n00b q: how to deal with a wobble?

[nhlkats]

not sure if this is the correct forum for this topic?

Noob rider I am with less than a year under my experience belt, just out on the freeway enjoying the /7 and the pleasant sunny day when I started to wobble.
I've never had a wobble before. It was unnerving. At the moment it happened I couldnt remember what my MSF instructor said about wobbles either.
So I just eased off the throttle and held the throttle steady then squeezed in my legs to the gas tank hoping that would calm down the wobble. Conveniently there was all of a sudden an off ramp exit that was completely straight, and i took it, wobbling down the majority of it. I was able to regain control at the bottom of the exit before the stop sign, thankfully.
I feel this was very lucky that it ended all well. I would like to know how I should have behaved in this situation. Next time I may not be so fortunate.
Thank you.

 

[belquar]

Was it this kind of wobble?

http://media.skoopy.com/vids/vid_01044.wmv

If so read this thread:

http://forums.bmwmoa.org/showthread.php?t=9475

I personally have never experienced that.

Brian

 

[nhlkats]

it was that kind of wobble, minus the idiot trying to show off, and no fall.

that video is just brutal

edit: Belguar, now that i've peaked into the thread you posted, I'd like to add that I was not attempting any sort of fancy moves. I was trying to go in a striaght line with both wheels grounded @ the speed limit when my wobble developed. My education was expensive...I'd like to keep it inside of my head.

 

[kbasa]

Were you slowing down? If so, I'd bet you that your steering head bearings are either loose or need to be replaced.

 

[MOTORMAN]

Did you just change tires on the bike? Some combos do not do well on some bikes. Have you done any maintenence to the bike especially dealing with suspension? Have either of the front forks bled the oil out?

 

[belquar]

Yeah, I wasn't suggesting that you were goofing off. Just remembered that thread from a while back and was curious to know if the wobble was that violent. If so...kudos to you for keeping it under control. I know a lot of people posted on what to do when that goes on. I personally have never had the misfortune but am always looking to glean a little know how from those who have experienced them so that I keep it together if/when it does happen to me.

 

[jerryb]

Were you slowing down? If so, I'd bet you that your steering head bearings are either loose or need to be replaced.

If nothing is really obvious I would second that.
And I don't know about a /7 but I destroyed the steering head bearings on my '90 GS even though I checked the play with all three of the standard methods, (1) Bumping the front wheel against something solid while feeling for play with your finger on the fork steering head pivot point (2) Holding the front brake on while pumping the forks up and down and ditto on the pivot point (3) Putting the bike on the center stand and yanking on the fork tubes and etc. on feeling at the pivot point.

I couldn't figure it, the only clue I got was a metallic clunk if I hit a sharp highway ridge of some sort. After checking everything else out, including changing fork tube slider bearings I took the top nut off the steering head and sure enough I could see the play in the fork shaft while looking down into the tube. I've been told since that to check the steering head bearing (on that bike) to use a slow deliberate motion and not a quick bumping motion. I don't know about that. As I think about it now I think there is a better way. With the front wheel off the ground and while someone else is feeling for play at the pivot point lift the front wheel assembly in a straight up and down motion instead of the rock back and forth motion used by dirt bikers.

jerryb

 

[pmdave]

Let's note that all two wheelers tend to weave as they self-balance. Generally, we're unaware of this "weave", but if something happens to make an input in the correct phase, the front end can increase the weave until it grows violent. "Something can include suspension components that are loose or damaged, surface grooves, and rider input. For some reason, /7 airheads seem to like to wobble slightly when decelerating through about 38 mph. But after many years, I no longer notice this.

It might seem that a rider can steer the bars to reduce the wobble, but we're too slow to react, and the result of attempting to strong-arm the bars may be an increase in the wobble to the point of a "tank slapper". (the bar ends hit the tank.)

Changing speed seems to help, since the wobble can be amplified by the natural resonance of the bike. I've managed to pull out of a wobble that was just starting to get serious, by rolling off the throttle and braking on the rear wheel.

Once you manage to get out of the wobble without crashing, it's worthwhile to start checking the bike. Wheel bearings, swing arm bearings, steering head bearings, fork sliders, all can create a condition that encourages a wobble to progress. One very prime wobble source is notched steering head bearings, but don't ignore the rear end.

If your steering head bearings seem smooth and lubricated, or if you replace the steering head bearings, it's important to adjust the bearing preload correctly. If you don't understand how to do this, I suggest you find a fellow BMW rider or shop "technician" to show you.

One other rare source of /7 wobbles is the cushion (ramp & spring) in the driveshaft. Under a modest load (say two-up at 70 mph) the spring winds up slightly and then releases, which imparts an up-down oscillation in the rear, that feels similar to a very out-of-balance front tire. This seems to be self-healing, as the ramp and cam wear into a better fit. My point is, if you can get past the terror, try to figure out whether the problem is at the front or at the rear.

pmdave

 

[beemokat]

Interesting...

"One other rare source of /7 wobbles is the cushion (ramp & spring) in the driveshaft. Under a modest load (say two-up at 70 mph) the spring winds up slightly and then releases, which imparts an up-down oscillation in the rear, that feels similar to a very out-of-balance front tire. This seems to be self-healing, as the ramp and cam wear into a better fit. My point is, if you can get past the terror, try to figure out whether the problem is at the front or at the rear."

Interesting that you should mention this, the spring in my driveshaft actually broke into 3 pieces last week. Made for quite a ride! Has this ever happened to anyone else? My mechanic buddy said he'd never seen or heard of this. I'll post a picture of the broken spring a little later, probably in the "Airheads" section.

 

[pmdave]

I've never seen a broken driveshaft spring, but anything can break. Be sure to clean out all the metal debris from the pinion splines and the U joint.

Years ago, when I was trying to diagnose the occasional "hopping" behavior of my 1980 R100t, Oak Okleshen suggested checking the front forks. There have been a variety of washers and noise dampers, including a plastic ring that can disintegrate and affect the damping.

In my case there weren't any problems with the front forks, but I did follow Oak's advice to remove the fragile plastic part (O ring or whatever--I can't remember).

While we're talking about front ends, note that on the /5 "toasters" with the drum front brake, the studs holding the cross brace to the sliders can leak fork oil. It appears the holes are drilled through to the inside, and are then tapped. Fork oil can pump back through the threads. If you get oil mist down the front of the sliders, you can solve the problem by cleaning the holes and sealing the stud threads with a dab of Loctite.

pmdave

 

[nhlkats]

no i was not slowing down, i was at a constant velocity. i came across a patch of uneven highway road with ridges, and then the wobble started. and i did not know how to properly react? to calm the bike down.

 

[braddog]

Ah Ha!

no i was not slowing down, i was at a constant velocity. i came across a patch of uneven highway road with ridges, and then the wobble started. and i did not know how to properly react? to calm the bike down.

Ridges you say? Was it one of those stretches of highway that had been "stripped" off, ready for resurfacing? If there were ridges, the wobble was your motorcycle trying to find a straight path.

PMDAVE, weigh in this one now that we have more information. I believe this is covered in PM #1.

 

[pmdave]

OK, hang with me here.

A two-wheeler balances itself by countersteering. If the bike starts to lean over to the right, the leaning moves the contact ring more toward the right, which causes more drag on the right side, which steers the front wheel more to the right. The mass of the bike resists moving sideways as quickly as the wheel, so the bike straightens up, and perhaps leans a little left. The process repeats over and over. So, even in a "straight line", the front wheel weaves slightly left-right.

However, for this self-countersteering to work as planned, the surface needs to be relatively level, so that the contact ring shifts position smoothly and predictably.

If the surface has grooves or ruts (caused by cracks, tire wear, or trucks pounding the asphalt down in hot weather) a motorcycle tire reacts differently than on a smooth, level surface.

When the front tire contacts the side of a groove, the contact ring instantly moves up the tread, suddenly increasing the torque on the front end. The wheel is dragged toward the edge of the groove, felt as a sudden pull on the handlebars and a swerve away from center. Then as the tire crests the groove and drops over the other side, it suddenly tries to steer itself back the way it came. The rider feels this as a swerving from side to side, rapidly wresting balance from the rider. Yes, there have been crashes on roads with significant grooves ("ruts") parallel to the lane.

It's important to recognize what's happening when the bike starts to dart left-right as the front tire is grabbed by the edges of the ruts. You can usually see the ruts, in the same position as truck tires. In states where studded tires are legal, the ruts will be more dished, but will still have an effect. Trucks and cars are also affected by ruts, but not as violently as two-wheelers.

The correct tactic for negotiating grooves/ruts is to forcefully countersteer the bike out of the rut, either to the center of the lane, or just outside the outer ruts. If only one lane is rutted, move over to an adjacent lane.

Some stretches of highway are seriously rutted, and wise motorcyclists take alternative routes. For instance, I found US 200 across North Dakota badly rutted several years ago. At one point the bike changed lanes left-to-right even though I was resisting it. Fortunately, there was no vehicle in the right lane at the moment.

Work zones often have serious "edge traps" wherever repaving is going on. When the crew grinds away the old pavement there is a steep edge formed. It may not seem hazardous to have a 4" to 6" "curb" at the edge of a lane, but it's an EXTREME hazard for a two-wheeled motorcycle. The significant number of motorcycle crashes in work zones is the reason for all those "Motorcycles use extreme caution" warning signs.

Unfortunately, work crews do not always recognize what the danger is to motorcyclists, and sometimes they actually position the cones to direct traffic over a raised edge.

If you don't have to cross over an edge, don't. Just ride out the rough surface. But if traffic is directed to bounce over an edge, swerve away aggressively and then back, so you bounce the front wheel up over the edge at a minimum angle of 45 degrees. The less the attack angle, the greater your risk of the tire suddenly darting or sliding along the edge, at which point you lose control of balance and crash. Once your front tire is trapped by the edge, there is nothing you can do to regain balance, which is why I call raised pavement edges "edge traps".

If any of this tickles your curiosity, there is a much more detailed explanation of steering/balancing in the book "Proficient Motorcycling", and a healthy description of edge traps and other surface hazards in the book "More Proficient Motorcycling". (available at bookstores and online at www.amazon.com) Thanks for the opportunity to put in a shameless plug.

pmdave