18x8 Rim with 255/40-18; Downsides?

Posted By: Fred SS

18x8 Rim with 255/40-18; Downsides? - 08/26/19 09:55 PM

I have a question concerning tire fitment. All tire manufacurers say the minumum recommended rim width for a 255/40-18 tire is 8.5 inches. What would be the downside of running it on a 8 inch wide rim? I'm toying with the idea of getting G-Body Parts new GNX replica rims in 18x8x4.0BS, with 245/40-18 front and 255/40-18 rear. Comments?
Posted By: AkronAero

Re: 18x8 Rim with 255/40-18; Downsides? - 08/27/19 03:49 PM

Fred - always good to connect. Still owe you one!
Here's my take on this as a (somewhat) tire guy and from discussions with my favorite dealers:
It appears you are OK with this set up.
The contour (axial profile) of tire treads has evolved and these guide lines are recommended to give optimal foot print (contact patch) assuming you don't have a specific tire/wheel preference.
Of course all this changes anyway when you alter inflation pressure.
Generally the tire industry offers this as a useful (necessary) means to guide optimal tire fitment (fuel efficiency, braking and handling), and minimize liability (from a really stupid mismatch).
Dealers install outside of this and see this all the time; my guys report no problems. 1/2" outside the recommended rim is reported to not be an issue and even 1" is not felt to be outside of the norm.
I personally was less worried about the tread than I would be about seating the bead, but again this does not appear to be an issue.
I like the wheels BTW. Might have done this myself at one time.
In fact, I now regret having given away my near mint stock 15x7 wheels as I could have put on the 275 Nittos, which are listed as preferring 7.5" rims!
Please note that these are just my current opinions and I accept no liability for what you do - hahaha
Reach out to me anytime if you want to discuss.
Best as always,

Afterthought - Fred, you know those wheels are only rated for 145 mph?
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 08/28/19 01:20 AM

Thanks Gordon for your insight. I did not know the wheels are only rated for 145 mph. I never knew there was a speed rating for rims. Not that I plan on going that fast. No place around here to get the Monte up to that speed safely. How did you find the speed rating on the GNX replicas?
Posted By: AkronAero

Re: 18x8 Rim with 255/40-18; Downsides? - 08/28/19 02:13 AM
First line of the large paragraph in the middle.
Teasing you a bit. I don't recall ever having seen a speed rating on a wheel before either.
145 mph seems reasonable in any case.
Possibly some unique speed testing done to gain basic safety approval, yet avoid using expensive design/testing protocols/costs (possibly destructive testing) which only the big guys have readily available????
Insight from anyone?
One wonders if OE wheels were ever rated? Probably not. After all many of these cars had 85 mph speedos.
I see they have the stock Monte Carlo "Chevrolet" center cap design that came with our cars on that page, too. You might want to look for an "SS" center cap somewhere else or something custom to compliment your paint job.?
Let us know how it turns out.
Again - a very nice looking wheel with large appeal.
So glad you found this.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 08/28/19 08:11 PM

Hi Folks,

Using this equation from the sticky:

Wt = (Wr-8.4mm)/[1-0.42*((AR-5)/100)]

Which cane be re-arranged to solve for Wr as follows:

Wr = 8.4mm + Wt*[1-0.42*((AR-5)/100)]

Wt = advertised tire width
Wr = rim width (inside of lip to inside of lip)
AR = advertised tire aspect ratio

Get for 245/40-18 for the front: Wr = 217mm = 8.6"
Get for 255/40-18 for the rear: Wr = 226mm = 8.9"

To improve grip with the car undergoing roll in a cornering situation, the better direction to go with the rim is wider rather than narrower, than what this formula suggests. All "super cars" are set-up with this bias, often with the rim 1" to 2" wider than sidewall verticality, which is the basis for my equation. See the sticky comment about tire "self-cambering."

8" is definitely narrower than optimal, especially at the rear. The result will be that you won't get full performance from the tires for roadhandling, and you'll get higher wear in the center of the tread than at the edges for straight-line driving. But as Akron says, the difference with an 8" rim isn't big enough to obsess over IMO. Now having said that, I wish I could tell you what fraction of cornering acceleration you'd be losing compared to an optimum rim width, but I can't. Insufficient data!

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 08/28/19 08:44 PM

Thanks MAP. Definitely something to think about. GBodyParts do have the rims available in 18x9x4.25 BS. But, I don't think a 9 inch wide wheel with 4.25 backspace will work very well on the front of our Monte's. Would hit the top of the wheel well opening on bumps. I could run the 18x9 on the rear with the 255 tire. But at 4.25 backspace, my measurements show that I will have to roll the fender lips. I'm currently running 17 inch SLP ZR1 replicas with 245/45-17 front and 255/45-17 rear. Looking for something different without spending thousands. I draw my line at about $2000 for new rims. Forgline has a couple of great looking concave wheels, but at $1500 a wheel, I cannot justify spending that much.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 08/28/19 09:31 PM

Hi Fred,

I truly wish I could say you were wrong, but unfortunately, you're exactly right. Our cars weren't designed for very wide wheels. My past experience was that tire widths going in excess of about 245mm rapidly engendered fitment issues. Must say that was my main motivation for wanting to stretch the width of the car by about 4" at the front and rear, with gentle bulging of the fenders and quarters. It would have definitely changed the lines of the car, but in a nice way, or so I thought, according to some clay mockups I did on a scale model. Or, you could do it the way GM did that one-off MCSS about five years ago, by adding pronounced upper-wheelwell "eyebrows" that projected outwardly to about the same extent, preserving the 1980s theme that they executed on their IROC Camaros.

So yes, you're in a tough spot and I feel for you. In light of all of the other costs involved with making things right, putting tires on rims that are about an inch too narrow, doesn't look quite so bad. Best of luck to you on this quest.


On edit: I'm amazed to see that my old photos and sketches are still in the album repository! Look under MAP and there's a good sketch from 2005 of a front 3/4 view that shows what a stretched-width MCSS would look like. There are two MS-painted photo concept views as well. (These show width-stretching in conjunction with moving the front wheels 3" forward. Must say that after several years of not looking at this concept, it still strikes me as surprisingly viable.)
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 08/31/19 04:17 AM

I have had several email exchanges with G-BodyParts sales department. I mentioned to them about getting a "SS" center cap inlay like Gordon mentioned. The sales person says they have graphics people who could get it done. I sent them a picture of an SS emblem and that I would want red "SS" letters on a black background. I have to take a few more measurements on the Monte before I hit the "Buy" button. Need to see how centered my rear axle is. I have UMI adjustable rear control arms on the car so I could adjust if needed.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/02/19 03:53 AM

I have taken allot of measurements and I think the GNX Reproduction Rims will work on my SS, but depending on how lowered the car is, it could be an issue. My Monte is lowered about 1.5 - 2.0 inches. I have OPG 2 inch drop springs on the front, but my front end is lighter due to aluminum heads, alum radiator and fiberglass hood. The rear has Detroit Speed 2 inch drop springs. My car has a slight rake. I may have to roll the rear fender lips. but I will wait until I have the rims and tires. Eastwood's fender roller is about $89 bucks. The sales person at seems to think that all G-Bodies are the same. They invited me to check out their Oldsmobile H/O Cutlass with 305 tires on their 18x9.5 rims that fit. The Cutlass has wider wheel wells than the SS. But I decided to leave it alone and not get into an argument. I appreciate them at least discussing the issues with me. My rear is centered within an 1/8 inch, relative to the fender lips. When I originally centered the rear, I used the frame as my reference. Tires are going to be Firestone Firehawk Indy 500 Summer tires. 245/40-18 front and 255/40-18 rear. I have been running Firestone Firehawk Indy 500 Summer tires for about 9 years now on 17 inch ZR-1 Replica rims. Those tires are awesome. Stick like glue and predictable. Rims will be 18 x 8 x 4.0 BS front and 18 x 9 x 4.25 BS rear. When I get the rims I will start another thread for the benefit of the forum.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/02/19 06:30 AM

Hi Fred,

Just one comment from me: in terms of A/G-body room for wheels, they are definitely not all created equal. Close, maybe, but not equal. It's been quite a while, but I seem to remember that my '78 Malibu had about 3/4" less width clearance per tire in the front compared to an MCSS, and about 3/4" more in the rear compared to an MCSS.

I also seem to remember about 7(+/-?) years ago that someone made GNX-like flares for the MCSS. I thought the styles clashed, but that might just be me.

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/02/19 11:04 PM

Thanks MAP. I do remember someone selling GNX style rear fender flares for Monte Carlo SS many years ago. Never saw a picture of them.

The person I have been exchanging emails with at sales dept says that other Monte Carlo owners have bought their GNX reproduction rims without clearance issues. If so, those monte owners are not advertising it. I'm interested to see what GBodyParts can do for me concerning center caps with a "SS" emblem/inlay.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/03/19 08:25 AM

Hi Fred,

It took a while to dig-up this information, but it turns out it was 12 years ago, and the company was Prodigy Customs in FL. The flares were made from fiberglass, and only for a single car. AFAIK they never made it to production. The owner shared photos of the car on this site, but all the photo links I found are broken. The owner of Prodigy Customs posted here once, that many people had seen the car at a certain car show. He seemed to let-on that the overall reaction to the flares wasn't very positive.

The shape of the flares clashed badly IMO with the downwardly-swooping crease lines the factory put into the MCSS fenders, doors, and quarters. But again, that's probably just me. The real GNX lacks those crease lines, so the conflict doesn't exist on that car. The GM MCSS show car from roughly 5 years ago (?) had flares similar to an IROC from the 1980s, and those visually worked far better. They covered only the top half of each wheel arch, extending down to the horizontal beltline of the car.

Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/03/19 02:46 PM

Moving back to the subject of the 18" "GNX replica wheels" I'm the owner of 8 16" GTA wheels, 0 offset. One is an original GM wheel, 5 are Classic Industries bought in 1999 manufactured by the original Japan manufacturer and two are Classic Industries repops I bought several years later which are Chinese.
The first 6 wheels all have JWL cast into the wheel meaning they are from Japan and approved by JWL. Here's WIKI info on the JWL markings. Few people know about this spec on wheels.

What i found on the Chinese wheels was the clear coating was junk, the hole for the valve stem compromised install of the stem, and who knows about the quality of the alum used, and no JWL on the wheels.

Kirbin tried to offer a "replica of the GNX wheel many years ago in 16", I looked at it, not even close, he didn't sell many.

Have watched the "GNX replica" ordeal as it has been a hot/cold subject over the past decade. I'd be a little leery of the quality being you know they are Chinese repops. If just for looks they may be ok, as a race wheel I'd be hesitate.
Can't speak about the available offsets. My car is a modified B spindle setup to get to 9 1/2 caster in front, 255/50x16. In the rear an 8 1/2, alum drum, 10mm spacer so 255/50x16, 275/45x16 and 11.5x26x15 QTP Hoosiers all fit nicely. Absolutely no tire rubbing anywhere running a 16x8 zero offset GTA front and rear. QTP are on a steel rally wheel, 15x8.

The original GNX wheels had unique wheel offsets front and rear.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/03/19 03:32 PM

Thanks Bob for the info. No, I'm not racing (neither autocross/nor drag racing). I just cruise till the sun goes down. I do have a photo of a Monte that I got off the internet, I forgot where, that shows a white Monte with what appears to be 16 inch GTA wheels with drag radials. It does look good.
Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/03/19 09:10 PM

Fred, what spindles are you running up front?
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/03/19 10:44 PM

Bob, I'm running stock G-body spindles with the larger metric calipers.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/04/19 04:17 AM

Hi folks,

Not to slow-down the current progress of this thread, but I finally did find information on that (1988 as it turns out) MCSS:

The "eyebrow" flares are a nice compromise for additional width without getting into the major bodywork of my approach. And they look far better than the GNX flares. (Hmm.. maybe someone can mold those up and sell them instead?)

Fred, somehow I got the wrong idea about how serious you were about getting the ultimate handling performance out of your car. "I just cruise til the sun goes down," was a major recalibration for me. Sorry if I was pulling you in a direction you didn't want to go. Maybe this is a good place to say that going a bit narrow with the rims (8", specifically,) doesn't sound like as big a compromise for you as I had first guessed.

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/04/19 04:17 PM

Thanks Map, I appreciate your help and the help of other forum members. I am indeed concerned about handling performance. I do not plan to autcross my Monte, but I do want my Monte to handle good and predictably. I have UMI rear adjustable control arms, stiffer spings, 1-5/16 front roll bar, 1 inch rear roll bar, a front brace that ties the front frame horns together (bought from Dennis Kirban) and Kirban rear seat cross brace. Someday I may get the UMI tubular upper control arms with the tall ball joint and an improved steering box.

As of this post, my current plan is to get the 18 x 8 x 4.0 Backsapce rims (245/40-18 tires) for the front and 18 x 9 x 4.25 Backspace rims (255/40-18 tires) for the rear. The reason for the slightly larger size in the rear is that I always did like a staggered setup. My Monte is lowered about 1.5 inches. My measurements indicate that I will have to roll the rear fender lips or raise the car. I ordered the Eastwood Fender roller yesterday.

GBodyParts says that they can do a centercap with a red "SS" inlay.

The backspace dimensions of the GNX reproduction rims do present a problem. They will restrict my ability to do a big disk brake conversion for the front. For instance, Baer Racing's big brake kit for G-Bodies increases the front track width by 0.400 inches per side. With the 4.0 inch backspace of the GNX front rims, another 0.400 inch movement outward would probably cause contact at the top of the wheel well when hitting bumps.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/04/19 09:38 PM

Hi Fred,

Ah, the limitations of language. I wish I could get inside your head to find out exactly what "good" means. But even if I could, then it would take potentially years research to determine which package(s) would satisfy that definition.

9" rim width in the back: please don't forget that you need additional transverse clearance around the tire for unexpected things like:

1. transverse compliance in the suspension between the rear and frame;
2. transverse compliance in the connection between the body and frame;
3. transverse migration of the wheel as the suspension moves, considering the instant roll center location;
4. rim/axle-flange flex;
5. tire section distortion while cornering and with road undulations.

There are probably more considerations, but that's what immediately comes to mind.

Posted By: BadSS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/05/19 01:49 AM

Originally Posted by Fred SS
As of this post, my current plan is to get the 18 x 8 x 4.0 Backsapce rims (245/40-18 tires) for the front and 18 x 9 x 4.25 Backspace rims (255/40-18 tires) for the rear. The reason for the slightly larger size in the rear is that I always did like a staggered setup. My Monte is lowered about 1.5 inches. My measurements indicate that I will have to roll the rear fender lips or raise the car. I ordered the Eastwood Fender roller yesterday..

Fred, I plugged in the info you provided into the following web application (compares two wheel/tire combos)

If you have the SLP ZR1 17x8 with 4.5” backspacing, the front and rear will have more clearance toward the inside than you have now. The GNX front tire/wheel combo will stick out about 0.5” more and the rear will stick out about 0.8” (plus or minus a bit due to varying section widths).

I’ve been srtuggling a lot on wheels but finally made my mid up on a set of Intros - more than I wanted to spend but I figure if I don't get what I want I'll end up spending more later. If you’re not set on the GNX replicas, the AR Super Nova wheels below have the same offset in a 8" and 9" rim that you're running now (0) and wouldn't stick out any more than what you're running now.

[Linked Image]

These Vision 143s in a 18x8.5 with -6 offset (4.5" backspacing) just might fit all four corners with a 255/40/18.

[Linked Image]
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/05/19 03:55 AM

MAP, I have considered allot of the issues that you mentioned. Thank You. I try to avoid making rush decisions and try to have a plan. At my job, it is called operational risk management. I have not laid it all down on paper in a spread sheet, but I have looked at several of the issues.

Kevin, I looked at the AR Super Nova, Visions 143 wheels and allot of others. I like the Vision wheels. They have the same offset as the stock rims. A forum member bought those rims about a year ago I think. But I really want a gloss black center. The Vision 143 wheels are a dark gray.

Really, the only thing that is holding up the purchase is trying to get an SS center cap inlay, instead of the standard "Chevrolet" inlay they sell now. I want red SS letters on a black background. GBodyParts wants me give them a graphics file and they will print it. I'll see what I can come up with tomorrow.

I always did like the GTA and GNX mesh wheels. Even though they are probably time consuming to clean. All those nooks and crannies. Will need a bottle brush.
Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/05/19 05:05 AM

Fred, actually for the GTA wheels you need a few sizes of bottle brushes. If it wasn't for the dusting of the Hawk HPS pads cleaning the wheels is usually just a microfiber wash rag on the polished Seal and Shine finish. They are very easy wheels to maintain/clean after I got rid of the clearcoat. MUCH easier than the stock SS wheels that would cut you hand if not careful. I dislike (you can't say hate anymore) cleaning wheels!

Fred you mentioned the Baer brakes pushing the wheel outboard .400", got a Baer link to that setup? As a comparison the B spindle moves the wheel outboard about .440", an 8" wheel with 4 7/16" backspacing, zero offset, running a 255/50x16 BFG Comp 2 (ht is 26.1"- section width 10.4"), 5 degrees caster was my setup for many years before extensive LCA relocation. Only rub was at 9 o'clock, back, inside of well at full lock. No rub at the top of the wells. Have run a Camaro XH the whole time the 16" were on the car, the limited travel of that box prevents rubbing the 36mm bar or the frame in the rear at full lock.
Now run 9 1/2 caster by moving the ball joint forward 11/16" and absolute zero rub anywhere. Anything over 7 degrees before the mod and tire rub was not acceptable in the rear of the well.

Ride height has everything to do with tire rub. Using a drywall T-square on the centerline of the spindle, a small T-square at the opening lip has been my standard to keep a very accurate ride height measurement for decades. For the type and location of the driving I do I run 26 1/2" ride height up front, 27 1/4 - 27 1/2 in the rear. The 255/50x16 is about 3/8-1/2" taller than most choices so it adds a little to the ride height. Any lower than that you really limit the compression travel up front, which is limited to start with. On both the front and rear you end up running on the bumpstops. Ride height is one of those subjects i don't like to discuss, to each his own.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/05/19 10:32 PM

Bob, the link to the Baer front big brake upgrade is below:

About a 1/3 of the way down the page is "Track Width Increase".

Posted By: AkronAero

Re: 18x8 Rim with 255/40-18; Downsides? - 09/06/19 12:25 AM

Fred - will you be eventually upgrading the rears too? How about the master cylinder?
Haven't talked to Marcus Savitske at SC&C recently but had scoped out some changes a while back.
So the track 4 fronts are new (maybe replacing the SS4+ fronts?).
Like to follow what you are doing, and reconnect with Marcus this fall; lots of Baer stuff on his site.
Keep us posted.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/06/19 04:01 AM

Gordon, I only looked at the Baer front brake kit because Baer tells you the amount of track width increase There are other less expensive front brake upgrades, like LS1 and of course the C5 upgrade using blazer spindles. When will CPP have their G-Body/C-5 spindles ready? I have been watching their website for years and it still says "Coming soon". But I have to admit, Baer is a one stop shop. Their brake upgrade is bolt on. But Flynbye also has bolt-on kits. But I want to do the C5 front brake upgrade. I have the blazer spindles, adapter plate and other pieces from Kore3 but I am not sure if it will fit the GNX reproduction rims. I have the brake template from Kore3 and that will be the first thing I check when I get the rims. I also do not know how much of a track width increase I will see with the blazer spindles. Maybe someone can chime in who knows if there is a track increase with blazer spindles.

I managed to whip up an SS emblem today. Red letters on a black background. GBodyParts told me that they sent it to their graphics dept. I am ready to hit the buy button, but this center cap thing is holding it up. I think what is happening is that GBodyParts is concerned about liability. Their last email indicated that they plan to make 100 of these SS inlays in hopes that others will want them. I think getting me to do the graphic relieves them of some liability. Never thought I would need a lawyer to buy a set of rims.
Posted By: AkronAero

Re: 18x8 Rim with 255/40-18; Downsides? - 09/06/19 01:44 PM

Fred - share when you get the graphics. Our virtual team will provide confirmation, if not confusion....
I scanned SC&C again last night to see Marcus' list of what fits G-Bodies.
Seems some of the large ticket items are higher priced than what I recalled.
Will you upgrade the master cylinder too?
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/06/19 10:29 PM

Gordon, when I first researched the C5 front brake upgrade, I emailed Kore3. I asked them will I have to change my master cylinder for their C5 brake upgrade. They told me no, because the G-body has a "Fast Take-up" master cylinder. I do not know what "Fast Take-up" means.

Below is the SS center cap emblem that I thru together on AutoCad and sent to GBoyParts:

[Linked Image]
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/11/19 02:02 AM

I want to keep the forum updated on what is happening. I emailed GBodyParts yesterday and asked what is happening with the "SS" center cap inlay. I have not heard from them yet. Maybe they were effected by the hurricane. If I do not get a response about the SS caps soon, I will go ahead and order the rims with the standard monte carlo center cap inlays. I want to be able to cruise with the new rims before winter sets in.

Oh, I did get the Eastwood fender roller a few days ago. Nice piece of equipment. I have not used it yet. I want to wait until I get the rims/tires installed.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/11/19 06:48 AM

Hi Fred,

I have to assume the fender roller exerts an outward, and maybe simultaneously upward force on the fender lip, probably in reaction to an inner force it simultaneously exerts on - what - presumably the frame? Or maybe the axle flange?

My only advice would be to do this slowly and very gradually in repetitive passes. The danger is that if you exert too much force, you may buckle the fender in a way that would take major bodywork to correct.

About the logo: is there any way you could make it yourself and attach it permanently to the flat, central hub covering of the rim? (The backing material and the ink used would have to be waterproof and UV-proof as well.) Maybe there's an online source that would make this logo for you with a very strong PSA backing, like a sticker, similar in consistency to the body stripes GM used on the sides of the car?

On edit: Just found this possibility:

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/12/19 02:10 AM

MAP, the fender roller bolts to the axle. Then you adjust the roller. I agree that this has to be done very slowly. The G-Body rear fender lips are double thickness, two pieces of sheet metal spot welded together. The eastwood instructions show doing it in a manner that will definitely warp the quarter panels. I have a plan to perform the operation in a safer manner. I could still simply cut the fender lips, but I want to avoid such a drastic operation.

Concerning the SS center cap inlay, I designed it on AutoCad. I could print it, then cover it with clear laminating plastic, then glue it to the center cap. But I'm sure GBodyParts would provide a better product than I could make.

Thanks for the link. A company that can make vinyl weatherproof round stickers to your design. If they can make the stickers the right size to fit into the center caps, that may be a plan.
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/12/19 09:06 PM

Hi Fred,

It's exactly that construction: two layers of sheetmetal separated by a space - that increases the danger of buckling per unit transverse deformation compared to, say, deforming just a single thickness of sheetmetal. The inner layer will buckle first, and immediately cause a gross deformation in the outer layer. So again, just proceed with caution. (I'm sure you'll get this right; writing this mostly for the benefit of others reading here who may be considering doing the same thing.)

In the one part per billion chance a designer of this type of tool is reading here: multiple rollers that float to cause an equal division of contact force, instead of a single roller, is a good way to minimize this problem. Even two rollers on a hinged coupling would be a big improvement.

On edit: if the tool looks something like this:

It may work well enough for all I know, but there are several features of this tool I don't like. Bending that quarter panel lip is going to create an enormous reaction moment on the axle flange. There's a real danger it could permanently bend.

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/13/19 01:16 AM

Yes, the link you have is one of the many copies of the Eastwood fender roller. Eastwood does say that the tool should not be used on double thickness fenders. But their instructions on using the tool is a bit aggressive in my opinion. They show the roller against the edge of the lip, forcing it upward and outward if the quarter panel begins to warp. If I do decide to use it, I plan to take a more gentle approach. Have the roller against the bottom of the lip and angle the roller up slightly to gradually bend it upward. Also, I cannot see using it to bend the lip all the way up, 90 degrees. That would surely warp the fender. A more conservative figure would be about 45 - 60 degrees. I hope to order the rims next week.
Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/13/19 05:13 AM

I believe Lance used the Eastwood roller with good success. Maybe he'll jump in here.

Fred do you have a local guy that does vinyl lettering for cars, like stock cars. Here I have a friend of my son who does just that for the locals. Oddly, his name is also Fred. I created the fonts, from his catalogs we picked the colors and then sized it. He printed me a dozen 427 with the hood fonts from the late 60s Vettes.. Always loved that car for that reason, always wanted a tri-power with that hood and badging,
The letters are two stage letters, perimeter is gun metal and inside laid over that is a smaller mate black letter, very subtle on a black hood you can hardly notice it.
Did those decals after the hood finally got a heavy coating of black lacquer, over 10 years in primer was that hood. Won that Goodmark at Monte Madness in like 05 on a 20 dollars chance. The previous year at Madness our fearless leader won the Goodmark, Paul,

Are the center caps on the new GTA wheel the same used on the old GTA. I've got a long history with the aftermarket caps, have bought more than enough for a few cars, have lost or damaged my share. The plastic tabs that hold the cap to the groove inside the hub opening are soft, removing them can easily damage one of the eight tabs, one gone and you may get the cap to stay on, two doubtful. At the drags I would need to remove them to run, so they were on and off many times.

The original GTA caps had a steel insert to hold the cap to the wheel. You couldn't find a set of the OEM caps, if you did find one it was beat up and way over priced. But just recently available are these repo ones. Pricey but they are nice, good copies. To insure the metal stays bonded to inside of the cap I cleaned everything and used RTV for what should be a permanent fix. Only paid 64 bucks for 4 caps with no centers installed. The CHEVROLET logo on the original SS wheel is installed in the center of those caps. Unfortunately the OD of that stick-on emblem is bigger than the recess in the cap. A trip to the lathe for a small trimming of the hole and the emblem is a drop in. Have made dozens of caps for these wheels over the years. I think the four caps with the steel insert will be around for a long time.*881189.html
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/13/19 04:48 PM

Thanks for the info Bob. If I cannot get GBodyparts to do an SS inlay then I will look at the company MAP provided the link for:

Funny you should mention the plastic tabs breaking on the center caps. My current SLP ZR1 replicas has a broken tab on the front passenger side center cap. Unfortunately, the center cap is held on with only 4 tabs. So with only three, it would not stay on. So I super glued it in. SLP could not help me since they stopped selling those rims awhile ago.

I believe the GNX reproduction center caps are held on with a metal insert of some kind. I think I saw that info somewhere on Gbodyparts website.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/14/19 08:26 AM

For the benefit of the members, I setup the Eastwood fender roller and took some pics. I used a heat gun to soften the paint like the instructions said.

The roller did not work like I thought. The way it is designed, it pushes out on the fender lip more than push up. Pushing out on the fender lip could cause the quarter panel to bend or warp like MAP said.

I jacked the car up and placed jack stands under the frame ahead of the rear wheels. Then I let the rear axle drop until it was hanging by the shocks. The fender roller can be setup for a long length or short length. It was delivered setup for a long length.

The first photo shows it installed per the Eastwood instructions after I rolled it back and forth a few times.

The second pic shows how it attaches to the hub. The small hydraulic jack is there to push up on the axle. I thought that I could use the jack to push up on the axle thereby placing a upward load on the edge of the fender lip to bend it upward. It actually worked, but is tedious.

The third pic is a closer view of the bent fender lip. If you look closely, you can see a crease ahead of the roller where the roller stopped. That black spot ahead of the roller is where the paint flaked off. I knew that was going to happen. My Monte was repainted a little over 10 years ago.

The roller actually curved the fender lip up about 1/4 inch, maybe more, instead of a straight bend.

At this point, I'm not going further until I get the GNX rims and new tires.

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Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/15/19 01:48 AM

I used the roller on the passenger side rear fender. It actually turned out better than the driver's side. I had less paint flaking probably due to heating the lip to 130 - 150 degrees. At the top of the wheel well opening, the fender lip is bent upward like a U-shape. Takes allot of time and patience to continue this all the way around the wheel well arch. I stopped before I went to far. I tried to take a few pictures, but none of them showed the rolled lip very well.
Posted By: AkronAero

Re: 18x8 Rim with 255/40-18; Downsides? - 09/15/19 12:35 PM

Fred, sorry about the paint chip. Not in an obvious spot though and could get by with touch up I hope. Still its better than what I would have done rolling it with a baseball bat...
On the center caps, what would you think about the red outline letters with a slight lean? They have been used elsewhere by others. Traveling or i would research a bit.....
Keep us posted....
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/15/19 09:40 PM

Hi Fred,

If the biggest result of this exercise is to roll the inner lip upward, so you get a J-section instead of an L-section, then all you've done is bought a little more transverse clearance for the tire in what - the first 1/2" of upward travel of the tire into the wheel well? Maybe 3/4" if we count the 1/4" upward displacement of the entire lip? Btw, that last photo confirmed my recollection that the stock wheel well contour in a transverse sense tapers pronouncedly with increasing height.

All in all, it doesn't seem like this method accomplishes much. However, when you consider the low money and time investment, it seems quite reasonable.

Must say that if this were me, I'd gladly put up with the bodywork for either the bulged-quarter approach, or at least GM's project Monte style of an "eyebrow" flare. The former goes, of course, with a complete re-doing of the outer half of the wheel well housing so the resulting transverse section looks more like a |_| instead of a U. (Hope the idea comes through OK with simple ASCII characters.) That way you get a very big increase of transverse tire clearance even with deep wheel travel inside the wheel well.

In the realm of custom bodywork, this is actually a fun and rather easy project. You just have to be comfortable with sheet metal fabrication, contouring, and welding. But for folks who've only taken bodywork as far as dent repairs, no way.

I'd start with a car that needed a complete paint re-finish, needless to say.


Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/16/19 01:14 AM

Gordon, I actually wanted letters with a slight lean but I am not a graphics artist. So I threw together something and sent it to GBodyParts. What I really wanted was SS letters like what GM placed on the rear of the trunk lid. I do not think that is an actual font but was probably done by a graphics artist. I tried allot of different fonts in the software program, but could not find anything close to the OEM letters.

Map, I agree that I did not do much with rolling the fender lips and may not be needed. My measurements and calculations show that the sidewall of the rear tire will be approx 1/2 inch past the inside edge of the fender lip. The lip is 1 inch wide. My car is lowered about 1.5 inches all around. I think it helps that I am staying relatively conservative on tire width. Rear will be 255/40-18 on 18x9x4.25 bs rim.

Thanks Guys,
Posted By: MAP

Re: 18x8 Rim with 255/40-18; Downsides? - 09/16/19 03:10 AM

Hi Fred,

I think you'll be OK. Stiffer springs would help, too, to keep the wheels from encroaching much on the interior space of the wheel well. It's never a good first path to avoid interference, but sometimes you have to do what you have to do (and it should be done with a proportionate change to the front spring stiffness.) Side note: I'm always thinking in three different levels when I post: first, to the OP; second, to the much larger audience who reads but doesn't post; third, to everyone about boldly going where no one (or at most few) have gone before(!)

About the SS emblem: if you Google "SS emblem" (surprise!) and click on "images," you'll find the font you're looking for. You basically want a 10-degree forward tilt to a very bold, squarish appearance. The only problem with about 90% of the forward-tilting images I see on Google is that they're inclined at about 30 degrees instead of 10, but some can be found, like this one:;zenid=96b594430eb993226736bd7928f7b09a Or maybe this:

Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/17/19 02:21 AM

Well, I ordered the rims, 18x8x4 BS for the front and 18x9x4.25 for the rear. When I receive them I will start a new thread.

Thanks MAP for the links. I'll wait to see what GBodyParts does for me.

Thanks everyone for your help. Stay Tuned.

Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/17/19 02:42 AM

Did you pick a tire yet?
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/17/19 03:56 PM

Bob, yes I have. Firestone Firehawk Indy 500. 245/40-18 front & 255/40-18 rear. I'm running 17 inch Firehawks on the Monte now and I really like them. Been running them for about 9 years. So I decided to stay with the same brand.
Posted By: mmc427ss

Re: 18x8 Rim with 255/40-18; Downsides? - 09/19/19 01:14 AM

Can't say anything bad about Firestone. Have run several sets of Destination LE on my AWD Astro, love them, just would like to get more miles out of the set, but that may have something to do with driving style. Had to make the decision between the Firestone Firehawk and the BFG T/A Advantage V for my wife's 02 SS, bought the BFG because it was USA and liked the tread pattern better. They are a little noisier than I'd like, only fault to them.

On the 86 run BFG Comp II 255/50x16 on the 16" GTA wheel on all four corners, a very good street tire. Quiet, good in the wet, very good in the dry and wearing good, made in the USA. What you will find on BFG tires is they generally run a little more "advertised" tread width than other manufacture's tires in the same size. It may have something to do with who's doing the measuring but look at the specs for the 255/40x18 in a Firehawk and the BFG Comp II Summer. Over 1" more tread width on the Comp, same pricing for both tires. Comp USA, Firehawk is Thailand. More tread width is the rear is usually a good thing. I've autoxed the Comps, and drag raced them, about 8K miles and 4 years old. Will need to replace them maybe next years, they will be 5 years old. What I found on all the previous 16" Summer HP tires I've had on the car, BFG VR4, BFG KDW (set before Comps) the tread grip changes, harder, and they don't perform as well. Running a set of performance tires past their prime years isn't good.

My wife's 02 SS had two sets of AS hp touring Yokohama, the last set turned 5 years old, very low miles and were junk for cracking in the tread. Needed to make a long trip in that car and installed new tires because I didn't trust them for sustained highway driving at speed. And I hate changing flats. Did three for others in the past week, my kids, well not kids anymore, 40 and 46, but we know how that goes.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/20/19 10:36 PM

I found a source for the SS emblems to go into the center caps in case GbodyParts cannot provide it:

The Motor City emblems come in various diameters, so I should be able to find one that will fit the GNX center caps.

I dropped the rims off at Firestone to get the tires installed today. Should have pictures uploaded Saturday afternoon. I will start a new tread then.
Posted By: Fred SS

Re: 18x8 Rim with 255/40-18; Downsides? - 09/22/19 12:29 AM

I posted a new thread with the GNX rims with photos and measurements.
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