdaroofer, 9:03 PM 6/12/2003]

 

:seeya Jack,
Thanks for the feedback. Your recommendation sounds reasonable. Based on my description ~ would you say add pressure, or decrease pressure?

Thanks for the Kudos Jack. I have really enjoyed working on making the Vette look good. One of my Buddies is a Master at painting small parts. He just painted my ASR Cover in Chameleon. We selected the Blue/Red color, but used Purple for the base coat instead of black. It changed the color transition to Purple/Red. Too cool. Now I will do the fuel rail covers in the same color.

:thumbs:

 

:cheers: Stan, we really miss you here on the East Coast! Maybe we will get you back someday!

I would start by adding air pressure, sounds to me like the walls of your new tires could be flexing more than the old.

Sounds "****" but I would work in 1 pound increments and drive the same roads at the same speeds

I finally bought a $60 tire pressure gauge so I can read it down to 1/2 lb.

You just need to play around with it, you can play around I know!

I was really amazzed at the difference a little air pressure makes when running twisty roads.

I wanna say :seeya soon, but somehow I know that might not happen :sad:

Jack

 

I agree with the post that adding a little toe in would help.

check out these settings and comments from http://www.vettebrakes.com

________________________________________ ____________________

Daily Driver Settings: These are designed to minimize tire wear and the dynamic forces on the front-end parts such as steering and ball joints. Driver effort should be minimum and the vehicle will steer very light. The downside is that the car may wander or could be “darty” on roads with wear ruts. To eliminate this feeling, you can get your alignment specialist toe the vehicle in up to a maximum of 1/8” total toe-in.

Front: Toe 1/32 inch
Camber 0 degrees negative
Caster 5-7 degrees positive

Rear: Toe 1/8-inch toe-in
Camber 0 degrees negative


--------------------------------------------------------------------------------

ADVANCED STREET


In 1989, this Callaway street driven “Sledgehammer” was clocked at 254.6 mph on a closed course.

Advanced Street: For a sportier feel, Vette Brakes’ recommends these settings that will give you quicker steering response and minimum tire wear. As we mentioned before, if the vehicle is “darty” especially under braking then toe the vehicle in. By toeing the vehicle in you will lose some “turn-in” qualities gained by these initial specs. The driver must feel comfortable with the feedback from the car, so adjust accordingly.



Front: Toe 0”
Camber .25 degrees negative
Caster 5-7 degrees. pos.

Rear: Toe 1/8 inch toe-in
Camber .50 degrees negative


--------------------------------------------------------------------------------

AUTOCROSS


C4 Corvettes make excellent autocross racers

Now we are getting serious. These settings are a good baseline to start. But, remember Reeves Callaway’s quote, “adjustability is the key to success”. Each course is different and suspension setting, tire compounds and pressures are the key to winning an autocross. The driver must take all three into consideration before a winning combination can be achieved. These specs do work for street applications, but are not recommended. These settings will cause adverse tire wear and the vehicle will become very nervous on the ever-changing street surfaces. But, on the race course, watch out! Your car will corner like a slot car!

Front: Toe 3/16 out
Camber 2-1.5 degrees negative
Caster 4-5 degrees positive

Rear: Toe 1/16-inch toe-in
Camber .75-1.5 degrees negative


--------------------------------------------------------------------------------

TRACK


C4 Corvettes are very successful in the SCCA ITC category.

Track: Now these specs are really base line. Racer know that alignment specs will not only change based on weather, but also track to track, set up to set up. When you go to set up your Corvette for the weekend, Vette Brakes’ suggests talking to someone who is familiar with you, your Corvette and the course. These settings are a good solid, “middle of the road” base line in which your car will be stable at speed and provide a base set up to adjust after you get driver feedback when they are on the track.

Front: Toe 0”-1/16” out
Camber 2-1 degrees negative
Caster 1/8” toe-in

Rear: Toe 1/8” toe-in
Camber .75-1.5 degrees negative


--------------------------------------------------------------------------------

To try out Vette Brakes’ recommendations, we took our project car, an 87 Z-51 coupe, to Kauffman Tire’s alignment shop to change the alignment. Under Paul’s guidance, Joie Casta performed his magic and adjusted the suspension to advanced street settings that are provided in this article. We were amazed at the transformation in the car’s handling!


Kauffman Tire set the alignment per Vette Brakes' specifications.

Joie Castas performs his alignment magic on the C4 test car ...


The turn-in to corners are crisp, when you point the car it reacts immediately with no steering wheel hop. Slight corrections to the wheel provide an immediate response from the suspension. Straight-line performance is very stress free. The car does not wander at higher speeds like it used to and it tracks very well. Even under hard braking, we could not find any vises with the new suspension settings. Tire wear seems unaffected. Overall, we were impressed with the driving improvement of our 87 coupe.

Thanks to:

Kauffman Tire
2701 Tyrone Blvd.
St. Petersburg, FL. 33710
(800) 334-3321