I was looking to get some 18x9.5 and 18x10.5 Z06 Rims and was wondering where I could locally get spacers, etc for it, and what size tires would be best to order em in... Id ask this in another board, but I trust all of your advice much more, thanks in advance!

 

One of the guys where I work put 18-inchers on his 3rd Gen. It looks out of proportion. The wheels are huge and lift the car high off the ground, so now it looks like a truck. Additionally, because the tires have a smaller, stiffer sidewall, the ride is harsher than before. The wheels themselves are chromed, so they are bright, gaudy and will begin peeling in a couple of years. IMO, 16's fit 3rd gens well and the tires are large enough to soften the ride. 17's allow a larger selection of tires, if thats the goal, but 18's and up are a waste of money unless the suspension and body are modified. In the end, the car will look weird and you won't like the ride and handling.

 

**** would look nice as hell...locally get spacers?...I don't know about that man I think you'd have to go online. Get them from that one company...****...what company are my spacers. Okay I don't remember sorry man O_o but their pretty good. I mean I've been drifting on them for the longest time and there's been no problems.

 

I thought you had Skulte's? (http://www.skulte.com). For a 18x9.5 in front you want a 275/35/18 and for 18x10.5 rear I think either a 285/35/18 or a 295/30/18. You should use the online wheel calculators and compare different sizes to OEM size 245/50/16 and see what setup will be closest to OEM overall dimensions. Are you gonna drop the car?

I'm running 18's on my 91Z and I'm really happy with the handling. I did do quite a bit of suspension work to get it where I wanted it and it does ride hard, but at higher speeds its very very nice. The smaller sidewalls did add to the hard ride, but the springs made the biggest change. I dont recommend going stiffer than 800# front/175# rear for a street car.

 

Yeah I saw your car recently and it looks fine with the big wheels, but it sure was more than simply bolting the on. Aside from the cost of the wheels and tires, how much were the suspension mods? Would air bags be a reasonable solution?

 

I'll ask one of my coworkers; he used to work at WMR

Scott

 

skulte,

or

vette brakes and products...


I'm sure there are others...

 

You can order those spacers directly from Skulte, send him an E-Mail.

Airbags are the best for on the fly adjustability, very nice, but expensive. Changing the ride height by pushing buttons must be great, low as you want, when you want, and you can go anywhere you want (dont have to avoid certain roads or driveways for fear of bottoming out). They also ride great, comfy like a Caddy. If I didnt plan to build an insane motor for that Z28 then I probably would have wanted Airbags. But since I plan to blast into space I opted to stick with the OEM style suspension. I have around $1000 into the suspension and the wheels were $2500 for everything. They did bolt on and I was really **** about the sizes/specs because I was afraid they would rub and scrape. Every local shop I talked to said it was impossible to run 18's but I knew it was BS. One of the users on this forum (powermite) had 18's. I spent alot of time on the wheel calculators and eventually came up with a setup that had the exact same overall dimensions of a OEM front 16x8 with 245/50/16 tire, and the same overall dimensions of known good 275 wide rear tire setups on 17's. Then I decided on the backspacing, again making sure to be the same as stock in the front and known safe in the rear. Ends up these 18's have no issues with rubbing or scraping at all, even dropped over 2.5" low they have full turning radius. The tires really drove up the price, those potenza S-03's are expensive but worth every penny. 18's are only worth it if you want 18's.

 

And I hope you went back to all those shops just to show them afterwards! I didn't get much info, feedback, & help either when me & my wife went shopping around for rims. Everything is more geared for imports & SUVs now......that's why I love this forum cause I got all the info I needed to run the setup I want. It made my job easier when doing homework on sizes, backspacing, etc. also! ............17's coming soon!

 

Thanks for all the help guys, I appreciate the information divulged here. I'll definately look into the 17" vs 18" issue, the price difference is something to be considered most definately. So, from what I understand from Ed's response, 18's kill both handling and ride correct? Would 17's detract from perfomance as well?

 

Oh yes the contact providing the set-up recommended 17" fronts and 18" rears... would this be an option to even consider?

 

My response concerning 18's is only based on input from my coworker. He had a great handling 90 RS on 16's, put 18's on it without making any other changes, and succeeded in raising the car higher, making it ride harsher, and corner like a 4x4. So, why spend $2,000 to throw away some of the best qualities of a sports car just to make a fashion statement? To do 18's right takes an additional $1-2,000 in suspension work, like air bags. That's a lot of money just to have "big wheels" and does create a "show car" appearance.

I've read about road racing 3rd Gens using 17's with great success and will get some research feedback to you. And 17's have some great wheel designs available!

 

Yeah, but 17"s aren't as cool to some people.

Run whatever you like. Check out other thirdgens with both sizes and different styles and go from there.

Also, if your Z28 is staying on the island, the 18"s won't be too bad because your hill was repaved... lucky!

Scott

 

I went back to each of those shops and did burnouts on my 18's ...

I think it comes down to someones personal preferance or how they plan to use the car. Smaller sidewalls wont absorb as much force as bigger sidewalls, instead they transfer it to the suspension, but they also dont flex as much so they provide faster response when turning. Its like a balance of ride quality versus tire response and the stock 50 series on 16's is a good all around match. Start running 45, 40, even 35 series tires and you start giving up that ride quality, but the tires get much more responsive. I'd prefer 50 series or higher for a daily driver, 45 and lower for a drift car or roadrace/autox car, and 40 and lower for a top end freeway car (response is pronounced at higher speeds), just my preferances though.

One major thing, you need to decide if you're going to maintain OEM overall height as far as the tire on the rim or just run what you want. This is an important choice because you can alter the handling characteristics of the car as well as your speedo reading by running taller or shorter tire setups. I recommend you try to stay as close to stock overall dimensions as possible unless its for racing or something, like .5" off at most. Those online wheel calculators really help because you can compare two different setups and find the right combo for what you want. Keep in mind that tire width (and thus rim width) play a role in determining overall height. You'll notice you need to run bigger wheels to maintain overall height and run the smaller sidewalls. If you dont care about maintaining OEM tire height then you can run whatever size tires you want, but watch out for side effects. Going too tall can cause issues with suspension bottoming out or rubbing as well as raising the center of gravity of the car and causing it to handle like a boat. Going too short will lower the center of gravity, possible cause the chassis to bottom out. Mismatches front/rear of different heights will change the oversteer/understeer characteristics of the car. Any change from stock in the rear will result in wrong speedo readings.

If you are really concerned about performance look into the wheel weights. Wheels and tires are unspring weight, makes a big difference to have lighter stuff. This is one thing I sacraficed that I wish I hadn't, those boyds aren't lightweights. Another big difference is tires, dont skimp out on tires they make all the difference. Lightweight 18's and the right tire choice should not be decreasing the cars performance potentials as far as handling. I'd expect the car to be much more responsive and possibly pronounce any sloppyness in the suspension (that previously didnt feel sloppy because the sidewalls were absorbing more force). And as with all smaller sidewall setups, ride quality would be sacraficed.

 

Here's some tech info on using other rims. Also, while doing the research, I noted a 200+ mph 3rd Gen racer mounted Michelin MXX3 255/40ZR17 on American Racing 17x9.5 in front, 315/35ZR17 in rear on 17x11 wheels.

-----------------------------------------------------------
How to bolt on different rims
Also known as "Can I bolt on (insert rim name here) rims?"

We will use an '82-92 Camaro as the example.

Offset
Offset is the distance from the rim's mounting surface to the centerline. This Camaro originally came with 16x8" rims with 0mm offset in the front and a positive 16mm offset for the rear rims. Positive offset means the mounting surface is moved towards the outside (away from the center of the car) of the rim. Negative offset is the opposite.

Backspacing
Backspacing is the inside depth of the rim. It can easily be measured by putting a yardstick across the backside of the rim, and measuring the distance between the mounting surface and the yardstick.

It can also be calculated, as shown below. Don't forget to add for the rim's lip and tire bulging past the rim (I use about .25"). Our 16x8" 0mm offset front rims would have 4.25" of backspacing. The positive 16mm rear rims (16mm/25.4 = 0.63") have about 4.9" of backspacing

Rim Width / 2 = Centerline
Centerline + Offset + Rim Lip = Backspacing

8" wide rims / 2 = 4" Centerline
4" centerline + 0.63" Offset + 0.25" Lip = 4.88" Backspacing



Measuring Maximum Backspacing
The 89 Camaro can fit rims with a maximum of 5" front and 5.85" rear backspacing. This can be measured, or found out the hard way through trial and error. To measure it, bolt a flat piece of metal or wood to your hub using 2 studs. Towards the end of the metal, drill a hole and screw a long bolt through it. This bolt should be 1 radius from the hubs centerline (If you will be putting on 26" dia tires, the bolt should be 13" from the hubs centerline). Spin the measuring tool around, and screw the bolt in untill it no longer touches anything. The length of the bolt is your max backspacing. If you have suspension pieces jutting in the wheelwell, try different bolt locations to make sure nothing is in the way. Do this with the wheels turned left and right as well.

Measuring Bolt Circles
All Camaros and Firebirds had 5 lug on a 4.75" bolt circle. If you're adapting to a different bolt circle, it can get tricky to measure it. Four and six lug bolt circles can be measured from the center of a stud to the center of the opposite stud. 5 lug bolt patterns have a bit of trigonometry involved. The online 5 lug bolt pattern calculator below will give you the bolt pattern based on a quick measurement.


5 Lug Bolt Circle Calculator

Adapters
Adapters move the rim further out. They let you bolt on rims with too much backspacing. If you decide you want to bolt on a pair of Corvette ZR1 rims (17x9.5", 50mm Offset) you would first need to calculate the backspacing.

9.5" / 2 + 50mm / 25.4 Offset + 0.25" Lip = 6.97" Backspacing

Rim Backspacing - Max Backspacing = Adapter Thickness

6.97" - 5" = 1.97" Front Adapter Necessary
6.97" - 5.85" = 1.12" Rear Adapter Necessary

Ideally, you would want some clearance on the inside of the rim to compensate for suspension movement, etc. In this case, we recommend 2" adapters for the front and rear. You can run the 2" adapters in the rear, even though you only need an extra 1.12" backspacing. This will move the wheel further out in the wheelwell, matching the front, and the wider track will help cornering as well. The only time to not match the front adapters is when you have wider wheels in the back (17x11 ZR1's for example). In that case, the wheel will fit in the wheelwell if the 1.25" adapter is used, but will protrude past the fender lip if you have a wider than necessary adapter.

For all fourth-gen rims - 2" adapters front and rear should be used on a third-gen. For C5 and 17x11 ZR1 rims, please do the math!

Using a 4th Gen Rear
If you've changed your third-gen rear to a 4th gen rear, you do not need adapters. The 4th gen rear is approximately 2" wider per side. This is the same as using a set of 2" bolt on adapters

Adapter Design
You have two choices when the rims need to be moved out - slip on spacers or bolt on adapters.

Slip-on Spacers
These are the discs that slide over your studs. For small thicknesses (1/4" or less) they are fine. For greater thicknesses, the wheel studs are seriously weakened. The reason is that the studs have a greater bending moment since the lugnuts are further away. Under braking or acceleration, the studs would be stressed more, and might break.

Bolt-on Adapters
Billet adapters bolt onto the car just as a wheel would. The adapters have their own studs that the rim bolts onto. This design is just as strong as without adapters, since the stud forces haven't changed. The adapters are made from a billet cylinder of 6061 T6 Aluminum. The billet is machined to fit over the hub, with stud holes drilled to fit. Studs are pressed through the adapter to which the rims are bolted onto. The adapter is then slipped over the car's studs and bolted on. The rims finally bolt on as usual.

There are two ways of bolting the adapters to your hub. One uses a lugnut with a long shank and washers. The clearance needed for the holes ends up as a slight bit of slop when they are bolted on. This isn't usually noticeable when driving. The other method is to use acorned lugnuts to bolt on the adapters, just like for the rims. The lugnuts center the adapter when they are tightened. This is a significantly more precise way to bolt on the adapters, and is how we make them.
--------------------------------------------------------------------------------

Various Rim Dimensions

Rim Name Size Offset Backspacing Suggested Thickness (3rd Gen)
Corvette 84-87 16x9.5 38mm 6.6" 2"
Corvette 88-96 17x9.5 56mm 7.3" 2.25"
Corvette GS ZR1 style 17x9.5 50mm 7" 2"
Corvette ZR1 style (Low Offset) 17x9.5 38mm 6.7" 2"
Corvette ZR1 style (Low Offset) 17x11 36.5mm 7.397" 1.25" Rear
Corvette ZR1 style (High Offset) 17x9.5 56mm 7.4" 2.25"
Corvette ZR1 style (High Offset) 17x11 50mm 7.93" 2" Rear
C5 Corvette 97-2000 17x8.5 front 56mm 6.8" 2"
C5 Corvette 97-2000 18x9.5 rear 63mm 7.6" 2"
C5 Corvette Z06 17x9.5 front 54mm 7.2" 2.25"
C5 Corvette Z06 18x10.5 rear 58mm 7.9" 2" Rear
Camaro 82-92 16x8 front 0mm 4.35"
Camaro 89-92 16x8 rear 16mm 5"
Camaro F1 ZR1-style 17x9 50mm 6.8" 2"
Camaro 93-97 16x8 55mm 6.5" 2"
ROH ZS 17x9.5 5 mm 5.472"
ROH ZS 17x8.5 -7 mm 4.5"

Disclaimer - These dimensions have been gotten from many sources, and are not verified. Use at your own risk. If you see an incorrect number, please let us know. The suggested thickness may not match based on offset numbers. They are based on experience fitting those specific wheels to third-gen f-bodies, and reflect feedback from customers.

--------------------------------------------------------------------------------
Return to SPD's Billet Adapters
Return to SPD's Tech Center
SPD's Home
Email Andris

 

a 16x8" rim with a 5" backspacing will not fit the front of a third gen without metal to metal contact. (There are a couple exceptions to this, see below)

OE wheels are approximately 4.5" BS front, 5" rear(distance from wheel mounting surface to the outer edge of the lip). They are marked accordingly "Front" and "Rear"... From experience... the fronts will fit the back... but the backs will not fit on the front.

now, a 17" or larger may clear the front with a 5" backspacing, but since I havent done it, I wont say you can...

you can apply the same logic to the G bodies as well... 4.25" BS, 15" rim on the front. 4.375" BS for 16" rim, 4.5"-4.75" BS on a 17"...

They type of wheel can also have an affect on how much BS you can run without contact. GTA wheels, there were two styles... early ones were forged (thin) laters were cast (thick) the forged wheels actually fit the front using 5" BS but are extremely close. the cast wheels dont fit.... at least not in my experience anyway...

 

Might as well postwhore some pics of my 18's

 

hey Shawn, what kind of BS are you running front and rear?

 

How about a straight-on side view to see the change in proportion...

 

I'm running 8" wide front w/ 4.5" BS and a 9.5" wide rear with 5.5" BS. The rears sit where I wanted them, dont require the inner fender lip to be rolled (could go wider for sure). The fronts are currently sitting a little inset at 4.5" BS, I ordered them like this because the brake upgrade I have planned will be pushing them out a bit. But I wasnt sure how far so I decided I will run a spacer to even it out after the brake upgrades are done. I also mis-calculated the room in the front inner fenderwells before ordering the wheels, might not be able to push the wheels out as much as I want without creating problems with rubbing (mainly because of the ride height)

Here's an older shot from the side when I had sportlines on the front and the weight jack setup in the rear (front sits higher haha):

 

Well guys thanks for all the input, i'm still deciding on whether to go 17" fronts and 18" rears, or just 18" all around..... I'll let you all know when i've decided.

 

I'd go 17's just to mount those gorgeous Ronals, sigh.

 

hehe, Ronals.. those are nice too, havent seen in in person yet though.

 

Well, guess what, in the end I decided to go with 17 inchers instead, OE Creations just started to produce a direct bolt up Z06 Rim that fits Thirdgens without adapters at all, the catch is they only make it with the rivets surrounding the rim, so i guess itll look quite different from the usual Z06's. Gettin 245/40/R17 fronts and 275/40/R17 rears in Nitto NT555R's... are these tires good? Haven't heard much about em before...