Page created by MRHZV8 January 28th 2005:
Here is the answer to the age old question:
Q. Will commodore mags fit on my HQ-WB??
A. NO!!! here is the reason why.....
It is quite important to get the terminology correct when ordering or inspecting new wheels (or second hand)...Offset and Backspace are different terminologys that describe the same thing....Offset is the distance between the rims centreline and mounting face...if the mounting face is exactly in the middle, The wheel has zero Offset....If the mounting face is closer to the back of the rim/mag, The wheel is said to have negative offset....Naturally if the mounting face is further towards the front,then the wheel has a positive offset...Older cars (LIKE OLD HOLDENS) use negativley offset wheels (DEEP DISH)....While newer cars (LIKE COMMODORES) use a positivley offset wheel...Backspace is simply the measurement from the wheels/mag mounting face to the back of the rim/wheel.....PCD- pitch circle diameter is the imaginary circle that passes thru the centre of the wheels mounting holes....Falcon has a 5 on 114.3mm PCD while commodore has a larger 5 on 120mm...PCD is independent of the number of studs,you could have 4,5 or 6 stud wheels on the same PCD....Finally the last one is the wheel spigot or centre bore (THE HOLE IN THE BACK OF THE WHEEL)...The wheels spigot SHOULD fit the hub reasonably but, in an old Holden, it is the studs that carry the car's weight. Other vehicles have "Hub-centric" wheel fitments, old Holdens have "Stud-centric" wheel fitments. Even despite this, older-style mag wheels that use shank lug nuts are illegal(in some states).
48-215 (fx) - FJ: 5 on 162 mm (6.375") Backspace: 2.875 inches on the early - pre-1951 - 3.5" wheels and 3.125" on the later and much more common 4" wheels (Thanks to Eric for this information). Converting this to Offset, we have 29.85 mm positive offset for the early (3.5") rims and 25.87 positive for the later 4" rims. FE - HR: PCD 5 on 107.95 mm (4.25"), Offset 6mm positive.
HK - HG: PCD 5 on 107.95 mm (4.25"), Offset 30 mm Positive (except HK and HT GTS which had an Offset of 13 mm Positive, HG GTS went to 30 mm Positive)
HQ - WB PCD: 5 on 120.65mm (4.75"), Offset 30 mm Towards the inside of the rim for standard offset wheels.
Torana LJ/LC, LX/LH: PCD 5 on 107.95mm (4.25"). Same stud pattern as HK-HG.
Torana LH with option L34 and LX with option A9X: PCD 5 on 120.65mm (4.75") with -1/4" Offset. Same stud pattern as HQ-WB with a different offset.
So, it seems that it was only the HK and HT GTS Monaro Coupes that had a different Offset in the HK to HG models. The Track on an HK is narrower than either HT or HG, so there must have been some difference in the suspension or suspension mounting points.
Commodores use a 5 on 120 mm (4.724") PCD. Very close to the HQ - WB PCD but not close enough. If you put Commodore wheels on an old Holden (or vice versa), you will break your studs and be overtaken by your own wheel...not a good look.
What PCD do I have? The calculation for any five stud P.C.D. is from the centers of two of the closest studs divided by 0.58778 pretty hard to do by eye as Commodore an HQ are close, but if you have a vernier and measure from the outside of one stud to the inside of the next one is pretty accurate. To accurately measure your PCD. for 5 stud pattern. (in metric) measure as accurately as you can the distance between the centre of one stud to the center of the next closest stud, and then using a calculater divide that measurement by 0.58778 to attain your PCD. Be carefull to measure as accurately as you can because, for example, HQ is (close to 71mm) 70.915657 divided by 0.58778 = 120.65 (4.75") PCD. Commodore is (close to 70.5mm) 70.5336 divided by 0.58778 = 120.00 (4.724") PCD. To go from metric to imperial divide by 25.4. When measuring the stud centres you could also measure to the outside of both studs and subtract one stud diameter.