Originally Posted by cyccommute

Do you need them? Probably not. Does the bike handle better with front bags? Definitely yes. Given the choice, I’d use low mounted front pannier over rear panniers. Even with 4 panniers, the fronts are more heavily loaded than the rear.

Look at it this way: the rear wheel is already heavily loaded with the rider. Putting more weight on the rear with all of a touring load puts that weight even further back. This lightens the front wheel and can make steering vague. A heavy rear load will also cause the rear to sway. The tail starts to wag the dog. Putting the majority of the load (or at least the small heavy items) up front and down low tames that wag.

Adding a some kind of bag to the rear rack and filling with stuff makes the problem even worse. If the bag on top of the rack is to carry a tent and/or sleeping bag, don’t bother. Get a dry bag for the sleeping bag and just use the stuff sack for the tent. I’ve pedaled through 70 miles of driving rain with that arrangement and had a dry bag and a dry tent at the end of the day.