Here is a good article that covers a lot of issues with tires:
http://www.ehow.com/how_5077858_check-tires-maintain.html
No, tires have treads.
Yes, all vehicle tires have treads on them. Truck tires will usually have larger and deeper treads than regular sedans.
The treads are generally about a half inch deep. To check for safe tread depth use a penny, if you can't see the top of the head of Abe Lincoln then the tread is fine.
The answer is: have
Bike tires have hairs on them, called treads, to provide better grip and traction on different surfaces, like roads or trails. The treads help the tires grip the ground and prevent slipping, especially in wet or slippery conditions.
Tires are pro-rated based on the amount of wear they have. This is largely determined by the depth of the treads.
Because the rubber in tires was being used for war supplies including tank treads and jeep tires.
Because the tire is very thin when there are no treads unless they are racing tires and it is very dangerous
If the treads lack definition and/or if the car "pulls" to the left or right.
They are 255 mm wide over the treads.
You will lose traction especially on wet roads.
A tank uses caterpiller-like treads instead of tires, because the treads give much better traction when traveling cross country (where most tank battles take place).