Why does my motorcycle wobble at high speeds?

One of the scariest things that can happen to a biker while riding is a 'speed wobble', otherwise affectionately known in the bike world as a 'tank slapper'.

A tank slapper occurs when the front tyre's contact patch isn't lined up with the steering axis and when this happens, your bike will try to fix the problem on its own. It does this by swinging the steering over to attempt to realign the axis, but overshoots it and goes too far on the other side, then repeating the process over and over, gaining strength each time with the handlebars violently shaking and hitting (or "slapping") the fuel tank. Oftentimes, this will cause a crash and they can be very serious.

There are a number of reasons that can contribute to a speed wobble, mainly due to the way the tyre is set up and balanced.

1. Irregular Balance

A tyre that is incorrectly weighted may cause the front tyre to wear down unevenly and faster than normal; additionally, it can cause additional stress on the spindle and bearings, causing these items to wear down excessively too.

An unbalanced tyre is dangerous and can create an accident stemming from a speed wobble as the motorcycle will prefer one side over the other, thus creating favourability and potentially misaligning the contact patch and steering axis when riding.

An unbalanced tyre can also affect the performance of the motorcycle, from the fuel economy to its ability to brake and corner effectively. You may also feel like you're riding on a bumpy road despite the tarmac being smooth.

2. Misaligned Tyre

A misaligned tyre is often harder to spot for most riders as it may just feel like a regular part of the motorcycle as some days the motorcycle will feel better and more comfortable than others. Wheel alignment is an incredibly important part of riding, and ensuring it is correct could be the difference between an accident and getting home safely.

There are a number of ways you can check for misaligned tyres, these include:

Uneven tyre wear
Wobbling of the tyres at higher speeds
Rattling noises from the wheels
A strange sensation when handling
Lack of grip in corners

A tyre that is uneven will start to wobble at higher speeds, indicating there is an issue, even at 40mph the sensation of a misaligned wheel can be evident. Issues with wheel alignment force the motorcycle to try to regain traction and realign itself when moving forward in a straight line, causing the motorcycle to wobble.

Poor handling of the motorcycle due to a misaligned tyre is likely to make you feel like you need to have more input when cornering or braking; the handlebars may feel unnatural, and the motorcycle may feel like it's favouring one side over the other.

3. Tyre Pressure Issues

Checking your tyre pressures is incredibly important and should be a routine task. A front tyre with lower pressures will often look flatter and be more difficult to ride on, so weekly checks on the pressures can help to stop any issues before they arise. As with most of the issues on this list, incorrect tyre pressures can create uneven tyre wear across the entirety of the front tyre, plus it can cause damage to the tyre.

It is one of the main reasons why a motorcycle wobbles at higher speeds because the tyre doesn't have enough pressure to work at its full capacity. This means that the tyre can move around and throw off the motorcycle's centre of gravity.

4. Tyre Tracking Issues

If your tyres are wearing unevenly, your chain is hitting your bike and making strange noises, and your bike handles in a strange way, it's possible that your front wheel's tyre tracking isn't aligned with the frame.

You may find that the motorcycle has a tendency to gravitate and pull you in one direction more than another, particularly when riding in a straight line, which requires you to constantly straighten the motorcycle, or when you turn it a specific way you need to input more force to make the motorcycle behave as desired.

Riding like this can mean that you must grip the handlebars tighter in order to maintain control. This can cause high-speed wobbles because you have to keep adjusting the bike.

Also, if the back and front tyres aren't lined up right, the bike will want to go in its own direction, which can also cause problems and make the bike wobble.

How To Stop a High-Speed Wobble

A high-speed wobble requires quick thinking to deal with, and as you're riding and the handlebars are moving side to side quickly, it can be hard to stay calm and know what to do. Here are some tips on how to avoid a crash.

Firstly, ease off the throttle and stop the motorcycle from accelerating. Accelerating more will make the situation worse, as one of the reasons the motorcycle is wobbling is that you are moving fast.

Next, hold onto the handlebars firmly and do not try to correct or move them, as you will likely make the situation worse. Also, do not try to brake; let the motorcycle's engine braking slow you down naturally. Finally, try to lean forward over the tank to help improve the aerodynamics of the motorcycle.

Unfortunately, there is no surefire way to stop a speed wobble, but these steps may help to stop one in the process, but there is no guarantee that this method will be successful, and a speed wobble may still result in a crash even after following these steps.

This is why it's important to ensure that there are no tyre-related issues; it may also be worthwhile purchasing a steering damper, which works to inhibit the violent shaking and uncontrollable movement of the handlebars in a situation where a speed wobble might occur.