NTMD8R my wheels should arrive soon, same set up as you except for alignment. In the process of ordering tires now, do you recommend 305/30/20 in the rear since you had a slight rub with your 315 tires? My C7 is lowered all the way down stock bolts.

And yes agree LG sway bars rock!!

 

After having my new wheels and tires on for a couple of weeks now,
and driving to/from the race site (25 miles each way) 4 times now.....

Oh, and here is my setup....
Rennen Monoblock (Monolight) M5S aluminum wheels (chrome finish)
fronts 19x10 56 mm, rears 20x11 79 mm
Toyo R888 Tires 295/30/19, 315/30/20
Car is lowered all the way on the stock bolts.
Originally I had -1.8 front camber, -1.2 rear camber.
LG G7 swaybars.... front set to not firm adjusting links tightened,
rear set to only hole, adjusting links tightened

With this setup I did get rub..... essentially when driving on the highway.
It actually did concern me when I first saw it. The very outer rolled edge of the tires
was rubbing on the inner fender liners at the top and a little forward.
Enough to actually accumulate warm rubber "blobs" inside the wheel well lip.
Examining the tires, obviously it was not doing any damage... merely shaving a very
small amount of the rolled edge off.

So, to remedy/address this, I removed the washers from all the upper control arms.
Each washer is 2.5 mm thick, and each bolt has 2 washers.... 5mm.
So the upper control arms (all 4 of them) are now 5 mm (.19 inches) further inside
the wheel well.
I also adjusted the camber... -2.2 front, -1.8 rear.
I also extended the adjustable link on the front swaybar (extended it about 1/2"),
and put some toe out (1/16") in the rear.
(I know... that's not what you are supposed to do)
I also ran with much less tire pressure this last weekend.... I was doing 38/33,
I am now doing 32/25.
I did all this stuff to try to get more grip.
That worked for the grip.

But..... I am still getting some fender lip rub from the tires while driving on the highway.

How do I know this ????
When I arrive at the race site, I can see/feel the rubber on the inner lips.
I remove it... just a cloth rubbed along the inside of the lip does this.
Then we race (autocross) .... 6 - 12 runs each.
I check the fender lips, and no rubber.
So we drive back home.
Guess what... some rubber on the inner lips.
So it has to do with the undulations and rises and dips, etc. on highways.

This week I am going to raise it back up the 5/8" I got when I lowered it.
I am also going to do some more sway bar adjustable links adjusting....
tighten up the front, loosen up the rear.
And I'll set the rear toe to zero (or maybe 1/16" in).

By the way, it does not seem to have done any damage to the actual fender lips.
I can feel a little "roughness" along the inside edge for a few inches on all 4 lips,
but when I look at the width of the lips it has not rubbed any fiberglass off.

My next event is Aug 14 and 15, so I won't be able to report anything till after that.

As for 305 tires..... it depends on what brand.
Toyo R888 tires are actually a bit narrower than other brands.
If I could have gotten Toyo R888 in 305/30/20, I would have... but not available.
Likewise, if I could have gotten 285/30/19, I would have... but not available.

Good Luck

 

NTMD8R

Thanks' for the details on your set up, looks like it improved your run times with the sticky wider tires!! I'm also working with the sway bar adjustments.

I'm thinking on playing it safe and going with F265/35/19 R305/30/20
some other forum members have recommended this set up with no rubbing issues. Hopefully this set up will work with 10 and 11 width rims.

Thanks so much for the great info and vids

 

360,
what brand tires ?

 

Michelin super sports non run flats, this will be my street set up.

 

BIG THANKS, "Savage" for the research and trial runs.

During my last 500 miles of winding mountain road drivings I had been increasingly unhappy with the substantial understeer of my FE3 suspension. Thanks to your research and documentations I purchased the FE4 rear-swaybar and bushings. The FE4 bar was only $71 from GM Parts and the bushings were a few dollars more.

I was shocked initially at the diameter differences between the FE3 rear bar and the FE4. 26mm vs. 31mm. That is a HUGE difference. So, I pulled my swaybar software to do some calculations; the only unknown that I had to "guess" was the wall thickness of the hollow bar tube. I did two calculations, one for 1/8" and one for 3/16".

1/8 assumed wall thickness:
Stock FE3 rear bar = 546 lbs/inch
FE4 rear bar = 749 lbs/inch

3/16 assumed wall thickness:
Stock FE3 rear bar = 679 lbs/inch
FE4 rear bar = 961 lbs/inch

What matters is the percent change between the FE3 and FE4 bars. Frankly, I was rather intimidated taking the car out on my ultra narrow winding roads with big dropoffs into the canyon below. I am NOT used to increasing rear bar rates by such large margins.

But... the improvements are substantial. Interestingly enough, during my medium speed hard cornering (35-60 MPH) the car still displayed some mild understeer even with this large rear bar. But, it was very easy to modulate with the throttle and trail-braking felt still secure. In one higher speed corner (80+ MPH) the car was fully neutral but, still allowing me to pour on the throttle past the apex. Still to be seen the high speed cornering (100++).

So, altogether this is a super change for anyone with the FE3 suspension or with the base suspension. For people changing from the base suspension, get the FE3-4 front bar and the FE4 rear bar with their associated bushings.

Again, thanks, Savage, I had no idea that the FE4 rear bar was different from the FE3s.

 

Can you elaborate on the differences in the bushings by year? Which are the hardest?


Am I right in assuming you have a non-Mag Z51, then? And that your car is otherwise stock?


Thanks for your review and detailed comments on the differences between the FE3 and FE4 rear bars!

I don't understand suspension well enough to know whether there is an interaction between shocks, wheels, and sway bars. Of course, (non-Mag) Z51s have stiffer shocks and bigger wheels than base cars. Would owners of base cars necessarily have the same handling improvement with the FE4 rear bar? Or might it go too far in reducing understeer?

I've ordered Gene's Cultrag kit, but I'm now wondering if I should seek the FE4 rear bar . . .

 

I purchased the base car for wanting to do only the mods that I needed. My suspension mods are as follows:

Car lowered all the way on stock bolts.

FE3 non-mag Z51 shocks.

18 & 19" black crome Z51 style reproduction wheels.

All four corners are at -1.3 camber (negative).

Z51 FE3 front sway bar and bushings from Cultrag.

Z51 FE4 rear sway bar and bushings from GM Parts (installed yesterday).

Definitely, owners of the base cars will find the largest improvments. The base car does not even have a rear swaybar. I found definite improvement by installing the Cultrag kit but, you will only notice it on winding roads. Still, after driving multi-days and many miles I began to dislike that "push" or, "understeer". Too much for my taste. I could reduce the push by judicious applications of the throttle to make the rear-end come around but, that got old eventually.

As it appears the FE3 rear sway bar is a step-up from the base suspension but, still built for largely unskilled drivers, providing a large degree of safety if/when the driver goes into a corner too fast and the understeer will force him to steer the front wheels too much, crossing up the front tires and thus rubbing off speed. Safe but, not fun.

In my short 12 miles of winding road driving I found the FE4 bar to be much closer to neutral, making the turning of the steering wheel and the car less of an effort, reducing the body roll while, for me, there was still plenty of "safe" understeer to prevent an unexpected rear-end spinout. As it appears, this is the swaybar setup that the mag shock Z51s as well as all ZO6s come with so, you know that the factory could not afford to make them unsafe even for the average driver.

From what I had seen from my test drive I can definitely recommend the FE4 rear bar, particularly at those really low prices.

If you have the base car, you will be replacing all sway bar bushings with ones that come with the Cultrag kit. The stock base front bushings are extremely flexible, concentrating on smooth ride instead of precision handling. I elected to leave the Cultrag front bar and bushings as I am not certain that the bushings recommended by Savage are actually stiffer. I have them but, can not really tell the difference.

 

Thanks for another detailed reply!

Just to confirm, you stayed with the base-sized wheels (and tires)? In other respects, it sounds like you basically had non-Mag Z51 suspension after installing Gene's kit (and before switching to the FE4 rear sway bar). Is that right?

I'm figuring on keeping my base shocks and installing Z51 sway bars and I'm trying to figure out which Z51 rear sway bar to install. I hate to beat a dead horse, but given that you have Z51 shocks, will your experience (with regards to under/oversteer) translate for owners of base cars who don't change their shocks?

 

You are very welcome

Yes, I stayed with the factory wheel offsets and simply transferred the tires to the new wheels. I stayed with the 18" & 19" wheels because they give me 0.5" taller tire sidewalls that reduce the chances for wheel damage when driving over potholes while not appreciably effect street/road cornering performance (I raced cars for decades)

Yes, I had a non-mag Z51 suspension with the Cultrag sway bar kit and the Z51 FE3 shocks. When I purchased the Cultrag kit I did not know that the mag-shock Z51s had the much larger rear sway bar.

There is very little functional overlap between the shocks and the swaybars. Each has a dedicated role in the suspension movement. Thus, if you keep your stock shocks you will be expected to gain just as much by upgrading your swaybars only. I know many people mistakenly think that body roll can/should be controlled by the springs and shocks but, that is not the case. To eliminate body roll by either one, you would have to make an unbearably stiff set of springs and shocks that no-one would want to drive.

The stock shocks are, again, rather soft and the FE3 Z51 shocks are, again, just one step higher but, still relatively soft dampening. If I knew that going in, I probably would have purchased the Z51 model with Mag Shocks for even better dampening control.

For most drivers, including some demanding ones, like myself, the base car with stock springs, FE3 shocks and FE3 F, FE4 R swaybars/bushings will provide more than enough high performance handling for any kind of driving.

 

Just some more FYI stuff, I was not the first but close to buy one of gene's sway bar kits for my base car last year, there was much talk of the mag ride rear bar being larger but many of us thought the rear spring rate would be greater on the base car because it had no rear bar! No one had spring rates( I still have not seen them) there were no tests yet , it was winter here in pa. Every thing was a guess and a skinny rear bar had to be better than no bar. Then you had guys talking about balance , matching this with that! We did not even know all z51 and z06 front bars were the same. We have come a long way in a year with no help from a GM T1 kit that Never Showed Up!! I also thought hard before I ordered a z51 car for this year without mag ride , my only reason for non mag ride ( I know c7 mag ride is best ever) in 25 years of autocross I have never seen a mag ride car the car to beat unless they unplugged it and put on high end shocks , with that being said I know the high end big money shocks and coil overs that are for sale now are much better than mag-ride factory shocks I'm just sitting/ waiting on price drops along with real testing that I trust , I can live with my 45 mm shaft shocks z51's until then. One thing for sure, we can count on aftermarket taking care of us sooner or later .

 

I'm still not sure if we've found that answer. I'll check with Gene to see if he's learned anything new.

 

Gene said he would research it further in Monday.

 

In the name of data gathering since it interests me and the release of Hotchkis' swaybar set reminded me, I'll get all this info together in one post.

He also mentioned that the stock Z51 bushings are polyurethane.

***note*** The Z06 and Z07 use identical swaybars as the Z51 w/MRC.

C7 base Stingray
Front - 26.2mm (hollow, 7.85 lbs)
Rear - N/A
Rubber bushings

C7 base Z51 ($300)
Front - 28mm (hollow, 7.95 lbs)
Rear - 26.5mm (hollow, 6.9 lbs)
Polyurethane bushings

C7 Z51 w/MRC ($300)
Front - 28mm (hollow, 7.95 lbs)
Rear (Z51 w/MRC) - 31mm (hollow, ? lbs)
Polyurethane bushings

Hotchkis ($400)
Front - 32mm (hollow & fixed, 9.2 lbs) +35% stiffer vs. all Z51
Rear - 33mm (hollow & 3-way adjustable, 9.0 lbs) +20-70% stiffer vs Z51 w/MRC
Polyurethane bushings (reuses stock brackets)
Reuses stock end-links

aFe PFADT ($732)
Front - 35mm (hollow & 2-way adjustable) +??% stiffer vs. all Z51
Rear - 32mm (hollow & 3-way adjustable) +??% stiffer vs. Z51 w/MRC
Polyurethane bushings & CNC brackets
Includes heavy-duty end-links

LG Motorsports ($750)
Front - 35.6mm (hollow & 2-way adjustable)
Rear - 38.1mm (hollow & fixed)
+45% stiffer vs. Z51 w/MRC (for the set)
Polyurethane bushings (reuses stock brackets)
Reuses stock end-links
Optional heavy-duty end-links (+$245)

Chevy Performance T1 ($600)
Front - ??mm (hollow & fixed, ? lbs, +40% stiffer vs. all Z51)
Rear (same as Z51 w/MRC) - 31mm (hollow & fixed, ? lbs, +20% stiffer vs. base Z51)
Polyurethane bushings
Reuses stock end-links

 

Don't forget that the Z51 model uses different rear bars depending on the options; Mag Ride vs Non Mag Ride.

The Non Mag Ride option comes with the 26.5 mm rear bar.
The Mag Ride option comes with a 31mm rear bar.
The front bars are the same for both options.

 

Adding this now along with more data; please see edited post above. Thank you!

 

IS there any merit to swapping out the shocks?
Mag ride car.
What are guys doing there?

I see that the T1 GM suspension package is more then just bars.
What do you guys think?

 

Added more info. Vendors, please feel free to post up or message me with any data that is incorrect and/or missing (weight, stiffness, etc.).

 

My Hotchkis bars arrived today so I've updated the above with their weights. Heavier than stock as to be expected, but not by too much since they are hollow.

 

oh please let us know how you like the hotchkis bars.. what is your setup now?

Im a MRC/Z51 and feel this car rolls much more than my c6 did.