Automobile Engineering in ME
The main function of the tread pattern on tyre is that

The tread grooves pass air between the tyre and road surface, thereby preventing tyre from overheating
The tread pattern protects the tyre's inner carcass from small stones and pieces of glass
The crests between the tread grooves absorb road noise
In wet conditions, the tread grooves expel water that is drawn between the tyre and road surface

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Automobile Engineering in ME
The difference between DOT 3 and DOT 4 brake fluids is

DOT 4 fluid is more resistant to freezing than DOT 3 fluid
DOT 4 fluids have a higher boiling point than DOT 3 fluid
DOT 4 fluids have a lower boiling point than DOT 3 fluid
DOT 3 and DOT 4 fluids have the same boiling point, but DOT 4 fluid has a longer service life

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