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  2. Because it is very complicated, the subject of friction between rolling rubber and pavement has been and will be debatable. It goes beyond the simple empirical determination of a coefficient between two sliding surfaces. Rubber is a material which properties change a lot under mechanical and thermal stresses. It acts like a viscous-elastic material and it suffers from elastic hysteresis. When the same area of rubber hits and partially slides over pavement, internal chock waves develop and the original softness of the rubber has less time to recover. It has been demonstrated that for stationary surfaces and for light pressures in the contact area between a tire and a road, the rubber will only make contact with about 5% of the road surface. As the contact pressure increases, the rubber gets squeezed into many of the smaller-sized cavities. The coefficient of friction is not constant for different conditions. Many universities have studies and papers explaining this. If interested, you can research "elastoplastic contact between randomly rough surfaces". https://en.wikipedia.org/wiki/Viscoelasticity https://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis Nevertheless, let's assume that friction and area are more or less independent in this case. The useful range of traction of any tire depends on the pressure/temperature/stress over the contact patch. If that is true, then the rider needs to unload the front tire some, and overload the rear tire some, in proportion to the differences in the areas of both contact patches. If the rubber compound and manufacturer of both tires are the same, he/she wants to achieve the same pressure/temperature/stress on both contact patches while cornering. The whole idea of proper throttle control to achieve a proper weight distribution while cornering is based on that concept. "To determine an ideal scene for traction, machine-wise, we start by simply measuring the contact patches of the tires to discover what the basic distribution of loads should be while cornering. Roughly speaking, those measurements show that 40 percent of the total load should be up front, 60 percent at the rear.......... At the point where the correct transfer of weight is achieved by the rider (10 to 20 percent rearward) by using the throttle, any big changes in that weight distribution reduce available traction." - ATOTW-2
  3. That should bring your chest closer to the tank and your head a bit forward and to the inside. But some of it could be your fit on the bike, if you feel there is a reach to the bars then it's hard to get a good position. If looking from the front, you should be to the inside of the centerline and along side the bikes CoG.. as shown by Marquez and tried by me..
  4. Your shoulders and arms look tense, try letting the inside fall into the apex.
  5. someone suggested to me a body positioning tip. It's essentially the same advice as above. But if you think armpit over gas cap, you'll have an extra cue to help remember to move that upper body over.
  6. Thank you for sharing your insight, Hotfoot. I've never thought about the bars moving when being hit by gusts, but since the bike is often blow off course that seems quite likely.
  7. If you look at the rider's body movement, you can see that it's not a smooth ride. I'm thinking a combination of bumpy road, wind buffeting (the riders are pretty close together and the speeds are high, getting up into the 150mph range), and a much stiffer suspension and tire carcass than you'd see oh a street bike, plus a bike setup that is much twitchier than a cruising bike so it reacts more. Also the hard acceleration and braking may cause the rider to add some unwanted bar input, you can see from the rear view how much the riders are moving around. On my racebike at one particular track there is a high speed section (150-170mph range) close to a wall and the wind buffeting from the wall or any nearby rider is very noticeable, it wobbles your head around and makes the bike move around, you can feel the bars move, even though you are going straight. Have you felt your handlebars move in wind or when passing a large vehicle?
  8. I agree that managing the contact patch, for all practical purposes, is the way to improve cornering performance. It may or may not be the size of the contact patch vs the forces you apply on the patch, but the logic to balance the chassis and the weight on each tire gives the same result. I don't see this is contradicting anything of the Code principals.
  9. Drag racers rebuild their engines after each run. You really think cost is preventing them from running a skinny tire if they could gain a tenth? No. I have corresponded with the author of the article you link and while he might understand physics, I'm not convinced he understands motorcycle dynamics in a practical sense. The truth lies somewhere between the two. I have yet to find the answer. But the closest reasoning I've read that the coefficient of friction rather than being a constant can vary with temperature. Large contact patch might resist temperature change hence resist changes in coefficient of friction. Additionally, coefficient of friction does not accurately describe a rolling and cornering tire that operate with some slip angle. The tire is not stationary but not sliding either. No, it is too simplistic to say contact patch doesn't matter. From a practical motorcycling sense, much of Code's teaching talks about contact patch and friction. Based on all that practical experience of thousands of riders, there is some truth to the statement. Just my opinion.
  10. If a fully heated race tire balloons then it makes sense. But since there is still some flex in the carcass I think there's something else going on. I will concede that I don't know what or why. I'll get back to you after I study more on the lack of relationship that surface area has to tire grip.
  11. If you read through the article I posted a link to, it concludes that wider tires primarily are for wear reasons. As we all know, a rubber tire sacrifices itself to provide the friction (all the gum balls on your front tire after a track session prove this is so). A small tire dealing with significant friction demands, and in drag racing probably being overloaded will wear fast. So if you had the smallest tires that could support the weight of the car and did a run, you would likely destroy them due to friction heat and mechanical stress. If you were really serious about winning a drag, you could have single pass tires that had just enough strength for a run and then die. They would be smaller and lighter. But you would change tires every single pass. So the extra rubber is for wear and handling of forces - vertical, lateral, roll on the sidewalls/carcass, flex to absorb acceleration and deceleration shock, bumps and so on. It doesn't provide more friction or grip.
  12. Great. Practice is a good way to improve your BP. What I see from your photo, you might put some attention to your head position. In that photo a good head position will be if your head is near of your left hand, close to touch it. I know, it isn't easy but if you practice often you will get it. If you Focus in that your back also will form a V shape with the bike axis, and your right arm will be fully extended. thats was my 2 cents. keep riding!
  13. Pressure... bigger the tire the more pressure it can handle. Ignore street riding where tires don't heat up as much as racers on a track and temperature/pressure (direct linear correlation) becomes a major issue for the tires. Heat building up inside the tire creates more pressure; pressure is also the force over an area so the smaller the contact patch the more pressure on the tires once again... nobody wants a blowout http://www.autosport.com/news/report.php/id/122707. Of course heat on the exterior of the tire and shearing also becomes an issue and you can control it to an extent w/ the size of the contact patch but becomes a careful balance; which is why in this regard I said larger contact patch is better for the most part.
  14. I took Level I & II last year and since then I've practiced trying to improve my BP. It was an amazing full 2-day experience! Those one-on-one sessions with coaches were super helpful. I've tried to apply those skills whenever I ride. Relaxing the arm, strengthen core, half-cheek off, head/eye movement, Quick turn etc. Here's a recent photo attempting to improve BP by applying those skills and techniques learned at the camp. Not trying to become a racer but simply to gain proper BP while riding. See photo below and please provide any constructive criticism to further improve my skills. Thanks, Will PS: plan to return and finish up Level III & maybe even IV.
  15. When I shop for clothes I always have to take into account my requirement for long sleeves. Couple that with a torso thats taller than average and it's a non-aerodynamic recipe. It's one of the fun things about engineering- making wise compromises. I would just like to be able to get through a full track session at 80%+ without cramping.
  16. To serve what purpose?
  17. The problem with contact patch is majority of racing community (motorcycle, car, drag) don't have the correct understanding of it; because they get their info from other people in that community that also got it wrong to begin with (ie. "my tire guy said..." or "(some famous racer or person involved in the community) said this and I'm going to take his word over something from physics" which then follows up with "yeah that may be true on paper but in the real world there are a lot of other things going on and I know contact patch gives better grip"). Personally I always feel someone loses credibility when they say more contact patch gives more grip. As for the drag racing guys here's an article from someone in drag racing giving his explanation and clearly stating contact patch is does not give more grip but for shearing purposes and pressure. http://www.onallcylinders.com/2016/07/14/drag-slicks-traction/ One could go on stating contact patch and larger contact patch is a good thing and leave out any physics aspect of it; don't ever say gives more grip and would be 100% correct. But they go on to give the "science" explanation for no reason w/o knowing any science but what they heard or read on some forums and give the wrong information to many innocent bystanders. In fact if you take any classical mechanics in physics and get to the chapter on friction most common question in class given to students is "If the friction force equation is solely dependent on the coefficient of friction and the normal force and has no input based on the size of the contact to the surface then why do race cars have larger tires?" I promise almost everyone taking physics google this question and most information out there especially on forums including physics forums get it wrong. For those that say it's to get more grip; all you need to do is ask where did they learn that from? It's never from a physics class. You can watch the MIT Physics class on youtube that covers this exact topic and that question being asked as an assignment. Just know contact patch does not give more grip... but contact patch is important and you want to have the largest contact patch possible (for the most part). As for why it's important if you really care it's primarily for pressure. When dealing with fields like drag cars, and to some extent with motorcycles with softer compounds it also has to do w/ shearing. Sorry just a pet peeve of mine -.- (something CSS UK at some seminar also got wrong w/ some tire rep at an expo; need to find that video link) P.S. on a side note... not one instructor at CSS lvl 1+2 at NJMP said this so I was very pleased They left it at more contact patch and nothing else (intentional or not). See you guys at NJMP again in a little over a week.
  18. The handlebars move a lot and quite violently. Not unusual per se, but quite strange for me to see it also in virtually straight line riding. The few times I've filmed myself, that doesn't happen to me, so I guess it's down to me being slow, but it would be interesting to hear why all the movement in the front.
  19. Better aerodynamics primarily.
  20. I know that's what physics says but the guys that do drag racing have a different experience. They put the widest tires they can muster on the rear of the car/bike to increase contact patch. The result is better ability to put power to the ground.
  21. What are the designers trying to achieve with low bars?
  22. If that didn't compute for some folks, remember friction is proportional to the normal force applied between the two surfaces. On a flat road, that only comes from Gravity. On a banked corner just standing still you feel like you might slip down, because you have less friction (Gravity is not perpendicular to the surface, so you have less force creating less friction). When you ride at speed around a banked turn you get more friction leaned over because some of the inertia will add to the normal force and increase friction. This is why you can go faster on a banked turn. Likewise, as stated in Twist II, as you come off a banked turn you need to watch your lean angle, because friction will reduce and therefore your demands on grip might exceed what you have. I don't think it actually because the lean angle increases, for if you are on the same arc and have the same lateral forces applied your demand for grip has not changed, but it is because the amount of grip available decreases.
  23. MOTORRAD tested a ZX-7R (so a long time ago) stock and with 4 inch riser. Eveybody went significantly faster through the slalom tests with the taller bars. The less experienced riders gained more than the experienced racer. After doing a ton of laps, pushing himself to his limits, the racer finally managed to set the fastest time around the race track with the stock bars - it was a pride thing for him - but it took a lot more effort to ride with the lower handlebars. Take a look at the handlebars used in the early Superbikes AMA days. Pretty tall and especially wide to gain leverage. Now look at the handlebars of Kenny Schwantz' RG500. That's a bike only 285 lb light, yet Kevin still had wide and tall bars compared to most of his competitors. In my humble opinion, you would love moving the handlebars up.
  24. Slightly off topic, but this is not correct. The contact patch size has no impact on traction. It is a complex topic, and I like this explanation best http://www.stevemunden.com/friction.html. The second law of friction states "Friction has no relation to contact surface area". Friction depends entirely on the Force (not pressure) applied between the two surfaces. If we assume the rubber compound and road surface of both tires are the same at any given point in time, the grip on front and rear has nothing to do with the size of the contact patch and only to do with the amount of force applied. Moving around on the bike changes the forces applied to the tire and the MotoGP style uses less of the available friction than other styles - it is not because the contact patch is different specifically. The grip at all angles of lean on the same tire on the same surface is the same.
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