Motorcycle Weaves and Wobbles: How to avoid them and deal with them
November 17, 2009
Filed under Motorcycle Features: Bikes, Blokes, Culture and Beyond
There are some aspects of motorcycles that motorcycle manufacturers are reluctant to talk about. Weave and wobble are two of them. Either can put you down and hurt you, so you need to know what these things are, and how to prevent their onset. We all know that motorcycles are not inherently stable. When stationary, they require stands to hold them up, and when in motion, they must have a balance of dynamic forces to keep them upright and pointed properly. Should those stabilizing forces become inadequate, motorcycles weave or wobble and sometimes fall over.
Your Harley consists of two main sections, the front and the rear. Everything that moves with the handlebar is the front; everything else is the rear. They pivot around one another at the steering head. Anytime you ride, both parts are trying to wiggle like upset gyroscopes. If the rear wiggles and doesn’t stop, it is a weave. If the front wiggles and doesn’t stop, it is a wobble. The faster you go, the more powerful those weaves and wobbles can become. Speed matters.
This natural tendency to weave or wobble is resisted by friction between tires and roadway. When a wheel is turned from the straight-ahead direction by a pebble, expansion joint or whatever, its tire produces a torque that works to straighten the wheel and everything attached to it. You may notice only a small and very temporary wiggle of the handlebar or seat. Thousands of hours of development and testing are behind making this event a minor one. Stability is a complicated matter.
Every component from the tire to those steering-head bearings must do its part to ensure that the wiggle stops. Steering-head bearings are the most critical and merit special attention; they must be exactingly adjusted; there is no “good enough.” Tires must be properly inflated. Wheel bearings must have minimum play. Spokes must be tight. The rocker bearings on a Springer must be correctly adjusted. Suspension dampers must work properly. The swingarm pivot must be firm. Rubber engine mounts and control links on FLs must be without significant play. More than one bagger has gone down because its control links were worn out, and they can wear out as often as every 25,000 miles. The ship must be tight.
It must also, in critical ways, remain close to stock. Earlier I mentioned that both the front and rear try to wiggle (weave or wobble) when you are under way. They tend to wiggle at a particular frequency. Fronts typically have a frequency of six to 10 complete cycles per second and rears three or four. Harley has tuned its bikes to damp the frequencies of each model. You can easily change these frequencies and get in trouble by doing so.
Anytime you add weight to the front or rear sections of your bike, you change its natural wiggle rate. The effect is very small if the weight is near the center. A piece of lead tied to a handgrip is more destabilizing than if it were tied to the center of the handlebar. Similarly, a weight back up in a Tour-Pak is more likely to lead to weave than if you were sitting on it. (Note: Harley’s Tour-paks and saddlebags are engineered to safely accept specified loads. Pay attention to these limits.)
Aerodynamics also matter. Harley’s windshields have compound curves and allow air to flow smoothly around them. Some of you may remember when the old flat windshields would sometimes cause a speed wobble. Air spilling unevenly around those shields would pump the handlebar from side to side and overcome the bike’s damping reserve. Big square boxes high up on the rear can lead to a weave. More than once, I have stopped a customer’s weave problem by simply removing the box they bolted on the back.
What to do if you get into a weave or a wobble:
You can almost always get out of a weave. It’s mostly a matter of knowing what to do and having a little space to do it. I’ve had weaves start when entering corners at high speed and thanks to preparedness I’m still here.
• If you’re cornering when a weave starts, do not straighten up. Going vertical seems to be our gut reaction to any riding emergency. Train yourself not to do that.
• Continue to steer. You still have control of the front and can pretty much go where you need to go.
• Apply the front brake. Apply it as hard as can be done safely. The quicker you lose speed, the quicker the weave stops. A weave is speed dependent; the faster you go the more likely it is to happen.
A full lock-to-lock wobble is very dangerous and usually results in a crash. You cannot steer and your bike will continue in the direction it was headed when the wobble started.
• If there is room and time, gently apply the rear brake. Braking may intensify the wobble but the bike will still slow. Slowing will stop the wobble although the speed at which it stops will be lower than the speed at which it started.
• If you are headed for a wall or some similar deadly obstacle and it becomes clear that you are going to hit it—bail off. It is the better choice. A wobbling motorcycle decelerates at about one-eighth g. A rider sliding along slows at closer to 1 g. You’ll stop sooner and in less distance than the motorcycle.
• Wobbles, like weaves, are speed dependent. They typically begin above 75 mph. However, if the steering bearings are loose, a wobble can begin as low as 45 mph.
I have never examined a weaving or wobbling stock Harley-Davidson motorcycle that did not have a fault. Most were maintenance or wear related. A few developed weaves from being loaded improperly.
I remember one Springer that had loose rocker bearings, loose spokes, and loose front-wheel bearings. The owner had paid for service he never received; none of those parts had been touched since they left the factory even though he had paid for a couple of services.
Any number of FL touring bikes have delivered their riders a weave or two because the upper and/or front stabilizer links were worn and loose. Be sure to check yours.
I recently examined a Softail that had been lowered. It was stable until the rider loaded his bags for a cross-country trip. At 75 mph the bike developed a weave and he fell with injury. At stock height and with full suspension travel this accident most likely would not have happened.
Should you be unsure about whether you have a tight ship, have it checked over by someone you trust. Although few of us will experience either a weave or a wobble, I want the number to be zero—please pass the word.