please bare with me on this one. i ve search and still dont all the way grasp the concept. i hope someone can take the time and straighten me out. on our cars can you describe what rims will fit on there without modification, like grinding the caliper, will any 4.75 bolt pattern work and will it only work. im guessing the smaller the backspace the wider the rim. i seen some pretty nice fwd rims that i think meet all the specs, will they work. help me out, tell me what to look for and how to understand. thanks a whole bunch ahead of time.

 

First, you need to be able to bolt the wheels on the car.... that requires that you have a wheel with 5 holes on a 4.75" bolt-circle. As long as you have that bolt-circle, and the hole for the "hub" in the rear of the wheel is large engouh, the wheels will fit correctly. I mention the hole in the back of the wheel because the early (93-95?) F-Bodys have a problem with the rear axle hub being about 0.030" larger in diameter than the front hubs. This was correct on later years (96+), and only becomes a problem when you try and put a set of 99 wheels on a 94 car... the inside of the wheel hole needs to be ground or sanded slightly to allow the wheel to fit over the hub on the rear axle. This will not hurt anything... the wheel is "centered" by the conical lug nuts, not the hub.

Note that 4.75" can also be expressed in milimeters, and 4.75" = 120.65mm. I believe that BMW wheels are 120.00mm bolt-circle, and some people have used these on 4th Gens. I'd be very cautious about doing this, since you might have a problem with the lugnuts coming loose or wearing the wheel.

Next, you need to look at the width of the wheel. Our cars came with 8" (all except WSW6/SS) or 9" (WS6/SS) wide wheels, with a 55mm offset. Remember, the width of the wheels is measured between the edges (flanges) that hold the tire on. An 8" wide wheel will actually measure closer to 9" wide on the outside, because it includes the bead width of the tire AND the width of the two flanges.

Offset tells you how far the hub of the wheel is moved outward from the "centerline" or the wheel width. That is what you see in a "front wheel drive" wheel, where a large positive offset is used, moving the wheel center disc outward toward the edge of the fender. The 4th Gens use a wheel offset similar to FWD cars. There is not much "dish" to the wheels, taking away the agressive, deep dish look of earlier muscle cars.

Offset is expressed in "milimeters" and 25.4mm = 1-inch.

Backspace can be calculated from "offset". Take the "nominal" wheel width (the distance between the tire bead retaining flanges), and divide it in half. For a stock wheel:

8 / 2 = 4

Then add the offset:

55mm /25.4 = 2.17"

4 + 2.17 = 6.17"

Then add the width of the flange that retains the tire, usually in the range of 0.45 - 0.50":

6.17 + 0.45 = 6.62"

The "backspace" of the stock wheel is about 6-5/8"

 

holy crap, i think i got it now. ill have to print this out for sure. thanks a bunch.

 

so will 17 X 9.5 wheels with 275/40-17 tires fit no problem. They should just bolt right up?

 

i'm getting 17x9.5 all the way around with 275/40-17 all the way around. Boyd Coddington Blaster wheels and Firestone Firehawk tires.

 

They will bolt up if they have 5 holes on 4.75", and if the hole in the back of the wheel is large enough to fit over the hub... exaclty what I said above.

Whether the tires will rub depends on the "offset".... exactly what I said above. If you get the wrong offset, the wheels could stick out of the fenders, be in so deep they hit the steering knuckle, or something in between, where only the tires rub.

What is the EXACT offset and backspace of the wheels you are buying? If the offset is between 45 and 56mm, there will be no major rubbing.... that's essentially the same as the stock WS6 and SS wheels, which come with 275/40-17 tires.

 

yea they're 4.75 with 55mm offset

thanks for all the help.

 

55mm offset is about perfect.... they will sit just where the front tires on my car sit:

Front - 17x9.5 56mm offset

Pic #2

 

Ok I understand most of this stuff now but how do I know what the offset is for the rims I want? The website doesn't say it...as a matter of fact...none of the sites I look on have the offset for the rims I like. They are 17x9 ROH RT's. I'm sure they have the right bolt pattern for that rim too cuz they prolly make more than one bolt pattern. I've seen those rims on a camaro on car domain b4 so.....ya know

 

that's one reason i got boyd coddingtons they're custom made to fit ur car. but u pay for it lol

 

Go directly to the manufacturer's website - not a vendor. I know Weld had extensive charts showing various width, backspace and bolt circle choices. If they give you "backspace", you can calculate the approx. offset as described above. Or simply send a tech question to the manufacturer.

 

I got myself some Weld Pro Star XPs with 15x10 in the rear with 5.5 backspace. Reminds me of the early 70s, yeehaw billy bob them tires is stickin out just right.
Nobody but me likes it but tough titty.