I often get the question from new cyclists wondering whether only having a pannier bag on one side of the bike causes unbalance. I have always only used my pannier bag on the left side of my bicycle - the opposite side to the chain - and never felt unbalanced, but i thought i'd do a little bit more investigation to see what other people thought.
Bev from Stack Exchange says: I carry one if it's just a few light things and it's never a problem. If I have a good load (over 10 or 15 pounds?) I prefer two panniers only for getting on and off the bike and for stopping at lights. If you're only taking 1 bag I recommend putting it on whichever side you lean to when you stop at red lights!
This is what Lovely Bicycle says: Speaking from personal experience, my answer to the first question is "Usually, no." When riding an upright commuter bike - even a fairly lightweight one like my 25lb mixte - I simply do not feel the asymmetrical pannier load (typically 10-15lb on the lefthand side - though on other bikes I've tried as much as 40lb) once the bike is in motion. I do feel it when walking the bike. And it makes keeping the bicycle upright on a kickstand tricky. But once I put foot to pedal, the weight more or less disappears and I think nothing of it. Even when cornering, I've never felt it to be a problem on this type of bicycle.In general, I would say that the average utility bike can certainly handle uneven rear load distribution, and as long as you feel comfortable with the bicycle's handling there is no need to worry.
Griffin on Bike Forums says: I never ride with two. It is hard to walk the bike or carry it down the stairs with only one loaded down, but I have not noticed anything while riding.
Flatlander on Bike Forums says: I ride with one Ortlieb pannier every day to work, 10 mi round trip. It's moderately loaded, maybe 10 pounds. it works just fine and i've gotten totally used to it. I don't want to corner sharply like on my road bike, but you don't need to do that on a commuter anyway. It actually only feels weird on the weekends, when i ride my road bike without the ortileb pannier. it's like i have trained myself to ride with it there and it only feels different getting used to it not being there! funny
It seems that its all a matter of what you get used to. Riding with just one pannier bag is more efficient for normal city commuting because you then only have to remove and carry off one single bag. Some people do find it a little unbalanced when the bag is really heavy, but, most people don't notice the difference at all. My advice is that it may take some getting used to, especially when you first start using a pannier bag (as opposed to a backpack for example) but once you get used to it, it will not cause any problems.
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