Roll, Wobble, Weave and High-Side
In my interaction with motorcycle riders across the country, I have found that many think that weaves, wobbles, or high-sides only happen to sport bikes at very high speeds, but nothing is further from the truth. All motorcycles are susceptible to four different wobble phenomena: (a) front-end wobble, (b) induced wobble, (c) high-speed weave, and the dreaded (d) high-side.
Front-end wobble, or as it is sometimes called “low-speed wobble,” most commonly occurs at speeds of 40 to 45 mph with a side-to-side oscillation of eight to ten cycles per second. Wobbles can also self-initiate at higher speeds, and can become so violent that the handlebars will contact the fuel tank; this is where the term “tank slapper” comes from.
I have seen riders at Harley-Davidson testing Road Glides take the handlebars at speed and purposely put the front end into a high-speed wobble by whipping the bars in one direction and then removing their hands to demonstrate the positive dynamic stability (the front-end wanting to return to center) of the machine. I’ve always said that motorcycle test riders are a special breed, or just plain crazy.
A wobble is often induced by a rut, pothole, or some other irregularity in the pavement, and the inability of the suspension to react fast enough. Because of the effects of positive dynamic stability, as mentioned earlier, the motorcycle will tend to correct itself, but too often the rider will over-correct and put excessive input into the handlebars, causing the situation to amplify. If you encounter induced wobble, the best course of action is minimal handlebar input by the rider and allow the motorcycle to decelerate.
High-speed weave usually occurs at speeds in excess of 70 mph, and the motorcycle will follow a sinuous path of three to five cycles per second at the beginning, and can increase at such a dramatic pace that the rider will quickly lose control of the motorcycle. One of the most common causes of high-speed weave on touring motorcycles is the uneven and over-loading of the saddlebags.
Combine this with an owner who has neglected maintenance of his motorcycle-items like low tire pressure and worn wheel or neck bearings can be a recipe for disaster-and this can actually cause a high-side. The only real way out of a high-speed weave is to detect the instability early and decelerate. I have personally accelerated through a high-speed weave and the motorcycle did straighten out, but the weave returned as I decelerated. Not fun stuff!
Most riders don’t recognize the dreaded high-side as a wobble, but it is. A high-side is basically a wobble that becomes catastrophic in just one cycle. A high-side crash typically happens in a corner when the rear wheel of the motorcycle spins out, causing the bike to slide. The actual high-siding occurs when the rear tire regains traction with the road, flinging the rider off the bike with great force, usually over the handlebars.
Most high-sides are caused by the improper use of the rear brake while cornering at a high speed or sudden loss of friction between the tire and the surface caused by sand, oil, or some other debris. As the rear slides out it may quickly find grip, and then begins rolling in a direction other than the one the motorcycling is traveling sending the rider over the bars as the motorcycle begins to right itself.
MotoGP World Champion Valentino Rossi sustained a compound shin fracture from a nasty high-side crash in 2010. The best way to avoid a high-side is to ride within your limits on a properly maintained motorcycle. ABS brakes and traction control are quickly becoming more common and will help in preventing high-sides because we just can’t react as fast as a computer can. Although as in Rossi’s case, no technology is fool-proof.
There are many causes of weaves and wobbles-most are maintenance related and could have been avoided. Items like loose wheel bearings, improperly adjusted or worn neck bearings, loose axles, pivot shafts, neglected tires, worn shocks, leaking front forks, missing fork braces or stabilizers, and engine mounts can all cause a catastrophic accident. A rider should have his or her own pre-ride checklist and use it before each day’s ride begins. It might just save your life.