See also:

Treadwear indicators
Narrow bars (tread wear bars) that are distributed over the tire tread. If the tire tread is level with the bars, the wear limit of 1/16 in (1.6 mm) has been reached. ...

Problems with the engine
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Important safety notes
WARNING Gasoline and diesel fuels are highly flammable and poisonous. They burn violently and can cause serious injury. Never allow sparks, flames or smoking materials near gasoline or die ...