Firestone Destination LE2 is absolutely the smoothest riding tire I've ever run (at least the last 20 years or so I can remember), with very low steering effort needed. 215 75-15 as pictured. Street tread, light duty.

I've got a set of 16 inch wheels with larger diameter 215/85-16's Capital H/T's I run about half the time. Steel belted but ride like bias plys in comparison to the Firestones.
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Matthew 6:33

1952 Chevy 1/2-ton 3100
Late '55 235/SM420/torque tube 3.55
Dalton Highway survivor (using original 216)
www.truckwithaheart.com