Let me ask a couple questions..

What type of tire?

How old are they?

What tire pressure?

What temp do your warmers go to?

Sounds like you might have been experiencing cold tearing. I had the same trouble with my tires the first day at HPR but after bumping up the rear tire pressure, the problem went away. Unless you are down to the tread depth indicators I think you should be fine running these tires still, given they are newer tires not old takeoffs from last year.