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Wheels and Tires

17 questions

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Question 1Question →

An automotive technician is inspecting a wheel and tire assembly for ride disturbance and vibration concerns. Match each balance or runout condition with its corresponding mechanical characteristic.

Click a left item, then click its matching right item

Items

Static imbalance
Dynamic imbalance
Radial runout
Lateral runout

Matches

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Answer

Static imbalance matches a single heavy spot causing vertical tramp; Dynamic imbalance matches dual-plane weight asymmetry causing lateral shimmy; Radial runout matches out-of-round geometric variation causing vertical hop; Lateral runout matches axial side-to-side wobble.
Each condition matches its specific mechanical and directional definition: static imbalance creates vertical tramp due to a single heavy spot; dynamic imbalance generates lateral shimmy due to two-plane mass offset; radial runout represents out-of-round geometric eccentricity; and lateral runout represents axial side-to-side wobble.

Step-by-Step Solution

1
Distinguish between mass imbalance and geometric runout conditions
Imbalances relate to mass distribution (static and dynamic), whereas runout relates to physical/dimensional deviation (radial and lateral).
Correct automotive diagnosis requires isolating weight defects from dimensional defects.
2
Correlate single-plane and dual-plane mass distribution with their directional vibration modes
Static imbalance creates single-plane vertical hop (tramp), while dynamic imbalance creates two-plane rotational rocking (shimmy).
Static imbalance acts purely radial-centrifugal, while dynamic imbalance produces a rocking torque across the wheel centerline.
3
Correlate radial and lateral runout with their geometric axes of deviation
Radial runout is variation in radius/roundness, while lateral runout is axial side-to-side rim/tire wobble.
Dial indicators placed perpendicular to the tread measure radial runout, whereas indicators placed parallel to the axle against the sidewall or rim lip measure lateral runout.

Key Concept

Wheel and Tire Balance and Runout Diagnostics
Estimated Time:1m 15s
Question 2Question →

A vehicle is equipped with directional (unidirectional) tires that have arrows molded into the sidewalls indicating the required forward rotation direction. When performing a routine tire rotation on this vehicle without dismounting the tires from their wheels, what is the correct procedure?

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Answer: Swap the front tires straight to the rear and the rear tires straight to the front on the same side of the vehicle.

Answer

Swap the front tires straight to the rear and the rear tires straight to the front on the same side of the vehicle.
Directional tires have a tread pattern designed to operate in a single direction of rotation, indicated by an arrow on the sidewall. When rotating directional tires without dismounting them from the wheels, they must remain on the same side of the vehicle (front-to-rear and rear-to-front) so that their direction of rotation does not change.

Step-by-Step Solution

1
Identify the specific tire construction and tread type from the sidewall markings.
The tires are directional, meaning the tread pattern is engineered to rotate efficiently in only one direction.
Directional tread grooves are angled to evacuate water and maintain road grip exclusively when rolling forward as indicated by the sidewall arrow.
2
Determine the allowable rotation path without dismounting the tire from the rim.
Tires must stay on the same side of the vehicle (left-front to left-rear, right-front to right-rear).
Moving a mounted directional tire across to the opposite side of the vehicle causes it to rotate backward during forward driving, degrading traction and wet-weather performance.

Key Concept

Directional tire rotation patterns and maintenance constraints
Estimated Time:1m 0s
Question 3Question →

During a multi-point vehicle inspection, an automotive technician observes several distinct tire wear patterns across different fleet vehicles. Match each observed tire wear pattern with its primary operational or mechanical root cause.

Click a left item, then click its matching right item

Items

Symmetrical wear concentrated along both outer tread shoulders with minimal center tread wear
Rapid, accelerated wear localized strictly along the center tread rib
Directional saw-tooth or feathered edges across individual tread ribs felt when wiping across the tire
Scalloped, localized scooped-out dips and cupped bald spots around the tire circumference

Matches

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Answer

Match symmetrical dual-shoulder wear with chronic underinflation; center rib wear with chronic overinflation; feathered saw-tooth wear with improper toe alignment; and cupping or scalloping with worn shock absorbers or dynamic wheel imbalance.
Each tire wear profile represents a distinct mechanical or operating fault: underinflation unloads the center and overloads both shoulders; overinflation crowns the center rib; toe misalignment causes horizontal dragging that feathers tread blocks; and weak suspension damping allows uncontrolled vertical bouncing that cuts rhythmic cupped dips into the tread circumference.

Step-by-Step Solution

1
Analyze contact patch physics related to pneumatic inflation errors.
Determined that dual-shoulder wear indicates low tire pressure (underinflation), whereas center-crown wear indicates excessive tire pressure (overinflation).
Inflation pressure controls the transverse contact patch profile across the tread.
2
Distinguish between lateral alignment friction and vertical suspension/balance oscillation.
Determined that feathered edges result from lateral scrubbing caused by toe angle misalignment, while cupping and scalloping result from cyclic vertical impacts caused by failing dampers or wheel imbalance.
Toe angles create continuous horizontal dragging across the tread face, whereas degraded suspension dampers permit dynamic bouncing along the circumference.

Key Concept

Tire Wear Pattern Diagnostics and Chassis Alignment Relationships
Estimated Time:1m 30s
Question 4Question →

During a routine vehicle maintenance inspection, a technician discovers a distinct cupped and scalloped wear pattern across the tire tread. Which worn or defective component is the most likely cause of this specific tire wear?

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Answer: Shock absorber

Answer

Worn shock absorber
Worn shock absorbers fail to control spring oscillations, allowing the wheel assembly to bounce excessively as the vehicle travels. This continuous bouncing causes the tire to repeatedly hit the road surface with high impact, resulting in a scalloped or cupped wear pattern around the tread.

Step-by-Step Solution

1
Identify the characteristic tire wear symptom described in the stem.
The symptom is cupping or scalloping (alternating high and low dips along the tread circumference).
Recognizing the physical wear pattern is the first step in automotive wheel and tire diagnostics.
2
Determine the mechanical mechanism that produces repeated vertical bouncing on the road surface.
Shock absorbers and struts are responsible for dampening spring oscillations; when worn, they allow uncontrolled wheel hop.
Uncontrolled bouncing repeatedly slams the tire tread into the pavement at periodic intervals, digging out distinct cups in the rubber.

Key Concept

Tire wear diagnostics and shock absorber dampening function
Estimated Time:45s
Question 5Question →

A passenger vehicle is fitted with tires marked with the sidewall designation P215/65R15. Match each component of the tire specification code to its correct physical measurement or construction feature.

Click a left item, then click its matching right item

Items

215
65
R
15

Matches

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Answer

215 matches Cross-section width of the tire measured in millimeters; 65 matches Aspect ratio representing sidewall height as a percentage of cross-section width; R matches Internal carcass ply construction type indicating radial design; 15 matches Wheel rim diameter measured in inches.
In standardized automotive tire markings, the format P[Width]/[Aspect Ratio][Construction][Rim Diameter] is used. For P215/65R15, 215 is the tire width in millimeters, 65 is the aspect ratio percentage, R indicates radial construction plies, and 15 is the rim diameter in inches.

Step-by-Step Solution

1
Decode the initial 3-digit number after the service indicator prefix
215 represents the section width of the tire in millimeters.
Standard metric passenger tire codes list the width across the widest point of the tire in millimeters first.
2
Decode the 2-digit number following the slash
65 represents the aspect ratio percentage.
The aspect ratio expresses the sidewall profile height as a proportion of total cross-sectional width.
3
Identify the internal construction letter
R denotes radial construction.
The letter code directly specifies the orientation of the internal body plies.
4
Decode the final numeric value
15 represents the wheel rim diameter in inches.
The last number in the sizing sequence designates the rim size required for mounting.

Key Concept

Tire sidewall specification and dimensional coding
Estimated Time:45s
Question 6Question →

A driver reports a distinct lateral steering wheel wobble (shimmy) that occurs only when cruising at highway speeds between 55 and 65 mph. The vehicle tracks straight without pulling, and the symptom is not related to braking. What is the most likely cause of this condition?

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Answer: Dynamic wheel imbalance creating alternating lateral forces across the centerline of the wheel assembly

Answer

Dynamic wheel imbalance creating alternating lateral forces across the centerline of the wheel assembly
Dynamic wheel imbalance is caused by an unequal distribution of mass on opposite sides of the tire's vertical centerline. As the wheel rotates at highway speeds (typically 50 to 65 mph), centrifugal force generates an alternating side-to-side twisting moment around the steering knuckle pivot, felt directly as steering wheel shimmy.

Step-by-Step Solution

1
Analyze the operating conditions and directional nature of the symptom.
The symptom is a lateral side-to-side steering wobble occurring specifically in the 55-65 mph highway speed range without pulling or braking involvement.
Speed-sensitive vibration without directional pull points directly to wheel and tire assembly balance rather than alignment or braking defects.
2
Differentiate between static and dynamic wheel unbalance modes.
Static unbalance creates vertical forces (wheel tramp/hop), whereas dynamic unbalance creates an alternating force couple across the tire centerline (lateral shimmy).
Dynamic unbalance requires spin-balancing with weights placed on both the inner and outer rim planes to counteract side-to-side wobble.

Key Concept

Distinction between dynamic wheel imbalance (lateral wobble/shimmy) and static wheel imbalance (vertical tramp/hop)
Estimated Time:1m 30s
Question 7Question →

When cruising at highway speeds of 55 to 65 mph, a driver experiences a noticeable rhythmic vibration in the steering wheel, but the vibration subsides at lower city driving speeds. Which condition is the most likely cause of this symptom?

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Answer: An out-of-balance front wheel assembly

Answer

An out-of-balance front wheel assembly
An out-of-balance front wheel assembly produces an uneven distribution of weight around its axis of rotation. At highway speeds, this mass imbalance generates substantial centrifugal force that translates into an oscillating steering wheel vibration.

Step-by-Step Solution

1
Analyze the reported symptom and conditions
Vibration is felt in the steering wheel at highway speeds (55-65 mph) and disappears at lower speeds without braking.
Speed-sensitive mechanical vibration indicates rotating mass imbalance rather than braking or structural alignment faults.
2
Identify the rotating component connected directly to the steering system
The front wheel and tire assemblies rotate at high speeds and transfer dynamic forces directly into the steering knuckles and tie rods.
When a heavy spot exists on a front tire or wheel, centrifugal force causes wheel hop or shimmy that peaks within standard highway speed ranges.

Key Concept

Wheel and tire dynamic balance diagnostics
Estimated Time:45s
Question 8Question →

An automotive technician is replacing a wheel assembly on a passenger vehicle following standard shop safety and torque procedures. What is the correct chronological sequence of steps for mounting and securing the wheel to ensure proper clamping force and prevent brake rotor distortion?

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Answer

Clean and inspect the hub and studs, mount the wheel and hand-snug the lug nuts, lower the vehicle to partial ground contact to prevent spinning, tighten all lug nuts in a crisscross pattern with a calibrated torque wrench, and finally lower the vehicle completely to the floor.
Proper wheel installation requires preparing the mating surfaces first to eliminate runout, hand-snugging nuts while raised to ensure proper thread alignment, lowering the tire only enough to hold it stationary, achieving final torque with a calibrated wrench in a crisscross sequence to balance clamping stress, and lastly lowering the vehicle fully to the floor.

Step-by-Step Solution

1
Inspect and clean the hub face and studs with a wire brush.
Debris and corrosion are removed, preventing lateral runout or false torque readings.
Mating surfaces must be clean and flat so the wheel seats true to the hub.
2
Hang the wheel and hand-thread all lug nuts until seated.
All nuts engage cleanly without cross-threading.
Hand-threading centers the wheel on the hub and prevents thread damage caused by power tools.
3
Lower the vehicle jack partially until the tire just grips the ground.
The wheel is locked from rotating without bearing full vehicle weight.
Torquing while the full weight rests on the wheel can cause lateral misalignment and side-loading on studs.
4
Apply final torque in a star/crisscross sequence using a calibrated torque wrench.
Equal clamping tension is distributed evenly around the hub and brake rotor.
Even torque distribution prevents brake rotor warping, wheel loosening, and hub distortion.
5
Lower the vehicle completely to the ground and stow the jack.
The vehicle safely rests fully on its suspension with correctly secured wheels.
The vehicle is now safe for full static load and road testing.

Key Concept

Standard shop procedure for wheel installation, hub preparation, and star-pattern torque sequence to maintain correct clamping load and prevent rotor warping.
Estimated Time:1m 30s
Question 9Question →

An automotive technician needs to replace a flat tire with a spare wheel. In what chronological order should the technician perform these steps to ensure safety and proper wheel mounting?

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Answer

1. Break the lug nuts loose while the tire is on the ground; 2. Raise the vehicle and secure it on a jack stand; 3. Remove lug nuts, take off the flat wheel, and mount the spare wheel; 4. Lower the vehicle to the ground and torque the lug nuts in a crisscross pattern.
The correct sequence begins by breaking lug nuts loose while tire traction keeps the wheel stationary, followed by lifting and securing the chassis on a stand, changing the wheel assembly, and finally lowering the vehicle before applying specified final torque in a crisscross pattern.

Step-by-Step Solution

1
Loosen each lug nut approximately one-half turn before elevating the vehicle.
The initial high-torque resistance is overcome safely without spinning the wheel or risking vehicle instability.
Ground contact prevents wheel rotation and provides stability under heavy breaker-bar torque.
2
Elevate the axle or lift point using a mechanical or hydraulic jack, then place a rated jack stand under the designated chassis point.
The tire clears the floor and the vehicle is mechanically supported.
Jacks are lifting devices, not long-term holding devices; jack stands prevent accidental drops.
3
Spin off the remaining lug nut threads, slide the flat tire off the hub studs, and mount the spare wheel flush against the hub face.
The flat tire is removed and the replacement wheel is fitted.
Lug nuts can now be spun off quickly by hand or wrench, and snugged lightly against the wheel.
4
Lower the vehicle back onto the shop floor and use a calibrated torque wrench to tighten the lug nuts in a star or crisscross pattern.
The wheel is clamped securely with uniform clamping force.
Crisscross torquing prevents brake rotor warping and wheel hub misalignment.

Key Concept

Safe wheel removal and installation sequence
Estimated Time:45s
Question 10Question →

A technician inspects a vehicle and observes accelerated tread wear along both outer shoulder edges of a tire, while the center of the tread shows normal remaining depth. Which of the following is the most likely cause of this wear pattern?

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Answer: Operating the tire with chronically low air pressure

Answer

Operating the tire with chronically low air pressure
When a tire is operated with low air pressure (underinflation), the center section of the tread sags inward away from the road surface. This concentrates the vehicle's weight on both outer shoulders, leading to premature and accelerated tread wear along both edges.

Step-by-Step Solution

1
Analyze the observed tire wear pattern
Excessive wear on both outer shoulder edges with normal center tread depth
Identifying the specific wear zone narrows down whether the issue is related to pressure, alignment, or suspension damping
2
Correlate contact patch mechanics with tire inflation levels
Underinflation causes the contact patch to support weight primarily on the shoulders rather than across the entire width
Insufficient air pressure prevents the center carcass from maintaining firm contact with the road surface

Key Concept

Tire Inflation Pressure and Tread Wear Patterns
Estimated Time:45s
Question 11Question →

During a routine vehicle maintenance check, a technician observes that the raised rubber wear indicator bars molded into the bottom of the tread grooves are completely flush with the surrounding tread ribs. What does this condition indicate about the tire?

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Answer: The tire tread has worn down to 2/32 inch and the tire must be replaced

Answer

The tire tread has worn down to 2/32 inch and the tire must be replaced.
Tread wear indicators (wear bars) are molded across the base of the tire grooves at precisely 2/32 of an inch. When normal abrasive wear reduces the outer tread ribs until they are level with these bars, the tire has reached the legal minimum tread limit and must be replaced for safety.

Step-by-Step Solution

1
Identify the purpose of molded wear indicator bars in automotive tires.
Tread wear indicators are transverse rubber ridges molded into the primary longitudinal grooves at an exact height of 2/32 inch (1.6 mm).
Manufacturers build wear indicators directly into tires to provide a quick visual gauge of minimum legal and safe tread depth without requiring a dedicated depth gauge.
2
Evaluate the condition described where the wear bars are flush with the surrounding tread ribs.
The remaining usable tread groove depth is equal to or less than 2/32 inch.
When the tread surface wears down to the level of these indicator bridges, the tire cannot effectively channel water away, dramatically increasing the risk of hydroplaning and signaling required replacement.

Key Concept

Tread Wear Indicators and Minimum Tread Depth
Estimated Time:1m 0s
Question 12Question →

When running a hand across the tread ribs of a front tire, a technician feels that one edge of each tread block is smooth while the opposite edge is sharp and jagged. Which wheel alignment setting is most likely out of specification?

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Answer: Toe setting

Answer

The toe setting is most likely out of specification, as incorrect toe creates a classic feathered wear pattern across the tread ribs.
The toe setting controls whether the front edges of the tires point inward or outward relative to the vehicle centerline. When toe-in or toe-out is excessive, the tires scrub sideways against the pavement as they roll forward, resulting in characteristic feathered or sawtooth tread wear.

Step-by-Step Solution

1
Analyze the reported symptom and wear characteristic
The symptom describes tread blocks that are smooth on one side and sharp on the other across the face of the tire, which defines feathered edge wear.
Identifying the specific wear signature is necessary to determine the root mechanical cause.
2
Relate feathered tread wear to suspension and steering geometry
Feathering occurs when tires point excessively inward (toe-in) or outward (toe-out), forcing the tire to drag or scrub sideways across the road surface during forward travel.
Sideway scrub pulls and rounds one edge of each tread rib while leaving a raised, sharp lip on the trailing edge.
3
Rule out non-toe mechanical factors
Camber causes single-shoulder smooth wear, worn dampers cause scalloped cupping, and brake or differential faults do not produce directional tread feathering.
Eliminating alternative alignment and chassis faults confirms the toe adjustment as the correct remedy.

Key Concept

Tire Tread Feathering and Wheel Toe Alignment
Estimated Time:1m 0s
Question 13Question →

A service apprentice is using an off-car computerized spin balancer to balance an assembled wheel and tire. What is the correct order of steps required to properly execute this dynamic wheel balancing procedure from start to finish?

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Answer

The correct procedural order is: clean the mating area and mount the wheel using the proper cone, input the rim dimensions into the computer, lower the hood to run the measurement spin, attach the indicated counterweights to the rim planes, and respin the assembly to verify zero imbalance.
Computerized dynamic balancing requires a strict procedural sequence: mechanical setup (mounting and centering the wheel), electronic calibration (entering offset, width, and diameter), baseline measurement (initial spin with safety hood lowered), corrective action (attaching counterweights at designated inner/outer plane locations), and quality verification (final spin confirming zero imbalance).

Step-by-Step Solution

1
Center and clamp the wheel on the balancer arbor using the correct back or front cone.
The wheel assembly runs true without mechanical runout or off-center mounting error.
Improper mounting causes false imbalance readings and improper weight placement.
2
Use the machine gauges/calipers to record rim offset, rim width, and rim diameter, then enter them into the interface.
The computer calibrates its calculations to the exact dual-plane geometry of the wheel.
The machine cannot calculate the weight split between inner and outer planes without accurate dimensional data.
3
Lower the safety hood to initiate the high-speed measurement spin.
Sensors register the force vectors and output the required weight values and clock positions.
The hood engages the safety interlock and allows the wheel to spin safely up to measurement speed.
4
Align the wheel with the top-dead-center (or laser-guided) indicator and affix clip-on or adhesive tape weights.
Correction mass is added directly opposite the heavy spots on both rim planes.
Adding weight directly counteracts centrifugal forces generated by uneven tire/wheel mass distribution.
5
Close the hood and re-spin the assembly.
The digital display confirms OK or 0.00 on both inner and outer display windows.
Verification ensures that the attached weights fully eliminated dynamic imbalance without requiring further correction.

Key Concept

Off-Car Computerized Dynamic Wheel Balancing Sequence
Estimated Time:1m 30s
Question 14Question →

Match each standard tire sidewall specification term with its correct measurement description or engineering definition.

Click a left item, then click its matching right item

Items

Section Width
Aspect Ratio
Load Index
Speed Rating

Matches

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Answer

Section Width matches the linear measurement in millimeters from outer to inner sidewall; Aspect Ratio matches the sidewall height expressed as a percentage of section width; Load Index matches the numerical code corresponding to maximum load-carrying capacity; Speed Rating matches the alphabetical designation indicating maximum sustained speed capability.
Each tire marking corresponds to an exact metric: Section width specifies the millimeter width across sidewalls; Aspect ratio specifies the sidewall height relative to width as a percentage; Load index indicates maximum safe carrying mass; Speed rating designates the upper continuous velocity threshold.

Step-by-Step Solution

1
Identify the dimensional parameters on standard metric tire sizing codes.
Section width indicates physical tire breadth in millimeters (e.g., 225 in P225/50R17), while aspect ratio indicates sidewall height as a percentage of width (e.g., 50).
Dimensional markings establish the geometric fitment and clearance on wheel rims and chassis components.
2
Identify the service description parameters at the end of the tire size designation.
Load index provides a relative weight rating via a two- or three-digit number (e.g., 94), and speed rating provides maximum sustained velocity via a letter code (e.g., V).
Service descriptions guarantee that the tire meets or exceeds original equipment manufacturer payload and speed safety standards.
3
Associate each term to its specific technical definition.
Each tire specification metric aligns directly with its designated engineering meaning.
Accurate interpretation prevents improper tire selection, blowout risks, and speedometer calibration errors.

Key Concept

Standard Automotive Tire Sidewall Markings and Service Descriptions
Estimated Time:1m 15s
Question 15Question →

A vehicle exhibits cupped, scalloped dips and uneven bald patches spaced at regular intervals around the circumference of the tire tread. Which of the following faulty chassis components is the primary cause of this specific wear pattern?

Show answer & explanation

Answer: Worn shock absorbers or struts

Answer

Worn shock absorbers or struts
Worn shock absorbers or struts fail to dampen the natural oscillations of the suspension springs. This allows the wheel assembly to bounce rapidly off the pavement, creating localized bald spots and scalloped cupping along the circumference of the tread.

Step-by-Step Solution

1
Analyze the described tire wear pattern
The tire exhibits cupping (scalloped dips and localized bald spots around the tread circumference)
Cupping occurs when the tire repeatedly loses solid contact with the roadway and bounces excessively.
2
Determine which component controls spring oscillation and wheel bounce
Shock absorbers and struts provide hydraulic damping to suppress suspension rebound and wheel hop
When damping units fail, the tire bounces along the road surface, causing irregular impact wear at repeating intervals.

Key Concept

Tire Tread Cupping and Suspension Dampening Diagnostics
Estimated Time:1m 0s
Question 16Question →

An automotive technician is performing an industry-standard (USTMA/RMA) permanent one-piece patch-and-plug repair on a punctured tubeless radial passenger tire. In what sequential order should the technician execute the steps of this repair procedure?

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Answer

Dismount and inspect the inner liner → Ream the puncture channel → Buff the inner liner surface → Apply chemical vulcanizing cement → Install the patch-plug and stitch with a roller
The U.S. Tire Manufacturers Association (USTMA) and standard automotive service procedures mandate that any puncture repair must begin with dismounting the tire for internal inspection. Next, the injury channel is prepared by reaming out damaged steel cords. The inner liner must then be mechanically textured by low-speed buffing and coated with vulcanizing cement. Once the cement is dry, the combination patch-plug is installed from the inside and stitched with a roller to expel air.

Step-by-Step Solution

1
Dismount the tire and perform an internal inspection.
Confirms the casing has not sustained hidden belt separation or run-flat sidewall powdering.
Industry safety standards prohibit external plug-only repairs because internal damage cannot be verified while mounted.
2
Probe and ream the injury channel.
Removes jagged wire fragments and aligns the injury path.
Preparing the puncture channel ensures the rubber stem can seal the tread area completely against water intrusion.
3
Scrape and buff the inner liner around the injury.
Produces a clean, textured surface free of mold release agents.
Chemical bonding requires raw, clean rubber; over-buffing into cord plies must be avoided.
4
Apply chemical vulcanizing cement and allow to dry.
Forms an active chemical bonding layer.
The cement must dry to a matte, non-glossy finish so solvents evaporate before applying the patch.
5
Pull the stem through from inside and stitch down the patch base.
Permanently seals both the tread channel (stem) and the inner liner airtight seal (patch).
Rolling from the center outward expels trapped air pockets, ensuring total surface adhesion.

Key Concept

Standard radial tire puncture repair requires a combination patch-and-plug unit applied from the inside out following strict preparation, buffing, cementing, and stitching stages.
Estimated Time:1m 15s
Question 17Question →

A vehicle exhibits a rhythmic vertical vibration, often described as "wheel hop," while cruising in a straight line at 70 mph. The technician verifies the rims are not bent and successfully zeroes out all tire and wheel assemblies on a standard unloaded dynamic spin balancer. However, the highway-speed vibration persists during a follow-up road test. Which of the following best explains the most likely cause of this persistent vibration?

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Answer: Excessive radial force variation within the tire's internal construction is creating an upward force against the vehicle when rolling under load.

Answer

The correct answer identifies that the tire has excessive radial force variation, creating an upward force when the stiff spot in the tire's internal construction rolls against the pavement under the weight of the vehicle.
The correct answer accurately identifies Radial Force Variation (RFV) as a structural defect inside the tire where a portion of the sidewall or tread is stiffer than the rest. A standard unloaded spin balancer only measures weight imbalance and cannot detect this stiff spot. However, when the tire is placed under the vehicle's weight on the road, the stiff spot creates an upward thrust each time it contacts the pavement, resulting in a rhythmic vertical vibration or wheel hop.

Step-by-Step Solution

1
Analyze the symptoms provided in the scenario.
The vehicle has a high-speed vertical vibration that remains even after a standard dynamic spin balance.
Establishing the baseline rules out standard weight imbalance as the root cause.
2
Evaluate the capabilities of the diagnostic equipment used.
A standard spin balancer rotates the tire freely in the air (unloaded) and only detects weight distribution discrepancies.
Understanding equipment limitations helps identify faults the equipment cannot detect, such as structural tire defects.
3
Identify tire faults that only manifest under vehicle weight.
Radial force variation (RFV) occurs when a tire has a stiff spot in its internal ply construction, acting like a stiffer spring that pushes up against the vehicle once per revolution under load.
This precisely matches the symptom of an unloaded balanced tire that still hops on the road.
4
Evaluate and eliminate the distractors based on mechanical principles.
Identify fundamental mechanical contradictions in the wrong options (e.g., confusing shocks with springs, or disc components with drum components).
Ensures the selected answer is both mechanically sound and the only plausible choice.

Key Concept

Advanced Tire Diagnostics and Radial Force Variation
Estimated Time:1m 30s
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