racer
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Alright, I need to conduct an experiment on a bike that has a throttle. The bicycle in the parking lot just isn't going to get it.
I don't currently have access to a motorcycle, so, anyone out there who cares to assist, please try this at your own risk... run into a corner (not hanging off) and take your hands off the bars (roll out of the gas). The bike will run wider. But, I want to know if it will actually stand up as well merely by rolling out of the gas (with no steering input), or merely run wider.
Taking your hands off the bars should isolate the "self-countersteering" theory.
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Hey jim,
The bottom line is the need to get a grip or "lock" on the bike to create a base from which to freely operate. That is a fact of riding a bike. Whether you are holding on with your hands or your knees or squeezing the seat with your butt cheeks, you are always attempting to "lock on" somewhere all the time, even if you don't realize it. So, if you are just laying your thigh on the tank, where are you holding on? Where can you hold on?
I haven't heard it called a "calf raise" outside the gym, but, yes, without attending the school recently, I surmise that is the whole trick. And I find using it to lock on especially difficult (impossible) without grip pads on a bike with a flat sided fuel tank, ie. no lip at the top like the ZX-6R and 10R. Bascally, you put your toes right up on the footpeg, and use the same action as standing up on your tippy toes to jam your knee into that tank lip and/or the stomp grip pad. And that is how you hold on. If you do it right, you can take your hands off the bars and your foot off the other peg and even your butt off the seat and have only those two points, toes and knee, be the only thing holding you on the bike. Personally, I have short legs (29-30" inseam) and I find reaching the tank lip with my knee particularly difficult without higher footpegs. And, even being able to reach it, the grip pads make all the difference to really getting a good lock.
r
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Right, moving the contact patch further back is further back on the same side of the steering axis. More trail, shorter wheel base.
Im still trying to figure out how the "rear wheel steers the bike" thing fits into my theory.
And if the front wheel is turning out, won't THAT counter steer the bike down more? Argh.
Edit: Maybe the tendency for the bike to lift up with more velocity is sort of balanced by the tendency to countersteer it down again...
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I like to think of scenarios at extremes. So, What about negative trail? I mean ALOT lets say 50-70 mm behind the steering head.
I'm not sure I am clear about what you mean here. Do you mean the contact patch is behind the steering head itself or a line drawn through the steering head... ? That is what I call "normal" trail. "Negative" trail to me would be having the contac patch lead the steering axis.
To my understanding, "normal" trail puts the contact patch behind the point where an imaginary line extended from the steering axis meets the ground meaning the wheel will tend to self-correct into line with the direction of motion. Even when leaned over, there is a point or angle where the wheel will naturally balance or trail to. And I am proposing that, due to the compression of the suspension altering the rake/trail, the balance point or angle will be affected by more cornering force compressing the suspension. And, the more trail, the longer the lever that force has to act on. Actually, even if the suspension doesn't compress more, like with a bicycle, I think more downward force may still force the wheel to turn more outward.
I tested this idea on my associate's pro level racing mountain bike with disc brakes in the parking lot after work today and promptly crashed his bike... hard. He was not happy as he is training for the 24 hour endurance race at Big Bear next week and I tweeked the front wheel a bit...andy way...The left handle bar dug into my gut so hard that it tore a hole in my abdomen that is bleeding as I type this. No... really. I wish I had a video. I've never ridden a bicycle with disc brakes until today. I didn't stop to think that this guy routinely runs down mountains at like 60-70 mph or so and that his brakes might be different than mine. Me... I barely break 40 mph on my way to work everyday on my old road race bicycle... so there I was playing games trying to make the bike "run wide": around th parking lot and I barely touched the front brake, like a whisper of a hint of adding a microgram of pressure... like I laid my finger on the lever and the front wheel locked so hard I was over the handle bars and tangled up so fast my head spinning and I couldn't get untangled... not a dignified position for a man in his mid-forties. Anway... I just want you to understand my level of dedication to, er... stuff like this and to know just how much I have already sacrificed in pursuit of "the answer"... lol
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Wouldnt the bars turn inward slightly since its the inside, leading edge, of the tire bitting the surface (pulling inward). IE a bicycle ghosting down the road. the bars will turn slightly to the inside by themselves. That tells me that leading edge and trail as you said, has something going on which is pushing the bike wide. Obviously this is without rear wheel power being put on the ground. Does this idea go out the window on the gas? IE a bike leaned over on the gas with the front wheel off the ground. Thus rolling on thru the whole corner.
I like to think of scenarios at extremes. So, What about negative trail? I mean ALOT lets say 50-70 mm behind the steering head. How does that effect the self correcting properties of a two wheeled vehicle? Again I'm posing a question. I dont have the mathematical abilities to put this on paper. I'm more of a build it and see what happens kind of guy. I can relate with your playing with a bike in the show room to see what happens
OK, well I played with the KLX 110 instead of the CRF 80 today because it looked like it had more rake and might produce more pronounced results, which it seemed to. That said, we have indoor outdoor carpet and there are knobby tires on the bikes. Anyway, the more I played with the bike and looked at what happened and thought about what I wrote last night, the more sense it made.
I think if you apply force downward through the fork with "negative" trail, you will be forcing the wheel to turn more into the turn. I would define negative trail as a grocery cart with a front wheel turned backwards.
PS I'm not a big fan of using math to teach a concept. I think it acts like a wall to people who aren't skilled with it. My longstanding mantra is that I can teach the concept of any physics or engineering to anyone without the math easier than with it. That said, Tweek asked for a formula, so... I obliged. (That is the first time I have worked with math or equations of that sort since college... around 1986-87. That would be after slide rules and before cell phones and CD's. We had LCD digital watches and hand held scientific calulators, but no pc's or www.
Wait, not true. I used it a good bit when racing... like when deciding how much to drop my triple tree on my FZR's or add ride height on my GP bikes.
Oops, and I used it to win a bar room bet a couple of years ago ... I proved the altitude of geo-synchronous satellites was what I said it was ...very similar except using Pi and time instead of force, trig and vectors.
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OK, re-reading Chapter 13 of TOTW II...
"...once the bike is fully leaned into the corner, the rear end "steers" the machine." (p.58)
OK, so, adding more velocity, the bike wants to stand up due to increased cornering forces and we must apply force at the bars (or shift COG by hanging off) to maintain lean angle. But we have to lean even further than before to maintain radius. There seems to be a discrepancy. Something seems to be missing.
What happens when the rear wheel rolls faster? It must track a wider radius. Is it really "sliding"?
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*yawn*
*slurps coffee*
Yep... madman idiot.
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*blush*
Aw shucks you guys... fuhgetaboudit.
I'm glad just to have the opportunity to help out. The list of people who helped me and gave of themselves in ways that I can never repay or whose names I never even knew and helped simply because I was a rider or racer or human being in need is endless. Paying it forward doesn't quite say it. I owe a debt of responsiblity to help because I can. And, in any case, being part of the solution is gratifying to me. If something I've learned from my experience can be passed on to help an individual or the sport in general, then my life has meaning.
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And, taking it another step...
It has been suggested that when a rider rolls off the gas in a corner, the bike tries to countersteer itself up to less lean angle and that this is why a bike runs wide when we roll off in a corner.
However, given the line of thought in my last post, perhaps it is the forward weight transfer causing increased compression force at the front turning the wheel out to a wider angle. Hmmm...
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OK... intuitively, I agree with 2bigalow. Thinking about understeer/oversteer. The front pushing into the turn. But once the bike is leaned over or the car is in the turn, without sliding, I think the car's turn radius will follow the angle of the front wheels and won't increase radius unless you slide some. So, I'm still leaning toward the front wheel angle changing somehow on the bike. We know that having the front compressed prior to turning creates "quicker" steering geometry, ie a faster flick due to a steeper steering head angle which gives us a more effective lever due to the contact patch being closer to the COG and less trail making the bike less stable or twitchy.
If we take the example of a chopper with really long forks and think about what happens when we turn the handlebar, it seems to me that the caster angle, that is the axis about which the wheel turns (nearly vertical in a car and less so on a sportbike) is even less vertical (closer to horizontal) on the chopper, eh? That is the wheel doesn't really turn exactly left or right, it also turns "up" and "down" somewhat. The front wheel is sort of 'heeled back' and, when turned, the contact patch actually moves off center with the bike and sort of rotates rearward on the wheel/tire wrt vertical. (I need to make a diagram here. The front wheel actually tracks a different arc than the rear. There are actually two wheel tracks running side by side through the corner.) So... here's the rub... when cornering forces are applied "vertically" through the bike, the "downward force" is not centered over the front wheel or more importantly the contact patch. It is actually on the inside of the contact patch. And it is applied at a forward angle as well due to the rake and more importantly applied forward of the contact patch due to the trail! Remember, trail is the steering head angle extending forward of a vertical line dropped from the axle, ie the contact patch when the bike is straight up and down.
What happens to the trail when you are leaned over? The front is compressed from cornering forces... less rake... less trail? Now what happens when you apply that compression force while leaned over? The angle of the force application is ahead of the contact patch. Hence, downward compression forces the wheel to attempt to straighten itself by applying force ahead of the contact patch. Or something like that. I think. Maybe. Or maybe I am sleep deprived and having another brain fart. I am too tired to edit this or read for mistakes. There may be glaring flaws of logic or dyslexic sentence construction. Does this make sense to anyone? Would you admit it if it did? lol
I'm going to bed now. I hope this doesn't read like the raving rantings of a madman idiot when I wake up tomorrow.
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The Sportmax/D208's used to come in a street compound and a full race compound way back when I was running them. Now it appears the Qualifier is the official "street" tire and the Sportmax GP/D208 are the pure DOT racing tires. (With a dual compound rear to boot!) And even the Qualifier seems to be a full generation of technology beyond the last time I rode/raced on DOT tires. Wow. I can't wait to get back on track!
What is the major difference between the Sportmax and the D208? More grip? And more money?
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Hey guys, very interesting post.
Isnt a wider arc caused by rolling friction (or the lack of) when the lean angle is maintained? When tires wear, small balls of rubber are tearing of the tire carcass and being shed. The more speed that is added, the more the tires slide. IE a car for example (no lean angle here) making a left turn, at full wheel lock, at a slow speed, will create an arc, 'X" amount in diameter. When speed is added the arc becomes larger relative to the speed. Rolling friction? Forward velocity?
I'm posing a question, not making an argument. I will not even try to pretend my mathematical abilities are close to the hieroglyphics I've seen in the previous posts.
One would need to be biased toward more front sliding as rear biased sliding would tend to tighten the arc... no?
Ok... I slept on it.
Then I went to work and messed around with one of the smaller dirt bikes in the showroom. I am not certain yet, but, it seemed that as I compressed the suspension from a leaned over position that the front wheel turned outward a bit from its starting position. I can't verbalize why yet (probably to do with the rake and where the tire contacts the ground, etc), but, I will spend more time with it tomorrow.
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Now if somebody could figure out a way to make local adjustments to G we'd be in business.
ROFL
I was just saying that this morning in reference to my perpetual motion free energy machine....
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You know it is funny that you mention that. I was reading some of Racer's post this morning and was wondering who Racer was. Its like the wizard in Oz!
Erm... pay no attention...
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Hey racer where's your signature pic? You have more posts than me. Ha!
I have more posts because I've been a member longer. And because I got laid off the last two winters and there's nothing much else to do around here from January to March. Except go skiing. And I'm too old be a ski bum anymore. My knees can't take it.
As for my photo, well... being that I am so good looking, I don't want to give you guys a complex... lol. Honestly, I am working on it. My digital camera was stolen along with everything else in my storage including my last race bike, leathers, three helmets, two computers, a top and bottom racing tool box with power tools, starret mic's and calipers, HRC GP tools, etc etc etc.... so, a new camera is on the list. I suppose I could scan my passport....
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If the suspension/geometry compresses/changes with more speed.... can we even use such a simple model at all to accurately predict lean angles?
Descriptive vs prescriptive?
We could figure out specific forces from lean angles and velocities at given radii, but... I'm not so sure about this entire model after all if the radius is an active/dynamic variable affected by mass... eh?
Oh my head is starting to hurt...
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I have significantly edited my last post due to a brain fart regarding adding/losing teeth to the rear sprocket to compensate for a larger rear tire circumference.
My sincere apologies to anyone who was confused by the bad data I posted. Hopefully the new post makes more sense.
D'OH! My bad!
racer
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Aren't the coaches listed on the CSS Team page? And classified as "CSS Team" group members under their screen names and photos here on the forum? Well, I guess 2bigelow doesn't go by his real name or post a photo. (But, I would think that is his right. I'm sensitive about online privacy myself.) And "CSS Team" might be a tad ambiguous. I don't know... I always thought it was obvious who the coaches were... are other coaches "lurking" behind "screen names"?
OK, that's it! OUT THE COACHES!
Make their screen names or all their posts different colors and change their group classification to CSS COACH! Or some other obvious thing that allows them to retain their privacy if they prefer.
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No, I don't think you are making a hash of things.
I agree that adding in things like sliding and friction will unnecessarily complicate our admittedly simplified model, but, I don't believe the model is over-simplified for this particular question either, ie. I don't think we need calculus to answer the question, at least not conceptually.
That said, if the rear tire is sliding, won't the lean angle tend to decrease (er...lean more from vertical)? I am not sure what the answer is. My gut says that it must be mechanical. It says the front wheel must have some bearing on the direction relative to the amount of weight on it and that it must be the front wheel changing its angle of turn into the corner (maybe combined with a slight increase in wheel base) due to the front lifting more under acceleration. But... are we really talking about forward acceleration? At a higher constant velocity, won't the cornering forces increase and cause the suspension to compress more??? Argh!! Then again, maybe it is a matter of the rear wheel tracking a wider arc by itself, but, I don't know why. I'm going to have to sleep on it.
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Hi Stevo,
Yep. Given the known constant acceleration of gravity and the radius, circular acceleration can be found using either velocity or theta without needing to know the mass. And, whether a rider weighs 100 lbs or 200 lbs, the bike will (theoretically) lean the same amount for a given radius and velocity (assuming the rider is not hanging off). Thanks for pointing that out.
However, that said, I think that simply plugging in that mathematical 'shortcut' sorta sidesteps the fundamental physical concepts involved (like component force vectors, etc.) that many foundational riding techniques and concepts are based on. For instance... hanging off. And why hanging off allows you to corner faster.
In other words, while it is true that the ratio of the component force vectors (as opposed to the actual forces) is what is critical to mathematically solve this particular problem, I think seeing the actual individual forces drawn out in a free body diagram might be critical to learning/understanding why.
racer
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Welcome to the forum, bigdawg! Glad you could re-join us after such a long absence from the "scene".
As for "not staying in tune" over the years, I wouldn't worry about it. Judging by your photo, your body position looks picture perfect. Perhaps even a model for others to emulate...
racer
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in general I don't think a super accurate model is needed to get to what I was after.
Nnot sure what you mean by "super" accurate, but... the number significant digits after the decimal point in the solution are required to solve the math accurately. Remember how far off the reverse calculation was when I rounded off just a few hundredths?
simply - about 30mph is how fast you need to go in order to lean the bike over 50degrees.I don't mean to be pedantic, but... about 30 mph is how fast you need to go to lean the bike over 50 degrees for the given turn radius (50 ft). I'm sure that is what you meant. I just want to be clear for those who might not have your level of understanding.
So the answer to my original question - lean angle == turn radius is false. the two variables are part of a larger system affected by velocity and weight. For instance - keeping the lean angle constant, and increase velocity. Radius increases.Why is that? Why does the radius increase with more velocity? I mean, sure, there is more horizontal "cornering" force working to push the bike wider in the turn, but, mechanically speaking, what happens on the bike to cause or allow that to happen? The radius of the wheels doesn't change, neither does the wheelbase really. Are the tires sliding or "creeping" sideways? Does more weight shifted to the rear cause the front end to lift and alter the rake and front wheel angle into the turn? Or lengthen the wheelbase enough to describe a longer arc at the same lean angle? But, wait... isn't the rear wheel what dictates the direction of a motorcycle once it is leaned over?
The football half-back's radius is dictated by where he puts his foot which leads to how far he needs to lean to remain balanced. The side cut of the snow skier's ski largely dictates the radius the ski will carve at a given lean angle. And the same is true for the "rocker" or curve in the blade of an ice skate. These examples do not seem to follow the same formula as a motorcycle in a turn in that their turning radius is largely mechanically "pre-set".
So, what gives?
???
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It's a really sweet ride, Marty. Very classic lines from an era I miss. Thanks for sharing that.
So, is the upside down fork stock, then? Are the upper tubes anodized?
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I spent several years racing 125's myself. I outgrew them sideways when I turned 40 and my winter coat didin't melt like it used to... lol.
Seriously, though, you are right in that it seemed physically effortless compared to a larger four stroke like a 600. Or even a 400... having all that weight to throw around takes a bit more muscle. As far as mentally effortless... hmm. I don't know. I started out on 600's and then went to two strokes and, to me, it takes a lot more mental effort tuning the machine and constantly tearing it down everyday throughout the weekend to check the ring grooves, piston skirts, under the crown, etc, etc, etc. I miss just rolling the bike out of the van, filling the tank with gas and not having to do another thing to it until I put it back in the van Sunday night. Oh well, there's always a trade off somewhere I suppose.
I think the best place to get an objective opinion about your riding would be from the coaches at a UK school session. I don't put much stock in the "maybe it will just click" plan.
How To Handle Dipped Or Crested Turn?
in Cornering and Techniques
Posted
1. Vertically as possible.
2. Stay in the throttle. Do not roll off.
Yes.
Timing roll-on helps? Not if you are waiting until after the dip to roll on.
Rolling off for a dip or bump only makes things worse by weighting the front.
Check out page 59 of TOTW II.
Good luck,
racer