The present invention is directed to a pneumatic tire comprising at least one component, the at least one component comprising a rubber composition comprising a diene based elastomer, from 1 to 30 parts by weight per 100 parts by weight of diene based elastomer (phr) of cellulose fiber, and from 1 to 20 phr of a substituted polyisoprene comprising units of formula I, wherein --R comprises hydrogen and one substituent group of structure II ##STR00001## wherein the number of substituent groups of structure II occurring per substituted polyisoprene molecule ranges from 8 to 12, and the weight average molecular weight of the substituted polyisoprene ranges from 20000 to 30000.