New tires need some miles to get settled on the rims. It may occur that the wheels start to shudder after a while and they need to be re-balanced. That is perfectly normal...and that probably causes your 60mph shuddering.
I have renewed my C250D steering damper once by now. The car has run 365.000km. You can check the steering damper by loosening it on one side and push/pull it a couple of times. If it is rather stiff in pushing and pulling it is still all right.
You will notice when the steering damper is worn...
with a minor 600+k