greezemonkey

How to Measure Bolt Patterns----> http://www.rsracing.com/tech-wheel.html#patterns How to Measure Wheel Backspace or Offset---->http://www.rsracing.com/tech-wheel.html#backspace How to Determine Vehicle Fitment---->http://www.rsracing.com/tech-wheel.html#fitting Determine Wheel Caliper Clearance---->http://www.rsracing.com/tech-wheel.html#caliper Typical Lug Nut Torque Specifications---->http://www.rsracing.com/tech-wheel.html#torque Wheel Terminology---->http://www.rsracing.com/tech-wheel.html#wheeltrm From RsRacings Website http://www.rsracing.com/tech-wheel.html

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__________________

THE MACHINE 8.91 @ 158

crazyjim

nice. I new most of this info previously but it's niec to have it to come back to for referrence... this should be made a sticky

brutalform

Since this answers alot of questions that are frequently asked on this board, I am going to make this a sticky.
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You must have been replying as I was. Taken care of!

crazyjim

sweet

BioV

Brake setup also have different offset mounting surfaces. So a wheel that fits one car may rub on another with adifferent brake package.
Here are some guildline figures to calculate with.

PART1
Standard Non-1LE front -small bearings(10.5" rotor)
3.630"

1LE brake setup- large bearings (12" rotor)
*THIS IS THE FACTORY STANDARD FOR 245/50-16 tires on an 8"wide rim*
3.948" [+.318 offset, or just over 5/16"]

Custom Wilwood setup (RTFC)-large bearings alum hub (12.9" rotor) with a 3/16" wheel spacer for rim to caliper clearence
3.967" [+ .337" offset, or just over 5/16"}

13" C4 HD's on 1LE hub-large bearings(13" rotor)
4.248" [+.618" offset, or just shy of 5/8"]

13" C4 HD's on std hub-small bearings(13"rotor)
3.930" [+.300" offset, or just shy of 5/16"]


You can now see how a senerio like going from standard brakes to C4HD w/1LE hubs can change the backspacing by just over 1/2". Could mean the difference of someone using a 4.75bs front or a 5.25bs front on the same width rim.

part 2
Diameter does not change offset, width does.

So with the above figures on those perticular brake mounting surfaces and 8" wide rims, you should be able to simply add the width of the rim to the backside and subtract half the new rim width difference to the offset to match the same outer tire edge overall.

example- 8" to a 9" is 1 inch difference on the inner wall of the rim so half that difference is .5" or 13mm. Since the new rim is wider, the center line of the rim changes so a new offset calculation is needed.

We now start with a 9"rim that has a centerline (o offset) +.5" or +13mm inward from the 8" rim. Subtract the difference.
+5mm subtract +13mm = -8mm offset

So a 9" rim on Standard brakes would need a -8mm offset for maximum turning radius clearance without hitting the fender in suspension travel.

From what I have measured on my car and being so lowered, I would never go larger than a 9" wide rim and a 10.2" tire up front.
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part3
Now factory IROC fronts 8" wide are 0mm offset and rears are -16mm offset.

A 8" wide 0mm offset rim can be spaced out as far as .525" safely without the tire coming into contact with the fender on a standard 10.5" factory brake setup. you can go further if you choose, but any more just be warned that the tire will contact the fender if the car compresses to low. Its your option, I am just stating helpful info

So in laymans terms-
Max outer offset of a 8" wide rim on standard brakes is +13mm.
So if factory fronts are 0mm, you have a range of 0mm to +13mm offset on an 8" wide rim. I have gone as far inward as -11mm with very slight acceptable rubbing at full lock where I back off just slightly and still have a very good turning radius. This range from +13mm to -11mm with an 8" rim is equivilent to the inside edge of a 9" rim that is 1 inch wider of course (or 1.000) I was replicating a .944" wider rim than the 8" when I was slightly rubbing. So another 1/2" to a 9.5" rim will really restrict your turning radius while remaining the outer edges ability to tuck.

Max offset of 1LE brakes is +5mm on an 8" wide rim

Now these spec are the outer most edge of the tire clearing the fender still. With the outer edge sitting here, the widest rim you can get going inward from this vertical line is a 9" rim with very minimal and acceptible rubbing slightly on the inner fender well (frame area) at full lock left or right with a 10.2" tire width which is about normal tire width for that size rim.

So now you want to jump up to a 9" wide front rim?
Then the offsets change due to rim width and centerline changes.
Specs for 9" wide front rims on standard brakes is 0mm offset.
Specs for a 9" rim on 1LE brakes is -8mm offset.

Now if keeping the tires ability to tuck into the fender properly is not a concern for you, then skies the limit. Anything sitting outermost then these specs will hit the fender if the suspension compresses enough so it you want to run a 9.5, then you can also run a 20" wide rim. There is no limit once beyond this vertical barrier. Its your choice, you are armed with the facts.

Poject '86

I was lookin through an old Car Craft mag (from 2000), and thought I might add what they wrote. The article was called The Biggest Meats For Your Muscle Car. The info they gave for 3rd gens is:

'82-'92 Camaros and Firebirds

15-inch: 15x8 with 4 1/2-inch backspacing front and rear. Use tires with an aspect ratio of 55 or less with a section width of 255.
16-inch: 16x8 with 4 1/2-inch backspacing front, 5 1/8 backspacing rear. Use tires with an aspect ratio of 55 or less and a section width of 255.
17-inch: 17x9 with 5 1/2 inch backspacing front and rear. Use tires with an aspect ratio of 40 or less with section widths of 255 front, 275 rear.
18-inch: 18x9 1/2 with 5 1/2-inch backspacing front, 18x10 with 6-inch backspacing rear. Use tires with an aspect ratio of 35 or less with section widths of 275 fron, 275-295 rear.

I hope this helps someone.

Orr89RocZ

http://www.rims-n-tires.com/info_spe...20/%20Comparer

heres a good link on comparing different wheel sizes with tires. it will tell you how much further in or out wheels will stick out with different offsets and such. you choose the tire/rim size and offset and compare it to another rim/tire size. its pretty sweet

Hunter Motorsports

http://www.thirdgen.org/techboard/su...18-wheels.html

MaxxMitchell

Just thought I would chime in and say the RSRacing links no longer work. Delete this when they do.

greezemonkey

They are working for me just fine ?

MaxxMitchell

Huh, now they work for me, nvm, delete my post lol.

Ucantcme57

Which one of these goes over the specs with a 4th gen rear?

Charlie319

What I'd like to see is alist of compatible wheels for the third Generation F-series.

1991Camaroz28

my iroc replicas are bolt on with 245/45/17 tires.
hawks third gen has em but they aren't cheap.
i just wish i could have gotten 18's but $$$ is tight after i replaced my motor. and installed new seats, steering wheel, b&m shifer, and got a few tickets. just the bare essentials
i think it would look sweet with a lowering kit but don't know how much i should drop it.

Attached Images

DSCN0349.JPG (759.5 KB, 377 views)

91Z/28-406TPI

I have American Racing Rebels 17" x 9" with 1" wheel adapters on front and back. Front 245, Back 275 Riken Raptors. This application brought all four tires perfectly flush to the body panels for a nice aggresive stance.

Orr89RocZ

specs for 4th gen wheels and corvette wheels can be found here at Skulte.

http://www.skulte.com/adapterfaq.html

YigyYo

Do you have any pictures of you car with this setup? Is you suspension lowered? and by adapter do you mean spacer?
Thanks!

shanemacmahon19

dose anyone know if i could fit a 15x10 with 7.5 backspacing.they are 5x4.75 bolt pattern wheel onmy car and how big of a tire i could put on

greezemonkey

no way unless you have a 93-02 axle already installed ...15x10`s on a stock length 3rd gen axles are usually 5.5 bs....with ALOT of hammering/reshaping, one of the members here managed a 6.5

Cadillac

So why is there a different offset on the GTA wheels from front to back? I'm guessing it has something to do with fitment under the wheel wells.

I have a screwy problem. I have Ed's LS1 brake kit on my car that currently requires me to run 1/8th inch spacer on the front to clear the calipers with the GTA rims. It's real tight in there and my left wheel rubs the wheel well in hard right turn. Anyway, I have bent rims and am shopping for new wheels. I want to stay with 16 inch wheels and I would like to be able to do a 4 wheels rotation with the tires.

How do I know what to order?

Is this correct:

• 5 inch BS, 5X4.75 bolt pattern.

Will that be enough information I need to order the new wheels??

greezemonkey

Something to think about when you order tires, I`m currently running 29x11.50 LT hoosier quick time pros...that is dot sizing. I run them on a 10 inch rim, the advertised section width is 11.9 But, that is on a measured rim of 8 inches.

To calculate the section width change on a different size rim than the factory measured wheel use .4 inches PER inch of rim increase. or subtract for rim decrease

Example: My QTPs on a 8 inch rim would be a 11.9 section width but because I use a 10 inch rim it would be like this...

11.9 + .4 + .4 = 12.7 section width.

Just thought it would help anyone trying to stuff tires / wheels

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THE MACHINE 8.91 @ 158

Dennis-Z28

Here is a very usefull page for adapting wheels to a Third gen. They have all the popular swaps listed and the spacer size needed to do it.

http://www.skulte.com/adapterfaq.html

After looking at that just select the right tire size.

83 Crossfire TA

The car was originally designed when 215/65/15 tires were big/wide performance tires, and the base models got smaller 14” rims. The 245/50 16’s didn’t come along till 85, and they put thicker steering box stops in to prevent them from rubbing at full lock, and still had to space them out roughly ½” to prevent rubbing, unfortunately that same offset makes the rears stick out, and to make the setup legal everywhere, they actually had to tuck the rears in more to tuck the wider tires sufficiently inside the fenders.

OTOH, most people seem to like aftermarket wheels that stick out to the fender lips or more in the back, so they tend to run similar backspacings as the front. Personally, I don’ think it looks right.

No, that might sit correctly in the front wheel well for a 9” wide rim, but might hit the tie rod end depending on wheel diameter, and would pretty much stick out too far on anything wider then an 8” rim in the back.

Do a search on this board, I know I’ve posted how to figure out offset/backspacing/rim widths/tire widths in detail a few times, but it’s been a while.

F_N_JUNK

I would like to see pics of this as well please....

Dennis-Z28

Here is a template I made of the 1991/1992 Z28 wheels versus a C5 Corvettes rims. Tire sizes outlined are marked on the image, the tires on the C5 rims are the skiniest you can fit I think (or almost anyways) and a 1.5" spacer was used in the back which actually puts most of the added tire towards the inside. So if you track back to the document from Skulte you can see why they recommend a 2" spacer despite the 1.5" being what initially apears to make more sense.

Attached Files

Wheel_Offsets.pdf (19.6 KB, 264 views)

Fire"Dutch"Bird

What are the torque specs for the wheelnuts of original 16 inch Formula wheels?
As I live in The Netherlands, Europe, I have a metric torque wrench in newton-meters, Nm.
Thanks.

alcamaroz28

whats the max offset for 1984 z28

RockJay81

http://cgi.ebay.com/ebaymotors/WHEEL...mZ120389602923


So with these spacers i can put corvette wheels on my 84camaro?

shuanm

I have an 84 Z28 as well and have IROC wheels on it. Do I need to do anything to make them work properly? They seem to clear everything, but I have no adjustment left on my strut mounts and wondered if that was the reason.

regular6d

I have an 84 Z and I just got a set of used 18x8 Chrome Iroc's (I LoveThem) the tires that are on them now are toast and only 235's I was trying to figure out what the better choice of tire would be. I have read that some have 245/40's on front and 255/40's rear and some say 255/40 or 255/45 all the way around. I just put KYB GR2's all the way around and new stock springs in the rear, the front springs were replaced before I got the car and I now have that hi ridin look happening but I think it's only because the current tires are flat. Any light you guys could shed would be greatly appreciated the Z's down until I get some new slippers.

regular6d

Yes you can you can also put 4th gen rims on with the 2" adapters, and Shuanm Iroc wheels should fit fine if you have no adjustment left I would look into an alignment and or having your suspension checked out to make sure there's nothing busted, or bent. Also some Iroc wheels had different offsets front and rear, I believe they are marked though so as long as you didn't miss the markings you should be good to go. Good luck.

shuanm

I did put the fronts on the front and so on, but I don't have the thin spacer that goes on the back. Do I need it with drum brakes, or will the drum serve as the offset? I didn't really think the wheels would be the problem, but who knows with as many different setups as there are. I bet my alighment shop doesn't check caster. It doesn't track well, or recenter after a turn. I have a new gearbox and rag joint.

erick89camaroRS

hey im working on my 1989 camaro RS im redoing all my car from chasis to windows and i bougth some corvette rims aluminum polished 19x10 rear and 18x8.5 fronts and i would like to know what tires do u recomend me and where to get spacers at a good price and spacer sizes thanks!!

camarobird86

just curious, im lookin to getting the 20 inch iroc wheels for my camaro, but not sure what tire size, well actually the aspect ratio of the tires, i work at discount tire and have unlimited access to the wheels, but i was just curious on the tire size, i have mine lowered 1.75 inch and was just looking for someone with expirence in this field im trying to get into, lol.

Fords88Bird

Erick I had the wheels you have with 235/40 in front & 285/30 in rear with 2" adapters all around, needed to do a little hammering in inner fenderwell, sold those a few months ago. Got another set recently and put 255/40 up front & 275/35 in rear, I've heard guys going bigger front and back though. Camarobird a member named Sickness has experience with 20", maybe you can track him down.

pacocar

hi everybody i recently bought c6 wheels for my iroc 88 however i think i will need spacers but i dont know what kind i need and what size and if i will need to put them in the 4 wheels (car has 4 disk brake ) thanks for ur help

t1264rk

15x10 with 6.5 backspace