Read the guide: Why your car vibrates at 60 mph
How to use the tire frequency calculator
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Step 1: Find your tire size on the tire sidewall or the sticker inside the driver's door frame, for example 225/65R17.
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Step 2: Type the size into the tire size box.
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Step 3: Enter the speed where your car shakes and pick mph or km/h.
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Step 4: Read the wheel frequency in Hz and RPM. The chart shows how it changes from 20 to 80 mph.
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Step 5: Measure the shake with the car vibration test. A main frequency within about 10% of the wheel frequency points to a wheel or tire.
How the tire vibration frequency calculator works
A tire vibration frequency calculator answers one question: how many times does each wheel turn per second at a given speed? That number is the wheel rotation frequency. If your car shakes at the same rate, the wheels or tires are the likely cause.
The math takes four steps:
- Tire diameter (mm) = rim size × 25.4 + 2 × width × aspect ÷ 100
- Distance per turn = π × diameter
- Wheel frequency (Hz) = speed in meters per second ÷ distance per turn
- Wheel RPM = Hz × 60
One mph is exactly 0.44704 meters per second. One km/h is 1 ÷ 3.6 meters per second.
Worked example: 225/65R17 at 60 mph
- Sidewall height: 225 × 0.65 = 146.25 mm
- Diameter: 17 × 25.4 + 2 × 146.25 = 431.8 + 292.5 = 724.3 mm
- Distance per turn: π × 0.7243 m = 2.275 m
- Speed: 60 × 0.44704 = 26.82 m/s
- Wheel frequency: 26.82 ÷ 2.275 = 11.8 Hz, or 707 RPM
Worked example: 205/55R16 at 100 km/h
- Diameter: 16 × 25.4 + 2 × 112.75 = 406.4 + 225.5 = 631.9 mm
- Distance per turn: π × 0.6319 m = 1.985 m
- Speed: 100 ÷ 3.6 = 27.78 m/s
- Wheel frequency: 27.78 ÷ 1.985 = 14.0 Hz, or 840 RPM
Car vibration speed chart
Wheel frequency and RPM for three common sizes: a compact car (205/55R16), a midsize SUV (225/65R17) and a pickup or large SUV (265/70R17).
| Speed | 205/55R16 | 225/65R17 | 265/70R17 |
|---|---|---|---|
| 20 mph (32 km/h) | 4.5 Hz (270 RPM) | 3.9 Hz (236 RPM) | 3.5 Hz (213 RPM) |
| 30 mph (48 km/h) | 6.8 Hz (405 RPM) | 5.9 Hz (354 RPM) | 5.3 Hz (319 RPM) |
| 40 mph (64 km/h) | 9.0 Hz (540 RPM) | 7.9 Hz (472 RPM) | 7.1 Hz (425 RPM) |
| 50 mph (80 km/h) | 11.3 Hz (676 RPM) | 9.8 Hz (589 RPM) | 8.9 Hz (532 RPM) |
| 60 mph (97 km/h) | 13.5 Hz (811 RPM) | 11.8 Hz (707 RPM) | 10.6 Hz (638 RPM) |
| 70 mph (113 km/h) | 15.8 Hz (946 RPM) | 13.8 Hz (825 RPM) | 12.4 Hz (744 RPM) |
| 80 mph (129 km/h) | 18.0 Hz (1,081 RPM) | 15.7 Hz (943 RPM) | 14.2 Hz (851 RPM) |
Wheel frequency rises in step with speed: double the speed and you double the frequency. Every one of these values is well within what a phone can measure, which makes wheel problems a good fit for a phone test.
What the wheel frequency tells you
- About 1× the wheel frequency: imbalance, a bent rim, or a tire with a high spot.
- About 2×: a tire that’s out of round.
- The driveshaft turns faster than the wheels by the axle ratio, often about 3 to 4 times. For a 225/65R17 at 60 mph, that’s roughly 35 to 47 Hz, too fast for a phone.
- The engine turns at RPM ÷ 60, which depends on the gear, not just road speed. Convert it with RPM to Hz.
Where the numbers come from
The size code is the standard metric tire size printed on the sidewall. The diameter it gives is the tire’s size on paper. Three things shift the real number:
- Load. The tire flattens where it meets the road, so it turns a few percent faster than the math says.
- Wear. A fully worn tread makes the tire about 2% smaller than new.
- Your speedometer. It can be off by a few percent. A GPS speed from a maps app is a good check.
Tire makers publish revolutions per mile for each tire, which already allows for load. At 60 mph, wheel Hz = revolutions per mile ÷ 60. For sizes in inches like 33x12.50R17, the first number is the overall diameter: 33 inches is 838 mm, which works out to about 10.2 Hz at 60 mph.
Frequently asked questions
How do I read my tire size?
Look for a code like 225/65R17 on the sidewall. 225 is the width in millimeters, 65 is the sidewall height as a percent of that width, R means radial, and 17 is the rim size in inches. A P or LT in front doesn't change the math.
Why is my wheel frequency different from the real one?
The calculator uses the tire's size on paper. On the road, the tire flattens a little under the car's weight and wears down over time, so it turns a few percent faster. That's why the car tests allow about 10% either way when they look for a match.
Can I use km/h?
Yes. Pick km/h next to the speed box and the result is the same wheel frequency. For reference, 100 km/h is about 62 mph.
Why does a smaller tire turn faster?
A smaller tire covers less road in one turn, so it has to turn more often to keep up. At 60 mph, a 205/55R16 turns about 13.5 times a second, while a 265/70R17 turns about 10.6 times.
Does it work for motorcycle tires?
Yes, for metric sizes like 180/55R17, which use the same width, height and rim numbers. Inch-based sizes need the diameter worked out by hand. Test your bike parked with the motorcycle vibration test, never while riding.
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