What is a tank slapper?

A tank slapper is a severe oscillation of the front end where the handlebars swing quickly from lock to lock. It develops from a smaller wobble that grows when speed, load or a mechanical problem sustains it.

What do I do when my motorcycle starts to wobble?

Stay calm, keep a loose but steady grip, gently roll off the throttle and do not brake hard or fight the bars. Let the bike slow until the wobble dies down, then pull over and find the cause before riding on.

Can worn tires cause a speed wobble?

Yes. Low pressure, uneven wear, a cupped or flat-spotted tire, or a poorly balanced wheel can all start a wobble. Tires are among the first things to check.

Is it safe to ride a bike that wobbles?

No. A repeated wobble means something is wrong with the tires, wheels, bearings, steering head or load, and it can escalate without warning. Fix the cause before riding at speed again.

Motorcycle speed wobble: causes, fixes and what to do

A motorcycle speed wobble is a rhythmic side-to-side shake of the front end, often at a particular speed, and it is a sign that something in the tires, wheels, steering or load is out of order. If your bike starts to wobble, roll off the throttle gently, keep a firm but relaxed grip and let the speed bleed off. Do not ride it at speed again until you have found the cause.

This is a safety issue. Read the "when to stop riding" section even if you only skim the rest.

What a speed wobble is

A wobble, sometimes called a headshake or, in its severe form, a tank slapper, is an oscillation in the steering that feeds on itself. The front wheel swings from side to side. Each swing moves the bars, which push the wheel back the other way. Small versions feel like a shimmy through the bars or footpegs. Severe ones whip the bars from lock to lock.

Two things matter: how big the wobble is and how fast it starts. A gentle shake that fades is a warning. A wobble that grows with each oscillation is an emergency.

What to do when it happens

These are general technique points, not a substitute for rider training.

Do not panic or grab the bars hard. A tight death-grip can feed the oscillation. Keep a firm but relaxed hold.
Ease off the throttle smoothly. A sudden chop can unsettle the chassis. Let the engine braking slow you gradually.
Do not brake hard, especially with the front. Braking transfers weight to the front and can make it worse.
Stay centered. Keep your weight steady and your knees against the tank. Grip the tank with your knees and keep your weight off the bars, so your arms are not feeding the oscillation. The common thread is to avoid sudden inputs.
Once it settles, slow down and pull over. Check the bike before moving on.

If you ride regularly, consider a rider course. The Motorcycle Safety Foundation offers training for new and experienced riders, and a good instructor can show you how to handle an unsettled bike.

Common causes of motorcycle speed wobble

Tires

Tires are the most frequent culprit and the cheapest to check.

Low or uneven pressure. Check cold pressure against the number in your manual or on the swingarm sticker. Our motorcycle tire pressure guide explains how.
Worn, cupped or flat-spotted tires. A tire worn into a square profile or with scalloped edges can steer unpredictably. See how long motorcycle tires last.
Old tires. Rubber hardens with age. Learn how to read a tire date code.
Mismatched or wrong tires. Mixing sizes, brands or profiles that the bike was not designed for can upset handling. Our guide to choosing motorcycle tires goes over matching tires to the bike.
Bad balance. A wheel that is out of balance shakes at certain speeds. Lost balance weights are an easy fix.
Tire not seated properly or bulging. After a tire change, a bead that has not seated, or a bulge from damage, can cause shaking.

Wheels and bearings

Loose or worn wheel bearings. Play in the front or rear wheel bearings allows the wheel to wiggle. With the wheel off the ground, try rocking it side to side. It should not move.
Bent or out-of-true wheels. A hard pothole hit can bend a rim. Spin the wheel and look for a wobble, or have a shop check run-out.
Loose spokes on a spoked wheel can cause a shimmy.
Loose axle nut or incorrectly installed spacers. A wheel that is not properly clamped can move.

Steering head and suspension

Loose or worn steering head bearings. This is a classic cause of headshake. Lift the front wheel and see if the bars have notchiness, a rough center spot or play when you rock the fork back and forth.
Fork problems. Uneven fork oil levels, worn seals, a bent tube, mismatched springs or too little damping can cause instability. See motorcycle fork oil change.
Rear suspension issues. A worn shock, loose swingarm bearings or a bent frame can cause weaving. Our suspension repair shops category lists specialists.
Wrong sag or preload. Setting the suspension for the wrong load changes the steering geometry.

Load and accessories

Unbalanced or overloaded cargo. Heavy luggage placed high or behind the rear axle makes the front light. NHTSA's guidance on riding with cargo says to secure it, balance it, and adjust the suspension and tire pressure for the extra weight.
Loose bags and tank bags. A bag that shifts at speed is a hazard.
Windshield or fairing add-ons. Aftermarket parts that create lift or turbulence at the front can set up a shake.
Passenger weight and position. Adjust preload and pressure for two-up riding.

Frame and crash damage

A bike that has been in a crash or tipped over may have a bent fork, frame or triple clamp. If the wobble began after any impact, see what to check after a motorcycle crash and have the alignment checked.

Other contributors

Chain slack and rear wheel alignment. A misaligned rear wheel can make the bike steer oddly. Our chain maintenance guide covers adjustment.
Crosswinds and passing trucks can start a mild weave on a light bike. That is not a defect, but it is a reason to check that everything else is sound.
Recalls. Some models have had steering or suspension related recalls. NHTSA lets you look up open recalls by VIN, which is worth a minute if you have an unexplained handling problem. See how to check motorcycle recalls.

Symptom guide

What you notice	Likely area to check
Wobble at a specific speed, smooth above or below	Wheel balance, tire condition
Gradual onset, getting worse over weeks	Steering head bearings, tire wear, fork oil
Started after a tire change	Balance, bead seating, wrong tire
Started after a crash or pothole	Bent wheel, fork, frame
Only when loaded or two-up	Suspension setup, luggage placement, tire pressure
Wobble under deceleration	Steering head, front tire, fork
Wobble on rough pavement	Suspension damping, tire pressure
Rear end weaves	Rear tire, shock, swingarm bearings, chain alignment

A basic inspection

Do these with the bike on a stand, engine off.

Check both tire pressures cold, and inspect tread depth and wear patterns.
Look for bulges, cuts and flat spots.
Grab the front tire at 12 and 6 o'clock and rock it. Any clunk can point to the steering head, fork or wheel bearings.
Grab at 3 and 9 o'clock and push side to side. Movement means a wheel bearing.
Spin each wheel and watch for wobbling, hopping or drag.
Turn the bars lock to lock. They should move smoothly, with no notches.
Check axle nuts, triple clamp bolts, fork pinch bolts and swingarm bolts against the manual's specs.
Remove luggage and test again if you carry a load.

When to stop riding

Stop riding and do not return to highway speeds until the bike is inspected if:

The wobble has happened more than once.
It started suddenly after an impact, drop or tire change.
You find play in the steering head, a wheel bearing or the swingarm.
A tire is worn out, damaged, bulging or very old.
A wheel is bent or out of true.
Fork seals are leaking, or fork legs are bent.
You cannot find the cause.

A wobble that grows is one of the more dangerous things that can happen on two wheels, and the cost of a bearing or a tire is small next to a crash.

Typical repair costs

Costs vary by bike, region and shop.

Repair	Typical range
Wheel balancing	About $15 to $40 per wheel
Tire replacement	Varies widely, see our tire replacement cost guide
Wheel bearings	About $100 to $400 per wheel
Steering head bearing service	About $200 to $600 or more
Fork service or seals	About $200 to $600 or more, see our fork seal cost guide
Wheel true or replacement	From about $50 for truing to several hundred dollars or more for a new wheel
Frame alignment check	Varies; ask a shop

When to see a mechanic

Go to a shop if the wobble keeps coming back after you fix tires and pressures, if you find play in the steering head or wheel bearings, if there has been any crash damage, or if you are not equipped to measure and torque suspension components. A good shop can check wheel run-out, bearing preload and frame alignment. Look at tire shops and suspension specialists, or browse motorcycle repair shops in Arizona and cities such as Phoenix.