Dynamic Brake
Best Motorcycle Braking Practices
Several things affect your bikes braking ability, as well as your ability to avoid skidding or being tossed off your bike like a slingshot pellet. Weight distribution, road surface conditions, braking system type, tire condition, suspension, and most of all, rider skill.
First, let's consider what enables you to change anything about the speed and direction of your ‘object in motion' – two small patches of tire and road surface rubbing together. These few square inches are responsible for creating enough friction to influence, or ideally, control the motion of the object riding on them. Dictionary.com defines traction as “ the friction between a body and the surface on which it moves (as between an automobile tire and the road.)” What actually makes a bike come to a standstill? This process involves, first and foremost, the traction element described above, in combination with the friction developed in the braking system that tries to reduce the rate of spinning of the wheels (which are, we hope, bound to the road surface by the aforementioned traction.)
There are different types of braking systems. The most basic involves the front and rear brakes working completely independent from each other. (For the purpose of this discussion, we will not consider vintage bikes or early ‘choppers' that lacked front brakes.) This typically involves controlling the front brakes via the right handlebar lever and the rear brakes via the right foot pedal. A second scheme is to have the front and rear brakes linked so that they always brake together. There have been several variations on this theme. A third scheme is ABS that uses a computer and wheel spin sensors to detect locking, then releases and reapplies the brakes rapidly to prevent skidding. Of course, this opens up the possibility of combining the technology of integrated braking with ABS. This has been implemented on some high-end touring machines (and possibly more); however, the implications of this combination are still being explored.
Brake mechanisms, like brake systems, have also evolved. Disk brakes, which use a rotor fixed to the wheel in conjunction with a hydraulic caliper fixed to the suspension, have proven to be the most efficient and thus received the most evolutionary attention. With this system, one or more hydraulic cylinders in the caliper are used to squeeze the friction material ‘in' against the sides of the rotor. Drum brakes, still used on some lighter bikes and/or for the sake of economy, are typically actuated by a mechanical rod or cable. This type of brake causes friction ‘shoes' to be pressed outward against a drum – which is usually the hub of the wheel. Over the past 30 years I've experienced: front and rear drums, front disk/rear drum, front dual disk/rear single disk with partial integration, and currently non-integrated ABS (dual front/single disk rear). I believe that each iteration has represented a significant evolutionary step. Since each bike has been larger and heavier as well, the progression in stopping power has been welcome indeed.
Suspension and drive type also effects traction as well as the way the entire machine will respond to a given set of physical forces. The response of the suspension to the drive train (either accelerating or during engine braking) will be different on a shaft driven bike from that of a chain or belt driven machine. An engine whose crankshaft rotates on an axis that's perpendicular to the wheelbase of the bike will produce different gyroscopic forces from one that rotates on a parallel axis. There is so much diversity in motorcycle design today that we cannot hope to cover all the subtle nuances of any particular type without hopelessly boring the more general reader to death. Instead, we'd like to offer some general guidelines, in the hopes of stimulating your thought process and encouraging you to become more attuned to your particular machine and its interaction with the world of the open road.
An object in motion tends to stay in motion. We learned this in school. When you apply your brakes, the bike, cargo, and riders want to keep moving forward. This means that the total weight starts to shift forward as you brake, which in turn, wants to lift the rear wheel effectively reducing its contact area, while pushing the front tire hard into the road surface. Realizing this, it only makes sense that as stated by the Motorcycle Safety Foundation , (MSF), your front brake has 70%+ of your braking power and you should use your front brake every time that you want to slow down. In addition, the MSF recommends that you to use both front and rear brakes, and if necessary, apply them both hard, without locking them up. Do not stiffen your arms as you brake, just grip the bike with your legs and keep your arms free and relaxed. This is one of those “easier said than done” situations and you do need to practice.
Now, before I go off on a tear about panic braking and avoiding the dreaded and possibly lethal ‘high-side,' my inner parent will not rest without at least a passing mention of ‘Best Defensive Riding Tactics' as a precursor to ‘Best Braking Practices.' Unless you have a death wish, a good deal of your concentration while riding should be dedicated to avoiding panic braking situations. (The proverbial “…ounce of prevention…”) Try to avoid heavy traffic, have at least two escape routes in mind at any given instant, don't drive faster than a 12 second line-of-sight, brake before curves, and learn to brake while in curves without loosing control of the bike, you know, all that MSF stuff. You don't know, or maybe you did but it's been quite awhile? Maybe you should consider taking a course – what the heck, the worst that could happen is that you might learn something and you'll save some money on insurance. At best, it could save your life! (Or mine, if I'm anywhere near you.)
If these mentions don't sound very familiar, or even automatic, to you, please at the very least spend some time reading about, thinking about, and finally, practicing these defensive tactics when they aren't especially critical until they become automatic. By its very definition a ‘panic' situation is one where you literally don't have time to think and your ‘automatic' reaction can absolutely make a life-or-death difference.
Progressive braking:
This sounds like common sense, especially if you are traveling in a straight line, but the process becomes much less intuitive when you are in a curve and/or panic situation. The idea here is to apply both brakes with ‘progressively' more pressure until an acceptable deceleration rate is obtained. If you are in a particularly relaxed braking situation, such as approaching a red light or rolling down a deceleration lane toward an exit ramp, You Can also mix in a little engine braking via downshifting. This transfers some of the wear and tear caused by the deceleration forces from the braking system to the driveline, and it sounds cool. I've seen arguments for and against engine braking but they really lie outside the scope of this discussion, I'm neither advocating nor condemning the practice.
It is true that the ‘driveline' was designed for ‘driving' and the braking system was designed for braking, and the latter of those two is the intended point of this article.
Leaned over in a curve:
The best practice is to decelerate sufficiently before entering a curve to allow continuous acceleration through and out of it. Well, that's just wonderful in theory, but unless you're on a closed racing circuit, a road that you've ridden hundreds of times before, or you consistently drive like the proverbial ‘little old lady,' you've probably found yourself in a little over your head on at least a few occasions. Although I would hardly recommend it as a best practice, it is entirely possible to brake in a curve. I would suggest that you practice it when you don't need it so you're prepared in the event that you do. The suspension and drive characteristics of your specific machine will play a part here as well, so you might want to seek the advice of competitive or highly experienced riders of similar equipment. Key to all flavors of bikes is to avoid sudden or violent transitions – either on and off the throttle, brakes, or from throttle to brake, or brake to throttle. Back off the throttle gently and apply brakes gently and progressively.
If you find yourself going into a skid while leaned over in a curve and braking, you will probably be destined for a ‘low side' before you have a chance for any sort of intervention. The same policy stated below applies for a locked rear wheel – force it down on the low side with the front brake if you have to but – DO NOT RELEASE THE REAR BRAKE! (See below for the gory details.)
Traveling in a straight line:
In the best of all possible worlds, when you are traveling in a straight line, you may be able to anticipate the need to slow down or stop (i.e. approaching a red light) and entirely minimize your need for aggressive braking by easing off the throttle and letting the bike do what comes naturally. Be careful, however, not to surprise following motorists (especially the ones in large SUVs) by slowing abruptly without displaying your brake lights – as might occur with downshifting for the purpose of engine braking.
When the need for deceleration becomes more urgent, due to changing traffic conditions or the need to slow down for a curve, you are in prime territory for ‘progressive braking.'
If you jam on your front brakes, you could start a skid that will cause you to depart from your bike as your wheel slides out from under you. Your front wheel will not lock up easily if you have ABS brakes, or if you have mastered the progressive braking, but this can happen fairly easily (and VERY quickly) at low speed if you encounter a manhole cover, steel plate, or other slick surface. If you start to skid on the front wheel, release the brake momentarily and reapply it using less pressure. The bike will turn in the direction of the skid by itself. In the very low speed situation, and only as a last resort, putting a foot down may enable you to catch the bike before it passes that critical point. More than likely, however, this will happen so fast that you'd be best advised to try and get away rather than risk a foot, a knee, or being caught under the weight of the beast.
If you jam on your back brakes, you have a greater chance of locking the rear wheel, because it has less contact with the road surface as the weight shifts forward. If you start to skid with your rear wheel things will begin to happen very quickly and you are now in one of the most dangerous positions you can imagine. The best advice that anyone can offer is – DO NOT RELEASE THE BRAKE! Look forward and steer straight. If you are going in a straight line, you will (hopefully) skid straight and you can apply the front brake to achieve the stop that you need.
Consider for a moment, from the comfort and security of your desk chair, some of the dynamics that are involved here and if we're fortunate, we may never have to experience them from the saddle:
1) Once the rear wheel locks it will have less traction than the front wheel, which is still turning. Also any gyroscopic forces from the rear wheel (which would tend to help keep the bike upright) are gone.
2) With the combination of the forward weight shift and the lack of traction at the rear wheel the net effect is that the back of the bike wants to go faster than the front.
3) Due to the conditions described above, you are likely to find your rear wheel sliding up along side of you. Your front wheel, pointing straight ahead, will naturally be turned into the skid. From here there are basically three ways that things can go:
4a) You ride it out with the rear wheel locked, steering into the skid with the front wheel and maintaining pressure on the front brakes. Easing up on the front brake slightly should allow the front wheel to get back ahead of the rear wheel somewhat while increasing pressure on the front brake will tend to let the back wheel get further ahead, eventually forcing the bike down on the ‘low side.' (the side of the bike closest to the ground and opposite the skid)
4b) Disaster is imminent and you want to do everything possible to avoid a ‘High Side.' (See 4c below) Squeeze hard on the front brake, which will slow the front of the bike even more. The rear wheel will move further ahead and you will effectively force the bike down on the ‘low side.' If you go down, you will go down in the same direction as the bike and it will travel away from you. If you have the proper protective clothing you will probably not be hurt severely. Your bike may have the most damage.
4c) The ‘high side.' This is the worst possible case and also why you should NOT release the rear brake once it locks. Your rear wheel is locked and sliding up next to you. Your front wheel is still turning, in the direction of the skid, which is now at a considerable angle to the line of the bike. For whatever reason, you let up on the rear brake…
Immediately when the wheel starts turning it gains a considerable amount of traction, but the friction surface and direction of rotation are essentially sideways with respect to the direction of the slide. In addition, the front axle can form a pivot point in the direction of the slide, augmented by the application of the front brakes. The net effect is that the rear wheel digs in very abruptly while the momentum of the slide combines with the trajectory of the front wheel causing the entire bike to snap violently up and over the newly created friction surface at the back wheel.
This violent snap is usually more than sufficient to launch the unfortunate rider equally violently in the direction of the slide. To make matters worse, the bike is also likely to become airborne at close to the same instant, velocity and direction. Once airborne, with nothing to slow it down… you can paint your own picture, but color it potentially deadly.
When you are faced with an emergency situation, your instinct is to brake hard. Only insight, conditioning, and practice can prepare you to react the most effectively under pressure or panic circumstances.
What we have tried to present here is intended to be more thought provoking primer than any kind of comprehensive guide. We do not claim that it is either authoritative or comprehensive. There are any number of Very Good sources for information on safe/defensive riding tactics both on the web and in print, and we are in the process of trying to make this site one of them. We would like to encourage thoughtful, conscientious, and safe riding practices whenever and wherever possible.
About the Author
Chuck has been riding motorcycles for 30 years, starting with dirt bikes. He currently owns a BMW K1200LT which he takes on adventures through the country on twisty windy mountain roads with his wife Trish. Chuck and Trish have a family owned motorcycle accessory store http://www.2WheelTouring.net
Tags: ac, brake, dynamic, dynamic brake control, dynamic brake pads, dynamic brake proportioning, dynamic brake resistor, dynamic brakes, motor, regenerative
This entry was posted on Tuesday, August 4th, 2009 at 9:21 am and is filed under Trains. You can follow any responses to this entry through the RSS 2.0 feed.
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