Twin jaw coupling 25, 28 Twist axle beam 393, 394 Two speed axles 247 Two speed double reduction helical gear axle (Rockewell-Standard) 248, 249 Two speed epicyclic gear train axle (Eaton) 249, 250 Tyre profile and aspect ratio 288 Tyres considerations 270 Bald tyre 271 Braking characteristics on wet roads 273 Braking force 271 Coefficient of adhesive friction 270 Coefficient of friction 27 deformation slip 276 Grip 270 Grip control 27 Hysteresis 274 Scrub 369 Scruff 369 Slippage 271 Tyre construction Beads 281 Bracing belt 281 Carcass 281 Side walls 281 Tread 281 Tyre marking identification 299 Aspect ratio 300 Car tyres 300 European tyre and rim technical organisation 300 Light, medium and heavy truck tyres 301 Load index 300 Manufacture's tread pattern 300, 301 Nominal wheel rim diameter 300 Radical construction 300 Speed symbols 300 Tyre materials 277 Anti-oxidant and ozonates 279 Carbon black 279 Electrostatic bonds 277 Initiators and accelerators 278 Oil extension 279 Material fatigue 279 Material hysteresis 279 Material plasticity 279 Material resilience 279 Mechanical properties 279 Natural rubber 277 Structure and properties of rubber 277 Synthetic rubber 277 Vulcanization 278 Tyre properties Camber scrub 294 Camber steer 294 Camber thrust 293 Centre of pressure 291 Contact patch 289 Cornering force 289 Cornering stiffness (cornering power) 290 Lateral weight transfer 294 Pneumatic trail 291 Self-aligning torque 291 Slip angle 290 Static load and standard wheel height 288 Static steering torque 293 Tyre tread Bite 282 Blocks 283 Considerations 281 Drainage grooves 282 Patterns 284 Ribs 282 Slits or sipes 283 Tyre grip Road surface texture-macro texture and micro texture 27 Locked wheel 271 Peak coefficient of friction 270 Road surface wetness 272 Rolling resistance 274 Skid 276 Sliding coefficient of friction 270 Vehicle speed 272 Tractive and braking effort 275 Tractive force 271 Tractive and braking properties of tyres 271 Tread pattern 271 Tyre reaction due to concurrent longitudinal and lateral forces 276 Tyre wear 272 Tyre grip verses slip ratio 264 `U' channel section axle 394 Unbalanced wheel and axle 301 Uncompensated twin axle suspension 422 Uncoupled mounting geometry 14 Under body dams 606, 608 Under body rear end upward taper 602, 606 Under body roughness 603, 608 Under floor to ground clearance 598 Under floor venturi 598 Under gearing and overgearing 85, 86 Underslung springs 379 Understeer and oversteer characteristics 254 Unidirectional clutch 90 Unloaded valve (pneumatic suspension) 448, 449 Unlocked tyre grip 271 Upshift clutch overlap control characteristics 163, 165 Unsprung weight 385 Vacuum throttle valve 128±133 Valance front and rear 4±6 Valve plunger; flow control 333, 334 Van Doorn transmissie 150 Vane; impellor and turbine 98 652 Vane vacuum type pump 499 Variable load sensing valve 538 Variable rate leaf suspension springs 417±419 Vertical pillar strut suspension 378 Virtual instantaneous centre 377 Voltage signal 492 Vee mounting 14, 23 Vee-rubber block mounting 13 Vee slot wedge action 202 Vehicle body aerodynamics Aerodynamics 584 Aerodynamic drag 584, 590 Aerofoil 596, 601 After flow wake 593 Adjustable deflector 623, 626, 627 Aerodynamic lift 598, 606 Aerofoil lift drag 599 Aerofoil profile 599 After body drag 611 Air density 592 Air resistance 592 Air resistance opposing motion 562, 593 Air streamlines 586, 587 Air swirl 595, 596 Angle of attack 599, 602 Angle pf inclination 599 `A' post 597 Attached transverse vortices 597 Commercial vehicle aerodynamics 617 Backsloping front body 618, 618 Base area 594 Base drag 594, 595 Bobtailed 594, 595 Boot (truck) 589 Boot height air drag 615±617 Bonnet (hood) 589, 590 Bonnet slope 601, 604 Boundary layer 584, 585 Cabriolet car 616, 617 Cab to trailer body gap 623, 624, 628 Cab to trailer body gap seals 629, 630 Cab to trailer body roof height step 619, 620, 622 Cab extended side panels 629, 630 Centre line gap seal 630 Coeffiient of proportionality 593 Converging section air flow 585 Corner vanes 628 Critical slope angle 613, 614 Cross wind 624, 625, 629 Deflector plate angle 624, 626 Diverging section air flow 586 Drag coefficient 593 Drag due to trailer load position 634 Drag reducing devices 629±632 Eddies (vortices) 588, 589 Extended quadrant moulding 631, 632 Effective inclination angle 615, 616 Fastback drag 612, 614 Flow reattachment 590, 594 Fineness ratio 591, 592 Flow separation 589 Folded roof air drag 616, 617 Forebody coach streamlining 618, 619 Forebody pressure distribution 619, 621 Form (pressure) drag 590, 591 Hatchback drag 612, 615 High and low cab 626, 627 Interlayer air friction 587 Lamina boundary layer 587 Lift coefficient 598 Negative lift 598 Negative lift aerofoil wings 613 Negative pressure 594 Negative vortex 594 Negative wake area 613 Newton's second law 592 Nose profile 599 Notchback drag 615, 616 Off-set twin flexible gap seals 630 Pressure coefficient 587 Pressure drag apparatus 592 Pressure (form) drag 590, 591 Pressure distribution 588 Positive lift 598 Roadster air drag 616, 617 Rolled edge extended quadrant corner (Windcheater) 632 Rolling resistance 584 Rear end tail extension 602 Rear side panel taper 602, 605 Relative flow air velocity 624 Roof cambering 602, 605 Roof deflectors 621, 622, 626 Rounding leading cab body edges 617, 618 Separation bubble 590, 597 Sharp and rounded upper windscreen leading edge cab aerodynamics 619, 620 Side panel cambering 602, 605 Sleeper compartment 606 Skin friction (surface friction drag) 585 Skirting 632 Spoilers -aerofoil and lip type 610, 612 Sports car air drag 616, 617 Squareback drag 611, 614 Stagnant high pressure region 619, 621 sublayers 587 Surface finish 585 Surface roughness 585 Tear drop shape 594 Tractor and trailer skirting 632 Tractor skirt 632, 633 Trailer body flow pressure distribution 621, 622 Trailer forebody edging fairings 631 Trailer skirt 632, 633 Trailing vortex 596 Trailing vortex cone 615 Trailing vortex drag 595, 596, 597 653 Vehicle body aerodynamics (continued) Transition point for lamina/turbulent boundary layer 589 Transverse vortices 590, 597 Turbulent air flow 587, 587 Turbulent boundary layer 587±589 Underbody dams 606, 608 Underbody rear end upward taper 602, 606 Underbody roughness 603, 608 Underfloor ventui effect 598 Underfloor to ground clearance 598 Venturi 585, 586 Viscous air 593 Viscous air flow 584 Viscous drag 585 Viscous shear 595 Vortices 595, 596 Vortex swirl 594 Vortex wake 593, 564 Wake 595, 613 Wheel aerodynamic lift and drag 610 Wheel air flow drag 606, 607, 609 Wheel arch air flow pattern 610 Windscreen rake (tilt) 589, 601, 604 Wind-tunnel tests 587 Yaw angle 624±626 Vehicle lift 598 Vehicle retarders 547 see retarders Vehicle steady state directional stability Ackermann instantaneous centre 299 Directional stability on a curved track 298 Directional stability along a straight track 296 Oversteer 296, 298 Under steer 298, 299 Vehicle speed sensor 441, 447 Venturi 585, 586 Vortex flow path motion 103, 104 Vortex swirl 594 Vortex wake 593, 594 Vortices (eddies) 588, 595, 596 Vibration 12, 13, 16 Viscous air 593 Viscous air flow 584 Viscous coupling differential Comparison of limited slip and viscous coupling differential 241 Speed differential action 242 Viscous coupling differential 241 Viscous coupling action 242 Viscous drag 585 Viscous shear 595 Wake 595, 613 Water pump double row bearing 208 Watt-linkage 389 Wedge or vee-shaped belt and pulley wheel 150 Weiss costant velocity joint 220 Weissuch rear suspension 400 Wheatstone bridge strain gauge 440, 441 Wheel aerodynamic drag coefficient 610 Wheel aerodynamic lift coefficient 610 Wheel air flow drag 606, 607, 609 Wheel air flow pattern 606 Wheel alignment equipment calibration 339 Wheel arch air flow pattern 610 Wheel arches 6 Wheel balancing 301 Balancing machine which dynamically balance in two planes 307 Balancing machine which balances statically and dynamically in two separate planes 305 Critical period of oscillation 304 Cyclic movement of a heavy spot on a wheel relative to the ground 302 Dynamic balance 304 Lateral run-out 309 Methods of balancing wheels 304 Radial run-out 309 Static balance 302 Twitch 304 Wobble 304 Wheel and tyre run-out 309 Wheel bearing arrangements 404 Windage effect of ball or roller cage 193 Window 2 Wind resistance 61 Windscreen rake 601, 604 Windscreen 2 Windscreen rail 2 Windscreen tilt (rake) 589 Wind-tunnel test 587 Wiping action of tyre tread 283 Winter car tyre 284, 285 Worm and wormwheel inter-axle with third differential 253 Woven asbestos 41 Yaw 14, 16 Yaw rotation 14, 16 Yaw angle 624, 625, 626 Yoke 213, 215, 225 Zig-zag tyre tread pattern 282, 284 ZF AS Tronic 187 ZF Man Tip Matic 187 ZF Servotronic power assisted steering 354 654 . clutch overlap control characteristics 1 63, 165 Unsprung weight 38 5 Vacuum throttle valve 128± 133 Valance front and rear 4±6 Valve plunger; flow control 33 3, 33 4 Van Doorn transmissie 150 Vane; impellor. 594 Tractor and trailer skirting 632 Tractor skirt 632 , 633 Trailer body flow pressure distribution 621, 622 Trailer forebody edging fairings 631 Trailer skirt 632 , 633 Trailing vortex 596 Trailing. 299 Aspect ratio 30 0 Car tyres 30 0 European tyre and rim technical organisation 30 0 Light, medium and heavy truck tyres 30 1 Load index 30 0 Manufacture's tread pattern 30 0, 30 1 Nominal wheel