dbratten

Great information. Thanks.

I just did a closer measurement (by taping a 6" scale to the inner barrel of my 17" rims and rotating) to check clearance to use my new 17x11.5s which will have a 9.38" backspacing. Near as I can tell I will need an additional .170" to clear the control arm at full droop. This is with a CO suspension that I'll guess limits droop vs. leaf springs. It is with my race spec camber of -1.4 deg. also. All measurements were made off my 17x11" ZRI-GS repro rims with a 50mm offset & 7.97" backspacing.

So, a .250 spacer is in order, as you note, to provide airborne clearance.

I won't have the new wheels until the end of the month so I'll see if it all comes together as planned at that time.

--Dan

C6 CYAA

"On a side note, your car looks awesome and the gunmetal with the silver was a first rate choice. Its unique and doestn look like the chromey rice jobs some people try to have. I only like chrome on red or burgundy cars. Comp gray on my white car would look good as your wheels also would."

Thanks Spin, The current tires are 305's lowered about an inch w/ 1 degree of negative camber. There is plenty of room for more meat on the 11" rim. Maybe a 315 as lowered.
This picture may help.


And one on the road.

SpinMonster

Using an 18x11, it always hits the control arm when the suspension is unloaded and as a result you must jack the car up from the lower control arm to mount them. The same is true of the 19x11.5.

In well over a year (and a week of really trying to get the wheel to touch the control arm) I painted the edge of the control arm where the wheel would touch and after going over curbs, speed bumps and just about everything I could do to get it to touch and it hasnt in over a year of driving.

The rim touching the control arm would do nothing but scratch the edge of the wheel for the short time it would be in such a psoition and it hasnt ever done so.

DO NOT NOTCH the control arm to clearance it. It weeakens the control arm and nothing would happen even if it made contact for a second at any speed. It will never happen in normal driving and becomming airborn will not cause anything but a scratch to the inside edge of the wheel. It will not lock up the wheel and it will not break a control arm.

I have a friend with the 11.5 on the 19 and I have 5000 miles on the 18x11 with no contact with aggressive driving. A spacer for the wheels is better than a control arm notch. Use one that is hub-centric and longer studs if its an issue to you but dont cut into the control arm.

As I said, I cant get my wheels on with the car jacked up unless its jacked from the lower control arm, and mine has never touched.

The 18x11 wheel for the rear was the single best mod I ever did. No power mod would ever have made my car as fast and the number of race tires available for the 18x11 is staggering as is the lower cost of that size tire.

SpinMonster

My point was the OP was asking specifically about the 325 runflat and it will not fit that rim with that offset. It will touch the fender.
A 92mm offset will fit the 325 runflat.

PRE-Z06

I believe lakeshore wheel and tire has 19x11 (79mm) repos

scottycards

Don't really know how to say this, but I have to disagree on clearancing the control arm.

I think it absolutely should be done. We're talking thousandths, however- just enough so that you can barely feel a slight dip in the control arm, to keep it off the rim.

I am in the steel/metals business, and I'm familiar with how something like a control arm would be affected by a slight clearancing, in terms of strength. With that said, I have not done a complete analysis from a mathematical/engineering standpoint, but I can say that I've fully cycled my personal control arm, under high loads (including slight airborne), and it holds up fine. No strength issues.

I do events where the car goes slightly airborne, as well as fully unloaded, at speed. Sudden changes in wheel speed due to rubbing are not something I'm interested in dealing with when I'm coming back into suspension compression (or back into contact with the pavement) at 150+ MPH.

So with respect, I'd recommend a slight clearancing of the control arm to fit your widened wheels. I can put my wheels on with the car jacked from the rocker panel, but I always re-torque once the car is on the ground, and torque again after a short number of miles.

Each person will have their personal comfort level, and clearancing or not clearancing is a choice, without a right or wrong answer. I'm just trying to share my personal experience (~500 miles of high speed racing on the 325's last summer), so that others can make their decision on whether or not to do it.

FWIW, my wheels that are widened, worked flawlessly, and have also presented no issues wtih either their performance, or with my tech inspectors. They're fine up to 170MPH. I have not gone faster than that for any extended periods of time, so I can't comment from experience about running faster than that.

My .02, and I hope it doesn't ruffle any feathers. Just sharing.

Edit to add:

I don't have specific measurements, but I just replaced my GYSCRF's with Bridgestone RE050A Runflats in a 325/30/19 size on the rear. I would swear that the "bulge" from the rim is less with the Bridgestones than with the GY's. There is virtually no bulge with the newer tires. I can take a photo, which could be compared with Gotcha's original photo, if anyone is interested in seeing the difference in bulges (yikes- that didn't sound right).

I could take the photo tonight when I get home, and post it then, if anyone is interested.

knkali

Scotty, I would like to see the dif in bulge since Joe(GOTCHA) is asking to use the 1/4 spacer with ET lugs with my widened 19's(1 inch). He said the innerfender liner will be close so if I can reduce that sidewall bulge, I should increase my chances of no rub and no mod needed to the liner if possible.

SpinMonster

I just dont see what danger there is in the rim touching. It isnt going to stop the wheel from turning. You will have a tiny area of the wheel in contact for a very short time and it will not be any worse than a metal on metal situation with a brake pad that is gone.

To clearance an 18x11 or a 19x11.5 would be much more than a few thousandths and my rim has never contacted in use. The 18x11 is far worse than the 19x11.5 since the rim is a smaller diameter and touches much sooner. My poiunt is if my car with an 18x11 has no ill effect what is the situation that you have envisioned that is so bad? The wheel stops? The wheel breaks? I'm not seeing what the issue is.

The above example with the car going airborne has a lot more wrong with it than just wheel contact with a control arm. Its just bad judgement and there would be no ill effect if it did touch.

SpinMonster

Mine worked flawlessly with high speeds too without clearancing.

scottycards

I'm with you, Spin, and agree. It's all good.

I do have a tech rule that says nothing can rub. One look at the rim by my tech guy, and I wouldn't be allowed to run, so I made the necessary mod. I don't want my super pretty powdercoated rims to be scratched, either. Because, as we all know, it's not how it works, it's how it LOOKS. HA!

I asked my wife to take a photo, knkali, so hopefully she'll email them to me sooner, and I'll post.

What I did with the fender liners I got from Gotcha was to install them- he had cut out the necessary area. But I went and bought some adhesive-backed sound deadening pads that are used in auto body shops. Maybe about .050" or so, and stuck them on the body in the same place where the fender liner had been cut out- I was trying to eliminate any potential noise from gravel hitting the inside of the fender (just a little annoyance I didn't want to deal with).

It works great. Since it's bonded to the body, unlike the fender liner (there's a small air gap with the stock fender liner), there's no rub, and I get the sound deadening- no gravel noise- and it also looks just a bit cleaner if you're peering in there. Since I like to show off my fattie tires, I wanted it to look good in there when people were peering in.

When Kelly sends me the photos, I'll post.

SpinMonster

My rim never touched as indicated by my painted mark on the control arm so it passes your nothing should rub rule.

No problem as you are entitled to your opinion. I would lose more sleep over the amount of a notch in the control arm required for a 18x11 is waaaaay more than for a 19x11.

scottycards

Thanks to my dear, sweet, wonderful wife, here are the photos. You know you've got a keeper when you ask your wife to take a photo of your rims and tires, and she isn't even surprised, and does it.

Here's Gotcha's setup- same rims, with the GYSCRF's on them:


And the same rims with the Bridgestone RE050A Pole Positions on them- both tires are 325/30/19. Maybe there is a slight difference, maybe not:



Another, maybe better light?



I think there is a bit less of a bulge. Maybe it's just what I want to see, I don't know. This would lead me to believe that the width of the Bridgestones is just slightly less than the Goodyears.

Hope it helps.

knkali

Scotty,
That does look less bulged. Very nice to know! Thanks

Also looks like bringing them out 1/4 inch with a spacer wont look bad either.

scottycards

I think there is definitely room to bring them out, if you wanted to.

I'd swear there's less of a bulge, but I wasn't sure. Wishful thinking and all, you know.

Glad it helped.

Gotcha

Who notched their control arm? Are you talking about mine?

I'd hardly consider .02" (radiused off with a file) a notch. And it probably makes it stronger there, not weaker. Not that it matters, as the control arm gets much wider in this area anyway. There are 8 and 9 second C5's & C6's out there, with stock control arms, so I'm thinking they are plenty strong

Here's a pic of mine for reference


I'm not comfortable with a wheel that hits the control arm. A 19 x 11" widened wheel barely touches and wouldn't be a problem but I wouldn't run anything with less clearance than that. Factory wheels are usually cast aluminum and not very thick, the control arm is cast aluminum also. Even brief contact at 60 mph could do structural and thermal damage to the wheel. Besides the force from the leafspring, the momentum of the suspension unloading would increase the pressure of the contact area. The wheel, at 60 mph, would be over 3500 surface feet per minute at the point of contact...

Control arm clearance is easy. If you dont want to run a thin spacer, the LPE shock mounts are $30 and give you 5/8" additional control arm clearance.

BSheppard

Help me out here guys, I'm learning.

Option 1) If Lakeshore has rims to match my front in a 19X11 with the 79mm offset, I could buy them BUT they would stick out. Way out about 8mm?

Option 2) If they had them in a 88mm offset or so they would not stick out but I would have to cut the inner fender? Or is that only when you add all the extra to the back of the rim?

Option 3) Just do exactly what scotty did and widen my rims and cut the finder?

I understand that the 325 30 19 runflats will not have as much traction as on a 12 inch rim but I will be able to use runflats and in the 305 thats just not an option since they don't make the runflat in that size. It seems like the best option is #2 if they make it. Also will this set up work with the active handling? I'm slow but work with me. What is the best option? Where am I wrong? It's looking more and more like I should go buy that Z06!

Gotcha

What wheels are on the front? If they are stock with stock offset I would widen the rear thus making both offsets look stock. If you had an aftermarket wheel in front, with a slightly more aggressive offset, I'd probably go with the 79mm offset to sort of match the offset in front.

I think the 19 x 11 wheel with a 79mm offset would be OK with the 325/30-19 tire. I think some of the advise
given was based on issues in the past with the Ace Slick 19 x 11 wheel. That wheel has an offset of 73mm and
is not the same as the 79mm offset wheel your asking about. As far as aftermarket wheel offsets go, that 79mm
offset is better than a lot of other wheels out there. The 79mm offset would stick the wheel face out 1/2" (13mm)
from stock.

Heres a list of some common rear wheels and the offsets for comparison.


Stock-------19x10-----79mm offset----------stock
CCW--------19x11-----80.0mm offset---------wheel face out 12mm
Ace Slick----19x11-----73mm offset----------wheel face out 19mm
Forgeline----19x11-----72mm offset--------- wheel face out 20mm
HRE --------19x11-----72mm offset--------- wheel face out 20mm
BBS--------19x10.5----75mm offset--------- wheel face out 17mm

The width of the hubs in relation to the body width of the C6 requires a wheel with an unusually high offset.
For some reason the one piece wheel manufacturers have done a lousy job with their offsets. The three piece wheel
makers are bound by the rim barrels which they all buy from pretty much the same source. They can't make their
offsets any better to suit us. When I needed wheels for my car (mini-tubbed) CCW was the only place that could
give me the offset I wanted 19 x 12 with 100mm offset.

BSheppard

Just stock size on the front. So I need to look into a set of CCW. With those wheels (19X11 with 82.5 offset) I would not have to cut anything to put the 325/30/19 tire under the car?

If I can find a set of look-a-like rims, that look just like my factory wheels, I would need to buy the whole set? Maybe a 18X9 in the front? What offset for the front?

PRE-Z06

have you looked at lake shore wheel and tire's website? I think they're $979/set grey, black or chrome w/ 18x8.5 or 9.5" fronts

jittrbugg

Just to be clear our 19x11 for the C6 runs at 80mm offset. Here is a link to another picture of a C6 with C6Z06 runflat tires. http://www.ccwheel.com/files/gallery...6/505a/14l.jpg