I was doing my own alignment on the 71 GS that I converted to front disc brakes and put new tires on. Got it done but maybe have to center the steering wheel a little closer to level but feels and drives good. So, I decided to check the 70 GS toe while I still had my tape measures and levels out. I discovered that my 70 with Wheel Vintique 15x7 Buick-ish wheels has a 72 1/8" measurement and the 71 with factory Buick 15x7 wheels has 72 7/8" measurement. Both have the exact same tires and typically the same level, stock ride height. The alignment is pretty close to the same, +5° caster and -1° camber. So, what accounts for the extra 3/4" or 3/8" per side? Are the Wheel Vintiques narrower or is the track different? Would 71 rotors vs 70 two piece rotors make a difference? It isn't a problem, I just discovered it and was curious.
It is likely due to differing backspacing between the factory wheel and the repop wheel. Factory wheels had ~4 - 3/8" backspacing. Most Wheel Vintiques 15X7" wheels will be 4" unless a specific backspacing was ordered.
You could put both front ends up,with the wheels off,and measure the distance from each wheel flange/surface. I have a set of of original 2-piece rotors on my 70,but I don’t have another car with the exact same brakes,with 1-piece rotors,to compare.
I think that would have the opposite effect. The Wheel Vintiques are on the narrower track. If they had less back spacing, it would go the other way. I might try that in the near future. Was just curious if anyone had an answer. I also have tubular upper control arms on both with tall ball joints and tubular lowers on the 70 with the narrow track.
I don’t think there are any two cars or frames that are exact to each other. Variances in machining hole placements,etc. could yield that difference in track widths.
