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

In wet conditions, the tread grooves expel water that is drawn between the tyre and road surface
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

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Automobile Engineering in ME
A worm gear is used as the pinion for the rack and pinion type of steering gearbox, because it

Makes the steering more responsive
Allows the steering wheel to be turned by a greater amount when steering
Improves steering comfort when steering wheel is turned to effect small changes in the direction of forward motion
Reduces the amount of kickback for large steering angles

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