Some cars are even sold with tires that already have those green caps on the tire stem because they automatically come with nitrogen according to Consumer Reports. That said, nitrogen comes at a ...

Some cars are even sold with tires that already have those green caps on the tire stem because they automatically come with nitrogen, according to Consumer Reports. That said, nitrogen comes at a ...

Green caps on tire valve stems usually mean the tires are filled with nitrogen instead of ordinary air. ... The absence of moisture in dry nitrogen ensures a more steady temperature inside the tire.