Understanding the Causes of a Death Wobble on a Harley

The death wobble is a frightening and dangerous shaking that affects many motorcycles, particularly Harleys. This condition can be caused by a variety of mechanical issues, rider position, and tire or suspension faults. But what exactly causes it? This article explores the various factors and provides tips on how to prevent this from happening.

Inspect Your Motorcycle for Mechanical Issues

Before the death wobble can be diagnosed, it is crucial to inspect the motorcycle for any mechanical issues. Start from the ground up:

Wheels and Tires

Tire Balance: Ensure your tires are properly balanced to avoid excessive vibrations. True Rims: Check if your rims are true, i.e., not bent or out of round. Wheel Bearings: Make sure they are in good shape to ensure smooth and stable rotation. Forks and Swingarm Bearings: Ensure these parts are in good shape without any play or wear.

Steering Components

Steering Head Bearings: Check if they are too tight or too loose; this can cause significant front-end wobbles. Is It Modified? Check if the bike has been modified in any adverse way.

Rider Position

After eliminating mechanical issues, it is important to look at the rider and how they interact with the bike:

Steering Head Bearings and Tyres

Worn Steering Head Bearings: Faulty steering head bearings can cause vibrations that lead to wobbling. Tires Not Properly Inflated: Ensure your tires are inflated to the correct pressure. Worn Swing Arm Bushings: Worn or damaged swing arm bushings can cause instability. Rear Shocks: Ensure they are in good shape and not worn out.

The Two Types of Wobble

There are two types of death wobble, and they can be attributed to different factors:

Front-End Wobble

This type of wobble is generally due to frame geometry and front tyre traction. You may experience this when slowing down to about 20 mph or as the front wheel starts to lift:

Hands Off: If this happens while your hands are off the handlebars, it is a front-end wobble. Steering Damper: A steering damper can effectively stop this from happening if it goes out of control. All production bikes racing on the Isle of Man must have a damper fitted for this reason.

High-Speed Weave

This type of wobble is caused by an interaction between frame geometry and rear ride height. The actual cause is an oscillation being promoted by the interaction, trying to push the rear tyre from side to side. The resistance of the tyre contact patch causes the motion to appear at the bars.

There are several factors that can push the rear down, such as drag on the rider's upper torso. This leverage can compress the rear suspension if you apply pressure. Other factors can include soft rear springs, soft rear tyres, headwinds, or worn rear tyres.

The Historical Context

Kawasaki's Two Stroke Triples are famous for their sudden death weaves at high speeds. Initially, the bikes were designed with slightly shorter rear shock absorbers to make them visually appealing. However, when heavier Western riders added weight, combined with slow wear on tyres, headwinds, and other factors, the rear weave started at much lower speeds, eventually causing fatal consequences.

Tips to Prevent the Death Wobble

Here are some practical tips to prevent the death wobble:

Handlebar Position and Rider Posture

Euro Touring Bars: If you have high, pulled-back handlebars, consider using euro-style touring bars, which put your weight and seat further forward. Weight Distribution: If you are very big or fat, ensure your rear suspension has proper sag. Stiffer rear springs can help, but make sure the bike is set up for your average weight.

Choosing the Right Tyres

Bridgestone BT45/6: These tyres are engineered to manage side-to-side forces effectively and are taller for their size. They can significantly reduce weaving at higher speeds. Bridgestone BT46: For standard or touring bikes, a BT46 can make a huge difference in preventing the death wobble.

Stronger Rear Springs

If you have a decent rear tyre and are comfortable with your position, stronger rear springs can effectively tackle the death wobble.

Exceptional Bikes

The BMW air-cooled twins of the 1970s and 1980s were set up to sit below the oscillation 'sweet spot,' making them prone to weaving. However, as the tyres wore, the threshold for the death wobble increased. BMW recommends using Continental Classic tyres, which are designed to be lower in profile than others, leading to a noticeable difference on Japanese bikes.

Experience has shown that bikes like the Kawasaki W650, ridden into a strong headwind, can start to weave dangerously at 65 mph with a new Continental Classic tyre on the rear.

Conclusion

The death wobble is a serious issue that can be caused by a variety of factors. By understanding the causes and taking the necessary steps to address them, riders can significantly reduce the risk of encountering this dangerous condition. Proper bike maintenance, choosing the right components, and adjusting your riding habits can all help prevent the death wobble from ruining your ride.