It had happened to me once, when i let a small pickup truck sit in a garage for 18 months, the Continental tires were NEVER the same after that, no matter what I tried. Was pretty depressing actually, as they still has plenty of tread left, but that thumpity thump thump ride drove me nuts and I ended up changing them out.

Because your tires are still sort of new-ish, is there any chance of getting a local tire dealer to warranty them, even if only partially so?

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2007 Dodge Ram 3500 Cummins Turbo Diesel 4x4
1994 GMC S-15 pickup 4.3 5MT
1985 300 SD
1978 300 CD
1962 220-S Fintail - awaiting restoration