It depends on how long the dogs are chained for. If they are kept outdoors on chains 24/7 then yes by all means I think its cruel. If they are chained outside to go potty for brief periods of time during the day then not at all.
Theres an organization called Dogs Deserve Better that does everyuthing it can to get dogs out of situations where they are chained 24/7. I donate to them a lot!
You might want to check your local ordinances and state laws about tethering animals, too -- even our podunk little Texas town prohibits dogs being tethered between 10pm and 6am, and anytime certain weather conditions (extreme heat or cold) exist. And many cities across the US have banned tethering altogether. I'm not judging you for chaining your dogs, just urging you to check out dogsdeservebetter -- they really are a great organization and we support them too!
If the dog has a nice, weather-tight house, access to good, clean, fresh water, plenty of food, and several opportunities to exercise, then tying up the dog shouldn't pose any problem, but the dog also needs a blanket or something to keep it warm.
