When a tire causes extreme vibration or trembling at SPECIFIC SPEEDS, say between 55-75, is that because of balancing, or a defect in the tire?

My 76 F-100 rides smooth as silk up to about 60, trembles like hell from 60-70, then smooths out over 70 mph. Is that the tire, or the front end? All my kingpins and steering components are good, I've always been a grease gun fanatic.
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NMCB 28 Seabee Battalion

Take it to a tire shop. I had a tire where the belts had seperated and was giving me fits...

you are experiencing harmonics that just happen to compond at that speed... you could have moisture inside the tire, or more likely, a ball joint or tie rod or alignment that acts up at that speed. does it do it on wet roads too? if not, it's alignment.. find a shop with a balancer that can add road force to the tire while on the machne...