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Physics geeks: Effect of unevenly loaded panniers?

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Physics geeks: Effect of unevenly loaded panniers?

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Old 11-05-09, 02:40 PM
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cccorlew
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Physics geeks: Effect of unevenly loaded panniers?

I'm arguing with my office mate who also bike commutes.

He says I'm a dangerous fool because I don't bother to evenly distribute the load between my two panniers. Indeed, I sometimes load a bunch a papers on one side, and not much on the other.

I contend I can't feel it, and it doesn't matter. He says that being unevenly loaded could cause a problem in a corner, a big wind gust or an uneven surface.

He even got a science guy at our college to support his viewpoint.

I contend that the weight is relatively close to me, and being as I can't feel it, it really doesn't matter.

Weigh in. Science facts will help.
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Old 11-05-09, 02:52 PM
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I can attest that I ride with one pannier on the non driveside that is usually around 12lbs and do not really notice. I did notice when I first started but don't now. I do not think it is dangerous unless your rear stays are really flexy or your rack is trash. For what it is worth without a single non driveside pannier your drive train still has weight so is it unsafe to bike then?
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Old 11-05-09, 02:53 PM
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It doesn't matter because your bike handling compensates for the uneven weight. If you load up one side and not the other, you will just lean your bike slightly towards the lighter side to maintain balance. I often ride with one pannier and I don't really notice the difference while riding either.
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Old 11-05-09, 02:53 PM
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Sorry, no science to back me up. All I have is my own personal experience. I usually only have one pannier on my bike. I don't even notice it unless there is a huge load in there, (i.e. a gallon of milk or a bunch of canned goods).

The differential between the two sides becomes more noticeable at lower speeds and I usually try to ride fairly quickly.
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Old 11-05-09, 02:58 PM
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Non scientific:
I was riding home with groceries yesterday. Baguette and eggs on one side. Beer, milk, canned goods, fruit etc on the other. 15-20lb differential. I found it hard to take my hands off the bars to do up my jacket zipper. Bike was significantly leaned to compensate for the load.
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Old 11-05-09, 03:01 PM
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Science: yes, it matters ever so slightly.

Real life: Inconsequential.
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Old 11-05-09, 03:03 PM
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If you were to pack say 60 Lbs on one side and none on the other you might have some problems, but otherwise its no big deal. When I leave for work one side had cloths the other side has lunch. Lunch includes a thermos with milk, and possibly a few cans of pop (I take them in batches). I might have a 10Lbs difference at worst. I do notice it a bit when going over the speed bumps in my neighborhood so I take those slowly, otherwise you'll never notive.

Clearly your co-worker has never been to Holland. Just stand outside the train station in Amsterdam and I guarantee you that within a minute you'll see some dapper young lad come by and pickup or drop off a girl friend. The young ladies always sit on the super heavy duty european rear racks with their legs to one side... talking about balancing a large asymetric load. The Dutch has been doing this for over a hundered years. Clearly the bike is a pretty easy thing to ride.

Happy riding,
André
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Old 11-05-09, 03:32 PM
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Ask him if he has taken into account the fact that the pavement is not level, but roads are designed with a crown in the middle so that rain runs to the gutters. As a result of that, a bicycle with no panniers, going straight on a level road could expect to see a greater load on the left hand side of the tire. To even this out, you would want to add a loaded pannier to the right hand side of the bike.

Don't forget to experiment on a frictionless roadbed with no winds...

95% of the time I ride with one pannier, on the non drive side of the bike. I place it there because it is big and red, and if a motorist is using that as their visual indication of my lateral position, I'd rather have them think that I am further to the left than I am to the right. Once you add in the effects of riding on a real road, the fact that there are turns, potholes etc any effect of non symmetric loading is balanced out - if not, I would see more tire wear on one side of my tires than the other - but I don't.
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Old 11-05-09, 03:37 PM
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Seems to matter at low speed/ accelerating from a stop, but once in motion, no problems. A couple times this summer I had my grocery panniers evenly weighted on the rear and a fairly typical commuting load on one side of the front rack and steering was sketchy to say the least. I don't want to repeat that experience ever.
More scientifically, if the weight is over the rear wheel which has a more forward moment, the lateral effect is less significant than if an asymmetrical load is applied to the front wheel which has a more extreme lateral moment. I cannot offer more detailed physics than that, sorry.
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Old 11-05-09, 03:45 PM
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Originally Posted by sauerwald View Post
Don't forget to experiment on a frictionless roadbed with no winds...
Assuming a spherical bicycle...
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Old 11-05-09, 03:51 PM
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Your office mate is a doofus. I ride with a single 8-12 lb Ortlieb most days, to no ill-effect, whatsoever.

Two loaded panniers makes it much harder to get my bike down the aisle of the train without whacking folks, which creates it own hazards.

Frictionless roadbed - ouch.
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Old 11-05-09, 03:51 PM
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Center of mass for the pannier is low to the ground, fixed and very small compared to your mass (say 150 lbs to 10 lbs).

Your center mass is high and produces a much longer fulcrum when you use it to control the bike. Your center of mass is NOT fixed. Your mass is large compared to the unbalanced mass of the panniers.


Therefore:
Unbalanced weight in pannier is inconsequential.


Is his science guy one of those "Climate Change Type Science Guys"
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Old 11-05-09, 04:03 PM
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Back when my wife and I were both physics grad students we regularly commuted to campus on our tandem with only a single pannier. Never noticed any difficulty as a result of the unbalanced load, nor did anyone else in the department ever express any concerns about it to us.

Certainly having the extra weight on one side meant that the bike was leaning very slightly to the other side so that the center of gravity was kept centered over the line between the tire contact patches. But I don't see any harm in that nor was it perceptible to us while riding. And I still sometimes go grocery shopping with only one pannier and may have it loaded with up to 20 or 30 lbs. depending on what I'm buying. I do notice the slight lean with a very heavy pannier on one side of a single bike, but it's still not a problem and the bike handles fine.
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Old 11-05-09, 04:05 PM
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Originally Posted by cccorlew View Post
He says I'm a dangerous fool because I don't bother to evenly distribute the load between my two panniers......
Weigh in. Science facts will help.
Tell your office mate he is a "dangerous fool" since he apparently lacks the judgement to compensate a load imbalance.
Did his "science guy" offer evidence that included auto sensing weight distribution and compensation? doubtful.
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Old 11-05-09, 04:12 PM
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Originally Posted by sauerwald View Post
Ask him if he has taken into account the fact that the pavement is not level, but roads are designed with a crown in the middle so that rain runs to the gutters. As a result of that, a bicycle with no panniers, going straight on a level road could expect to see a greater load on the left hand side of the tire. To even this out, you would want to add a loaded pannier to the right hand side of the bike.
Are you sure about that, it seems to me that if you were to load the left side of the bike it would cause you to lean the bike to the right to compensate, therefore actually causing you to ride on the center of the tire on a crowned road.

In reality, I used to ride with a single pannier (because I only own one, an Arkel Utility Basket) with as much as 50lbs in it, it was never noticed past the first turn of the cranks...
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Old 11-05-09, 04:14 PM
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Originally Posted by sauerwald View Post
Ask him if he has taken into account the fact that the pavement is not level, but roads are designed with a crown in the middle so that rain runs to the gutters. As a result of that, a bicycle with no panniers, going straight on a level road could expect to see a greater load on the left hand side of the tire. To even this out, you would want to add a loaded pannier to the right hand side of the bike.
No, you'd want to place the pannier on the left side of the bike. That way the bike will be leaned slightly to the right to maintain proper balance (center of mass over the wheels) and would then be closer to perpendicular to the road surface if that's crowned in the center.
Somewhat paradoxically, adding weight to the right side of the bike will result in added wear on the left side of the tire.
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Old 11-05-09, 04:19 PM
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I can't ad much from the bicycle perspective, but can tell you from years of riding a motorcycle with hard luggage that rarely balanced it doesn't make much difference. Having the passenger change positions did, but not the luggage.
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Old 11-05-09, 05:42 PM
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Makes your center of gravity off-center sideways, how much depends on the amount and placement of the load. Easy to compensate for, esp if you're used to it. Nothing to worry about, IMHO.
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Old 11-05-09, 06:00 PM
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Thanks all! I will show this, and future entries to my colleagues.
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Old 11-05-09, 06:27 PM
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I concur. Doesn't matter.

Now, here's a situation where I have noticed impaired handling - large, heavy bag on top of my rack. It was OK until I tried to do some out-of the saddle acceleration, when the high load really affected my ability to rock the bike back and forth.

But even that wasn't a big deal outside of sprinting.
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Old 11-05-09, 07:19 PM
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Originally Posted by cccorlew View Post
Thanks all! I will show this, and future entries to my colleagues.
A lot of people only use one pannier. A lot of panniers are not even sold in pairs, for this reason.

One pannier has one huge advantage over two. It has much less aerodynamic drag than two panniers. It's center of gravity is low by design. A backpack that carries the same load is much more aerodynamic but the cg is much higher.

I've commuted 11 miles one way on a laser beam straight flat road. Going to work was always into a headwind of varying strengths. Use one if that's all that is needed. You will get to work faster. A backpack will be even faster but not as comfortable.

Another advantage of one vs two panniers is that one is much quicker to dock and undock than two. It always goes on the same side. I have reversed my side specific panniers after work in the dark. I didn't know why I was getting heel strike until I got home and took the panniers off the wrong sides of the bike.

And, before I forget, I have gone to work into that 11 mile headwind with two full up panniers and a 30lb backpack. more than once. Don't ask.
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Old 11-05-09, 08:19 PM
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I can never ride no hands if I have anything on my bike that's no on the other. My 2 lb lock makes me drift to the side. It probably does effect the bikes balance. But no where near the point where your coworkers is expecting the change to be.
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Old 11-05-09, 09:26 PM
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great, you are asking for us to calculate rotational dynamics, vector accelerations and to know the perceived handling ability of an individual assuming there was no other forces (all others being equal)

though I am an engineer and architect and not that into physics I say one cam safely assume that compensation in angle of attack (reproach?) would nil out any ill effects, minus of course the tropical storm force head or cross winds... geez.


You should ask your science friend if centripetal or centrifugal force is the real force acting or not in a turn...
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Old 11-05-09, 09:30 PM
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When commuting I nearly always have 1 pannier on the left with a heavy notebook, some clothes and misc junk.

I can easily ride no hands to put on gloves, zip/unzip jacket, etc.

The only time it matters is when I am not on the bike. It's harder to balance it against something to stand it up.

Anyone who rides a bike moves around to balance.

Tell him that's he's a dangerous fool for having his keys and cellphone on the same side. It makes just as much sense as his theory.

In theory, there is no difference between theory and practice. But, in practice, there is.

Joe
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Old 11-05-09, 09:39 PM
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I have ridden with my wife side saddle on the back rack. You compensate. I was doing it in Netherlands where I felt like folks were aware of cyclists but, it wasn't a huge issue, even in traffic.
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