PhysicalProperties.Friction cannot be assigned to?

Hello everyone! I have a quick question about coding the friction property of a part. I want to change the friction of each tire every single time when it touches parts named Red, Yellow Blue and Pit, however when I test this in studio, it doesn't change the value. After that I noticed that ROBLOX had changed their friction property into CustomPhyiscalProperties so I added that before friction and it still didn't work. Do you have an idea's on how to fix this?

function onTouched(hit) if hit.Name == "Red" then script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction - .005 script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction - .005 script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction - .005 script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction - .005 else if hit.Name == "Yellow" then script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction - .007 script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction - .007 script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction - .007 script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction - .007 else if hit.Name == "Blue" then script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction - .009 script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction - .009 script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction - .009 script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction = script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction - .009 else if hit.Name == "Pit" then script.Parent.Parent.Tire1.CustomPhysicalProperties.Friction = 1 script.Parent.Parent.Tire2.CustomPhysicalProperties.Friction = 1 script.Parent.Parent.Tire3.CustomPhysicalProperties.Friction = 1 script.Parent.Parent.Tire4.CustomPhysicalProperties.Friction = 1 end end end end end script.Parent.Touched:connect(onTouched)