Which side to have one pannier if trying to minimise spoke load on a disc brake bike?

Question

I have a (non-electric) disc brake bike with 28mm wheels with quite a heavy NuVinci hub and am on the heavy side (maybe 130kg with me, bike and pannier).

The whole set-up is at the limit of wheel strength design and my previous wheel popped spokes and I had it rebuilt with a rim with extra strengthening around the spoke holes (sorry forget the exact term) as well as electric wheel spokes (I think 2.3mm throughout?) to give me the strongest wheel possible.

The whole exercise made me think about spoke loading and which side of the bike to have the pannier on as I only ever use one (and I don't want to have the hassle of two half full ones).

I sat down this morning and scribbled a force diagram and I got to this conclusion.

1. Putting the pannier on the drive (i.e. right) side of the bike increases spoke tension when pedalling and decreases spoke tension when braking vs. no pannier.

2. Putting the pannier on the brake side (i.e. left) side of the bike increases spoke tension when breaking and decreases spoke tension when pedalling vs. no pannier.

3. Spoke loads induced by breaking are higher than those induced by pedalling as you tend to brake quicker than you accelerate.

Therefore if the goal is to minimise chance of popping spokes you should mount your pannier on the brake side of the wheel.

Do people agree with this or have I messed up a sign somewhere in my force diagram and the exact opposite is true?

And please I know there are lots of other things I could improve in my set-up to reduce chance of breaking spokes (lighter hub, bigger tyres etc., diet!), but I like the set-up just the way it is. I want it to work as it is but don't care which side the pannier is on so my goal is helping it with that.

Many thanks in advance.

Answer 1

1. Spokes usually don’t simply break because the forces get too high (i.e. above their yield strength). What really kills them is when they repeatedly get unloaded which allows them to move and rub at the hub. It can also allow them to loosen over time which makes everything worse. So what you need for the wheel to live long is sufficiently high and even spoke tension and the load must not get high enough to unload spokes.
2. I think the torque on the rear hub is higher during acceleration than during braking. During braking the rear wheel locks up pretty quickly because the bike tips forwards. Depends a lot on gear ratios, how strong you are, weight distribution etc.
3. I think what’s pretty bad for the rear wheel is when you have luggage, sprint out of the saddle and start throwing the bike left and right. With my 28 spoke rear wheel I think I can actually feel the wheel flex (or maybe it’s the frame). Wheels are pretty weak against forces from the side because the spoke angles are so steep. That’s why you can (almost) unload spokes with just your static body weight when applied from the side like this. Can be used during wheel building to properly seat and untwist spokes.
4. Hitting bumps is pretty bad, especially with completely unsprung mass like a pannier on the rear wheel.

So I think the worst case scenario is actually a combination of all four: Hitting a bump during acceleration while you are out of the saddle and throwing the bike around and doing so repeatedly.

I don’t think it makes much of a difference if your pannier is on the left or right side, especially with your NuVinci hub which should be pretty symmetrical. The overall center of mass doesn’t change much anyway, even with a heavy load in one pannier you barely have to lean to the left or right to counteract.