Carlisle Trac Chief 14 - 17.5 R4 Tires Sidewall Cracking

Has anyone else had the sidewalls crack on their rear tires? I have a new (18 months) 2520 and noticed that the rear Trac Chief tires have cracks all round the sidewall on both tires. I store the machine in a climate controlled garage all year and only have 50+ hours on it.

Is this a concern or just cosmetic?

Thanks

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