This post compares the advantages and disadvantages of bicycle panniers and trunk bags in relation to one another.
The Advantages of Panniers
1. Enormous capacity
The main advantage of panniers is their enormous volume and capacity. Currently, there are panniers that go up to 90l and satisfy the needs of dedicated touring cyclists who carry half-a-house on their trips.
Also, you can install a total of 4 panniers on a bike (2 per rack).
A trunk bag offers substantially less volume. (The average trunk bag is about 5-10l.)
Therefore, if you plan to transport massive cargo, panniers win by a large margin over trunk bags.
2. Fully Waterproof
A set of quality panniers is 100% waterproof and would let water in only if submerged. Conversely, many trunk bags have zips and are only water-resistant. In a heavy storm, the bag may fail to protect its contents.
3. А Universal Quick-release System
The quick-release attachment of panniers works with all kinds of rear racks. Meanwhile, the quick-release of some trunk bags is proprietary and operates properly only with specific racks made by the same company.
4. Lower Center of Gravity
One of panniers’ strongest sides is that they are positioned closer to the ground. The result is a lower center of gravity providing greater stability.
If the rack comes with pannier rails welded a couple of inches lower than the main ones, this effect is even greater.
In different, a trunk bag sits on top of the rack and thus has a higher center of gravity that could potentially make the bike more unstable. In reality, however, this is difficult to happen because trunk bags are too small to carry truly heavy cargo.
The Disadvantages of Panniers
1. Uneven Loading (potentially)
The large capacity offered by panniers has a negative side. If one of the panniers is empty or lightly loaded in comparison to the other, the bike will be imbalanced and will pull the rider in one direction. The effect is a lot more noticeable when riding with one or no hands.
The only way to minimize this problem is to make sure that the cargo is evenly spread between the two panniers. However, this is not always possible, especially when your commute does not require a large amount of gear.
If you want to read more about single pannier loading, check out the dedicated article on the topic.
Panniers are easy to take off the rack when they come with a quick-release mechanism, but carrying them around isn’t the most comfortable experience even when they have a shoulder strap.
A decent pair of panniers will set you back a couple of hundred dollars. The investment is worth it because they will last you a lifetime. However, not everybody is ready to invest so much into bike gear right away.
Panniers notably hurt the aero properties of the bicycle by acting as a large parachute. The effect is stronger when the panniers are loaded to the maximum.
The Advantages of Trunk Bags
Unlike panniers, trunk bags are sitting in the middle of the rack and thus do not create uneven loading to the left or right.
Most people have a hard time filling a pair of panniers for everyday commuting. Truth be told, most commuters can fit most if not all of their gear in a trunk bag.
And if storage capacity is an issue, one can purchase a trunk bag with expandable pockets which increase the bag’s volume to very respectable levels.
On average, a trunk bag costs less than a set of panniers. Of course, the final price depends on the model and the brand. Some trunk bags are overpriced.
A trunk bag is neatly hidden behind the rider similarly to a saddlebag and does not increase drag as much as panniers. This is another quality of trunk bags which makes them suitable for riders who want to carry stuff but also go fast.
5. Extra Pockets
Most panniers are basically dry bags with an attachment mechanism. There are no external pockets for organizing storage and easy access to frequently needed items.
Conversely, trunk bags often come with external pockets, a bungee cord for bulky items (e.g., a jacket), and a mesh compartment for a water bottle.
The Disadvantages of Trunk Bags
1. Limited Capacity
The main weakness of trunk bags in comparison to panniers is the limited cargo capacity. If you have to transport a lot of baggage, trunk bags just won’t cut it as they’re a light-duty storage option.
2. Quick-Release Issues
The quick-release of trunk bags works best when the bag and the rack that it sits on are made for one another.
Also, some trunk bags do not have a quick-release mechanism and attach to the rack via Velcro loops. This is a secure mounting system but makes commuting with a trunk bag less enjoyable because you can’t just get off the bike and grab the bag (which is the case for high-quality panniers such as Ortlieb Classics and the likes).
Trunk bags have zips and are made of non-fully-waterproof materials. Hence why many trunk bags come with a separate rain cover.
4. Higher Center Of Gravity
A trunk bag is placed on top of a rack – a position that results in a higher center of gravity and subsequently instability.
In practice, however, this is rarely a problem because trunk bags do not have volume for truly heavy cargo.
5. Interfere with Seat Post Accessories
A trunk bag may interfere with some seat post accessories like a clip-on rear fender or a light.
This issue can be circumvented by installing a full fender which works better than clip-on models anyway and by placing a rear light directly on the bag (most trunk bags have a dedicated mounting spot for a rear light).
When To Choose Panniers
Panniers are a good choice when:
1. You have to transport lots of cargo.
2. You need maximally waterproof storage compartments.
3. You don’t mind the extra drag added by the panniers and the inconvenience that comes with carrying them around.
When To Choose a Trunk Bag
Trunk bags are a good solution when:
1. You want to travel light and fast.
2. You don’t have a lot of cargo to transport.
3. You don’t have seat post accessories that interfere with the bag.