I just put in some 42mm offset volk t37 17" 205/40 I have skunk2 coilovers with koni yellow. Since I put the new 17 up from stock 15 i get terrible ride quality the car is unstable at high speeds and the wheel follows every road irregularity. I have a feeling the geometry is off any advice ? ...What can I do or what is the problem?

 

go get an alignment done. That'll take care of it

 

thats what happens when you have sidewall size of a toothpick.
When you upsize wheels your sidwalls have less flex in them making the daily driving horrible experience, especially with stiff springs (anything above 250lb/in)
have fun