Custom guys/galls aren't looking at your tires.. It's all up to you if you declare them or not. I can't count the number of things I've brought up and never declared.. Tires would be the last of my worries. Usually I do though, especially if I go over for a few cases of beer while visiting a buddy and maybe some nice steaks. 99% of the time, they don't care and wave me through, I think I've been stopped once for a case of beer and had to pay duty on it. If you want to declare them, by all means do it. You'll still pay less then you would here, which was the entire point in the first place.