Hand-considered hypotheses, 4401–4500
Automotive vehicle systems, written one at a time. Tyres and the contact patch, brakes as a thermal and hydraulic circuit, suspension and steering as load paths, the powertrain as a chain of losses and lags, aerodynamics as a balance of momentum, and noise as the sum of paths. Each entry carries the logical form chosen for it, printed above the claim, so structural repetition would be visible rather than taken on trust; no two entries share an opening. None has been tested; no citation is invoked, and every number offered as an estimate is marked as one.
Tyres and the contact patch
Misattribution
H4401. Footprint pressure recorded on a pressure-sensitive plate is read as the pressure the tyre would put on a road, yet the plate's own bending stiffness keeps the carcass from sinking into its cells, so the edges come out flattened. The plate alters the boundary condition it is meant to observe, and the error grows as its stiffness approaches the tyre's. Two plates of different stiffness, one steel and one compliant, should give edge-to-centre ratios that differ by fifteen per cent or more at the same inflation and load (estimate).
Hidden term
H4402. Vertical stiffness of a tyre is quoted as a property of the tyre alone, but every measurement made through a wheel carries the rim's radial compliance in series with it. On a light forged rim that term can reach a fifth of the total at low inflation (estimate), so the same tyre tests stiffer on a heavy steel wheel. Measuring one tyre on three rims whose radial stiffness is known separately yields the series sum, and the intercept at infinite rim stiffness would recover the tyre.
Threshold
H4403. Full aquaplaning needs a water film deeper than the tread can drain, and below roughly two millimetres the film is thinner than the texture's escape path, so no speed a passenger car reaches will lift the tread clear (estimate). The controlling quantity is displaced volume per unit contact time, not hydrodynamic pressure alone. A flooded straight with depth stepped in one-millimetre increments, steering torque logged at each speed, would place the threshold where the tread's void volume predicts it.
Identity claim
H4404. Radial force variation measured on a uniformity machine and the rim's own runout are treated as separate quantities, yet once the tyre is mounted they are one: the bead conforms to the rim and a runout of two-tenths of a millimetre appears as a first-harmonic force at the spindle. The tyre's stiffness supplies the conversion factor, which means the same tyre measures differently on different rims. Mounting one tyre on three rims of measured runout and regressing the first harmonic against runout should place the points on a line through the origin if the identity holds.
Inversion
H4405. Widening a tyre at fixed load and pressure is supposed to lower rolling resistance by shortening the sidewall's deflection, but the belt's bending loss grows with width faster than the contact pressure falls, so resistance can rise past a width where the two terms cross. The crossing depends on the belt's construction angle and on how the contact pressure is distributed. Coast-down resistance for three widths of one construction, all at the same load and pressure, would show whether the curve has a minimum and where.
Scale argument
H4406. The speed at which a standing wave locks onto a rolling tyre should vary as the square root of inflation pressure and inversely as the square root of tyre radius, since both enter the wave speed along the deflected carcass. That makes the pressure sensitivity mild, about five per cent of critical speed for a ten per cent pressure change (estimate), which is why pressure checks alone seldom explain a failure. A speed ramp on a drum, deflection measured at the crown and repeated at three pressures and two tyre sizes, would test both exponents at once.
Crossover
H4407. Tread pattern noise is made by two mechanisms, block impact at the leading edge and air pumped out of the grooves, and they cross over at a speed set by the void ratio rather than by the pattern's pitch. Below the crossing a high-void tyre is the quieter one and above it the louder, so ranking two patterns from a single coast-by is worthless. Coast-bys at four speeds with both patterns on one car, third-octave spectra recorded at each, would show the rank reversing and place the crossing.
Count
H4408. Vehicle shake attributed to a tyre is carried by at most three harmonics of its uniformity, the first, the second and the tread pitch, because contact filtering attenuates everything shorter than the contact length. A complaint assigned to uniformity at a higher order is therefore almost always a wheel or hub problem. Order-tracking the spindle force with the tyre on a hub whose runout is separately measured would mark where the tyre's contribution ends and the hardware's begins.
Path dependence
H4409. Flat spotting after a car stands is treated as a function of load and time, but the depth also depends on how the tyre cooled after the last drive, because the cords relax into the deflected shape only while warm and cooling locks that shape in. A tyre parked hot therefore takes a deeper set than one parked cold after the same standing time. Parking two identical tyres, one pre-heated and one at ambient, and measuring the first-mile radial force would isolate the thermal history.
Memory effect
H4410. The relaxation length of a tyre's lateral force is longer on the first manoeuvre after a long stand than on the second, because the carcass's cords recover their as-built path slowly, so a handling model calibrated from one step steer is fitted to a transient state. Repeated step steers with dwell times of one second and ten minutes would give two different relaxation lengths from the same tyre. A difference that vanishes after a warm-up manoeuvre marks the effect as mechanical rather than thermal.
Surface-versus-bulk claim
H4411. Tread temperature read by an infrared pyrometer is a surface value that falls within seconds of stopping, so a paddock reading taken a minute after a run is not the running temperature and cannot be compared between cars with different cool-down times. The tread's bulk temperature is set by the belt's heat capacity and lags the surface by minutes (estimate). Recording surface and embedded-probe temperatures through a stop on the same tyre would let the bulk value be extrapolated back to the instant of stopping.
Boundary-layer argument
H4412. Convection from a tyre's sidewall is set less by road speed than by the local flow in the wheel arch, which the rotating wheel drags around with it, so a sidewall's steady temperature changes when a deflector is fitted at unchanged speed. Above roughly sixty kilometres per hour the wheel's own pumping dominates the arch's through-flow (estimate). Sidewall thermocouples at three angles, with and without the deflector, would decide whether the temperature's angular variation collapses when the flow is blocked.
Non-monotonic window
H4413. Cornering stiffness rises with inflation pressure to a maximum and then falls, because the contact patch first lengthens and then stiffens until the tread's lateral deflection per unit slip drops. The maximum should sit near the pressure that maximises footprint area, not at the manufacturer's recommendation. A pressure sweep on a flat-belt machine at fixed load and slip angle locates the peak, and the peak's position moves with load if contact geometry is the mechanism.
Limit-point claim
H4414. The peak of a tyre's lateral force curve is read as a friction limit, but its slip angle is set by how the contact patch divides into an adhering front region and a sliding rear one, so the peak angle should move with inflation at constant load while the peak force barely does. A friction-limited peak would not shift that way. Varying inflation in three steps while recording peak slip angle and peak force separately, on the same tyre, separates the geometric explanation from the frictional one.
Contact-geometry claim
H4415. Ink footprints are used to judge contact patch size, yet ink transfers only above a threshold pressure, so the printed area is smaller than the load-bearing area and the shortfall changes with load. The missing region is the low-pressure shoulder, which carries a growing share as the tyre deflects. Comparing an ink print with a pressure film at three loads on the same tyre and inflation would yield the threshold pressure and test whether it stays constant.
Asymmetry decomposition
H4416. A car that pulls only when loaded has conicity rather than misalignment, because conicity's lateral force scales with vertical load while ply steer's is nearly load-independent. Swapping the tyre left to right separates them further, since conicity reverses its pull and ply steer does not. A load sweep before and after the swap would yield both coefficients in an afternoon, and the sign of the load slope names the mechanism.
Nonlinearity claim
H4417. The effective rolling radius grows with speed as centrifugal force stretches the belt, but the growth saturates once the belt's hoop stiffness carries the load, so speedometer error should curve rather than rise linearly. A constant correction factor calibrated at one speed therefore misreports at another. Comparing satellite speed with wheel speed at five steady speeds on one tyre at one pressure gives the curve and locates the knee.
Braking as a thermal and hydraulic circuit
Thermal mismatch
H4418. Pedal pulsation that appears only after a hard stop is called a warped disc, but a disc heated unevenly through its thickness cones rather than thickens, and the coning relaxes as it cools while true thickness variation does not. The two therefore have different recovery times, which is the whole diagnostic. Pulsation and thickness variation measured cold, immediately after a fade and again an hour later separate the coning term, which vanishes, from the geometric term, which stays.
Wear-step attribution
H4419. Inner pads usually wear faster than outer ones, and the step is put down to caliper flex; on a sliding caliper the inner pad also runs hotter because it sits on the piston's heat path, and wear rises with temperature. The explanations differ in what a swap does. Exchanging the pads' positions and repeating the duty cycle should reverse the step if heat is the cause and leave it in place if flex is.
Dead band
H4420. Pedal travel's first few millimetres are lost before pressure builds, and that loss is normally blamed on pad knock-back, though most of it is the master cylinder's seal lip rolling over and the booster valve's clearance. The dead band is nearly independent of how far the pads have been pushed back, which is what distinguishes the two. Bleeding the system, then measuring travel against pressure with the pads clamped solid and again retracted, would put a number on each contribution.
Compliance audit
H4421. Long pedal travel when the brakes are hot is attributed to fluid compressibility, but the fluid's bulk modulus falls by only about a fifth at a hundred and fifty degrees (estimate), while a rubber hose's expansion can account for several times that volume. The hose's contribution scales with pressure squared and the fluid's linearly, so the two are separable. A pressure-volume measurement with a rigid line substituted for the hose, at three temperatures, would apportion the travel.
Sign reversal
H4422. Drag torque judged by spinning a wheel by hand is a poor diagnostic because the drag from a correctly retracting caliper and from a sticking one change in opposite directions with temperature: seal roll-back improves as the seal warms, while a corroded piston's drag worsens. One cold measurement therefore cannot separate them. Drag torque logged through a full heat cycle, cold to hot and back, reveals which way the curve runs.
Degeneracy
H4423. Disc thickness variation and disc runout produce the same once-per-revolution pedal pulse, so a pulsation measurement alone cannot say which is present, and the repair differs. The degeneracy breaks on the pulse's shape, because thickness variation gives a pulse symmetric in apply and release while runout gives one biased toward the high spot. Recording pedal force and hydraulic pressure at high resolution over one revolution on a disc of known geometry would expose the asymmetry.
Lag
H4424. Regenerative and friction braking are blended so that the sum matches demand, but motor torque falls with a lag of tens of milliseconds while hydraulic pressure rises almost at once, so the blend is never exact during a transient and the car decelerates in a step. The step's size is set by the lag, not by the blend map. A step demand on a chassis dynamometer, hydraulic pressure and motor torque logged together, would expose the mismatch and tell whether the map has been tuned around it.
Order-of-limits
H4425. Fade is measured either by a series of constant-pressure stops or by constant-deceleration ones, and the two give different curves because disc temperature and pad condition are coupled, so the order in which the limits are taken changes the answer. A pad taken once to its upper temperature behaves differently on the next stop at the same pressure. Running the same total energy through both protocols on identical hardware decides whether the difference is protocol or hardware.
Worst case
H4426. Thermal design is checked against the worst single stop, but the binding case for fluid is often a long descent at low power, where the caliper soaks and the fluid reaches a higher steady temperature than in any single stop. That soak is limited by convection from the wheel rather than by the disc's mass, which is why identical brakes behave differently behind different wheels. A descent profile repeated with two wheel designs, caliper temperatures logged throughout, identifies which case sets the limit.
Conservation audit
H4427. Dust collected from a wheel is used to estimate pad wear, but much of the wear leaves as airborne particles and a further part sticks to the wheel's inner barrel rather than its face, so the collected mass is not the worn mass. The ratio between them changes with pad temperature. Weighing the pads, the wheel and a filter downstream of the brake in one enclosure over a fixed duty cycle would close the balance and give the airborne fraction.
Sequence inversion
H4428. Bleeding is normally run until clean fluid appears at the caliper, yet on a system whose master cylinder sits above the caliper the air collects at the highest point, which is the master's secondary seal and not the caliper. The standard sequence can therefore leave the air in place while the fluid at the bleed screw looks perfect. Pressure-bleeding from the caliper upward, or drawing vacuum at the master, settles which direction actually removes the soft pedal.
Selection effect
H4429. Reported pad life is biased upward because pads replaced early for noise are not counted as wear-out, and the bias grows with the fleet's sensitivity to noise. The reported distribution is truncated at the noise threshold rather than at the wear limit. A fleet trial that records every removal with its reason, noise included, separates the two populations and gives a wear life shorter than the published one.
Spatial confound
H4430. Caliper temperature measured at the bleed screw is quoted as the brake's temperature, but the screw sits in a stagnant pocket and reads lower than the piston crown by a margin that grows with speed. The offset is a function of local flow, not of the brake's duty. Three thermocouples, at the bleed screw, the piston crown and the disc's inner face, taken through one fade cycle, would yield the offsets and name the location that tracks the fluid.
Extrapolation error
H4431. A dynamometer curve taken from a fixed initial temperature is extrapolated to road use, but the first stop of a day starts from a colder disc than any schedule reproduces, and the pad's transfer layer is in a different state. The extrapolation is therefore least reliable at the condition that matters most. A cold-soak stop series, with the assembly held at ambient overnight and the first stop measured before any warm-up, measures how far the dynamometer curve misses.
Calibration error
H4432. Wheel-speed sensors are calibrated against a nominal rolling radius and every anti-lock threshold is expressed in that unit, so a tyre worn by five millimetres changes the speed the controller believes it sees by about one and a half per cent (estimate). That is enough to move a threshold tuned at the edge. Fitting tyres in three wear states and logging the controller's computed speed against satellite speed exposes the offset and tests whether the thresholds move with it.
Load-path argument
H4433. Reaction torque passes through the caliper's two sliding pins, and the pins' clearance lets the caliper rotate slightly before the load path stiffens, which softens the initial torque rise and sets the pad's taper wear. The clearance is a build tolerance that changes with wear. Torque against time at the first application after a direction reversal, on a caliper with new pins and again with worn ones, would give the dead travel and link it to the taper.
Rate dependence
H4434. A caliper's torque response to pressure is quoted from a slow apply, but on a fast one the same caliper gives less torque for the same pressure because the pads' compressibility and the seal's deflection need time to settle. The response is rate-dependent even when nothing in the pad has changed. A pressure ramp at three rates, with torque logged, would give the compliance term directly and test whether it saturates.
Suspension, steering and ride
Stability condition
H4435. Hop is often tuned out by stiffening the damper, but the frequency is set by the unsprung mass on the tyre's vertical stiffness, and the damper changes only how fast the oscillation decays. Stiffening it past the point where damping force and tyre force act in phase can make the hop worse. A modal test with the damper removed, then refitted at three settings, would locate the frequency and identify which parameter controls the decay.
Two-regime claim
H4436. A damper's force-velocity curve has two regimes separated by the point where the shim stack opens, and the quoted low-speed and high-speed coefficients describe the two sides rather than one continuous law. Tests at amplitudes that straddle the knee therefore yield coefficients that cannot be compared. A sinusoidal sweep at three amplitudes, force and velocity plotted on logarithmic axes, would locate the knee and test whether it moves with temperature.
Series-term omission
H4437. Ride frequency computed from static deflection treats the tyre as rigid, but the tyre's vertical stiffness sits in series with the spring and lowers the body's bounce frequency by five to eight per cent on a typical car (estimate). The error is small enough to hide in build variation and large enough to matter when a suspension is tuned to a target. Measuring body bounce on a four-post rig against the static-deflection prediction would expose the series term.
Fixture artefact
H4438. Damping measured on a damper dynamometer includes the rod seal's friction, which appears as a force offset roughly constant with velocity and therefore inflates the low-speed coefficient. The error is largest at the small amplitudes that matter for ride. Running the damper at zero velocity with the gas charge fitted, then with it released, would separate seal friction from gas force and leave the hydraulic coefficient.
Amplitude dependence
H4439. Bench tests quote a rubber bushing's rate at small amplitude, but the installed bushing sees larger deflections and stiffens as its voids close, so the bench value is the softest the part will ever be. The installed rate can be half again as high at road amplitudes (estimate). A wheel-rate rig sweeping amplitude in situ, with the bushing loaded as installed, would give the rate the chassis actually sees.
Temperature-confounded claim
H4440. Bump-stop engagement is set by the gap between stop and seat, a cold dimension, but the microcellular stop's stiffness rises steeply in the cold, so the same gap produces a much harder engagement in winter. Drivers report the change as a damper fault. Static load-deflection on the stop at three temperatures, plus body acceleration over the same bump, would tie the seasonal complaint to the material's modulus.
Kinematic ambiguity
H4441. The roll centre is drawn from the suspension links' instant centres, yet the height that matters for the lateral force's line of action is the force-based one, and the two diverge as the car rolls, by roughly twenty millimetres at three degrees (estimate). The divergence makes measured roll gradient disagree with the kinematic prediction. Measuring the lateral force's line of action with wheel-load transducers at a series of roll angles would give the force-based height directly.
Stiffness-matching claim
H4442. An anti-roll bar's rate is quoted at the arm, but the drop link's ball joints and the bar's bushings sit in series with it, and on a production car those compliances can cancel a third of the bar's contribution at small roll (estimate). The bar then works mainly in the large-roll regime it was not designed for. Replacing the link with a rigid strut and repeating the wheel-rate measurement would give the compliance's share.
Progressive-rate claim
H4443. A coil spring's rate is quoted from the linear middle of its travel, yet the end coils close against each other as the spring compresses and the rate rises steeply. A car lowered onto its stops has a spring rate several times the published value (estimate). Compressing one spring to solid with load and deflection logged continuously would map the progressive region and show where the published rate stops applying.
Sensitivity bound
H4444. The steering's self-aligning torque is dominated by the pneumatic trail at low speed and by the mechanical trail at high speed, and the two trade places where their contributions are equal. That crossover bounds what a steering-feel change can achieve at low speed without altering the tyre's contact. Steering torque against speed at constant lateral acceleration, on one car, would place the crossover and show which term dominates where.
Loading-state bias
H4445. Alignment is set at curb weight, but the rear subframe's bushings deflect under driver and fuel load, so the running thrust angle differs from the one on the rack. The bias is systematic and explains why some cars pull only when fully loaded. Toe measured optically at three load states, with pressures and ride heights held, would give the compliance steer and its direction.
Impedance argument
H4446. A hydraulic engine mount's damping peak is a resonance of fluid in its inertia track, so the peak's frequency is set by the track's length and area rather than by the rubber. Installing the mount at an angle changes the fluid column's effective length and moves the peak. A bench sweep at two orientations, fluid temperature fixed, would yield the shift and confirm that the peak is fluid-borne.
Time-constant claim
H4447. An air suspension's height sensor reads through a linkage whose thermal expansion moves the target by several millimetres over a forty-degree swing (estimate), so the system levels the car to a height that changes with the weather. The controller's slow time constant hides the error as drift. Sensor voltage and independently measured body height, recorded through a cold-to-hot cycle, would separate the linkage's error from the set point.
Non-reciprocity
H4448. Road harshness is usually reduced by softening the damper, but on a suspension with a fore-aft compliant lower control arm bushing the impact's high-frequency content reaches the body through the bushing rather than the damper, and softening the damper changes nothing. The two paths transmit different frequency ranges. Bushings of the same radial rate but different fore-aft rate, with the damper unchanged, would decide whether the harshness follows the bushing.
Contact-loss claim
H4449. Contact force dropping to zero over a broken surface is read as a damper fault, yet once it is zero the wheel has left the road and no damper setting can restore grip; only reducing the unsprung mass's kinetic energy helps. The signature is a force trace that reaches zero, not one that oscillates. A wheel-force transducer on a broken section at two rebound settings would tell whether the force actually reaches zero, and where.
Residual-force claim
H4450. Corner weights are set with the car empty, and any adjustment at one corner changes the diagonal sum, so a car can sit level and still carry a wedge that pulls under braking. The residual force at each corner is what the driver feels, and it is invisible in ride height. Corner weights measured at four load states, ride height recorded at each, would measure how much of the wedge the level condition hides.
Phase-lag claim
H4451. Body roll in a steady corner is smaller than the roll during the entry to it, because the anti-roll bar's bushings and the dampers add a transient contribution that decays once the corner is established. A suspension tuned on steady-state skidpad data is therefore tuned to the wrong condition. Roll angle logged through a step steer alongside lateral acceleration traces the overshoot and its decay.
Powertrain and driveline
Solubility trap
H4452. Mount fluid is chosen for its viscosity, yet the damping peak also depends on gas coming out of solution when the fluid is hot, and a mount filled correctly at build can be partly aerated in service. The change is in the fluid's bulk modulus rather than its viscosity. Force-velocity sweeps on the same mount before and after a hot soak, with the fluid sampled, would test whether the peak's height falls without its frequency moving.
Harmonic attribution
H4453. At eighty kilometres per hour a boom is usually chased in the tyre's first order, but a two-piece propshaft with a universal joint at each end generates a second-order excitation whenever the joints are out of phase, and that order peaks at a different road speed. The phase is a build tolerance, so only some cars do it. Running the car with the joints in phase and then ninety degrees out, at the same speed, would move the boom's amplitude as the joint kinematics predict.
Control-loop artefact
H4454. A dual-clutch transmission's flare after a hot restart is a fill-time problem, but the adaptive routine learns fill from the previous shift, so a cold-fluid shift teaches it a value wrong for hot fluid and the error persists for several shifts. The controller is learning the temperature, not the clutch. Logging the adaptive cell's value against fluid temperature through a warm-up would tell whether it tracks temperature or cycle count.
Pulse-duration artefact
H4455. Internal resistance quoted from a ten-second pulse includes the diffusion overpotential, which keeps growing during the pulse, so the number falls as the pulse shortens and no single value describes the cell. The ohmic and diffusive parts are separable by their time constants. A pulse-length sweep from a tenth of a second to a hundred seconds on one cell at one temperature would yield both parts and place the reported value.
Efficiency misattribution
H4456. Transmission efficiency measured at high load is used to predict cruise consumption, but at light load the oil's churning and the seals' drag dominate the mesh loss, and those terms do not scale with torque. A gearbox efficient at full throttle can be poor at a hundred newton-metres. A torque sweep at fixed speed with oil temperature held constant would separate the load-proportional loss from the offset.
Thermal-lag claim
H4457. Turbo boost limit is set by the wastegate actuator, whose spring preload changes as the can heats, so the boost curve drifts over the first minutes of a pull. The drift is a spring-rate change, not a control error. Boost logged against time with the can's temperature measured, on a rig where the can is heated independently of the turbine, yields the preload's thermal coefficient.
Flow-pulsation claim
H4458. EGR flow inferred from a delta-pressure orifice is biased low by intake pulsation, because the square-root relation is concave and the mean of the square root is not the square root of the mean. The bias grows with pulsation amplitude, which is why apparent flow falls at low speed. Fitting a settling chamber ahead of the orifice and comparing inferred flow with a direct measurement would quantify the bias against engine speed.
Vapour-lock claim
H4459. Injector dead time is calibrated on a bench at room temperature, but fuel vapour pressure at the tip rises with temperature and a bubble forming during the low-pressure phase delays the needle's opening. The error appears as a lean excursion at hot idle rather than as a constant offset. Dead time measured at three fuel temperatures, with the tip instrumented, would locate the step and its onset.
Depletion claim
H4460. An oil-pressure warning at hot idle is read as bearing wear, but the pump's relief valve spring relaxes over time, and a healthy engine with a tired spring crosses the same threshold. The two differ in how pressure behaves at speed. Pressure logged against speed and temperature before and after a known spring change would separate the term that dominates at idle from the one that dominates at load.
Coupling claim
H4461. Accessory belt squeal is treated as a tension problem, but the noise is a mode of the tensioner's arm against the belt's span, and its frequency is set by the arm's inertia and the belt's stiffness rather than by tension alone. A tensioner with more damping moves the noise without changing tension. Belt vibration measured with a laser at three tensioner dampings, tension held constant, would test whether the noise follows the mode.
Sideband claim
H4462. Gear whine is assigned to the mesh's transmission error, but the dominant order's sidebands come from the shaft's runout, which modulates the mesh and spaces sidebands at the shaft's rotation rate. Mesh error alone would not produce that spacing. An order spectrum from a gearbox with a deliberately eccentric shaft would show the spacing and give the runout's size.
Order-separation claim
H4463. Whine from an electric axle is assigned to the motor's cogging, but cogging appears at the slot-and-pole order while the inverter's current ripple appears at the switching frequency and its sidebands, and the two scale differently with speed. Cogging's frequency is proportional to speed and the ripple's is not. An order spectrum at two speeds with the switching frequency held constant would separate them without changing hardware.
Actuator-hysteresis claim
H4464. Opening temperature is quoted as one value for a thermostat, but wax thermostats open and close on different curves, so warm-up and subsequent regulation run at two temperatures and the coolant temperature oscillates with a period set by the hysteresis width. That oscillation is often misread as a faulty sensor. Coolant temperature at the radiator's inlet and outlet, logged through a warm-up and a load step, would map the loop and give the width.
Start-transient claim
H4465. Hybrid engine starts are judged by the vibration at the seat, but the dominant transient comes from the mount's unloading as engine torque reverses, not from combustion roughness, and an active mount tuned to the firing frequency does nothing for it. The transient is broadband and its amplitude scales with the torque step. A start with fuel cut, so the torque step exists without combustion, would separate the mount's response from the engine's.
Cooling-drag claim
H4466. Fan power is measured on a bench at fixed speed, but on the car the fan's operating point is set by ram pressure at the radiator face, and at speed the ram flow can drive the fan backward so that it draws power instead of moving air. Fan drag is therefore a function of road speed, not a constant. Fan shaft torque and radiator-face pressure logged across a speed sweep would place the point at which the fan stalls and reverses.
Resonance claim
H4467. Exhaust drone at a particular engine speed is a quarter-wave resonance of the tailpipe, so its frequency is set by pipe length and the gas's sound speed and moves with exhaust temperature even at constant engine speed. A drone that moves during a pull is therefore acoustic, while one fixed in speed is mechanical. Changing the tailpipe length in two steps and tracking the drone through a pull would expose the temperature shift and confirm the quarter-wave mechanism.
Torque-split claim
H4468. Torque split is quoted from a differential's geometry, but the split at the wheels is set by the tyres' rolling radii, and a pressure difference of two-tenths of a bar between sides is enough to bias it measurably (estimate). The bias then feeds back into differential temperature. Wheel torques measured on a split-roller rig at matched and mismatched pressures would give the bias and its sign.
Aerodynamics
Ventilation claim
H4469. Cooling drag is estimated from the radiator's ram flow, but much of the air entering the grille leaves through the wheel arches and the underbody, so drag is set by total inlet flow rather than cooling flow. Sealing the arch exits changes cooling drag without changing radiator flow. Radiator flow and total inlet flow measured together, with exits sealed one at a time, would apportion the two.
Helmholtz claim
H4470. Sunroof buffeting is treated as vortex shedding, but the peak's frequency follows the cabin's Helmholtz resonance, set by cabin volume and the opening's neck, so moving the seat backs changes the frequency without changing the roof. A shedding peak would not shift with volume. Seat-back angle and opening size swept independently, with cabin pressure spectra recorded, would identify which variable sets the peak.
Ground-boundary claim
H4471. Downforce normally rises as ride height falls, but below a clearance where the underbody's boundary layer fills the diffuser's throat the trend reverses, and the reversal is sharper on a rough underbody because the layer is thicker. The minimum is therefore a property of surface finish as much as of shape. A ride-height sweep with two underbody finishes on a moving-ground tunnel would locate the reversal and its dependence on roughness.
Reynolds claim
H4472. Drag coefficients from a quarter-scale model are higher than the full-scale value, and the difference is charged to Reynolds number, but much of it is the model's boundary-layer transition position, which trips elsewhere on a smooth model. Transition strips placed at the full-scale location should remove most of the discrepancy without changing Reynolds number. Two scales, with and without strips, would separate the two causes.
Yaw-asymmetry claim
H4473. A car's drag usually rises more in one yaw direction than the other, and the asymmetry is attributed to body shape, but it can come from separation hysteresis at the A-pillar, which depends on the direction the yaw was approached from. Sweeping yaw upward and downward through the same range would show a loop if hysteresis is present. Surface pressure at the pillar, recorded on both sweeps, would place the separation's jump.
Wake-recovery claim
H4474. In a two-car platoon the follower's drag falls by more than the leader's rises, according to the usual reading, but a separate balance on each car shows the leader's drag rising by nearly the follower's gain, so the pair's total saving is small. The gap that is best for the follower is not best for the pair. Two instrumented models at a series of gaps, each on its own balance, would produce both curves and the pair optimum.
Induced-drag claim
H4475. A rear wing's downforce is bought with induced drag, and the induced drag depends on the wing's height above the deck because the deck acts as a reflecting surface, so the effective aspect ratio changes with mounting height. A wing tuned at one height is not equivalent at another, even at the same angle. Downforce and drag measured at three heights with angle fixed would expose the induced term's dependence.
Blockage claim
H4476. Wind-tunnel blockage is corrected by a formula that assumes the wake's displacement is proportional to the model's drag, but a bluff body's near wake displaces more than the formula allows, so the correction under-predicts blockage at high drag. The error is largest for the configurations that most need correcting. One model run in two tunnel sizes, uncorrected coefficients compared, would give the empirical correction and test the formula's slope.
Leakage claim
H4477. An open window's buffeting is the same Helmholtz resonance as a sunroof's, so its frequency falls as cabin volume grows and a larger cabin booms at a lower speed. The speed that excites the resonance is set by the shear layer's shedding, not by the resonance itself. Two cars of different cabin volume with the same window opening should differ in peak frequency at the same road speed.
Separation-hysteresis claim
H4478. A diffuser's angle has a critical value at which flow separates, but the critical angle measured on a rising ramp is higher than on a falling one, because the separation's position is history-dependent. A diffuser set just below the rising critical angle is therefore not safely attached in a transient. Angle swept up and down through the critical region, with pressure taps along the ramp, would trace the loop and its width.
Support-interference claim
H4479. A model's drag measured on a strut support includes the strut's interference, which alters the wake's pressure and the base drag, and the interference is not constant across configurations. The strut's own wake sits inside the model's near wake, so the correction it implies depends on the model's base pressure rather than on blockage alone. The same model on a strut and on a sting, at matched blockage, would give the difference and test whether it depends on base pressure.
Momentum-balance claim
H4480. The drag of a cooling inlet is computed from the momentum deficit of the flow entering it, but the air leaving the underbody has already exchanged momentum with the wheel wakes, so the inlet's deficit is not the drag it adds. The two differ by the exit's total pressure. Inlet mass flow, inlet total pressure and overall drag measured at three inlet sizes would close the balance.
Skin-friction claim
H4481. Skin friction on a fastback's rear glass is neglected because the flow is assumed separated, but the flow can reattach ahead of the spoiler and the friction there becomes a measurable share of drag (estimate). That share grows with speed while pressure drag saturates. Oil-film interferometry on the rear glass at three speeds would locate the reattachment line and give friction's contribution.
Similarity claim
H4482. Yaw sweeps are run at a fixed yaw rate, but the parameter that matters is the ratio of yaw rate to wind speed, so a test at one speed does not represent another. The side force's lag with yaw is set by that ratio. Yaw sweeps at two speeds and matched yaw-rate-to-speed ratios, with side force logged, would collapse onto one curve if the scaling is right.
Vent-reversal claim
H4483. Exposed wheels are often fitted with arch vents, yet the vent's flow reverses at speed because the arch's pressure falls below the underbody's, so a vent that helps in the tunnel at low speed can hurt on the road. The reversal speed is where the two pressures cross. Vent mass flow and direction measured at four speeds, with the wheel's drag on a separate balance, would show the crossing.
Cross-coupling claim
H4484. Front and rear lift are treated as separable, but on a car with a large underbody the diffuser's exit pressure sets the flow under the front floor, so a rear change alters the front's lift coefficient measurably. The coupling is strongest at low ride height. Rear ride height changed in steps, with front and rear lift measured separately, would give the cross term and test whether it is symmetric.
Noise, vibration and harshness
Path-sum error
H4485. Structure-borne road noise is apportioned by measuring each mount's blocked force and multiplying by a transfer function taken with the mount removed, but removing the mount changes the path's stiffness, so the blocked force is not the force the mount delivers in service. The apportionment can be wrong by several decibels where the mount is stiff (estimate). An in-situ method that leaves the mount in place and applies a known force would recover the operating force without breaking the path.
Modal confusion
H4486. A mode found at a hundred and twenty hertz on a body-in-white is carried into the full vehicle's model, but in the complete car the same mode sits lower because the mounts and interior mass load it, so treating the two as one mode misplaces the resonance. The shift is mass loading, not a stiffness change. Modal testing the body alone and the complete car with the same excitation would give the shift and identify which panels carry the added mass.
Mount contamination
H4487. Component modal tests use soft mounts to approximate free-free conditions, but the mounts' rigid-body modes sit inside the range of interest and contaminate the first flexible mode, which appears as a split peak. A mount that is soft in the test's axis can still be stiff in the mode's direction, so the contamination is directional. Testing the same part on two suspension systems of different stiffness would show whether the peak belongs to the part or to the fixture.
Transfer-function claim
H4488. Transfer functions measured with a hammer are used to predict road noise, but the hammer's force is weakest at low frequency while the road's input is strongest there, so signal-to-noise is worst exactly where the prediction matters. The measured function is therefore suspect at the low end even when it looks smooth. Hammer and shaker excitation on the same path, at equal force, would expose the discrepancy and its frequency range.
Order-tracking claim
H4489. A gearbox's whine is judged from its order spectrum at constant speed, but the mesh order's amplitude depends on load, and a coast-down at zero load does not represent the loaded condition. The noise heard on the road is at part load, not at coast. Recording order spectra at three loads and matched speed would test whether the order's amplitude is load-sensitive and which condition the road noise follows.
Coincidence claim
H4490. Mass per area is a poor way to choose a panel treatment, because coincidence sets the frequency above which the panel radiates efficiently, leaving a mass-only treatment ineffective below it and over-designed above. The crossing is set by thickness and stiffness. Transmission loss measured on one panel above and below its coincidence frequency, at equal mass, would show the transition.
Damping-misattribution
H4491. Body boom at forty hertz is damped by adding deadener to the floor, but the boom's amplitude is set by the cabin's modal damping, which is dominated by the seats and the trim's absorption rather than by the floor's mass. Deadener changes the panel's response but not the cabin's damping. Cabin decay time measured with and without the seats, at fixed excitation, would identify which element controls the mode.
Cavity-mode claim
H4492. The cavity resonance of a tyre near two hundred and thirty hertz is treated as fixed, but the contact patch shortens the effective cavity, so the resonance rises with load and the peak falls as the patch grows. The shift is small yet it moves the peak out of the band a wheel absorber was tuned to. Road-wheel force at three loads, with the cavity peak tracked, would give the shift and explain why one absorber does not fit all loads.
A-weighting claim
H4493. Improvements measured in A-weighted decibels can be insensitive to low-frequency changes, so a treatment that removes a thirty-hertz boom may show almost no dBA improvement while the car is plainly quieter. The weighting attenuates a change at that frequency by more than thirty decibels (estimate). The same measurement in unweighted third-octave bands would reveal the change the dBA number hides.
Structure-borne claim
H4494. Over a rough road a door's rattle is treated by adding felt, but the source is the latch's clearance, a kinematic gap, and the felt only changes the contact's damping. The rattle's repetition follows the road's input rather than the door's resonance. Accelerometers on the latch and on the door's skin, on the same road section, would identify which part carries the impact's high-frequency content.
Panel-cavity claim
H4495. The drumming of a roof panel is a coupled panel-cavity mode whose frequency is set by both the panel's stiffness and the cabin's volume, so stiffening the roof moves the mode less than expected because the cavity's compliance dominates. A rib and added absorption change different halves of the coupling. Panel velocity and cabin pressure measured together, before and after a rib, would give the coupling's strength and identify which side controls the frequency.
Source-path claim
H4496. Low-frequency road noise is attributed to the tyres, but on a coarse surface the suspension's linkage transmits structure-borne energy that peaks at the same frequencies, and the two sources add with a phase set by the texture. Changing only the tyres moves one source and not the other. Two tyres of different construction on the same car and surface would indicate which part of the spectrum follows the tyre.
Threshold-locking claim
H4497. Squeak from a seat frame is treated as a friction problem, but its amplitude is not proportional to excitation: it appears only above a threshold input and its repetition rate locks to a subharmonic of the drive. That locking is a signature of a nonlinear oscillator rather than of a stick-slip contact. Sine excitation at increasing amplitude, with the response waveform recorded, would expose the threshold and the locking, and a change of contact material would shift the threshold if friction is the mechanism.
Attenuation bound
H4498. No passive treatment can attenuate a cavity mode below the absorption its surfaces already provide, so a boom fifteen decibels above target cannot be fixed by mass alone; the mode's decay time sets the floor. The bound is set by the cabin's total absorption, not by the treatment's mass. Reverberation time before and after treatment, alongside the boom's level, decides whether the treatment moves the floor or only the excitation.
Insulation claim
H4499. Exterior wind noise measured at the door's surface is not what the occupant hears, because the door's seal leaks and the leak's flow noise dominates at speed; the seal's compression set, not its material, sets the leak. A seal of the same material but greater compression would change interior noise without changing the exterior measurement. Interior and exterior microphones on the same run, before and after the seal change, would isolate the leak's contribution.
Damping-split claim
H4500. Moan at very low speed is heard as a brake problem, but its frequency follows the driveline's first torsional mode and the brake is only the exciter, so changing clamping force changes the amplitude while changing halfshaft stiffness changes the frequency. That difference is the diagnostic. Moan recorded with two halfshaft stiffnesses and one brake, then two brakes and one halfshaft, would identify which parameter moves frequency and which moves level.
Status and plan
One hundred entries, numbered in sequence. Each was written on its own, with the argument shape chosen before the subject, so that no two share an opening and no two share a form label; the label above each claim is there to be checked against the sentence beneath it rather than accepted as a taxonomy.
The physics stays inside the vehicle: the tyre as a deflected membrane in contact with a rough road, the brake as a thermal and hydraulic circuit, the suspension as a set of load paths, the powertrain as a chain of losses and lags, the body as a shape exchanging momentum with the air, and the cabin as a cavity that turns structure-borne energy into sound. No claim here concerns a brand, a regulation, or a person.
If one of these is worth an afternoon, it is H4403: aquaplaning is usually treated as a speed threshold, and the claim is that below a film depth of about two millimetres the tread's drainage capacity exceeds any plausible input, so the threshold is a depth before it is a speed. A flooded straight, a stepped water depth and a recorded steering torque would either place that depth or retire it.
Incoprea Research · hand-considered hypotheses 4401–4500 · 3 November 2026 · ~/Desktop/Nov3/