No wiggle room

Ql love my 2007 Suzuki Bandit 1250, but it does one thing that I do not like. If I take my hands off the handlebars, the front end will start to wiggle back and forth, and if I don't grab the bars right away, the wiggling gets worse. I don't know if this is dangerous, but it scares me. I previously had a Honda 599, and it did not act this way. Is this wiggling normal for a 1250 Bandit? " " Tina Sherman Overland Park, Kansas

A I can't tell you with certainty that such behavior is "normal" for a 1250 Bandit, but it does occur on many different motorcycles and under a wide range of conditions. Some bikes do it consistently, regardless of the circumstances. Many others do it only after the front tire wears a bit, while some only act this way when fitted with certain front tires. Bikes that have only a single front disc brake often do it because the mass of their front ends is not equally distributed about the steering axis, while many other bikes never do it at all. Other factors—road surface conditions, steering-head bearing adjustment, swingarm-pivot freeplay and tire pressure, just to name a few, can also cause hands-off front-end waggling.

This behavior usually is triggered by the smallest of road-surface irregularities that hit the front tire's contact patch a little off-center, just enough so to divert the front wheel a fraction of a degree from its straight-ahead position. Normally, when you're holding onto the grips, your arms serve as dampers that absorb such movements. But when you release the grips altogether, those little deflections can quickly grow into the kind of wiggles you describe. The self-centering effect of front-wheel trail tries to return the wheel to the straight-ahead position; but between the considerable inertia of the entire front end (fork assembly, wheel, rotors, calipers, handlebars, hand controls, etc.), along with the elasticity of the tire around the contact patch and the energy infused into the process by the speed of the motorcycle, the trail's attempt to straighten the wheel causes the front end to go past center in the opposite direction. This, in turn, causes trail to induce an even more forceful attempt to re-center the wheel, but those same forces swing it farther past center than before. This process of over-correction continues with ever-increasing amplitude until it becomes a full-blown front-end wiggle.

I've never tried to rectify a hands-olT wiggling condition on a 1250 Bandit, so I cannot offer any conclusive suggestions other than for you to assure that all of the adjustment and maintenance factors I mentioned earlier (tire pressure, steering-head bearing adjustments, etc.) are in proper working order. If all those factors pass muster, the only other suggestion I can make sounds like a bad Henny Youngman one-liner: Tina: "It wiggles when I do this." Paul: "Don't do that."

Under the gyro-scope

Ql've got a question about motorcycle steering. I think I have a decent understanding of rake and trail, and I know that countersteering is what makes a bike turn. But every so


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often, I read or hear someone mention the "gyroscopic precession" of the front wheel, and that confuses me. Could you please explain what this term means and the effect, if any, it has on the way a motorcycle steers? Carl Fletcher

Marietta, Georgia

A Great question, but my answer is one that will prompt a number of engineers out there to write and complain that I did not explain the full context of the matter. But precession is a complex subject and I only have so much room to work with here, so I'll have to keep it simple and endure the wrath of those who believe that my response came up short.

Gyroscopic precession is a term that describes the way in which an object, usually a disc of some sort spinning on an axis (a motorcycle or bicycle wheel, a flywheel, a helicopter rotor blade, etc.), reacts to changes in the plane of that axis. The basic rule of precession states that when an outside force changes the plane of the axis, the resultant reaction will take place 90 degrees of rotation later.

You can witness this reaction by spinning a bicycle wheel while holding its axle (the axis) out in front of you in both hands, parallel to both the ground and—if you're in a room or a garage— the wall directly ahead of you; and we'll assume that the wheel is spinning clockwise when viewed from the right, just as it would on the bicycle. If you move the axle forward, backward, up, down or in any direction that keeps its axis in the same plane (parallel to the ground and the wall), you feel no resistance and the spinning wheel remains vertical. But if you tilt the axle by, say, moving its right end upward, you would think that the top of the spinning wheel would just lean to the left; but it doesn't want to do that. Instead as you try to raise the right side of the axle, you feel a resistance while the front of the wheel—which is 90 degrees of rotation later—turns to the left. You get the same sort of response no matter how or in which direction you alter the plane of the axle: The reaction takes place 90 degrees of rotation from where the input occurred.

Anyone who has played with a toy gyroscope has seen this phenomenon in action. It's a common trick to balance one end of a spinning gyroscope's axis on a taut string and then watch what happens. The gyroscope will try to fall


wiring harness. The Eliminators plug into the stock wiring harness, bypassing the pair of lambda sensors in the Due's exhaust and enabling the Z-Fi module to communicate properly with the Ducati's ECU. The Z-Fi comes preloaded with a fuel map configured for slip-on mufflers, but you can get a free stock-exhaust map from Bazzaz upon request and also upload custom fuel maps via a USB connection to a PC running the supplied Z-Fi Mapper software.

Once we installed the Z-Fi system with the stock-exhaust map, our Streetfighter's fueling was vastly improved. The low-rpm stumbles were gone, and so was the steady-state cruising surge. Bazzaz's maps don't alter fuel-delivery values below 3000 rpm, but the 02 Eliminators fix most of that problem on the Streetfighter, and the end user is free to tinker with the mix throughout the entire rev range. We also found that the Z-Fi's capability for on-the-fly toggling between two different maps proved very useful by allowing us to quickly and easily compare our own modified fuel values to the baseline settings.

In the end, our seat-of-the-pants experimentation determined that the provided map was sufficient to rid the Streetfighter of its fueling glitches. Even though stock vs. Z-Fi full-throttle pulls on the CtV dyno produced equivalent peak output the Bazzaz . package provided exactly what we had hoped for: much smoother power delivery throughout the lower rev range and while cruising at A smaller throttle openings. That's of great importance, because even on a bike like the hyper-naked Streetfighter, the vast majority of real-world riding is done at very slight throttle openings.

So, problem solved—and rather inexpensively, too. -Don Canet

When we tested Ducati's Streetfighter S in 2009, we were so enamored with that naked superbike that we voted it Best Open Streetbike in our annual Ten Best Bikes of the Year awards. But shortly thereafter, we rode a base-model Streetfighter and were shocked to find that it had some bothersome fueling issues. The bike's lean, emissions-appeasing fuel map caused a double-dip stumble at lower rpm, first as a sputter while pulling away from stops, then it would recover and stumble again at 3000 rpm; and during steady-state cruising, the Streetfighter would surge enough to be truly annoying. If the S-model we previously tested had acted this way, it would not have been a Ten Best winner.

Posts on a few Ducati web forums indicated that these same symptoms were a common complaint of numerous Streetfighter owners. The prescribed remedies were either a S3241 Ducati Accessories

Termignoni full exhaust system that included a new ECU with a different fuel map, or an $1877 Termignoni slip-on mufflers/ ECU combo. While both are reportedly an effective fix, they also are quite expensive. We had our hearts set on a more affordable aftermarket remedy.

Except that until just recently, lower-cost solutions were non-existent. Ducati had no other EFI options, and even Dynojet had never developed a Power Commander that was fully compatible with the Ducati's closed-loop fuel-injection system.

But now, Bazzaz Performance (www. bazzazperformance.com) has just begun offering its Z-Fi fuel control unit configured for the Streetfighter. The $399.95 package includes the Z-Fi controller itself, plus two 02 Eliminator modules and an adaptive

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