-
Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password. If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?
-
Beginning April 1st, and running through April 30th, there is a new 2024 BMW MOA Election discussion area within The Club section of the forum. Within this forum area is also a sticky post that provides the ground rules for participating in the Election forum area. Also, the candidates statements are provided. Please read before joining the conversation, because the rules are very specific to maintain civility.
The Election forum is here: Election Forum
A Study in Stability - Sidestand versus Centerstand
- Thread starter 20774
- Start date
rangerreece
RangerReece
Three points of contact
Just my thoughts,
I would imagine friction at the points of contact would weigh heavily into any literal or figurative equation. On the side stand my three points of contact are the side stand and two tires. Center stand; front tire and the two contact points of the center stand that are closely placed. The "maintenance" stand always feels unstable to me. It is necessary to access the rear wheel maintenance area. The side stand always feels very stable to me. Two years ago my bike was hit by a golf cart at work, it was on the side stand, the right rear wheel of the golf cart hit the right side of the front wheel of the bike. The OEM rain cover was on. The front wheel turned left with impact. No damage to bike no toppling.
Just my thoughts,
I would imagine friction at the points of contact would weigh heavily into any literal or figurative equation. On the side stand my three points of contact are the side stand and two tires. Center stand; front tire and the two contact points of the center stand that are closely placed. The "maintenance" stand always feels unstable to me. It is necessary to access the rear wheel maintenance area. The side stand always feels very stable to me. Two years ago my bike was hit by a golf cart at work, it was on the side stand, the right rear wheel of the golf cart hit the right side of the front wheel of the bike. The OEM rain cover was on. The front wheel turned left with impact. No damage to bike no toppling.
melville
Member
Theory is all fine and wonderful, but how about some actual testing?
How about a spring scale anchored to the frame at the rear of the tank to measure the amount of force ACTUALLY required to lift the bike off the stand? Checking from both sides, of course. While there is probably not much difference in tipover force required on the centerstand, on the sidestand is another story.
We're certainly a nerdy bunch, no?
How about a spring scale anchored to the frame at the rear of the tank to measure the amount of force ACTUALLY required to lift the bike off the stand? Checking from both sides, of course. While there is probably not much difference in tipover force required on the centerstand, on the sidestand is another story.
We're certainly a nerdy bunch, no?
I predict it is going to get worse for many as soon as cabin fever spreads. This is just the beginning.
nrpetersen
Curmudgeon
Kurt's analysis would be more complicated but more correct if the compliance of the front and rear suspensions is included in side stand performance analysis. On the other hand, the center stand isn't sensitive to suspension compliance.
When it goes onto a ferry, I try to use the center stand. Otherwise it depends on the surface and static loading of the bike.
When it goes onto a ferry, I try to use the center stand. Otherwise it depends on the surface and static loading of the bike.
I think you are on to something!
Before anyone reads any further, I think that Kurt's numbers ARE helpful when considering this ONE bike, based upon these assumptions. The numbers arrived at are relatively useful when considering THIS bike's leaning force and therefore the force necessary to "push" it back up into upright position (if on sidestand) or the force necessary to push a centerstand bike off center and over center to tipping point. I think it basically told us what we already knew, that the sidestand DOES provide a more stable overall position than the centerstand, but not that much so. But, when other factors are considered, such as ground density, or windage and direction, AND also the belief (or non-belief) of the oil situation concerning boxers, the decision to use either method of parking still resides with the rider who evaluates (and prioritizes) the situation at each parking time and chooses what he/she wants.
Kurt,
Can you provide us with the algebraic formula that you used to calculate the side forces? Did you derive your final data from actual testing on your bike in your garage? I.e. tipping it and then using measuring devices to see just how much force is needed to tip back up or tip to the point of T/O?
Did you basically use these numbers:
Total weight of bike
Lean angle (theta per your sketch)
Location of the center of gravity (assuming centered over tire patch left to right, and then measured height off ground)
Could it be that you used some formula that was used for "leaning" forces while riding? I would think that they could be similar, as one can imagine the "forces" when actually leaning into a turn, for example and the "forces" needed to straighten it back up after the turn.
Just asking....
Thanks,
jlc
What if the golf cart had hit the left side of the front wheel and forcing bike to the right? Would side stand have been as good in that situation?
How about if the cart had hit directly from behind, pushing the bike forward? Or form the rear left, pushing the bike forward and to the right?
Just to mention a few of the literally hundreds of situations that can occur. That is done simply to let us all know that we all must make our "decision" at the time we park our bikes. To one, one possibility may be higher than to another in a given situation.
My biggest dislike is when bike is parked and someone comes along and decides he/she wants to see what it feels like by sitting on it - all without permission, and even maybe when we are not around and behind our backs! This is when I wire my bike for 280 volts and anyone who touches it gets all of them!
Jimmy -
I did think about testing to see how my answers compare. I envisioned a fish scale of sorts attached as suggested. It would be easy enough to perform the tests on my Reynolds stand setup, although if the correct answer is near 130 pounds, that's going to be a bit scary to do the test...even if it is just to get the bike to start moving. My stock centerstand is in the attic. As for testing on the sidestand, I'd have to wire the sidestand down and block the front and rear wheels so it doesn't move. I don't have any "built in" helpers, so doing it solo presents some problems.
As far as considering other factors, yes, there's some simplification to my approach. I was just trying to get a general sense of the relative values. Bike with half fuel will have a different CG location and force vector; an R100 with the lousy/bent sidestand will have a different lean angle. But the scenario was basically a static situation...I don't think consideration of the suspension changes when trying to lean the bike over will change the results to a significant degree.
Regarding the forumulae involved, I indicated it was Statics 101 for anyone getting an engineering degree. I took the published weight for the R100/7 and used sines/cosines/assumed angles to resolve the gravity vectory (474 lbs) into it's orthogonal components. It's easy enough to do this computation which then gives you more forces to work with. And, knowledge of angles (interior angles of a triangle sum to 90 degrees, etc.) let you determine other angles of my diagram quite easily.
As for consideration of forces while turning, that would be another level of complexity. The gravity vector is always acting straight down. The radius of the turn and speed will identify a radial acceleration which then results in a force of the CG to move laterally. But that is resisted by the friction created by the tires and the contact surface. It's always amazed me how the MotoGP guys can go around a turn at 65 degrees lean angle at those speeds and not spin out. How in the heck does the tire do this? Well, as long as no other point of the bike touches the ground, if the vertical force at the CG is 474 lbs, then the sum of the vertical force at the two contact patches is also 474 lbs. That will be enough for the friction forces to do their job. But as soon as the rider touches a footpeg down or even puts too much weight on the knee puck, this transfers weight away from the two vertical forces at the tire contact patch, reduces the friction forces, and a lowside usually happens.
But I digress!
What you describe is exactly what I did when I worked for a company in their R & D department. Though we were not engineers, we would use the calculations told us by the various vendors (let's say for certain plastics, etc.) and then we would do actual testing using scales, hyd. pressure (gages) or air pressures. We also did lots of cycle testing - designing up a rig to put a part to test as similar to its actual designed use, and see how many repetitions it would go before failing. Often many of the same item were tested using various greases to see how each performed when lubricated differently. Also did under varying temp settings were possible.
Rarely, however did the actual tests reveal the same numbers as did the calculations.
To quote someone. "You done good!!"
dennisdarrow
#4869 Earned Lifetime mem
That does it. I have read this entire thread. I obviously need help.
I am going to buy a 45 year old Puch 250 twingle for a Winter project.
That'll do it, I'm sure.
Thanks for stepping in and bringing a bit of reality to the situation.......God bless........Dennis
akbeemer
SURVIVOR
That does it. I have read this entire thread. I obviously need help.
I am going to buy a 45 year old Puch 250 twingle for a Winter project.
That'll do it, I'm sure.
Now I'll have to spend the evening trying to find out what a Pooch Twinky is.
That does it. I have read this entire thread. I obviously need help.
I am going to buy a 45 year old Puch 250 twingle for a Winter project.
That'll do it, I'm sure.
Been there, done that! Ran pretty good as long as I didn't want to go over 35 miles per hour!
Last edited:
helmut_head
New member
Uhhh..
Kurt, Dude, Happy Thanksgiving.
Kurt, Dude, Happy Thanksgiving.
Hey, that bike doesn't seem to have a sidestand to get back on stability thread
Off Topic wise--------------------
Many years ago we watched the local spoiled teen drive one of those of a '1000 foot fishing pier/runway into West Galveston Bay...we were blown away...he had a new bike a week later
Bike never ran again, we watched it rust away leaned against his bayhouse wall for the next few years.
lmo1131
New member
See> http://suzukisavage.com/cgi-bin/YaBB.pl?num=1335871887/5
Google is our friend...
if you're really serious about a Puch, especially one with a side stand*, returning to topic, check out -> http://bike-urious.com/allstate-puch-quadfecta/ ... but you'd better hurry.
We now return to our regularly scheduled programming
* they all have side stands
