Larry, That chart cant be correct. It shows the 70 WG wheel to be the same backspace as the 71 up. Which I don't believe they are.
Now hold on. That chart can't be correct. I hought that the backspacing changed as between the '70 WG's and the '71 & later 15 x 7 x4.75 Rallys. To be sure, BOTH were 15 x 7's and, yet, the outer circular rim on the WG's stuck out further than on the '71 & later 15 x 7 x4.75 rims and the inner wheel centers on the WG's were, therefore, clearly INSET FURTHER than the '71 & later 15 x 7 x4.75 rims. So, with the WG center portions of the wheels having a different position as to the outer rim portions .... and the outer rings of the wheel were the same 'drop-center' design with the WG's and the '71 & later 15 x 7 x4.75 rims, it doesn't make sense that the both rims shared the same backspacing. The rim centers were in different positons.
Ok, here's the answer. You can go to George N's site for an article explaining the special features of the WG wheels for 1970, but here is a quote from that article (HERE): "Notice in the photo that the quarter overhangs the edge of the inner lip. The difference in the offset is 3/8" . WG wheels have a 1" lip while the standard 15" rallye have a 5/8" lip. The backspace on the WG wheel is 4" and the 71-up wheels are 4 3/8"
I have physically measured nearly two dozen original 1970 15x7" chrome wheels, with both the early "7.0" and later "WG" codes. There have been slight variations, some being 4.375" (4-3/8"), and some being 4.4375" (4-7/16"), but most were dead on 4-3/8". It must be understood that both the wheel center, and the wheel rim changed in dimension after the 1970 model year. These dimensional changes eliminated the "ledge" which would hold a quarter on the 1970 wheels. The 1970 rims carried a code of 890, and the 71-up rims carried a code of 903. Replacement rims being installed on current reproduction wheels match the 903 code rim very closely. To my knowledge no current rims are available to match the dimensions of the original 890 code rims. I had Steve Caruso re-rim a set of 1970 wheel centers, and he had to set the back spacing at 4-1/2" to make the wheels match the appearance of the WG wheel due to the difference in rim dimension.
All 15x7 Buick rally wheels that fit 4 3/4" bolt circle are 4 3/8" from the mounting surface to the innermost lip of the wheel. This can vary by about 1/16" due to the fact that the edge of the lip is not a controlled edge. The rim shell is the same on every one of these wheels as well. The difference is in the wheel centers. All 14 and 15 inch wheels up to 1970 had flatter centers. 71 thru around 82 were the same again either 14 or 15 inch. Then around 82 and newer the center got taller by 1/8". I've measured and cut apart nearly 400 wheels. Thats how I know.
Steve, So, on the new repro Ralleys what should the rear backspace be to match the WG look as closely as possible?
Jim. That will depend on which wheel centers are used. These pictures show an original 3-31-1970 WG wheel (left), and one of Steve's repro wheels which has a new rim on an original 1970 wheel center (right). They are closely matched in outward appearance, but the repro is set to 4.5" (measured 4.502") backspacing. If you are to use 1971 and later centers, it may require a different backspacing dimension. Note in the second photo the difference in the original and repro rim. The dimensions are slightly different, and the flat recessed area to which the center is welded is wider on the original. Note the F9 code on wheel center indicating June,1969.
Pretty much just as Jim explained. If you use a true 1970 and older center and set it with 4 3/8" BS it would look like an 8" wheel from the front. If you use a 1971 and newer type center set to 4 3/8" BS the ledge would look like a WG wheel except the center would look deeper because it is.
Some years back I had Wheel Vintiques build a set of 15x8" wheels for me with back spacing set to 4-3/4". the later (71 up) wheel centers were used, but at this point I don't remember the exact year of the centers. The "ledge" which people reference when d0ing the quarter test, was pretty close to that of a WG wheel. The outward appearance looked close, but the wheel center just looks wrong for a 1970 wheel. I'll try to get a photo today.
This photo is a quarter on the 15x8" wheel with 4-3/4" backspacing. This shows a quarter on an original 1970 WG 15x7" wheel. 15x8" Wheel again, with a rule on "ledge". Flat area from center to radius is approximately 1-1/4". And the WG wheel shown with rule. Flat area from center to radius is approximately 1". So in terms of simple mathematics, were a later (1971-up) center welded into an new 8" wide hoop with the back spacing set at 5", the front "ledge" dimension would closely match that of a 15x7" WG wheel. I apologize that I don't have 71-up 15x7" wheel, original or repro, to compare. But assuming the dimension of a new 7" hoop matches a new 8" hoop from the front lip to the flat "ledge", which is a big assumption, back spacing would need to be 4". Hopefully someone with such a 15x7" repro wheel will chime in.
I had nearly forgotten about a pair of repro 15x8" wheels I had squirreled away in the basement. In this photo the repro 15x8" (left) is aside the 15x7" repro from Steve (right), aligned at the front edge. It appears the entire additional width of the repro hoops is to the rear. This would indicate the front dimensions are identical, or nearly so. This would support the assumption of needing 4" of back spacing on a repro 15x7" built on a 1971-later center. As a precaution I would ask here first though, if anyone has photos of a such a (15x7" w/4"BS) repro.
Most likely they don't know the difference. But yes they would probably be using the newer cores. They would be less rusty and more of them available.
Can you explain the difference in the 70 and earlier and 71 and later centers? I just cant see the difference.
The triangular stamped pockets that the lug nuts are in are deeper. Look at the steps by the windows. Also the chrome ring around the pockets is a little wider. Measure from the rim shells drop center to the window in the center. If you do a search on V8 you should find the several posts about the differences.
