When you are in the settings menu go to the "change parts" button.
Select "Suspension"
Click on "Full Race" Suspension.
Your settings should be back to the original or "stock" values.
This also works with all other settings except TCS and ASM, and Downforce.
Hit the Search button above and to the left and type in "stock settings" I created a thread on this ages ago. Should be a tiny bit more explanatory.