Hi monster875:
I knew because I bought my first 240Z in March of 1970. The drove it across America. Started in Spokane, Washington and by the time I got past Idaho, I knew I had a problem with the tires. At Speeds above 70 mph they would shake you out of the car. Thought perhaps I had thrown some wheel weights...
Stopped at the first large town in Montana - no Bridgestone Dealer there, but they had a Goodyear Tire Store. We pulled a wheel/Tire off the car - and it was indeed out of balance. However no matter what was tried - it couldn't be brought into balance. Finally sat up dial gauges and measured radial and lateral run-run out on the wheels and tires.. The tires were out of round by quite a bit. That was true of all four tires..
So they wound up cutting about 3/32's of an inch off the tread..to make them round again. I went on across the top of the US to the Great Lakes, then South to Ohio. Once in Columbus, Ohio I finally found a Bridgestone Tire Dealer, as they were fairly new in the US back then... Since I had 3/32's of an inch of tread cut off - the Bridgestone Dealer offered very little allowance on a Warranty Replacement. So I then went to the closest Goodyear Tire Dealer and bought a new set of Goodyear tires... Drove from Ohio down to Florida, then from Florida back across the Southern US - to the West Coast - then up the coast back to Washington State.. The Goodyears were smooth as glass at 100+ mph..
Never bought another Bridgestone Tire until around 2006...
FWIW,
Carl B.