KF9BD

From the posts I have seen the C5 seems to normally understeer. If that is the case, assuming an FRC with Z51 suspension, would replacing the Z51 rear sway bar with the Z06 rear sway bar remove some of the understeer?

Also, would replacing the stock 17X8.5 front wheels and 17/45/245 tires with 18X9.5 wheels and 18/35/275 tires also reduce the understeer?

XmentalPilot

Rear sway bars are the same... tire size, inflation and alignment are where you should be looking.

see5

Depending on how much street driving you do you can go to ~ - 2 deg neg camber front and about 1.5neg rear. With Z06 bars F and R it is quite tossable.

KF9BD

Xmentalpilot: According to the part numbers the Z51 rear bar is not the same as the rear Z06 bar.

see5: Tossable is indeed what I am looking for. I do most of my driving on the street. I autocross 5 or 6 times a season, sometime more sometimes less. I am certain an alignment change would help and will be doing that, but I figured a stiffer rear bar might be the way to go. I am planning on changing my Z51 sways to the Z06s with addition of the Z06 rear spring. Do you have a full alignment recommendation?

see5

Z51 Z06

Front spring 525#/ inch 525 #/inch
Rear spring 634#/inch 696#/inch

Front Anti-sway bar 28.6mm, 4.15 mm thick 30 mm, 4.5mm thick
Rear Anti-sway bar 23.6mm, 3.0 mm thick 23.6mm, 3.5mm thick

I am running -1 camber all around now which is fine on the street and ok for the rear on autocross but not enough for autocross in front. My front Hoosiers are not getting good contact on the inside. I will try -2 front next year which will be a bit extreme for the street I fear. Toe in about a 1/16 front and rear. You should do a search on alighnment in this section for varing oppinions. I am only going from my experience.
With Z06 front bar and Z51 springs you should be able to bring the rear out with power. I only understeer when I am too fast into the corners.



[Modified by see5, 7:09 AM 11/10/2003]

jackmott

Theres lots of options open to you.
You could add more tire up front, add a stiffer rear spring, or a stiffer rear swaybar, or play with the alignment.

The alignment is probably the cheapest way and has little to no downside, but adding enough negative camber to get neutral handling will probably wear out the insides of your front tires pretty quick, since you do mostly street driving. If you don't mind dealing with tire wear, -2.0 degrees front camber, and -1 degrees rear camber should cure a lot of your understeer.

More tire up front could also cure it, expensive though since you have to buy new wheels, and it will add weight and such.

stiffer rear bar could do the trick, downside being increased weight transfer that swaybars cause.

stiffer rear spring is my favorite choice, grab a z06 rear spring put it on. Only downside is perhaps a harsher ride.

VetteDrmr

I had the same problem with understeer when I first started running my FRC. I went to 275s up front on stock sized wheels and solved my understeer problem. Lots of opinions and tire manufacturers will tell you that's too wide to work properly, but the tires are wearing quite evenly across (I flipped them once about 2/3s through this season).

I'm currently thinking about my next set of tires, and I'm considering going to 285s in back to fight a slight oversteer problem, still on stock wheels.

HTH, and have a good one,
Mike

Bill Dearborn

Given stock tires and a correct street alignment you may be trying to enter the corner to fast. It will understeer quite badly when you enter to fast. If you are on the bark hard and sart to make your turn in you will overload the front tires and it will just plow even with ABS. However, if you slow your entry down some and get your foot off the brake before turning in you will find that the back end will come around quite nicely under trailing throttle conditions. Between your steering input and getting on and off the gas you should be able to switch the back end around quite a bit to get through the turns.
Bill

AZGASSER

:iagree: Better driving/handling skill will by far make up for equipment downsides. Better tires and seat time will do wonders. Look at other cars in your class and see what they are running. Remember smooth is fast and not always the fastests car the quickest. I learned at Bragg Smith, that an experienced driver/instructor driving a Camaro SS, with lots of understeer, out drove me in a Z06. The driver will make more difference than equipment anyday. :yesnod:

KF9BD

Thanks guys for the input. I understand the driver over equipment thing. I had a Miata before my Vette and have a few season under my belt. I am just trying to tune this beast a little.

VetteDrmr: you indicated you were still on stock rims with 275s in the front. Have you had much roll over with that size tire on the 17X8.5 rims?

VetteDrmr

No problems with rollover, or poor contact patch, or anything else for that matter (except I keep getting beat!). The corners have worn right to the edge of the tread, never on to the sidewall.

That's probably a matter of tire pressure more than width. A wider tire will theoretically pull the edges off of the pavement more than a standard width, but I didn't have the money for a new set of rims.

HTH, and have a good one,
Mike

KF9BD

Thanks for the reply, Mike. What tires are you using? I would like to go with a 275 front, 285 rear, but I am not certain that the 285 is made in the GS D3. I need that tire for its wet performance. I assume you are presently running the 275/40/18 in the rear with the 275/40/17 on the front.

TedDBere

I just set my alignment to -1.6 Camber in the fronts and -0.9 in the rears. I also left the caster way out to 6.2 and 8.4 (to increase camber when turning). The last autocross I ran I couldn't get the car to understeer, even though on runs 6 and 7 I was trying to get it to understeer. Unfortunately that was the last event for the season, and I know there's more entry speed to be found by me with these settings. I finished 6th overall with my best previous finish at 14th. Now I'm dealing with a car the corners on rails and has so much cornering bite that I have to be careful of too much power oversteer. I have the toe-in at the back set to 0.15 on each side.

I could have gotten more front camber but didn't want to chew up the fronts on the street too much!! By the way I run Hoosiers.

:steering:


[Modified by TedDBere, 11:30 AM 11/11/2003]

KF9BD

It sounds as it you have your car setup well. I have done most of my autoX in a modded Miata, so I didn't have much power, but the handling was superb. Now I have to get the handling tuned in on the vette and learn to work the power. Next season should be a hoot (spin, spin, spin, etc.). I plan on run the GS D3 for the first season. Once I get my skills up to the car, I will go to R-compounds.

ifeeltheneedforspeed

The rear sway bar on a 2000 and newer C5 with z51 suspension has the same rear sway bar as all the zo0'6.

KF9BD

Thanks for the infor Speed. I have a 99 FRC, so if I don't have this messed up I will need the both bars.

VetteDrmr

Danny,

Actually, it's a long story (based on me being cheap and scrounging for throwaway tires ), but I'm actually running Toyo RA-1 275s up front and BFG TA/KD 265s in back. :skep:

I've been learning all about driving a car with oversteer. :lolg: :steering:
Can't wait until next season when I'll be running either 275/285 Kumho ECSTA V700s or 275/295 MXs (waiting on my BMW group to decide if they're going to break up my class into street and R compound tire classes).

Glad to help, and have a good one,
Mike


[Modified by VetteDrmr, 6:19 PM 11/11/2003]

see5

If you are cheap how about some 275/17 Hoosiers?
I have gone bigger and have 4 good ones.

adamsocb

Those Z51 dimensions may be correct for a 2000 and newer Z51, but I just replaced the bars on my 1999 Z51 Coupe with 2004 Z06 bars and there was a lot more difference. I will measure them tonight and post.

BTW: Going from the 1999 Z51 bars and Bilstein Sports to Z06 bars and 2004 Z06 Shocks made a great improvement!

adamsocb

The Z06 bars I have are the same diameter as above, however the 1999 Z51 bars are smaller:

Front 25.5mm, Rear 21.8mm

Before anyone says I don't have Z51, it is on the build sheet and all of the components had the white markings. Either Chevy changed the bars after 1999 or the factory miss-marked the parts before my car was assembled.