Quote:
Originally Posted by phunt
Changing from 185/7-15 tires (25.2” tall) to 205/55-16 (24.9”) would lower the car about 4mm. .3” difference in tire height. Half would be .15” since you are only dealing with the radius. Measurement a. From ground to center of the wheel. That would move your 212mm b height on US cars to about the 197 you say on Euro without changing the angle of the lower control arm or geometry.
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a is determined by the static loaded height of the tire not the tire OD, they all flatten to an extent that depends on PSI and sidewall stiffness. Sidewall stiffness depends on constituent material, design and wheel width the wheel width.
The a #s I quoted are the average static loaded height for the universe in my tire dB for that nominal size tire.
no matter how You choose to measure US 911 from '76 -83 were raised compared to RoW versions
The std. street spec for all 911s except those was 108+/5 mm, b w/ oe tires was 212 +/5 mm for cars that came w/ 185/70 by 15 and 197mm for cars equipped w/ 205/55 x16
the US cars for '76 & 77 would have 185/70 x15 and b of 221+/5 mm, a-b spec was 99+/-5 mm
specials like the '84 SCRS a-b spec was 144 +/5 mm and was 162+/-5 mm
'73 RSR a -b spec was 160, b was in the neighborhood of 130mm from the factory but each team did their own thing from there.