Could possibly be wheel run-out relating to the spacers.
All the balancing in the world wont fix it if it is.
Jack each corner up & check each wheel at some point on the rim for run-out.
You will need a dial indicator attached to either the car or something that won't move.
Similar process to indexing a brake rotor.
You may be able to fix it with cleaning all the mating surfaces inc the wheels & indexing the spacers, or maybe not.
P.S. your spacers are trying to Kill you.
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08 Skyline 370GT SP Coupe 5AT: Diy TT
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