johnparkercom

hi all,

Have a C6 Z51 with CCW 18x10"F & 18x11"R running SCCA ASP, mostly due to the non-stock wheel size. Probably would have gotten slightly wider wheels, but at the time (2006) that's all CCW could recommend for me.

Anyway, running stock Z51 sways & shocks, and Auto-X alignment (Front/Rear camber -2.5 & -1.2 respectively - toe out front 1/8 total, toe in a pinch in the rear) Also run Hoosier A6 & like them. Currently 315/30-18" Rear & 295's front. I am a pretty experienced and successful on the club level lifelong autocrosser, and though I've done quite well with the car, could use some opinions. (please)

Relatively speaking, I have trouble "hooking up" on launch & corner exit. Car feels balanced ok with current setup, though rear is plenty eager to rotate with little help from my foot. Also the Z51 suspension is great - wish it felt more connected, although know enough to know how it "feels" doesn't always = how it "is" - meaning tightening up the feel might not make me really any faster.

Have considered:

Trying 345/35-18 rear tire. Might have to use spacer, but seems it would fit - albeit sticking out - who cares its Auto-X. Size in diameter is still slightly smaller than stock, so as to gearing I don't really care - should still be plenty of torque.

In that I need to buy a set of tires now to start the year anyway - trying this would not be any more expensive, with the I would guess likely exception of spacers & longer studs & open nuts

Changing shocks, sways, springs (any or all) Currently considering the Pfadt shocks, street or pfatty bars (or street bars) and would even consider the Hypercoil leaf springs as well.

Changing wheel sizes altogether - wider - even maybe 17's if they'd fit. This is probably what I'm least inclined to change now as I already have nice light wheels that are fairly wide.

Hell I'm open to anything & appreciate any & all input as to how to make the CAR faster - I understand all the "nut behind the wheel" & EVO school concepts regarding my driving improvement - which is continual albeit sometimes futile - so would just like opinions on how to make the CAR faster - specifically rear wheel traction on acceleration on launch or corner exit. THANK YOU!!

drivinhard

Just my .02 (worth about .01 in this economy, or even in a good economy, lol) but I'd go to 17's. More sidewall = more linear grip. think floppy sidewall drag tire.

gkmccready

17s don't clear the Z51 brakes. And watch for tires sticking out unless you know you won't drive them up into the body work...

How much is a "pinch" of toe-in in the rear? I bet you need more toe-in and it'll help you get the power down on corner exit... I've been running 2mm toe-in *with* poly bushings. With rubber bushings you probably want even more. And that's for a road course, autocross probably wants even more than that.

When I got my C6 Z51 it felt very off at the track. I chased it with a bunch of combinations of swaybars. Tried KONI 3013Sport shocks. And after a couple of years and a bunch of cash I've come to realize these cars are *really* finicky about set up. Especially rear toe.

I honestly suspect I could go back to a stock C6 Z51 and apply what I've learned about alignment and be relatively happy with the results.

drivinhard

For auto-x though, you could run 17 rear and 18 front. I've seen guys do it.

gkmccready

On a C6 Z51 with the larger rotors?

drivinhard

Will the 17's not clear the rear PBR on the 13" Z51?

The chart I have says C5 OEM 17's will, although I'd have to say I've never actually tried. Obviously we are trying to clear the caliper, not really the rotor, but you are saying the rear calipers on the 13" interfere with 17"?

The rears mount a bit shorter than the PBR 2 pot fronts, I would think they would fit. Maybe not. I would imagine it's close either way. If not I stand corrected

gkmccready

I don't really know either way, honestly. In any case, before buying 17" rear wheels it's something to check out.

drivinhard

Just checked in the shop, I *think* it'll work @ about .200". But I can probably try something later tonight when I have more time.

BTW for my test I'd have to use a C5Z front, and something like the GS 17x11 barrels might measure out different. It looks to be close enough the specific 17" wheels you're using might make the difference.

FWIW the backside "ribs" on the front base C6/C5 PBR's have a .250" clearance to the (OEM 17") barrel.

mark b

What kind of tires are u running? How much pressure? Get some r compound track/street tires like nitto r2's and keep the pressure lower than 35psi that should help

Davinss

Try some more toe in, in the rear. If you mark your tie rods first you can always just turn them back if needed. Some people run as much as 1/2" of toe in for autocross.

LG Motorsports

Nevermind

Thanks guys.

Lou Gigliotti
LG Motorsports

TedDBere

The biggest suspension things the ASP guys do is increase the front spring rates and bar, put a smaller rear bar on, and lower the car. Toe-in to meet your taste. Oh, and lots of rubber!

RAFTRACER

Lets not forget simple things......Typically on asphalt, I will carry the wieght of FULL fuel tanks. Wieght planted directly over the rear wheels. Ever taken a passenger with you on a run and felt the difference in power application ??? Hell on asphalt, I'll take passengers and a full load of fuel....

In addition I agree to most of what is above....especially Teddy

LG Motorsports

who is newton?

RAFTRACER

Might have something to do with rear wieght percentage.....Hooking up 400+ rwhp in 1st and 2nd gears while pulling 1.3+ lat.g on sealed asphalt is not the easiest thing to do...Concrete is a different animal.....

I am all about be as light as possible..........

I wasn't going against any of your above comments, I believe them to be all true and thank your for sharing your wisdom.

0Randy@DRM

Adding weight is the same thing as soften spring rates. Kinda of anyways.

Randy

RAFTRACER

I must admit that my asphalt set up is a compromise....The car is set up for the concrete where I do run it light.....

I do what I have to do to make it work in less than ideal conditions for what the car is set up for... I have proven to myself (and many others) that this is the thing to do on asphalt, especially sealed.

SP cars can run whatever spring rates they want....stock class cars cannot.....

0Randy@DRM

You don't have a name like Raftracer without making it work with whatever the situation.

Randy

VetteDrmr

My comment is really basic (re. stoopid), but no one else has said it so I will:

I've found that my C5 really likes to have the steering as straight as possible before getting on the power. It's one problem with my technique that I've been concentrating on over the past several events. I expect your C6, with more torque/hp than I've got, will reward opening the wheel up as much as possible even more than mine.

HTH, and have a good one,
Mike

XPC5R

The 345/18 A6 is very tall and wide, which does not help your gearing, fender clearance, or rake. Try a 335/18 first, same height as the 315, just 1" + wider. Stretch it out on more rim and it will perform even better. 18x12 to 18x13 works well.