Car tires have numerous rating systems.
New car tires now also have ratings for traction, treadwear, &
temperature resistance (collectively known as UTQG ratings); as well as speed &
load ratings.
Some tread designs are unidirectional & the tire has a rotation direction
indicated by an arrow showing which way the tire should rotate when the vehicle
is moving forwards. It is important not to put a 'clockwise' tire on the left
hand side of the car or a 'counter-clockwise' tire on the right side. Tire
rotation moves tires between the different wheels of the vehicle as front & back
axles carry different loads & thus the tires wear differently.
Tire tread gauges are small rulers designed to be inserted into tire treads to
measure the remaining tread depth. Local legislation may specify minimum tread
depths, typically between 1/8" (3.2 mm) & 1/32" (0.8 mm). Wearbars may be
designed into the tire tread to indicate when it is time to replace the tire.
Essentially, part of the tire tread is shallower than the rest & will show when
the tire is worn down to that level.
There is currently an attempt to reinforce the tire with nanomaterial. This is
likely to increase the tire life, but may turn out to be a bad idea if the worn
out part of nanocarbon deposited on the roads is washed off & ends up in the
food chain.
