vairhead65

I recently purchased a 2009 Z51 w/auto trans which is mainly a street car and am experiencing understeer quite often, unfortunately purchased the car with Michelin run-flats on the rear and Bridgestone run flats up front. Immediate plans include Michelin Pilot Sport 4S tires and DRM Bilstein shocks, but I am a little befuddled as to the anti-sway bars on the Z51. Are they the same as Z06 or Grand Sport bars? What diameters? Rear bar adjustable? I would like to improve the car's cornering without breaking the bank, so would like to stay with the Z51 setup if feasible. Am I missing something...suspension bushings, end links, etc? As always, many thanks.

BWF07

Are you getting understeer on the street or track? I have a 2007 base with the Z51 package and autocrossing I found it to be fairly responsive maybe a little more oversteer then I would like. Not a Brainiac, but I have read many post on tires and it is not recommended to have mismatched tires (different brands). You might start with changing out all the bushings to polyurethane. The roll bars are not adjustable just a larger diameter then the base units.

4SUMERZ

I have a 2006 Z51, and with the original Runflats, those tires followed every groove in the road, and it always felt like I was fighting the steering wheel. I changed those out at 1/2 thread, and went with NRF Firestones Indy 500's, and what a differennce it made, both in handling and road noise, not to mention wet condition improvement.
I had 3 sets of those tires, and this year I changed to Michelin PS 4S, and I am equally impressed with those tires. I just changed out the OEM shocks to the Bilstein Sports (B8) and like those as well. The Z51 sway bars are the same as the Z06 for the front at 1.22", but the rear Z51 bar is smaller at 1.00" compared to Z06 sway in the rear at 1.20". Some have gone to Z06 bars in the rear for the Z51 optioned car to prevent a bit of understeer, but that tends to change it to a bit more oversteer.
I found that a good alignment does wonders as well, not only for tire wear, but steering performance as well.
Here is the recommended alignment guide

Andysherman

I second the new tires & Pfadt alignment... have an 07 Z51 & was much improved w/PS4's & the alignment, even better after the Bilsteins. Changing out the bushings never hurts, either.

Patsgarage

Replace all four tires with a matched set then see how it handles. I have never had understeer in a Vette on the street.

FAUEE

Agreed, you should not be getting understeer. New tires and alignment. If you still think you're getting understeer....then you're just wrong, lol.

vairhead65

4SUMERZ; Thank you for your response to my post and the Pfadt alignment info. I had suspected the tire mismatch was the culprit, but that will be corrected soon. Tx!

mikeCsix

Vairhead, check out post 9:
https://www.corvetteforum.com/forums...pfadt-one.html

It is a good comparison chart for sway bars and should answer some questions. Except for the Z-06, GM sets up sway bars for a but of understeer. I think you are correct in replacing the tires to get relatively equal traction on all 4 corners. The Z tends to oversteer and it occurs with little warning. One item you may want to analyze on the chart is front/rear bias on the sway bars which may help you should you decide to upgrade. On the race track, the Z-51 equipped cars seemed to have some body lean on sweeping turns, stiffer springs would help but it is a balancing act with sway bars. One of the vendors, Sam Strano has done a lot of work in this area and may be of some help to you.
My solution was to go with the JOC package, it is set up for a Z06, but so far seems to work well with the GS on the street. I have yet to take it to the track to see the response in the car and to see if it helped with the sudden snap oversteer. I know the speeds are higher. For the Z-51, the GS/Z06 bars may be a little big for street tires in Z51 sizes. It is all a balancing act.

strano@stranoparts.com

LOL at those specs. I don't want toe out in the back at all, and why that's funny is they say that negative toe means toe-in..... no. Well, maybe to them but not the rest of the world. Toe in on a rack is POSITIVE, and so if you took that sheet to a shop there is 99.5% chance you'd get -1/16 on the machine to match, which is OUT. The camber is laughable for performance driving beyond what they suspect and average person might do, and those are not likely to be in a Z51 as much as a base.

I know the Z51, I know the GS, I know the Z06 (and no, those aren't the same as each other despite looking the same). I sell parts here, and do setup stuff here. It's how I make a living, but I also run these cars, and I know them and how they relate and differ. Among the parts I have are Pfadt, and I use some of their stuff, but not a lot of it, often there are better options. And I don't toe any one particular brand's line either, because again, flexibility is key in getting things right for YOUR CAR, and YOUR needs.