Tuesday, July 28, 2009


Ask the Maniac

Dear Maniac,

I can always count on you to find yourself in unusual situations. I can't always count on you though to do the rebellious thing it seems.Maniac, perhaps you can redeem yourself by answering a high level technical question.

While looking at a Honda Goldwing I was told about the amazing and miraculous rear brake feathering technique that makes handling one of these behemoths during slow speed turns and maneuvers so simple that anyone can ride.

Now as a scooter rider I'm not privy to these most secret techniques. As I understand things it involves keeping your foot on the rear brake and the throttle on so you have constant, controlled power through a turn and don't have to worry about stalls. Too fast? A little more brake please and the bike leans a bit more. Leaning too much and about to drop? Ease up on the brake and upright the boat goes.I tried it with a Triumph on a little track and it seemed to work. But Maniac, is this good and proper technique or merely something for tricksters???

Helpless in the sticks.

Dear Helpless,

I'm not into rebellion much these days. My previous handcuff scars hurt me when the weather turns cold. It hurts my feelings when my reputation keeps me from getting invited to church socials. These days I'm only into tame and comforting pursuits. Thinks like watering and taking pictures of flowers.

The plants really need the water these days. Today's high was 108 degrees (f).

Yes, just like Ferdinand the Bull, I'm only going to do peaceful and law abiding things.

What's that? Did I hear laughter ringing around the internet? What's the matter with you all? Do you think I'm making this stuff up? Ok, Ok, I admit it. I still love getting into trouble. I just didn't happen to choose to do it in front of 19 police officers. I was representing our training program and had to behave, all right?

Anyway, back to your question.

First off, it's important to understand that we might possibly be talking about two different things, here. There is the matter of using the rear brake during low speed maneuvers. There is another trick to braking in faster corners called trail braking. I would caution street riders to not use trail braking. It's mostly a racing technique. These are two entirely different creatures. Since you mentioned that you tried it out on a track, this makes the distinction pertinent. With that in mind, I will cover trail braking in the next post.

In this photo you can see Julie executing a slow turn around a pivot cone. This is the type of slow maneuver where the rear brake is used as both a sort of rudder and anchor. Typically the speed would be at a fast walking pace or slower. The rear brake is used for speed control as opposed to controlling lean angle. It's actually the amount of power to the engine that determines whether the bike stays upright or wants to lean. Remember the instructor's coaching in the training classes? Riders need enough speed for stability. This applies when doing slow, tight, turns but it's complicated by the lower speeds required to actually make these turns.

There's the conflict. A certain amount of power is required to hold a bike up. Think for a moment of a spring. When you press your hand against the end of a spring you should feel resistance against your palm. Even though the spring isn't fully extended, you know that if you release the pressing force, the coiled tension will cause the spring to then fully extend. The tighter the coils and the stiffer the metal, the more coiled tension there will be and the more readily the spring will extend.

Now think of a motorcycle. When a bike is standing upright, the spring is fully extended. Making the bike lean, whether by pressing or steering, is like compressing the spring. The hope is that when the pressure is released, the bike will stand back up. The power of the engine applied to the rear wheel is the spring tension. The more power, the greater the tension. What you want to happen is that when you make a bike lean you are pressing against this tension just like you would press against the resistance of a spring coil. The bike should not fall, it should gradually lean like it's pushing against whatever is holding it up.

Normally this is accomplished on a motorcycle by using the friction zone. In other words, slipping the clutch. During a slow speed maneuver the clutch is never fully engaged nor is it fully disengaged. The friction zone is a place in the middle. The rider must keep a small amount of steady throttle and control speed and lean angle with the clutch. Take away a little power to make the bike lean. Give it back some power to make it stand up again. You could do the same thing with the throttle but it's almost impossible to control the power smoothly. Engine torque is a killer of smooth control inputs at very low speeds. Using the friction zone makes smooth control inputs an easy matter.

For most situations using the friction zone is adequate by itself. Depending upon the bike and the circumstances, however, additional help can be gained from using the rear brake as a sort of drag anchor. The rear brake is used along with, not instead of, the friction zone.

Where you would typically see the need to use the rear brake is in very slow speed turns with big, heavy bikes with a lot of trail. A prime example of this kind of bike are the big cruisers. In case you're not familiar with it, trail refers to the distance between where the theoretical steering axis would hit the ground versus where the tire's contact patch actually touches down. The more trail the bike has, the more resistant it is to turning. Sport bikes are designed to change directions quickly so they have less trail. Gold Wings are somewhere in the middle. Cruisers are primarily intended for straight line riding so they have more trail. This makes them pretty stable going down the road. There's a peculiar side effect of this trail, though.

The resistance to turning displayed by a bike with a large amount of trail causes the initial force required to initiate a turn to be fairly large. This resistance isn't totally linear, however. At some point the resistance abruptly decreases. Due to the physics of the configuration, the tire reaches a point where it suddenly "falls" into a turn. In normal cornering this point isn't usually reached. In slow speed turns, however, it happens right about the time the rider really needs the bike to be holding itself up. This is where holding more power and controlling the speed with the rear brake come into play.

Just to make sure we're not lost, let's do a quick summary. The bike needs a certain amount of power to the rear wheel to hold the bike up. When I say "hold the bike up" I don't mean that the bike is straight up and down. What I'm referring to is the force acting as resistance against the bike's falling. The coiled spring, as it were. Something to press against. At the same time the bike needs power to provide this resistance, the actual ground speed of the bike needs to be lower in order to physically accomplish the maneuver. Somehow this conflict between power and speed needs to be buffered.

That's what the rear brake is for. So let's talk specifics.

Here's a good practice exercise. Position the bike so that you can ride in a straight line for a few hundred feet. Roll the throttle on until the engine is at about 1500 rpm. This can be a little higher but don't exceed twice the idle rpm of the bike's motor. Keeping your head and eyes up level with the horizon, engage the clutch into the friction zone. This means letting the clutch out until the the bike just starts to move. Ease the clutch out just a bit more until it's just short of fully engaged. Remember, you don't want full clutch engagement. Stay in the friction zone. Once you're at this point, don't move either the throttle or clutch lever.

Now apply more and less pressure to the rear brake pedal. Find a point where you can keep the bike moving at a normal walking pace. You'll see how much pressure is required in short order. This is the sweet spot. The friction zone is providing enough power to the rear tire to make the bike stand up while the brake pedal controls the speed. Once you have a feel for that, the same technique can be used for tight turns like figure eights, u-turns, slow cone weaves, and so on. Many of these things are what we encounter in everyday riding like needing to turn around in the width of a standard roadway. I'd bet that the majority of riders out there can't do this. It's all about technique. Don't forget the power of head turns, either!

The Triumph you played with had a clutch. I realize your scooter does not. The same principle applies except you obviously can't use the friction zone. However, you can certainly roll on some throttle, hold it there, and use the rear brake for controlling your speed. I teach this to my scooter mounted students. So many times they try to use the throttle to control their speed in the offset cone weave or the 90 degree turn. What usually happens is that they make the first couple of cones but gain too much speed to make the rest. Or they blow outside the lines in the sharp turn. Steady throttle to provide resistance to falling and the rear brake to control the speed. It's that simple.

I know this got a little long. I sincerely hope it has been of value to you. Please feel free to let me know if I didn't explain something clearly or you need more information. Look for the post on trail braking next.

Miles and smiles,

The Maniac, a.k.a. Dan



7 comments:

Dean W said...

"You could do the same thing with the throttle but it's almost impossible to control the power smoothly. Engine torque is a killer of smooth control inputs at very low speeds"

Meh! Hold clutch in friction zone, modulate throttle. Hold throttle steady, modulate friction zone. As long as I'm using the friction zone, the power delivery is smooth.

Dave said...

Ok were was this post last year
when I spent hours in parking lots working it out for my self : )

I can do the slow cone weave with just the throttle its very tricky on a scooter
Dragging some rear brake is a heck of a lot easier an less nerve racking. : )

Old f

Steve Williams said...

This is great information. Unfortunately I'm too tired to absorb it right now. I will review more carefully tomorrow.

I did get that I don't want to be trail braking on the street. Looking forward to that post too.

As always, you seem to have the answers. Do you do mechanical and psychological questions too??

Steve Williams
Scooter in the Sticks

Steve Williams said...

By the way, about the flower photos. I know you were trying to make a joke of it but most of us about the Web know you really do probably like photographing flowers, kittens, old fisherman and sunsets. You're a good listener and you like to keep a clean house.

You can keep that Road Warrior designation in your banner but your readers know better. Why else would we feel all warm and fuzzy after reading your posts?

Jack Riepe can expand on this more insightfully than I...

Steve Williams
Scooter in the Sticks

Jack Riepe said...

Dear IronDad (Dan):

This piece wasn't too at all, and thoroughly explained a lot to me. I regret I am a classic case of "A little knowledge is dangerous." I have aspired to become a mediocre rider and have not overr achieved that goal.

Would it be possible to have someone, preferably a squad of police, take a picture of yiu sniffing these flowers?

Fondest regards,
Jack "reep" Toad
Twisted Roads

bobskoot said...

Irondad:

Actually I really thought that you were turning over a new leaf (so to speak). The picture of you watering the flowers. I thought you had discovered the Macro capabilities of your new camera. Next step would be to replace those rides into the twisties and replace them with a garden & park tours of Oregon

bob
bobskoot: wet coast scootin

Steve Williams said...

I just reread your post and it explains everything. It is a technique I didn't realize I use with the Vespa when making U-turns. Just sort of fell into it I guess.

With the Triumph I tried it a bit on the Penn DOT driver testing track. I was basically turning in a tight circle with the clutch in the friction zone, rear brake applied so that I could (sort of) control the speed and power. I did clockwise and counter clockwise but never felt real comfortable with the maneuver. I would have to practice more.

And I absolutely could not make a U-Turn on the country roads here but they are narrower than the standard state roads. I could U-turn there but again it was in an unpracticed manner.

Practice doesn't make perfect I guess but it does make better.

I'll be practicing more tomorrow with a big tall bike of the Frogwing sort that Gary Charpentier liked to ride.

Thanks again for the explanation. I can't imagine why more people don't take advantage of the Maniac!

Steve Williams
Scooter in the Sticks