Read the guide: Vibration frequency explained
How to test your motorcycle
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Step 1: Ride or idle until the engine is warm. Park the bike on its center stand, or its side stand on firm, level ground, and shift to neutral.
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Step 2: Read the idle speed on the tachometer and enter it with your number of cylinders. No tachometer? Keep the default 1,100 RPM.
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Step 3: Fold a cloth on the seat and lay the phone flat on it, screen up. Tap Start (on iPhone, tap Allow), then let go.
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Step 4: Keep hands off the bike for the 30-second measurement.
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Step 5: If you like, measure again while a helper standing beside the bike holds a steady 1,500 RPM, and enter 1,500 RPM.
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Step 6: Save the result so you can compare after a repair, or with a friend's bike of the same model.
What your result means
Your result lands on one of four levels. This page uses the machines and appliances scale, which is based on RMS velocity in millimeters per second (mm/s).
| Level | Range (RMS velocity) | What to do |
|---|---|---|
| Smooth | Under 0.71 mm/s under 0.028 in/s | Very smooth. Typical of many multi-cylinder bikes at idle. |
| Normal | 0.71 to 1.8 mm/s 0.028 to 0.071 in/s | Normal idle shake for most bikes. Save it so you can spot changes later. |
| Rough, check it | 1.8 to 4.5 mm/s 0.071 to 0.177 in/s | Rough for a smooth multi-cylinder bike, but it can be normal for a single or a big twin. Compare with the same model and check mounts and bolts. |
| Too much vibration | 4.5 mm/s or more 0.177 in/s or more | Strong shake at idle. Check for loose engine mounts, loose exhaust brackets and a misfire before you ride far. |
Why a motorcycle vibration test is done parked
You can’t safely hold a phone, read a screen or tap a button while riding. So this motorcycle vibration test measures the engine at idle with the bike on its stand. The engine is usually the biggest source of shake, and it doesn’t need road speed to show up.
The tool works out two numbers from what you entered:
- Engine rotation: RPM ÷ 60. At 1,100 RPM that’s 18.3 Hz.
- Firing frequency (four-stroke): RPM ÷ 60 × cylinders ÷ 2.
| Engine at 1,100 RPM | Firing frequency | Can a phone see it? |
|---|---|---|
| Single | 9.2 Hz | Yes |
| Twin | 18.3 Hz | Yes |
| Triple | 27.5 Hz | Only just, near the limit |
| Four | 36.7 Hz | No |
A phone measures up to about 30 Hz, so on a four the tool flags that the firing frequency is out of reach. On an even-firing engine (a 360° parallel twin, a flat twin, most inline triples and flat-plane fours), a steady peak at half the rotation speed (about 9 Hz at 1,100 RPM) can mean one cylinder is misfiring. Most V-twins, 180° and 270° parallel twins, crossplane fours and V4s fire unevenly and show some shake at this rate even when healthy, so compare with your own earlier readings or the same model.
Motorcycle vibration at speed
Shake that only shows up on the road can’t be measured safely with this tool, but a simple feel test helps. At a steady speed on a quiet road, shift to another gear without changing speed. If the vibration stays the same, it follows road speed: think wheel balance, tires, chain, sprockets or wheel bearings. If it changes, it follows engine speed. The tire vibration frequency calculator shows how fast your wheels turn at that speed.
Common causes and fixes
- Normal design shake. Singles and big twins shake more than triples and fours. Some have balance shafts and some don’t.
- Loose or worn engine mounts. Check the mount bolts and tighten them to the torque in your service manual. Replace cracked rubber mounts.
- Throttle bodies or carbs out of sync on multi-cylinder bikes. The idle feels lumpy. A shop can sync them with gauges.
- Misfire. Check spark plugs, plug caps and coils. Valve clearance that’s out of spec can also make the idle rough.
- Idle set too low. Set it to the speed in your manual.
- Parts that buzz. Exhaust brackets, heat shields, mirrors and fairing bolts can rattle. Tighten them and replace missing rubber washers.
- Handlebar buzz. Loose or missing bar-end weights. This buzz is often faster than a phone can read.
See a mechanic if the shake is new and sudden, comes with clunks, or comes with a loss of power.
What this tool can’t measure
- Vibration while riding, including wheel and chain problems at speed.
- Fast vibration. The firing frequency of fours and six-cylinder bikes, and handlebar buzz, are above about 30 Hz.
- Readings from different spots. A seat cushion softens the shake, so use the same spot every time you compare.
- A certified rating. The bands come from machine vibration guidance (ISO 10816-1), made for machines, not bikes. Treat every reading as a good guide, not a certified measurement.
Frequently asked questions
Why can't I test while riding?
Riding needs both hands and your full attention. A loose phone can also fall into the chain or wheel. Test parked, and use the gear test described on this page to learn about vibration at speed.
Is a lot of vibration normal on a single or a V-twin?
Often, yes. Singles and many twins shake more by design, and some use it as part of their character. What matters is change: compare with your own earlier readings or the same model, and look into any new shake.
Why do my handlebars buzz at highway speed?
Handlebar buzz is often a fast engine vibration passing through the frame, and it's usually faster than a phone can measure. Check that the bar-end weights are present and tight and that the handlebar clamps are torqued to spec. Heavier bar ends and grips are a common fix.
Does this work for a two-stroke?
Partly. The tool assumes a four-stroke engine, where each cylinder fires every second turn. A two-stroke fires once every turn, so its firing frequency is RPM ÷ 60 × cylinders, twice the number the tool shows. The rotation frequency is the same for both.
How do I find my idle speed without a tachometer?
Check your owner's manual, which usually lists the idle speed. Enter that number, or keep the default 1,100 RPM. If the real idle is different, the frequency match will be off by the same amount.
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