The Holy Grail
Reprinted from the February, 2009 BMW Owners News, with permission of the BMW MOA and Roger Wiles
By, Roger Wiles
What is that Holy Grail of motorcycling that is continually sought by competent riders? Cornering at high speeds? Emergency braking? Wheelies? Sliding the rear tire under throttle? What is your Holy Grail— the one riding technique you prize above all others?
Let’s consider some physics as we think about this. Try this: Lay a one-dollar bill in front of your bike’s front tire, and another just ahead of the rear; now, roll the bike onto the currency. Likely, you will still be able to see some part of either or both bills. So, your motorcycle is connected to the pavement with about two bucks worth of contact patch. Technically, a total of 31 1/2 square inches of connection, or contact patch—a bit over 15 square inches at each end, often a bit less. An auto, by contrast, has nearly five times as much contact-patch area, ten bucks or more, and that is spread out over four tires that are near all four corners, instead of just two tires in the middle of the vehicle.
What keeps the contact patch area of each tire connected to the pavement? Gravity, of course, which produces weight. By “connected,” we understand that the tire continues to roll at road-speed, without sliding, spinning or skidding. So long as both tires remain connected to the roadway, the rider has the capability of exercising full control over the motorcycle. The rider is able to change speeds, change direction and stop, precisely and at will.
If either or both tires slides sideways, skid or spin, that fragile two-dollar bond that keeps the motorcycle connected to the roadway is compromised, and often, gone altogether. Once that happens, the rider can suddenly become an unwilling passenger; never a good thing! So, how can we conserve, preserve and manage that meager little bit of connection, the contact-patches, our meager two-bucks worth?
What about weight? The forces of gravity, pressing the bottoms of the tires down onto the pavement produce an element we know as traction (the resistance to slippage between two surfaces which are pressed together, when there are opposing forces on each, i.e. the tire and the pavement), and the more weight atop a tire, the more traction exists at a given moment. So, weight is a good thing, right?
Sure, so long as the weight atop each tire remains near a constant amount, and the amount of weight atop each tire changes, when it does change, slowly, rather than abruptly, as the motorcycles accelerates, slows or changes direction. What can happen if there is not enough weight on a tire as the rider maneuvers? What if too much weight arrives atop a tire too suddenly? MotoSafe readers might feel a bit misled—you thought we were looking for the Holy Grail, and here you are studying physics!
Perhaps some science will lead us to recognize the Holy Grail, and help us find it. Consider competent operation of the front brake; professionally-trained novice riders learn to ‘squeeze’ the front brake, progressively and firmly, in order to slow or stop. What is the alternative? The rider grabs the front brake lever, traveling through the slack in the brake system at warp-speed, and applying a great deal of braking force all at one time. Why is the constant-speed squeeze preferred to a grab?
Think of how the hood of your car behaves when you apply the brakes; it goes downward, doesn’t it? This transfers more of the auto’s weight onto the front tires. Does your motorcycle do the same thing? Sure! As the competent rider operates the front brake lever progressively— let’s define progressively as an event that occurs over a period of time and at a near-constant speed—a substantial amount of the composite weight of the machine, rider(s) and cargo is, also progressively, transferring onto the front tire. What does more weight on the front tire provide? More traction, of course, which allows the rider to safely apply even more braking force and stop in a shorter distance.
Remember, we only have the potential for a dollar’s worth of traction on the front tire, at best, so the more traction we can get in a controlled manner, the better! Now, modern motorcycle brakes are often extremely powerful, and that’s a good thing; but if too much braking-force is sent to the dollar-bill front contact patch before all that helpful weight gets there, the front tire is no longer ‘connected’ to the pavement—we’re skidding, but usually not for long! Without that front-tire connection to the roadway, we cannot balance, and the rider usually crashes.
Have you guessed what the Holy Grail is yet?
What other motorcycle controls can affect how much weight we have on our tires at a given time, and how quickly the weight changes? The throttle? Clutch? Handlebars? Consider the throttle; when the throttle is rolled on from idle while riding, we often experience an abrupt jolt, the result of the transmission and drivetrain taking up its slack suddenly. The same jolt is often experienced when the throttle is rolled off to full-idle abruptly.
Try this: Tie a 10-foot rope to a lamppost, take the other end in hand and jerk it tight, quickly. Feel the jolt? Now, tie something heavy, like a good-sized sledge-hammer to the middle of the rope and try the same experiment. No jolt, is there? Could that drive-train jolt to the rear dollar-sized contact-patch cause the tire to slide or spin, especially in slippery conditions? Of course. Consider the rear brake as if it were the hammer; overlapping a small amount of rear-brake application while rolling on throttle, especially when the throttle is coming off idle, allows you to use the rear brake as something akin to a shock absorber, damping out the abrupt jolt.
When slowing, particularly for a turn or curve, what happens to the motorcycle’s chassis when the throttle is rolled off to full-idle abruptly? Much of the composite vehicle weight moves forward, also quite rapidly, doesn’t it. Is that effect even more noticeable if brakes are also applied hastily? Suppose the rider overlapped use of brakes and throttle, rolling off the throttle gradually, and beginning to apply brakes while there is still some driving force pushing the rear tire forward; do you suppose the weight-transfer would be more steady and easier to control?
Do you treat the clutch-lever like a light-switch, or like a radio’s volume control knob when shifting gears up or down? Light-switch mode is likely to produce the same kind of abrupt jolt. A rider using “volume-control” mode, using the friction-zone area of the clutch like a torque-converter in a car’s automatic transmission, can smooth out the power delivery or engine-braking forces as gears are changed, and will probably minimize the risk of over-spending the back tire’s one-dollar contact patch.
Did you find the Holy Grail? There was a good clue in the preceding paragraph.
As a rider accelerates or decelerates, we can see that composite weight shifts fore and aft; effective total vehicle-weight also INCREASES when we change direction, negotiating turns and curves. Why? Centrifugal force makes the motorcycle want to move to the outside of the turn along the surface of the pavement. The only force resisting this is your valuable two bucks worth of contact-patch. Worse, if weight is abruptly transferred to one contact-patch or the other, as the effective weight is increasing while we’re leaned over in a turn, we run the risk of quickly overspending our meager two bucks, with really bad results, like sliding, skidding or spinning the tires. Now it really gets complicated. We mustn’t overspend ourselves into bankruptcy by having too much speed while cornering, and at the same time, we have to keep a near-constant weight on both tires, with a slight majority of weight-bias on the rear tire.
MotoSafe readers certainly have figured out that the Holy Grail of proficient motorcycle operations is riding smoothly! Managing the transfer of weight back and forth, and managing effective-weight increases and decreases, slowly and progressively, over a period of time, is another way of describing smooth. We can add that handlebar-inputs are almost always smooth and progressive, although when we find it necessary to swerve so that we don’t bump into something, we are also quite firm with our countersteering inputs, but never abrupt.
How can you find your Holy Grail? Start by simply thinking smooth as you ride. Several techniques were mentioned briefly above. Skilled and smooth riders have learned how to overlap use of both the brakes and throttle, to achieve a smoother ride. Surprisingly, smoother riding gives us the ability to ride faster (within personal, legal and situational limits, or in closed-course situations, of course!) with a much greater sense of control, greater competence and far less stress.
The art of riding smoothly is even more critical when roadways become slippery. Consider advanced rider-training courses that focus on techniques that can help you discover the Holy Grail, riding smoothly. The MSF’s fine resource, “Motorcycling Excellence, Second Edition” (available form the MSF at www.msf-usa.org and online booksellers) features an essay on trail-braking from World Champion rider Freddie Spencer; the Lee Parks ‘Total Control’ curriculum, as well as Reg Pridmore’s CLASS, focus on these important techniques, as do many local track-school instructors. The MSF’s Experienced RiderCourse is a good place to begin, too, as well as the many writings of David L. Hough (Proficient Motorcycling and many others).
If you’ve not begun your personal quest for the Holy Grail of motorcycle operation, begin your pursuit today. If you are an experienced rider, perhaps you now have some new ways to think about becoming even smoother. Keep looking, keep learning! Let MotoSafe hear from you!
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The views expressed in MotoSafe are not necessarily representative of the BMW MOA, the BMW Owners News, or its staff. The views in this colum are solely those of the author or authors.
The BMW MOA Foundation’s “MotoSafe” is intended to present responsible viewpoints on thoughtful and safe motorcycling skills and practices; the authors, the Foundation, the BMW MOA and the Owners News do not guarantee readers’ personal safety and take no responsibility for readers’ application of this material. Professional motorcycle safety trainers are invited to submit articles for inclusion in the “MotoSafe” column. Please contact Roger Wiles (roger@rogerwiles.com) for submission guidelines and instructions. The BMW MOA Foundation is a not-for-profit, tax-exempt Public Educational Foundation dedicated to increasing and promoting the safe and enjoyable sport of motorcycling. Tax-exempt donations to the Foundation will provide funding for current and new Foundation Projects & Programs. Contact Foundation Headquarters at: PO Box 3982, Ballwin, MO 63022 - (636) 394-7277 for further information