The present invention relates to a tire wherein at least one of the tread, steel-cord skim stock, sidewall and carcass portions contains a rubber composition formed by curing a blend of a. natural rubber, polyisoprene or a mixture thereof, b. butadiene rubber, styrene-butadiene rubber or a mixture thereof, c. carbon black, d. activator, e. zinc oxide, f. sulfur or a sulfur donor, and g. curing accelerator, characterized in that said rubber composition has a heat buildup of 20-35 DEG C. These tires exhibit one or more improvements in a wide variety of properties. The present invention relates also to a belt which contains such a rubber composition, characterized in that said rubber composition has a heat buildup of 10-25 DEG C. These belts exhibit also one or more improvements in a variety of properties.