# Thread: A Study in Stability - Sidestand versus Centerstand

1. ## A Study in Stability - Sidestand versus Centerstand

With some regularity, often as a degradation of a sidestand/centerstand discussion, sides are drawn as to what is more stable...parking your bike on the sidestand or the centerstand. This is a somewhat polarizing subject and people tend to be in one camp or another...for one reason or another.

A recent discussion in Airheads (see "What are the chances") brought the subject up. The aspect of stability was mentioned and that looking at the contact points for the sidestand ("wide" triangle) and centerstand ("narrow" triangle) would clearly suggest that the sidestand is more stable. It's all about physics was the bottom line.

I contend it's not physics...that's a pretty broad term. Doesn't everything come back to physics?? I think it's more basic than that. It's Mechanics 101...it's free body diagrams...it's geometry.

What I'd like to do is offer a study in the forces involved and use that to put some numerical values to this to help illustrate what is more stable.

First, I'll define stability for this discussion, which I think is really at the heart of this discussion between the two stands. I'm not talking about a bike rolling forward when on either stand. Some Airhead models have the famous "feature" of a folding sidestand when load is removed...not talking about that stability. Yes, everyone is supposed to put the bike in first gear, supposed to park on solid ground, not mess up and park uphill/downhill/on a slant. Not talking about those situations.

Stability will be the force it takes to begin to move a bike from its parked position on either stand. This is the lateral force, that if big enough and sustained for long enough, will result in a tip over. So, what lateral (ie, horizontal to the ground) force does it take, to start this process. It would stand (no pun intended!) to reason that the higher this force, the more stable the position. The relative values of this force can be determined. That is the goal here.

2. ## Bluf

Bottom Line Up Front: For those who don't want to read any further.

My conclusions are that the relative difference between the lateral force to start a bike into a tip over for the stock sidestand or centerstand situation is small. Certainly as a percentage of the total weight of the motorcycle. The notion of stability for one way or the other is essentially rooted in one or more experiences which have lead to the owner to conclude that the sidestand (or the centerstand) is a less stable position.

I suggest that the actual stability difference is in the "noise" of everything else. And that people will, and should, make the choice that works for them.

In my opinion.

3. ## Assumptions

I'll need to state my assumptions. I can't accurately measure some of these, but I'm going to use what I believe to be reasonable values and approaches. Some of this is measured, some has been documented in various places, and some I just had to guess. Together, I believe these to be reasonable values to do this sensitivity study.

I'm using the stock R100/7 as a basis for this. There will some variances bike-to-bike, but hopefully, the changes in the final numbers would be small for other bikes or situations.

Weight (W)- 215 kg or 474 lbs (unladen and full fuel; BMW published value)
CG location - 30 inches from the ground (I looked at my bike and thought that the point of the bottom of the seat pan might be reasonable)
Width of contact points for stock centerstand - 9 inches
Width of contact points for Reynolds rideoff centerstand - 16 inches
Lean angle of bike on sidestand (theta) - 10 degrees (I tried to do some measurements on my /7 and came up with about 8 degrees on inch-size tires)

4. ## Basic Diagram of Bike and Forces

Here's a basic diagram that will be used in this development.

W - is the weight of the bike
Theta - lean angle of the bike (or angle used in the centerstand analysis)
1 - resolved force of the weight that acts on the contact patch (tires or centerstand foot; not the vertical load but the load along the vertical line through the center of gravity)
2 - resolved force of the weight that acts perpendicular to 1, a part of which must be carried vertically by the sidestand (applicable in the centerstand situation, too, as discussed)
3 - horizontal component of 2 above
TO - tip over force (equal and opposite to 3)

Basic.jpg

5. ## Tip Over Force for Sidestand

When the sidestand is deployed, the lean angle of my /7 is around 8.0 degrees. This is using the stock sidestand and inch sized Pilot Activ tires. For these calculations, I'll use 10 degrees for a "general" lean angle. The calculated forces are the following:

W = 474 lbs
1 = 467 lbs
2 = 82 lbs
3 = 81 lbs

TO (tip over) force (opposite to 3) = 81 lbs

6. ## Tip Over Force for Centerstand

As indicated, the angle between the vertical line through the bike's center of gravity and one of the centerstand feet is about 8.53 degrees. Using this angle, the calculations are as follows:

W = 474 lbs
1 = 469 lbs
2 = 70 lbs
3 = 70 lbs

TO (tip over) force (opposite to 3) = 70 lbs

Note that this assumes the situation where the tip over force has just been applied and the opposite centerstand tip has barely lifted off the ground.

7. ## Tip Over Force for Reynolds Rideoff Centerstand

Using the 16 inch spread for the contact points for the Reynolds rideoff centerstand, the angle created between the vertical centerline and one of the contact points is about 16.7 degrees. The calculations for this configuration are:

W = 474 lbs
1 = 454 lbs
2 = 136 lbs
3 = 130 lbs

TO (tip over) force (opposite to 3) = 130 lbs

8. ## Results Comparison

Finally, the results show relatively little difference in tip over forces for the stock sidestand and centerstand, but a large increase in tip over forces for something like the Reynolds rideoff stand.

Stock sidestand --> TO = 81 lbs or 17.1% of total bike weight
Stock centerstand --> TO = 70 lbs or 14.8% of total bike weight
Reynold centerstand --> TO = 130 lbs of 27.4% of total bike weight

Obviously, the lateral forces being applied gradually decrease as the bike nears the vertical, or in the case of the bike on the centerstand, the center of gravity nears being directly over the stand foot in contact with the ground. So the greatest stability is when the bike is firmly on the sidestand/centerstand. Once the bike has started to lift up, the stability (or tip over force) decreases quickly.

Other things to consider:
- metric sized tires makes things worse for the sidestand, doesn't really affect the centerstand setup
- higher center of gravity makes things worse all around
- fairings and bags provide more surface area for the wind to push on

9. When you're parking on a soft surface, you need one " beer can" for the sidestand and two for the center stand. Whatever is used, what you need for the centerstand is larger and more to carry. It's way more difficult to sink proof the centerstand.

You can tip over an Airhead on centerstand in either direction with essentially the same force. With a sidestand, a tipover to the right requires first lifting the bike to vertical. I posit it's essentially impossible to tip one over to the left unless forward force is also applied. Having bike in gear resists that. Bike in gear does not resist centerstand tip to front. Whichever is used, park into the wind with your RS or RT.

The fact I can rock an Airhead on centerstand from rear tire contact to front tire contact with one finger suggests something more than 20% of the bike's weight is supported by the centerstand. This for sure changes will full saddlebags, of course.

Center stands are significantly improved on newer BMWs. On Airheads pre-1985, they're an accident waiting to happen.

10. Interesting work, Kurt!

Originally Posted by 20774
Other things to consider:
- metric sized tires makes things worse for the sidestand, doesn't really affect the centerstand setup
- higher center of gravity makes things worse all around
- fairings and bags provide more surface area for the wind to push on

- many bikes on the sidestand will lean more than the 8˚ or 10˚ you measured. This greater lean would require more force to tip to the right, except that...
- an unmodified airhead sidestand will release (i.e., fold up) with a very small-force nudge forward or towards the bike's right.

11. Kurt,

Great job. You have attempted to "quantify" the forces to help us make intelligent decisions. But, as you see already, the numbers will not matter much to some.

One factor that could affect decision is the duration of the side forces that could cause a tip over. What had started some of the conversation on that other thread was some who had seen bikes fall over by some sort of noise (from trucks) or something else. One could take into account the "probability" factor of any sort of force happening, and the "probability" of the length of time that force is applied - that it would be strong enough and long enough to result in a tip over! This (or "these") element makes the "quantification" process much more difficult, maybe even impossible.

Since that is the case, most will go by personal preference which is usually based upon personal experience. One person criticized me for my notion about the wheels rolling when using the sidestand, and cited some motorcycle training course (I would guess) that said that any knowledgeable person would know that one should put the bike in gear to avoid this. I admit, this is a good idea. I had learned NOT to put the bike in gear in case it was bumped from behind, and there would be a shock put to the drive train that could cause damage. So I don't put into gear.

But, my reason in mentioning this criticism, is because it generated the notion that there was some "absolute" proof that I should have considered, and that had been incorporated into this M/C course material. Someone has determined that they "knew best."

As in the case of which stand is best, most will also argue similarly - one is better than another. However, as you know, quantifying each can be problematic, and when one adds the multitude of factors that could occur, darn right near impossible. Sooo ... most of us will go on using our "preferred" method and many of us will try to cite absolute proof that our method is the best or only correct one.

I am not that way, at least hopefully. My preferred method is centerstand where possible and sidestand where required. I decide at the time based upon my ability to guess what may happen while parked there (i.e. slope of ground, ground material: soft asphalt, grass, mud, etc., and what may happen with other vehicles/people). That is pretty much guess work!

I chose mostly centerstand as described above, probably because over all my years motorcycling, I started with Hondas, and none had sidestands, all centerstands, so it was habit for me. When I eventually purchased my BMW's, I kept up the habit, but my habit was reinforced at least by some old timers who stated the issue with the oil draining into left cylinder on a boxer. So, I kept up the habit. And will keep on.

Frankly, I think people should do what they want and admit the truth that it is probably some personal reason, not scientific fact that makes us choose one method or the other.

I really commend you for your efforts. Tough job.

We'll see just what conversations (attacks on those who disagree?) happen to occur!

In all my years of riding (40+ years) I have never seen a motorcycle just fall over when parked - either with the sidestand or with the centerstand, unless in mud of soft asphalt.

Most of the tip overs were due to the rider himself/herself, not being attentive and just when starting to take off stand, for a split second, they don't pay attention to tipping, and over the bike goes! I have had this happen a couple of times myself. It was my own fault.

However, both with myself, and with many others, I have seen MANY times the rider starting to ride off, and forgetting to put the sidestand up, causing a near crash, and many times at least resulted in a "high side" tip. Very embarrassing to them (thankfully this didn't happen to me as I was able to "catch" the bike beforehand), and also dangerous.

This, to me, is one reason to not use the sidestand, but for those who do as I do upon occasion, I hope they leave the "auto" feature intact so that the sidestand automatically retracts.

13. It wasn't noise from the huge truck with a load of steel, it was that it shook the ground as it went by. Another time, I had parked on the centerstand (I used to use the centerstand exclusively) and a terrific storm came and eroded the surface underneath my bike and over it went. I hauled it up and put it on the sidestand, and all it did was lean a little further, but didn't fall over. Gale winds have blown my bike over on the centerstand until I got wise and used the sidestand such that the wind blew in the same direction as the lean angle on the sidestand. Each will do things as they see fit and there are many variables to the equation. Do whatever works best for you with your bike(s).

14. I tell you what guys...the bike may be German and thus many people may feel compelled to tell others what to do and follow a "Fuhrer", but I will use whatever stand I want whenever I want. It may be the sidestand, it may be the centerstand.
I will just do my thing and there is nothing the "Stand Nazis" among you can do about it.....

15. Originally Posted by EMSimon
I tell you what guys...the bike may be German and thus many people may feel compelled to tell others what to do and follow a "Fuhrer", but I will use whatever stand I want whenever I want. It may be the sidestand, it may be the centerstand.
I will just do my thing and there is nothing the "Stand Nazis" among you can do about it.....
WOW!! How do you really feel about it?

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