If you have ever cycle toured with gear before, you’ll understand the importance of weight positioning on bike stability. This is most evident when your stopped at a light struggling to keep the bike upright before kicking off again. Or when trying to keep the bike on track when navigating a narrow winding trail at low speeds.
Effects of Side Panniers on stability
As a structural engineer, I understand that how you pack and position your gear affects bike stability. One way to increase stability is to place gear weight evenly on both sides of the bike. Another way is to get the weight as low to the ground as you can. The lower the weight the more stable the bike.
The reason for this is that placing weight higher increases the horizontal lever arm. This occurs as the bike rotates or leans over. And this lever arms impacts the overturning moment (Mot) and the overall stability.
To help understand how this works, see the schematic free body diagram of a bike with rectangular side panniers. The diagram below shows the forces in play.
Sketch showing side panniers and forces in play
Schematic showing how panniers affect bike stability
The overturning “moment” is equal to the weight (F) times the distance (d). When the distance d increases the moment also increases. The overturning moment for a bike acts about the point where the wheels touch the ground. This is indicated as point A on the sketch.
In the balanced vertical condition, the sum of the overturning moments about A is equal to zero (Mot=0). Here, each side panniers must weigh the same. The distances d1 and d2 must also be the same. If these conditions are met, the overturning from one pannier will counteract the other.
But as the bike leans over, the overturning moment Mot about A increases. This increase in moment is equal to the weight of the pannier “F.” It is multiplied by the horizontal distance. This is the distance that the center of gravity “cg” of the pannier is away from “A.” Refer to distance “d1” and “d2” in the sketch. You can see that in the leaned position, d1 has decreased and d2 has increased. The net difference between d2 and d1 multiplied by the weight F equals the net overturning moment about A.
Keep the “cg” of your gear as low as possible in the side panniers. This helps to reduce the difference between d1 and d2 as the bike leans. It reduces the overturning moment. This can be achieved by packing heavier gear (food, water, tools etc.), low in the side panniers.
Adding a Rack pack or Bar Rack for bike packing
Now if you add a high rack pack, the impact of its weight on stability can be dramatic. Adding a cantilevered bar rack will also impact stability significantly. In the sketch below, the offset distance d3 increases. This happens as the (cg) of this pack is located higher above point A. In addition, when the bike leans, the overturning moment increases. This is because there is no counter weight associated with this pack.
Sketch showing Rack pack / bar rack added to touring set up.
bike stability sketch when touring with panniers and bar bags added
So to minimize the impact on overall bike stability, keep the weight of these packs low. It’s important to keep the weight of these packs to a minimum.
In summary, the following considerations are key to minimizing the affects on stability of a bike touring set up :
- keep heavier items as low as possible in side panniers
- If a bar or rack pack is important to your setup, position them as low as possible on the bike. Keep them lightly loaded.
- Maintain a balanced weight for each of the side panniers.
Happy touring!
