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Discussion Starter #1 (Edited)
Our Miata is a 1990; built July 1989; and we are the third owner. We bought at 242,000 km and it now has 256,000 km; 160,000 miles; and a vibration starts usually over 90 kmph when you go over a rough spot in the road. There are new BFG G force Super Sport tire in stock size and they have been balanced. I had the car safety checked at purchase; 242 K; and all suspension points were tight/within spec; and within spec for wheel alignment. Most driving in our area is 80 kmph speed limit, so only notice the vibration on the highway. The vibration is not a steering wheel shake. I finally took the car to the local Miata dealer and noted the problem. They had a Miata knowledgeable mechanic test drive it and he noticed the vibration. Onto the hoist and they verified all suspension is tight and alignment within spec. A second mechanic was consulted and they ran it to 100 kmph on the hoist and no vibration and the tires looked fine; tracking and no out of round issues. They made a small adjusted the PPF bar to spec and then retested on the road with the same vibration returning at about 100 kmph if you hit a small road imperfection. The conclusion of the mechanics was the springs have sagged and do not provide enough resistance to eliminate any vibrations as noted. The shocks are KYB stock units and from the few details provided at the time of purchase for previous parts/service done, they likely are 100K km plus.
I was looking at Tein GMS64 1USS2 Street Basis Coilovers; not currently availabe to the Canadian supplier; and they suggested HSD HSDMA05DT Dual Tech Coilovers as a better quality shock. The car is only used for pleasure drives, mainly top down drives; and I have no plans to autocross or track the car. I also have replaced the front ASW links and bushings and have a new set of MOOG linls and bushings for the rear ASW. I also installed the Cobalt front and rear chassis braces from MossMiata. Thoughts on the HSD coilovers? Thanks for any help you can provide.
 
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