I lift 3x/week and commute to work 22 miles each way 4 days/week. I don't ride after leg day. That being said, I think people are afraid of "overtraining", and that fear is overblown. If you are in decent shape, the cardio of riding is not a big deal. As another poster said, lots of people do cardio after lifting anyway. When I wasn't bike commuting, I still did 45 minutes of cardio after lifting. Go for it.