SamSpeed
1 W
An Endlessly-Spherical coordinate system...
Mounting your battery, Center of Gravity.
- Thread starter Patriot
- Start date
johnrobholmes
10 MW
Awesome sequence there. He rode that thing out till the last second.
John in CR
100 TW
Actually Sam, I believe you were closer before, and yes you can see what appears to be a point of axis in the down tube while riding. You can't see it at the rear, because it's a lean that starts down at the tire. What occurs at the front and is visible, is that relative to your frame of reference the headset goes one way and the bottom of the downtube the other way as the frame leans and turns back and forth. Don't forget that your reference point is moving too. It's more complex than the simple "roll axis" that the motorcycle guys are claiming. A bike doesn't roll. A bike can't roll other than its wheels. If you tried to draw a line from the rear like in those motorcycle graphics, it would be up somewhere in the rider's body, but I still wouldn't call it a roll axis.
For those who want to talk about CG, you can't leave the rider out of the equation, so there are 2 options as ideals (ignoring traction & wheels sliding or going airborne):
1. Strap the added weight to your body to get it at the CG of the bike+rider. It really needs to be attached to you because on a bike more than on a motorcycle your body position changes relative to the frame, and you simply can't talk about the CG only of the bike. That point is almost inconsequential compared to a motorcycle, because the rider mass is so dominant on a bike.
2. Place the added weight where it affects CG the least. This point is closest to the rear contact patch (at the rear contact patch has zero effect on CG because being on the ground there is no energy potential from gravity relative to the ground). This point of view does ignore the greater forces involved with moving the added weight greater lateral distances during turns than it would if placed up higher, however, I still believe the difference is minimal because the angles are shallow.
This viewpoint may fail due to traction issues like such as Johnrob mentioned about braking in curves, and those observations along with the point about lean angle are great input. I even took note riding this morning, just like in a car I try to brake during curves as little as possible. It definitely fails with off road riding where sliding and catching air come into play. With normal street riding though, I still believe it's valid. The real question for those of us who want to go fast is do we really want our e-bikes to handle like bicycles at speeds exceeding 30mph. I suspect that answer is no.
I wonder how weight placement is addressed with the low slung recumbent racers. Does their longer wheelbase negate much of the problem or do they have to get crazy low in a curve?
Safe,
There isn't a matter of me "getting it", because I full well understood what you've been repeating over and over. I didn't and don't agree with it. Bicycles are different than motorcycles. If you want to add the weight in the center to make it feel more like a motorcycle then have at it. If you want to talk about CG, then you better get the weight up higher to where the CG of the bike+rider not below or in front of the CG. In either event your graphic of ideal placement is incorrect for a bicycle. If you want your bike to feel both on and off the bike most like it did before adding batteries then near the contact patch is the place to add the weight, but that has it's own issues.
You motorcycle riders need to stop patting each other on the back and put your thinking caps back on, because a bike isn't a motorcycle.
John
For those who want to talk about CG, you can't leave the rider out of the equation, so there are 2 options as ideals (ignoring traction & wheels sliding or going airborne):
1. Strap the added weight to your body to get it at the CG of the bike+rider. It really needs to be attached to you because on a bike more than on a motorcycle your body position changes relative to the frame, and you simply can't talk about the CG only of the bike. That point is almost inconsequential compared to a motorcycle, because the rider mass is so dominant on a bike.
2. Place the added weight where it affects CG the least. This point is closest to the rear contact patch (at the rear contact patch has zero effect on CG because being on the ground there is no energy potential from gravity relative to the ground). This point of view does ignore the greater forces involved with moving the added weight greater lateral distances during turns than it would if placed up higher, however, I still believe the difference is minimal because the angles are shallow.
This viewpoint may fail due to traction issues like such as Johnrob mentioned about braking in curves, and those observations along with the point about lean angle are great input. I even took note riding this morning, just like in a car I try to brake during curves as little as possible. It definitely fails with off road riding where sliding and catching air come into play. With normal street riding though, I still believe it's valid. The real question for those of us who want to go fast is do we really want our e-bikes to handle like bicycles at speeds exceeding 30mph. I suspect that answer is no.
I wonder how weight placement is addressed with the low slung recumbent racers. Does their longer wheelbase negate much of the problem or do they have to get crazy low in a curve?
Safe,
There isn't a matter of me "getting it", because I full well understood what you've been repeating over and over. I didn't and don't agree with it. Bicycles are different than motorcycles. If you want to add the weight in the center to make it feel more like a motorcycle then have at it. If you want to talk about CG, then you better get the weight up higher to where the CG of the bike+rider not below or in front of the CG. In either event your graphic of ideal placement is incorrect for a bicycle. If you want your bike to feel both on and off the bike most like it did before adding batteries then near the contact patch is the place to add the weight, but that has it's own issues.
You motorcycle riders need to stop patting each other on the back and put your thinking caps back on, because a bike isn't a motorcycle.
John
SamSpeed
1 W
I did an informal experiment shifting my CG to the side by filling my side/rear basket with 30 lbs. of groceries. Dunno, but when hauling a load I tend to drive more sedately but in the spirit of scientific investigation decided to push it. And you know, it was not bad. It was like instinct took over and it was just sortof natural. So what if the milk gets shook up? Even hands off was ok, just took a little more effort.
Someone in a post somewhere said to just put your batteries off to the side and get 'em out of the way. Think I'll try that, see if it really makes a difference. Gotta getta longer piece of wire first.
Another thing I wanna try is to put my old front wheel back on. My current setup is a bl36 and that hub and wheel is plenty heavy. My old wheel has a Vittoria tire on it and weighs next to nothing. I want to relive, to re-experience the handling with that wheel. Refresh my memory. I'll leave the batteries on the rear rack so I'm only changing one thing at a time. Wish I had a way to measure the response, instead of it all being subjective.
"We?" I tried to warn ya a few posts back. You're on your own pal 'cause I refuse a battle of wits with an unarmed individual. You could slap him upside the cranium with 372 pages of Vittore Cossalter, and he'd still argue the "R" word.safe said:Well folks what do we do now?
lostcoyote
10 W
- Joined
- Aug 26, 2008
- Messages
- 72
SamSpeed said:
so ya couldn't tell much difference in your experiment so far?
maybe 30 pounds of groceries doesn't make much of a subjective feeling that there is any difference since your own body weight dominates the loaded weight. if ya weight, say, 180 pounds, 30 pounds is only adding 20% more load and ya might have to shift it quite a bit to take notice
????
John in CR
100 TW
Papa said:John,John in CR said:
Speaking as a 15 year, professional recumbent designer, builder and rider, I'd be tickled pink to share what little I know. But your hard-headed attitude spoiled the incentive.
Papa,
Could it possibly be that you don't know as much as you think you do? I mean you can't even open you mind to there being a difference in CG with 2 wheels on the ground. I even pointed out how your online calculator is flawed, since it can't come up with an answer where the CG is below axle level. If you design and ride recumbents, some of your bikes must have a CG below axle level, maybe even with the rider. Plug actual numbers into the calculator and see the garbage it spits out if the CG is below axle level. Then come back and tell me how hard-headed I am.
John
SamSpeed
1 W
Papa? That is one sleek looking machine! The one in the front is not bad either..
Seriously, it is. And my hat's off to you. I like bent bikes. Bought a BikeE just before they went under. Still like it, and ride it. And it has it's handling quirks, some of which I'm sure are due to it's CG. Keep thinking of the best way to put a motor on it. Keep thinking to stuff the frame full of batteries. Either batteries or a fishing pole.
Question sir, with that rearward bend in the headset tube, the handlebars must swing from side to side. Is that noticeable riding? Or do you get used to it?
Seriously, it is. And my hat's off to you. I like bent bikes. Bought a BikeE just before they went under. Still like it, and ride it. And it has it's handling quirks, some of which I'm sure are due to it's CG. Keep thinking of the best way to put a motor on it. Keep thinking to stuff the frame full of batteries. Either batteries or a fishing pole.
Question sir, with that rearward bend in the headset tube, the handlebars must swing from side to side. Is that noticeable riding? Or do you get used to it?
Absolutely... But you, John in CR, haven't supplied any evidence to the contrary. Zero, nada, zilch. Start by posting your verifiable references and quantitative data which substantiates your claims and i'll be happy to embrace you with an open mind. All you've displayed so far is highly subjective keyboarding.John in CR said:
No,... you have NOT. You said it was, but again you've supplied NO such evidence.John in CR said:
The snap shot below, is IN FACT, the correct numbers generated on the very LWB recumbent posted above. You obviously DL'ed the very same claculator, so you can easily verify the numbers shown on your own computer. And if that fails to satisfy you, then SHOW ME THE NUMBERS using your own calculator.
John in CR
100 TW
Papa said:Absolutely... But you, John in CR, haven't supplied any evidence to the contrary. Zero, nada, zilch. Start by posting your verifiable references and quantitative data which substantiates your claims and i'll be happy to embrace you with an open mind. All you've displayed so far is highly subjective keyboarding.John in CR said:
No,... you have NOT. You said it was, but again you've supplied NO such evidence.John in CR said:
The snap shot below, is IN FACT, the correct numbers generated on the very LWB recumbent posted above. You obviously DL'ed the very same claculator, so you can easily verify the numbers shown on your own computer. And if that fails to satisfy you, then SHOW ME THE NUMBERS using your own calculator.
Papa,
For some reason I can't see images posted in that manner, but if the actual CG is not lower than axle level, then it's irrelevant to my argument. From Sam's post I wish I could see the images.
I'd think that low racers could easily have CG's below axle level. I haven't used any calculator, nor do I need to. I just ran different scenarios on the calculator you linked for us. I was trying to explore the effect of added weight at the tire patch, and quickly realized the calculator was giving me incorrect answers. If you don't believe me, just add the known effect of 500lb at the contact patch of one or both wheels of a 25lb bike to your precious calculator. There are 2 possible correct results depending on your POV.
1. The definition of CG to which you subscribe should definitely bring the CG below axle level.
2. Using the definition I believe to be more correct for a road bike, that only the "potential" energy from the effect of gravity is important in determining CG (ie weight at the ground has no remaining potential), then the CG wouldn't move with the added weight at the tire patch.
The calculator comes up with neither correct answer and reminds us to be careful of the crutches we use. IMO an understanding and feel for what is going on is often more important than the calculation, because it's very easy to become lost in the numerical explanation and lose sight of what is going on. I also believe the numerical analysis of bicycle behavior still falls short, and that's a big part of the reason that despite many attempts really smart guys have yet to make a robotic bike run any better than a 5 year old can learn to do in 5 minutes.
John
SamSpeed
1 W
About CG calculations. Googling around, I found this article. It shows a method of calculating CG location very similar to Tony Foale's. The article gives some explanation as well as the formulas used. There's also an Excel spreadsheet you can download and play with.
I ran the numbers for my ebike and the calculated horizontal CG point came out very close to my measured estimate (I just found a spot on the frame where it balanced). The verticle is a little harder to measure directly, but it looks about right.
The equation makes an assumption, based on the geometry that the vertical CG point will be at or above the front axle height. So you know, I would not say it's a flaw. If you want to assume a CG lower than the axle, think you'd have to look the geometry and re-do the math.
I want to try it again with me sitting on it. Maybe tomorrow.
http://www.msgroup.org/forums/MTT/topic.asp?TOPIC_ID=137
Also, lostcoyote...
I ran the numbers for my ebike and the calculated horizontal CG point came out very close to my measured estimate (I just found a spot on the frame where it balanced). The verticle is a little harder to measure directly, but it looks about right.
The equation makes an assumption, based on the geometry that the vertical CG point will be at or above the front axle height. So you know, I would not say it's a flaw. If you want to assume a CG lower than the axle, think you'd have to look the geometry and re-do the math.
I want to try it again with me sitting on it. Maybe tomorrow.
http://www.msgroup.org/forums/MTT/topic.asp?TOPIC_ID=137
Also, lostcoyote...
You know, you could be on to something. 180 is about my fighting weight, and I'm a wee bit over that now. When I first put on that side basket it was on the kickstand side. Now that was really dumb.
John in CR
100 TW
Sam,
Ok, I'll change my wording from "flaw" to "limitation" if it makes everyone happy. Now please bear with me through a simple mental exercise. Let's revisit a 500lb weight added at the rear contact patch. If you like put that into these calculators, but it's not necessary, because they'll say the CG moved. If you grab the frame and wiggle it side to side, or turn the front wheel and rotate the frame all with lifting that rear wheel (lift the front wheel though if you like), you'll find that the bike feels and moves exactly the same as it does without the added weight. How is this possible if we just changed the CG of a 25lb bike by adding a 500lb weight unless the calculators are flawed or simply inappropriate?
Now if we add the weight at a more realistic 2" above the ground at the rear tire like SteveCA did with his front wheel packs, and instead of 500lbs make it a heavy 50lbs of lead batteries, you're likely to feel it very little in the "wiggle test", however, these calculators are going to tell you the CG has moved dramatically. Pick up the front wheel, and guess what, it still feels the same too. This all tells me that unless you pick it up the bike is going to lean, steer and feel essentially the same as it did before. Any other place you add that 50lbs is going to make the bike "feel" different. Other than the effect on traction, which I'll leave to other more experienced riders to explain, the only difference while riding is that the weight will move laterally slightly more than it might with a higher mounting, but compared to being mounted in the triangle the difference in lateral acceleration of the weight is sure to be negligible if not less, and as I've said before the effect is spread over a long distance except during the most extreme riding. You'd probably have to raise it to seat level in order to minimize this motion, and that kind of high placement will have all kinds of other problematic accelerations of this weight both on and off the bike.
Papa,
Let's find out exactly who is "an unarmed individual" and who isn't.
John
Ok, I'll change my wording from "flaw" to "limitation" if it makes everyone happy. Now please bear with me through a simple mental exercise. Let's revisit a 500lb weight added at the rear contact patch. If you like put that into these calculators, but it's not necessary, because they'll say the CG moved. If you grab the frame and wiggle it side to side, or turn the front wheel and rotate the frame all with lifting that rear wheel (lift the front wheel though if you like), you'll find that the bike feels and moves exactly the same as it does without the added weight. How is this possible if we just changed the CG of a 25lb bike by adding a 500lb weight unless the calculators are flawed or simply inappropriate?
Now if we add the weight at a more realistic 2" above the ground at the rear tire like SteveCA did with his front wheel packs, and instead of 500lbs make it a heavy 50lbs of lead batteries, you're likely to feel it very little in the "wiggle test", however, these calculators are going to tell you the CG has moved dramatically. Pick up the front wheel, and guess what, it still feels the same too. This all tells me that unless you pick it up the bike is going to lean, steer and feel essentially the same as it did before. Any other place you add that 50lbs is going to make the bike "feel" different. Other than the effect on traction, which I'll leave to other more experienced riders to explain, the only difference while riding is that the weight will move laterally slightly more than it might with a higher mounting, but compared to being mounted in the triangle the difference in lateral acceleration of the weight is sure to be negligible if not less, and as I've said before the effect is spread over a long distance except during the most extreme riding. You'd probably have to raise it to seat level in order to minimize this motion, and that kind of high placement will have all kinds of other problematic accelerations of this weight both on and off the bike.
Papa,
Let's find out exactly who is "an unarmed individual" and who isn't.
John
Tiberius
10 kW
SamSpeed said:
No problem Sam. Interesting observation you posted about the Pawnee the other day. You will be pleased to hear that the most common use of my e-bikes is to go the 9 miles to my local airfield.
Nick
safe
1 GW
- Joined
- Dec 22, 2006
- Messages
- 5,681
Speed
This "rear contact patch" verses "middle axis" argument cannot be resolved without including speed in the discussion.
At zero mph the axis of rotation is at the rear contact patch.
At infinite speed the axis of rotation is level to the ground and at the height of the center of gravity of the bike/rider unit. (because turns don't begin until all the rotation is completed... the bikes center of gravity continues in a straight line until the lean is finalized)
...handling and speed are intimately related.
This seems to be the difference... at ultra low speeds (less than 20 mph) the dominant effect is the rear contact patch. At speeds above about 20 mph the dominant effect is the central axis of rotation.
So in effect "John in CR" is right! (partially)
Note: I did 47 mph on the flat and 54 mph on the downhill yesterday. (not normal for most bicycle riders) On my bike the dominant influence is the middle of the bike axis of rotation, but for someone that goes 10-15 mph most of the time my bike would feel top heavy.
For very slow speed "John in CR" is right.
So one needs to first identify the speed at which you want to travel before you can say how best to place the weight!
This "rear contact patch" verses "middle axis" argument cannot be resolved without including speed in the discussion.
At zero mph the axis of rotation is at the rear contact patch. At infinite speed the axis of rotation is level to the ground and at the height of the center of gravity of the bike/rider unit. (because turns don't begin until all the rotation is completed... the bikes center of gravity continues in a straight line until the lean is finalized)...handling and speed are intimately related.
This seems to be the difference... at ultra low speeds (less than 20 mph) the dominant effect is the rear contact patch. At speeds above about 20 mph the dominant effect is the central axis of rotation.
So in effect "John in CR" is right! (partially)Note: I did 47 mph on the flat and 54 mph on the downhill yesterday. (not normal for most bicycle riders) On my bike the dominant influence is the middle of the bike axis of rotation, but for someone that goes 10-15 mph most of the time my bike would feel top heavy.
For very slow speed "John in CR" is right.
So one needs to first identify the speed at which you want to travel before you can say how best to place the weight!
johnrobholmes
10 MW
I would go so far as to say John in CR is correct only at 0 mph. As soon as the bike is rolling a few mph the "weight at the contact patch" will affect handling in that the CG is lower and the mass is less centralized. Less flickablility and lower leaning for a given turn. Handling is affected greatly.
The wiggle test is only valid for a stationary bike. Personally I don't care how it handles stationary, I will build a bike to handle well when riding.
The wiggle test is only valid for a stationary bike. Personally I don't care how it handles stationary, I will build a bike to handle well when riding.
Tiberius
10 kW
johnrobholmes said:
Quite so. The important distinction is not actually how fast the bike is moving , but whether you are riding it or not. When you are standing (or walking or running) next to it, then you can indeed rotate it about the line between the tyre contact patches. But when you are riding it, you move the contact patches around to keep the bike balanced. This may have been mentioned before.
Nick
John in CR
100 TW
Will someone please define "flick" for me.
Regarding the weight affecting the feel during handling, the only way you'll feel it at the contact patch is when you accelerate it laterally. Without a slip or getting airborne, does it ever turn sharply, since all it does is follow where the front tire leads it? I submit that along the top tube like Johnrob has his batteries there will be many more bicycle maneuvers in ordinary riding where that weight will be accelerated laterally and therefore felt...less so when ridden like a motorcycle, and for Safe with his road racer position that is especially true.
Now if you're doing something like slaloming thru closely spaced cones on your bike, then anywhere low is going to be bad placement, and the only placement batteries wouldn't be felt is strapped on your back. At the rear contact patch would be felt significantly, since you must accelerate that weight back and forth to get around the cone. Very far forward like at the headset, may be even worse though because this is the kind of riding isn't possible on a motorcycle, because you would really move the frame under your body by pushing those handlebars quite a bit laterally to make the front to lead the rear tire around the cones. For a slalom through cones the best placement on the bike has to be at the rear axle in terms of front to back position and how high may very well be where Safe drew his line, though I think it's going to depend on the speed and riding technique and whether you stand up off the saddle, etc.
Another point Safe, I don't believe the lean on a bicycle is fully accomplished during counter steer. Maybe it's that way in road racing, but not riding a bicycle. The countersteer maneuver is long over before you get into the deepest lean in a turn. Countersteer just gets the bike out from under your weight to make it easy for gravity to do the rest.
You guys are really going to have to get out of the motorcycle mindset to really analyze added weight placement on a bike. While a bike can be ridden like a motorcycle, it doesn't have to be and typically isn't. There are a lot of times when you move the frame under you to keep your body going the straightest route and your narrow "roll axis view" falls apart in looking at what the frame does and where added weight should go.
John
Regarding the weight affecting the feel during handling, the only way you'll feel it at the contact patch is when you accelerate it laterally. Without a slip or getting airborne, does it ever turn sharply, since all it does is follow where the front tire leads it? I submit that along the top tube like Johnrob has his batteries there will be many more bicycle maneuvers in ordinary riding where that weight will be accelerated laterally and therefore felt...less so when ridden like a motorcycle, and for Safe with his road racer position that is especially true.
Now if you're doing something like slaloming thru closely spaced cones on your bike, then anywhere low is going to be bad placement, and the only placement batteries wouldn't be felt is strapped on your back. At the rear contact patch would be felt significantly, since you must accelerate that weight back and forth to get around the cone. Very far forward like at the headset, may be even worse though because this is the kind of riding isn't possible on a motorcycle, because you would really move the frame under your body by pushing those handlebars quite a bit laterally to make the front to lead the rear tire around the cones. For a slalom through cones the best placement on the bike has to be at the rear axle in terms of front to back position and how high may very well be where Safe drew his line, though I think it's going to depend on the speed and riding technique and whether you stand up off the saddle, etc.
Another point Safe, I don't believe the lean on a bicycle is fully accomplished during counter steer. Maybe it's that way in road racing, but not riding a bicycle. The countersteer maneuver is long over before you get into the deepest lean in a turn. Countersteer just gets the bike out from under your weight to make it easy for gravity to do the rest.
You guys are really going to have to get out of the motorcycle mindset to really analyze added weight placement on a bike. While a bike can be ridden like a motorcycle, it doesn't have to be and typically isn't. There are a lot of times when you move the frame under you to keep your body going the straightest route and your narrow "roll axis view" falls apart in looking at what the frame does and where added weight should go.
John
johnrobholmes
10 MW
Being able to flick a bike refers to how fast you can change direction. IE: I can flick my bike around and weave through cones, or I can't flick my bike and it feels like I am trying to steer a concrete boat.
Interesting point, I generally do not countersteer. Or at least I cannot perceive any. If riding on a white line and I want to turn, my turn is executed from the line and I do not countersteer my bike to the other side of the line before turning. I simply lead with my body and the turn starts.
Motorcycle and bicycle theories are one and the same. The only difference is power. Weight distribution and riding are mull points, as every bike and rider will be different.
John in CR wrote:
"You guys are really going to have to get out of the motorcycle mindset to really analyze added weight placement on a bike. While a bike can be ridden like a motorcycle, it doesn't have to be and typically isn't. There are a lot of times when you move the frame under you to keep your body going the straightest route and your narrow "roll axis view" falls apart in looking at what the frame does and where added weight should go."
Moving the frame underneath your body IS using the roll axis. The roll axis when your body is going in a "straight" line will be precisely at the CG of rider and bike combined, which is generally at your hips on a typical bicycle.
Interesting point, I generally do not countersteer. Or at least I cannot perceive any. If riding on a white line and I want to turn, my turn is executed from the line and I do not countersteer my bike to the other side of the line before turning. I simply lead with my body and the turn starts.
Motorcycle and bicycle theories are one and the same. The only difference is power. Weight distribution and riding are mull points, as every bike and rider will be different.
John in CR wrote:
"You guys are really going to have to get out of the motorcycle mindset to really analyze added weight placement on a bike. While a bike can be ridden like a motorcycle, it doesn't have to be and typically isn't. There are a lot of times when you move the frame under you to keep your body going the straightest route and your narrow "roll axis view" falls apart in looking at what the frame does and where added weight should go."
Moving the frame underneath your body IS using the roll axis. The roll axis when your body is going in a "straight" line will be precisely at the CG of rider and bike combined, which is generally at your hips on a typical bicycle.
John in CR
100 TW
johnrobholmes said:
Johnrob,
Mostly likely you've got some countersteer and don't even realize it. With typical bike riding it's small, and that's why I've been saying that the lateral movement of the rear tire patch is small and with little angular momentum of weight there. I like leisurely carving those turns too sometimes, but it's not really typical riding. Also, I'm not disagreeing with getting the batteries way up high at the rider+bike CG, but it's an axis point not a line and it changes location as soon as the rider moves relative to the frame. Mounting lead batteries there is all but impossible, and what I've been trying to point out is that at the rear contact patch added weight doesn't affect CG, and something Safe can't understand is that it doesn't matter if you're moving or not. Once you start moving the lateral acceleration of that weight is the only effect outside of traction issues, and you even admit that you don't perceive any counter steer, which is what would cause the lateral acceleration of that weight. Otherwise the front wheel is just towing the rear wheel behind.
You have to treat bikes and motorcycles as only cousins. Just stand up and pedal you bike vigorously with and without your top tube batteries and tell me you can't feel them. At the rear contact patch you wouldn't feel them as you push that frame back and forth. It's the movement of the frame relative to the rider and the much higher CG of the rider+bike that make it quite a bit different from a motorcycle in terms of handling, not just weight and speed.
John
John
Tiberius
10 kW
John in CR said:
Not so, but far otherwise.
John, I'm not a motorcyclist, but I'm prepared to believe the same laws of physics would apply if I became one.
There only two ways you can add weight without affecting the CG position. 1) add it to something else, 2) if the point you add it to is already the CG. Clearly, neither of these apply in this case.
Nick
John in CR
100 TW
Tiberius said:
As long as that wheel doesn't leave the ground or slip, it's as if it's not on the bike and being dragged around on the ground by the bike. The energy potential of that weight from gravity is zero, so it is like adding it somewhere else. I really don't see why everyone is having such trouble with this distinction once you look at a bike as having it's wheels on the ground. As the added weight is placed closer to the contact patch the less impact it will have on the CG of the bike with it's wheels on the ground. It's actually true of the front contact patch as well, and is why SteveCA reports good results hanging his packs below the front axle. At the front though there is more issue of lateral acceleration because the front wheel turns, which Steve reports in being felt because he has to push harder on the handlebars which accelerates that mass laterally.
I'll make one last attempt at an analogy. Take a wet mop, a big commercial size one that takes 2 hands to mop the floor. Pick it up and it's heavy at one end, with the CG well toward business end. Now put the mop end on the floor, and without moving it on the floor you can toss the mop handle around just that same as if it were just the handle with a piece of gum holding the other end in place. Now have someone stand on the mop, really changing what you guys are saying is the CG, yet the handle end still feels and moves exactly the same. As soon you pick it up off the floor though everything changes.
Now the roll axis guys will have you believe that the added weight at the contact patch it will be like the force you have to put into moving that mop back and forth as you mop the floor. That simply isn't the case and all you have to do is look at the gentle curves of the rear tire track on a wet road to easily see this. Instead it's like dragging the mop behind you, but the mop has far more friction that a rolling bicycle wheel.
John
Tiberius
10 kW
John in CR said:
Sigh. I don't think I will.
