The Z51 spring rates were much too hard for everyday driving. After the hoopla surrounding the introduction died down, owners started complaining about the Corvette's harsh ride. The car magazines, universally euphoric at first exposure to the new Corvette (at a smooth Riverside racetrack in California, by the way), changed their tune after extensive road testing. They became critical of the Corvette's ride quality, Car & Driver calling it an "F16" kind of car, unsuitable for "civilians." Rough ride wasn't the only problem brought on by the hard suspension; the 1984 was notorious for squeaks and rattles.
Chevrolet reacted quickly. The springs for both Z51 and base suspension 1985 models were softened, so that the Z51 in 1985 rode much like the base suspension of 1984. In 1986, the base suspension was softened again. In 1987, RPO Z52 combined softer base suspension springs with performance items previously part of the Z51 package; things like wider wheels, heavy-duty cooling, and quicker steering. To keep hard suspension models out of unsuspecting hands, Chevrolet started making four-speed manual transmissions mandatory with the Z51 option starting in late 1986. Even as spring rates were reduced, the Corvette's handling improved overall (skidpad numbers did drop a bit) as engineers were able to tweak and tune other chassis components.
89ZZ4 said:Bullwinkle: Look under Knowledgebase/then 1984-96/ then Chassis and Suspension/ then 84-96 Suspension Chart/ then Link. Takes you to Hib's chart with the spring rates/ bar, wheel, tire, shock specs.
Stop by this weekend and drive a stone stock Z51 to compare with yours.
Phil (aka 89ZZ4)