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Tmchcrk
| | Posted on Thursday, November 04, 2010 - 12:11 am: | 
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Ride we shall do.  |
Smit3833
| | Posted on Thursday, November 04, 2010 - 12:17 am: |
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All I remember from Eigenvalues in numerical methods class is that I never want anything to do with them again unless I am getting paid very well and using matlab. |
Fast1075
| | Posted on Thursday, November 04, 2010 - 05:49 am: |
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Step away from the calculator and think about tire dynamics...it is not a stable lab experiment....it is far more complex.
This discussion reminds me of some of the discussions I have seen between people about wheelie bars on drag bikes...dynamics. |
Clk92vette
| | Posted on Thursday, November 04, 2010 - 02:06 pm: |
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I find this to be a fairly interesting discussion filled with good information and bad. Most of the misinformation seems to be tied to the misuse of terms. I have come up with a definition to help out:
Traction Pie: A liquefied concoction of apples, brown sugar, flour, butter, and cinnamon sipped through a straw after a 90 mph highside.
Here is what I know to be true:
1) Ultimate grip is the amount of lateral force that a tire can resist before it breaks loose. The ultimate grip does not depend on the lean angle unless the surface area of the contact patch and/or the compound of the tire change as the contact patch slides radially on the tire. Multi-compound tires do have stickier rubber on the outer edges of the tires; but the contact patch has to decrease, at least slightly, since you are moving closer to the much stiffer rim of the wheel. I have not spent any time researching this subject, but I have to believe that the high performance bike tires are designed so that the ultimate grip is the same or slightly increasing as the contact patch moves toward greater lean angles assuming you stay inside the edge of the tire.
2) The amount of lateral force exerted on the tire in a corner is directly proportional to the location of the center of gravity of the rider/motorcycle combination. Leaning your body off the bike allows the motorcycle CG to become more vertical which in turn decreases the lean angle of the motorcycle. This decreases the horizontal component of the opposite and equal resultant vector on the contact patch which is what determines when you exceed the ultimate grip of the tire. Thus leaning your body off the bike allows for increased bike velocity for the same turn radius. |
Xl1200r
| | Posted on Thursday, November 04, 2010 - 02:38 pm: |
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2) The amount of lateral force exerted on the tire in a corner is directly proportional to the location of the center of gravity of the rider/motorcycle combination. Leaning your body off the bike allows the motorcycle CG to become more vertical which in turn decreases the lean angle of the motorcycle. This decreases the horizontal component of the opposite and equal resultant vector on the contact patch which is what determines when you exceed the ultimate grip of the tire. Thus leaning your body off the bike allows for increased bike velocity for the same turn radius.
Hanging off of the bike does not change were the center of gravity is - it may move it up and down, but the angle the COG makes with the contact patch and road surface cannot change for a given radius at a given speed. It doesn't matter if you're riding a Schwinn or a Goldwing - it has to be the same or the bike will fall over.
Proof? Ride down the road in a straight line. The bike stays upright because the COG is directly over the wheels. If you hang off to the left, the bike must lean to the right in order to keep the COG directly over the contact patch. If not, you fall over.
This same principle holds true at lean, in that the COG never moves laterally in relation to the contact patch (i.e., the angle never changes). This is basically the same thing as going down the road straight, except that the centripetal force from the turn more or less changes the direction gravity is acting. The fast you go or the tighter the radius, the sharper that angle needs to be in order to match the COG with the combined lateral force/gravity vector. How high the COG is makes no difference - you could strap a lead brick to your helmet, the angle has to remain the same. |
Anonymous
| | Posted on Thursday, November 04, 2010 - 03:15 pm: |
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Aaaauuuggghhh! Just ride. The actual math involved here is so far beyond what most people know it isn't funny. There are about 400 simultaneous equations happening here, and the importance of many only start to occur at the limit. People try to solve this with about 10 of them, or maybe 3 or 4. It really is complex.
But simply put from a rider's perspective, if you want to fast, do what the fast guys do. The human brain, properly trained, can solve a shitload of simultaneous equations intuitively even if you can't write down the math. And the math it takes to really do this right is way too rigorous to be fun for 99.99% of people. OK, 99.999999999 |
Stirz007
| | Posted on Thursday, November 04, 2010 - 04:14 pm: |
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Anon - well put.
There was a question about whether friction is generated at a standstill - I had tried to explain that even under static conditions, tire/pavement friction is present. In motion, not only are there tons of simultaneous equations, they are also constantly changing.
I have that issue here with some of my staff - I ask them what time it is, and they tell me how to make a watch. (BIG picture, guys!!)
Still, that photo Catalan posted is pretty incredible!!
JM |
Clk92vette
| | Posted on Thursday, November 04, 2010 - 05:29 pm: |
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Ano: What we have here is a good old disagreement regarding Newton's Laws...nothing but good clean fun.
XL: I agree that the combined CG remains in the same line with the contact patch for a fixed turn radius and a fixed velocity. The point you are missing is that leaning off the bike moves the location of the combined CG relative to the bike’s CG. This allows the bike to remain more upright which decreases the lean angle of the wheel and thus decreases the lateral load on the tire. Also, strapping a brick on your head will not change the lean angle of the wheel as long as it is in the same line as the combined CG and the contact patch. If it is not located in this line then it will change the lean angle of the wheel. |
Xl1200r
| | Posted on Thursday, November 04, 2010 - 05:46 pm: |
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I'll go back to my previous argument:
Changing the lean angle of the bike doesn't change any factor contributing to the lateral forces on the tire: bike weight, rider weight, speed, turn radius, tire compound, etc etc. So explain to me what changes that increases the grip? Lean angle is irrelevant as we've already agreed that the actual lean angle with the COG of doesn't change. This, of course, all assumes that you don't lean so far that you're over the shoulder on the tire.
So I'll pose the question again - assuming the contact patch doesn't change in size (it actually gets bigger as you lean, but for the sake of argument we'll keep it the same) and the tire compound doesn't change, why would the contact patch care what the angle of the bike is? |
Anonymous
| | Posted on Thursday, November 04, 2010 - 09:22 pm: |
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To do a motorcycle chassis design right you need to do more equations than most people know about is my point. Physics are always in play but then you need to know all the equations. I get frustrated when I read a "technical book" that's about as deep as a stone skipped off the surface.
And dragging your elbow on the ground is more common than you think with fast guys these days. Cory West's elbows were well scuffed after New Jersey AMA Superbike race in 2009. On standard Dunlop AMA spec tires. Doesn't take a Moto GP bike... |
Mickeyq
| | Posted on Thursday, November 04, 2010 - 09:30 pm: |
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Anon. You are right! I remember a pic of Ron Haslam on a 500 HondaNSR and he was dragging elbow. That's above my level of experience for sure. Bottom line, is riding ability--Road racing is high speed ballet. I have not felt more assured on any street bike as my 1125R. |
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