Credits: HI5__Shadow (or atleast the first person I saw doing this)
NOTE: THIS MAY/MAY NOT BE EFFECTIVE DEPENDING ON WHAT YOU'RE TRYING TO TUNE. THIS MAY BE COMPLETELY VISUAL.
Step 1: equip stage 1/2 of the part that you want to glitch the tuning of.
Step 2: go to the tuning slider (s) you want to glitch. Put the button at either of the extremes, until it touches the black bar.
Step 3: now equip stage 3/4 of the part you glitched the tuning slider of.
You now have more options to tune your vehicles, as the button(s) are in the 'half plane existence' now. The max you can go with this is 9.5, and the least is 0.5. going furthir or below resets the button to usual. This may or may not be significant depending on the slider of the part you're tuning.