Wheel and Rim Runout: Meaning and Tolerances

Wheel runout is how far a rotating wheel rim departs from a perfect circle (radial runout) or from a flat plane of rotation (lateral runout). It is measured in millimetres or thousandths of an inch with a dial indicator. The result is the total indicator reading: the highest reading minus the lowest reading during one full revolution. The acceptable rim runout tolerance comes from the vehicle or wheel manufacturer's specifications, not from the tire size. Many motorcycle service manuals give a service limit of around 2.0 mm for both radial and lateral rim runout, and some models specify tighter values. Always use the figure for your exact model.

Runout is measured in fractions of a millimetre, while tire sizes describe a wheel and tire in tens or hundreds of millimetres. The tire sidewall still matters, because it tells you the rim diameter, the construction type and the nominal size of the assembly you are checking. This article starts with those numbers and then explains runout itself.

What the Numbers on the Tire Sidewall Mean

A tire size marking combines dimensions, a ratio, a construction code and performance ratings in one line. On a motorcycle rear tire marked 180/55 ZR17 M/C 73W, each part describes something different. Some parts are measurements, one is a percentage and some are codes that refer to standard tables.

Dimensions, Ratios and Units

• 180 is the nominal section width in millimetres. It is the width of the tire from sidewall to sidewall, measured on a specified measuring rim.
• 55 is the aspect ratio, a percentage, not a length. The sidewall height is 55% of the section width.
• Z or R is the construction code. R means radial construction. ZR is an older marking for radial tires rated above 240 km/h. A dash (as in 110/90-19) indicates bias-ply construction, and B indicates bias-belted construction.
• 17 is the rim diameter in inches. It is the diameter of the bead seat on the wheel, not the outside of the rim flange.
• M/C means the tire is intended for motorcycles.

The units are mixed on purpose: width in millimetres, rim diameter in inches, and aspect ratio as a percentage. Some older or off-road motorcycle tires use an all-inch format such as 3.00-18. In that format, 3.00 is the nominal width in inches and 18 is the rim diameter in inches.

Performance Ratings: Load Index and Speed Symbol

The load index and speed symbol are performance ratings. They are not dimensions and have no effect on size or runout.

• Load index (73) is a code for the maximum load per tire at the specified inflation pressure. Index 73 corresponds to 365 kg, and index 58 corresponds to 236 kg.
• Speed symbol (W) is a code for the maximum sustained speed under specified conditions. H is 210 km/h, V is 240 km/h and W is 270 km/h. A symbol in brackets, such as (73W), is a common marking on ZR tires.

Sidewall Markings Related to Wheel Roundness

Several markings help you mount and check a wheel correctly, even though none of them is a runout value.

• Rotation arrow: shows the direction the tire must turn when mounted.
• Balance dot: usually a yellow or white dot that marks the tire's lightest point. It is commonly aligned with the valve stem.
• Uniformity mark: some tires carry a red dot marking the high point of radial variation. It is used for match-mounting against the low point of the wheel.
• DOT code: the last four digits give the week and year of manufacture. For example, 2324 means week 23 of 2024.
• Rim marking on the wheel: wheels are often stamped with a size such as 17 x MT5.50. This means a 17-inch diameter, a rim width of 5.50 inches and an MT flange profile used on many motorcycle wheels.

How Width, Aspect Ratio and Rim Diameter Set Tire Size

The nominal overall diameter of a tire is the rim diameter plus two sidewall heights. Sidewall height equals section width multiplied by aspect ratio. These are the calculation steps:

1. Sidewall height (mm) = section width (mm) x aspect ratio / 100.
2. Rim diameter (mm) = rim diameter (inches) x 25.4.
3. Overall diameter (mm) = rim diameter (mm) + 2 x sidewall height.
4. Circumference (mm) = overall diameter x 3.1416.

For a 180/55 ZR17 tire, the sidewall height is 180 x 0.55 = 99 mm. The rim is 17 x 25.4 = 431.8 mm. The overall diameter is 431.8 + 198 = 629.8 mm, and the circumference is about 1,978.6 mm.

The table shows that a wider tire can be smaller overall. A 190/50 ZR17 is 10 mm wider than a 180/55 ZR17, but its lower aspect ratio gives a sidewall about 4 mm shorter. Its calculated overall diameter is therefore about 8 mm smaller, and its circumference is about 25 mm shorter, a difference of roughly 1.3%. In the car example, moving from 205/55 R16 to 225/45 R17 increases the rim diameter by one inch while the shorter sidewall keeps the overall diameter within about 2.4 mm.

Calculated Geometry Versus Actual Tire Dimensions and Fitment

The figures above describe nominal geometry, not the exact size of a real tire. Actual width and diameter depend on the rim width the tire is mounted on, the tire's construction and profile, the inflation pressure and wear. Manufacturers publish measured dimensions, and two tires with the same size marking can differ by several millimetres.

A matching calculation also does not prove that a tire fits a vehicle. Fitment depends on approved rim widths, clearance to the swingarm, chain, fork or bodywork, and the approved load and speed ratings. These dimensional differences are measured in millimetres and percentages of diameter. Rim runout is measured in tenths or hundredths of a millimetre on the wheel itself, so changing the tire size does not change the rim runout tolerance.

What Is Wheel Runout? Radial and Lateral Runout Explained

Wheel runout is the variation in a rim's position as it rotates on its own axis, and it has two forms.

• Radial runout is up-and-down variation. It means the rim is not perfectly round or not centred on the axle, so its radius changes around the circumference.
• Lateral runout is side-to-side variation. It means the rim does not rotate in a single flat plane and wobbles left and right.

Rim runout should be separated from tire runout. A perfectly true rim can still carry a tire with uneven construction or a bead that is not fully seated. The tire tread will then run out even though the rim is within tolerance. Measuring the rim first shows which component is responsible.

Rim Runout Tolerance: How Specifications Are Given

A rim runout tolerance is the maximum total indicator reading allowed for a wheel, stated separately for radial and lateral runout. It is published in the vehicle service manual or by the wheel manufacturer. It may be given as a new-part standard, a service limit, or both. The service limit is the larger figure beyond which the wheel should be repaired or replaced.

Motorcycle Wheel Runout Tolerance

For motorcycle wheels, many manufacturer specifications list a rim runout service limit of about 2.0 mm for both radial and lateral directions. Other models, wheel types or manufacturers specify smaller values. Spoked wheels can be trued by adjusting spoke tension. Cast wheels usually cannot be straightened in the same way, so a cast wheel beyond its limit is usually replaced. Manuals often also give a separate runout limit for the axle and a check for wheel bearing play, because a bent axle or worn bearing adds to the reading.

Units and Reading Resolution

Runout tolerances are given in millimetres or inches, and 0.001 inch equals 0.0254 mm. Most dial indicators are graduated in 0.01 mm or 0.001 inch steps. That resolution is fine enough to check limits measured in tenths of a millimetre.

How to Measure Rim Runout With a Dial Indicator

Rim runout is measured by rotating the wheel slowly on its own axle while a dial indicator touches a clean rim surface. The difference between the highest and lowest readings is the runout.

Rim Measurement Surfaces

The measurement surface must be a machined or smooth part of the rim, not the tire. Radial runout is usually read on the bead seat area or the inner circumference of the rim edge, with the tire removed. Lateral runout is read on the side face of the rim flange. Avoid weld seams, paint runs, chips, dents and spoke nipples, because they produce false peaks. Follow the service manual where it names a specific surface.

Indicator Mounting

The indicator must be mounted rigidly so that only the rim moves. Common setups use a magnetic or clamp base on a truing stand, a wheel balancing stand, or a solid point on the fork leg or swingarm. The plunger should be perpendicular to the measuring surface. For radial runout it points toward the axle, and for lateral runout it is parallel to the axle.

1. Support the wheel so it turns freely on its axle, either on a stand or in the motorcycle with the wheel lifted.
2. Check the axle and wheel bearings for play or roughness, because movement here shows up as false runout.
3. Clean the rim measurement surface.
4. Mount the dial indicator with its plunger perpendicular to the surface and slightly preloaded, so the needle can move in both directions.
5. Rotate the wheel slowly until you find the lowest reading, and set the dial to zero there.
6. Turn the wheel through at least one full revolution, and note the highest reading and where it occurs.
7. Record the total indicator reading, which is the highest minus the lowest value.
8. Repeat on the other side of the rim and for the other direction, so you have both radial and lateral readings.
9. Compare each reading with the manufacturer's specifications for that wheel.

Reading the Result

If both radial and lateral readings are within the manufacturer's limit, the rim is serviceable. Remaining vibration then points to the tire, mounting, balance, bearings or other parts. A reading over the limit means the wheel needs truing (for spoked wheels) or repair or replacement as the manufacturer directs. A single sharp spike usually means a local dent or surface defect. A smooth rise and fall over one revolution suggests the whole rim is bent or off-centre. Always measure again after any repair to confirm the wheel is back within specification.