It all depends on where you put your priorities. If you want to get strong and build mass doing the 5x5, then doing cardio is not optimal as it does exhaust your legs as well as hinder recovery. You can still do it, by all means, but it's not optimal. The squatting isn't necessarily going to hurt your riding; more like the other way around. I will train my legs once a week, but volume is quite low--no more than four or five sets. Any more than this and I will experience DOMS which will make it very uncomfortable to ride.

Personally, I have been lifting for the better part of the last 30 years, always done cardio for 20 of those 30 years. In my youth I was just concerned with building mass, so I lifted heavy, ate a lot, and gained muscle, along with a good amount of fat. That was fine as that was my goal.

Now, I'm not concerned with gaining mass, but I am still lifting heavy, as heavy as possible in the 8-10 rep range. The goal now is to hold on to the lean mass that I do have and not to have it eroded away by the sheer amount of riding and running I do. At 5'9" and a fairly lean 145lbs (8-9%bf), my interest is just to maintain the status quo.