Tire Runout Tolerance: Understanding and Measuring Out-of-Round Tires

Tire runout tolerance is the maximum allowed deviation of a rotating tire and wheel from a true circle (radial runout) or from a flat plane (lateral runout). It is measured as total indicated runout (TIR), in inches or millimetres, with a dial indicator while the assembly turns slowly. The sidewall size code, such as 225/45R17, gives the tire's nominal geometry but not its runout tolerance. Runout limits come from the vehicle, wheel or tire manufacturer's specifications. Many service procedures for mounted passenger tire and wheel assemblies use limits of roughly 0.030 to 0.060 in (about 0.75 to 1.5 mm). A tire that exceeds its limit is called out of round. Typical symptoms are speed-related vibration, rhythmic noise and uneven wear.

What Do the Numbers on the Tire Sidewall Mean?

The sidewall size code describes the tire's nominal width, the height of its sidewall as a ratio and the rim diameter it fits. Separate markings show load and speed capability. None of these markings states a roundness or runout value. They tell you the size the tire is designed to be, not how precisely a particular tire turns on a particular wheel.

Size, ratio, construction and rim diameter

This guide uses the example marking 225/45R17 91W.

• 225 is the section width in millimetres. It is the nominal width from sidewall to sidewall, measured on a specified rim width.
• 45 is the aspect ratio, a percentage with no unit. The sidewall height is 45% of the section width.
• R is the construction type. It means radial. It is not a dimension.
• 17 is the rim diameter in inches. It is the diameter of the wheel's bead seat, where the tire bead sits.

The marking mixes millimetres for width with inches for rim diameter. You must convert to one unit before calculating anything. One inch equals 25.4 mm.

Performance ratings are not dimensions

• 91 is the load index. It is a code for the maximum load per tire at the specified pressure. In standard tables, 91 corresponds to 615 kg.
• W is the speed rating. It is a code for the maximum sustained speed under test conditions. W corresponds to 270 km/h (168 mph).
• The DOT code identifies the plant and production date. The last four digits show the week and year of manufacture.
• UTQG treadwear, traction and temperature grades are comparative performance ratings. They do not describe tire size or tire roundness.

How width, aspect ratio and rim diameter set sidewall height, diameter and circumference

Three formulas give a tire's calculated nominal geometry:

• Sidewall height (mm) = section width × (aspect ratio ÷ 100)
• Overall diameter (mm) = (rim diameter × 25.4) + (2 × sidewall height)
• Circumference (mm) = overall diameter × π (about 3.1416)

For a 225/45R17 tire, the calculation works out as follows:

• Sidewall height: 225 × 0.45 = 101.25 mm.
• Rim diameter: 17 × 25.4 = 431.8 mm.
• Overall diameter: 431.8 + 202.5 = 634.3 mm, about 24.97 in.
• Circumference: about 1,992.7 mm.

Size	Sidewall height	Overall diameter	Circumference	Diameter vs 225/45R17
225/45R17	101.3 mm	634.3 mm	1,992.7 mm	Reference
225/50R17	112.5 mm	656.8 mm	2,063.4 mm	+22.5 mm (about +3.5%)
245/40R18	98.0 mm	653.2 mm	2,052.1 mm	+18.9 mm (about +3.0%)

The table shows how each number in the size code affects the result:

• Aspect ratio: Raising it from 45 to 50 at the same width adds 11.25 mm to each sidewall, or 22.5 mm to the overall diameter.
• Width and aspect ratio together: A wider tire with a lower aspect ratio can end up with a shorter sidewall. The 245/40 tire has a 98 mm sidewall, compared with 101.25 mm for the 225/45 tire.
• Rim diameter: A larger rim raises the overall diameter. Going from a 17 in to an 18 in rim adds 25.4 mm before sidewall height is counted.

Calculated geometry versus actual tire dimensions and fitment

Calculated values are nominal. The actual dimensions of a mounted tire vary with several factors:

• the brand and model, because published dimensions differ slightly between makers
• the rim width it is mounted on
• inflation pressure and the load on the tire
• tread depth, because a worn tire is smaller in diameter than a new one

Matching calculated diameters does not prove that a tire fits a vehicle. Fitment also depends on:

• rim width and wheel offset
• clearance to suspension and body parts
• load index and speed rating requirements
• the sizes approved by the vehicle manufacturer

Putting runout into perspective against tire size

Runout is very small compared with nominal tire dimensions. A radial runout of 0.030 in (0.76 mm) on a 634 mm tire is about 0.12% of its diameter. That is far smaller than the 22.5 mm difference between a 45 and a 50 aspect ratio at the same width.

This is why runout cannot be judged by eye or from the size code. It can only be measured with an instrument. The wheel turns many times per second at road speed, so even a deviation of a fraction of a millimetre can produce a noticeable vibration.

What Is Runout Tolerance?

Runout tolerance is the specified limit for how far a rotating surface may deviate from its ideal path. The deviation is expressed as total indicated runout (TIR). TIR is the difference between the highest and lowest dial indicator readings during one full revolution. It is given in inches (often thousandths of an inch) or in millimetres.

Runout is checked in two directions:

• Radial runout is up-and-down deviation of the tread from a perfect circle around the axle centre.
• Lateral runout is side-to-side axial deviation of the sidewall or rim from a flat plane as it rotates.

Tire runout and wheel runout add together or partly cancel. For this reason, tolerances are usually given for the bare wheel and for the mounted assembly.

Type	Direction of deviation	Where it is measured	Typical felt effect
Radial runout	Up and down, toward and away from the axle	Centre of the tread, or the rim bead seat on a bare wheel	Vertical shake or hop, felt in the seat and steering wheel
Lateral runout	Side to side, along the axle	Smooth band of the sidewall, or the rim flange on a bare wheel	Wobble or side-to-side shimmy
Total indicated runout (TIR)	Highest reading minus lowest reading	Any measured surface over one revolution	The single number compared with the specification

Which tolerance value applies?

The applicable tire runout tolerance is the one in the vehicle, wheel or tire manufacturer's specifications for that application. Many service procedures for passenger vehicles use limits of roughly 0.030 to 0.060 in (about 0.75 to 1.5 mm) for a mounted tire and wheel. Bare wheels usually have tighter limits.

Sensitive vehicles can show vibration even within a general limit. Low-profile tires and stiff suspensions are common examples. Treat any generic figure as a guide, not a replacement for the published specification.

What Does Out of Round Tire Mean?

An out-of-round tire is a tire whose radial runout, measured on its correctly seated wheel, exceeds the allowed tolerance. Its rolling radius rises and falls once or more per revolution, so the axle is pushed up and down as the tire rolls.

The term is also used loosely for related problems:

• tires with excessive lateral runout
• tires that measure round but vary in stiffness around the circumference

Uneven stiffness is called force variation. It is detected with a loaded roller on a road force balancer, not with a dial indicator. It can cause the same vibration as a geometrically out-of-round tire.

Out of Round Tire Causes

Out-of-round conditions come from the tire itself, from the wheel, or from how the two are mounted together. The common causes are:

• Improper bead seating. If the tire bead is not fully seated on the rim bead seat, the tire sits off-centre. The visible bead line around the rim is then uneven. Lack of lubricant or insufficient seating pressure can cause this.
• Wheel runout. A bent, damaged or poorly manufactured wheel carries its own radial or lateral runout into the assembly.
• Manufacturing variation. Variations in belt placement, splices or material distribution can create a high spot or uneven stiffness.
• Temporary flat spotting. A tire left parked or stored under load can form a flat area. It usually reduces once the tire warms up while driving.
• Internal damage. Impacts, underinflation or age can cause belt shift or tread separation. This often shows as a bulge or local high spot.
• Uneven wear. Worn suspension parts or long-term imbalance can produce cupping or flat spots that make the tread surface irregular.
• Mounting and hub issues. Several mounting faults can cause runout at the hub or wheel:
  • rust or debris between the wheel and hub
  • an uneven lug nut tightening sequence
  • a wheel that is not centred on the hub

Out of Round Tire Symptoms

The main symptoms of an out-of-round tire are vibration that changes with road speed, rhythmic noise that follows wheel rotation, and uneven tread wear. These symptoms follow vehicle speed, not engine speed. They do not change when you shift gears or coast in neutral at the same road speed.

Out of round tire vibration

The wheel position affects where the vibration is felt:

• A front tire usually transmits vibration to the steering wheel.
• A rear tire usually transmits vibration to the seat and floor.

The vibration often appears in a particular speed range and continues after the tire has been balanced. Balancing corrects uneven mass. It does not correct a tire or wheel that is not round. A vibration that persists after a careful balance is a common sign that runout or force variation should be checked.

Out of round tire noise

Out-of-round tires typically make a rhythmic thump, hum or "wub-wub" sound. The pulses speed up as the car goes faster and slow down as it slows. The sound repeats once per wheel revolution, or several times if the tread has cupping.

Cupped or scalloped tread can also make a growl that resembles a wheel bearing noise. Comparing the sound on different road surfaces, and checking the tread by hand, helps tell the two apart.

Out of round tire wear

An out-of-round tire can wear unevenly because its contact force rises and falls around the circumference. Common patterns include:

• cupping or scalloping, seen as patches of alternating depth around the tread
• local flat spots
• wear concentrated on one section of the tire

Uneven wear is both a result of runout and a cause of more vibration. Worn shock absorbers or other suspension faults can create similar patterns, so they should be checked as well.

Tire Radial Runout Measurement

Tire radial runout is measured by holding a dial indicator against the centre of the tread while the tire and wheel rotate slowly through one full turn. The result is the total indicated runout in inches or millimetres. Accurate readings require these conditions:

• the tire is warm, so temporary flat spots are gone
• the tire is inflated to the specified pressure
• the wheel turns on a true spindle or balancer shaft

1. Warm the tire. Drive several kilometres to remove flat spots caused by parking.
2. Set the pressure. Inflate the tire to the pressure on the vehicle's tire placard.
3. Mount the assembly. Place it on a tire balancer, or lift the vehicle so the wheel turns freely. On the vehicle, check that the wheel bearing has no play, because play adds false readings.
4. Prepare the tread surface. Choose a continuous centre rib, or wrap tape around the tread so the indicator tip does not drop into grooves.
5. Position the indicator. Mount the dial indicator on a stable base, with the plunger perpendicular to the tread and slightly preloaded.
6. Zero and rotate. Zero the indicator, then rotate the tire slowly through at least one full turn.
7. Calculate TIR. Note the highest and lowest readings. TIR equals the maximum reading minus the minimum reading.
8. Mark the high spot. Chalk the high spot on the tire so it can be used for correction.
9. Repeat on other ribs. Measure at more than one tread position if the tread design allows, and compare the results with the manufacturer's specification.

Tire Lateral Runout Measurement

Tire lateral runout is measured by holding a dial indicator against a smooth band of the sidewall while the assembly rotates. The result is the side-to-side TIR. The setup is the same as for radial runout: warm tire, correct pressure, and a wheel turning on a true axis.

1. Find a smooth band. Choose an area of the sidewall clear of lettering, ribs and decorative markings, usually near the widest point.
2. Position the indicator. Place the plunger perpendicular to the sidewall with light preload.
3. Zero and rotate. Zero the indicator and rotate the tire slowly through a full turn.
4. Allow for normal irregularities. Sidewalls have small splice bumps. A sudden narrow jump in the reading is usually a splice. A gradual swing over the revolution is true lateral runout.
5. Record and compare. Record the TIR, mark the high point and compare the result with the specification.

Separating tire runout from wheel runout

To find out whether the tire or the wheel causes the runout, measure the wheel separately. Take radial readings on the rim bead seats and lateral readings on the rim flanges, ideally both inboard and outboard, with the tire removed. Some balancers can do this with the tire still mounted.

Interpret the results as follows:

• The wheel is within its tolerance but the assembly is not: the tire or its bead seating is the likely cause.
• The wheel alone exceeds its limit: the wheel itself needs attention.

Out of Round Tire Fix: How Runout Is Corrected

The right fix depends on the cause found during measurement. Balancing weights do not correct runout. Runout correction means making the assembly turn truly, or replacing the part that cannot be made true.

1. Rule out flat spots. Drive until the tire is warm, then measure again. Many parking-related flat spots disappear at this stage.
2. Reseat the bead. Deflate the tire, lubricate the bead and rim, and reinflate. Do not exceed the tire maker's maximum seating pressure. Then confirm that the bead line is even all the way around the rim.
3. Check the hub mounting. Clean rust and debris from the hub and wheel mating faces. Then tighten the lug nuts to the specified torque in a star pattern.
4. Match-mount the tire. Rotate the tire on the rim so the tire's high spot sits at the wheel's low spot. Their runouts then partly cancel. Road force balancers can guide this step.
5. Repair or replace a bent wheel. Do this if the wheel alone exceeds its runout limit. Repairs should follow the wheel manufacturer's guidance.
6. Consider tread truing only with caution. Truing shaves rubber from the high spot. It permanently removes tread depth and is not approved for every tire.
7. Replace a tire with internal damage. Bulges, belt shift, tread separation or an uncorrectable high spot are safety concerns. They are not just comfort issues, so the tire should be replaced rather than corrected.

After any correction, measure radial and lateral runout again, then balance the assembly. If the TIR is now within the manufacturer's specification and the vibration remains, check other rotating parts and the suspension:

• hubs and brake rotors
• driveshafts
• suspension components