183:. When the center of mass is moved rearward, the understeer gradient tends to decrease. The shifting of the center of mass is proportional to acceleration and affected by the height of the center of mass. When braking, more of the vehicles weight (load) is put on the front tyres and an less on the rear tyres. Conversely, when the vehicle accelerates, the opposite happens, the weight shifts to the rear tires. Similarly, as the center of mass of the load is shifted from one side to the other, the inside or outside tyres traction changes. In extreme cases, the inside or front tyres may completely lift off the ground, eliminating or reducing the steering input that can be transferred to the ground.
274:
262:
1081:
1071:
204:
147:
increasing levels of lateral acceleration are attained. The latter is concerned with the limiting friction case in which either the front or rear wheels become saturated first. It is best to use race driver's descriptive terms "push (plow) and loose (spin)" for limit behavior so that these concepts are not confused.
314:
Understeer gradient is one of the main measures for characterizing steady-state cornering behavior. It is involved in other properties such as characteristic speed (the speed for an understeer vehicle where the steer angle needed to negotiate a turn is twice the
Ackermann angle), lateral acceleration
305:
If a rear-wheel-drive vehicle has enough power to spin the rear wheels, it can initiate oversteer at any time by sending enough engine power to the wheels that they start spinning. Once traction is broken, they are relatively free to swing laterally. Under braking load, more work is typically done by
163:
If the rear tyres become saturated before the front, the front tyres will keep the front of the vehicle on the desired path but the rear tyres will slip and follow a path with a greater radius. The back end will swing out and the vehicle will turn toward the inside of the curve. If the steering angle
146:
Great care must be taken to avoid conflating the understeer/oversteer behavior with the limit behavior of a vehicle. The physics are very different. They have different handling implications and different causes. The former is concerned with tire distortion effects due to slip and camber angles as
99:
Several tests can be used to determine understeer gradient: constant radius (repeat tests at different speeds), constant speed (repeat tests with different steering angles), or constant steer (repeat tests at different speeds). Formal descriptions of these three kinds of testing are provided by ISO.
159:
Push (plow) can be understood as a condition where, while cornering, the front tyres become saturated before the rear and slip first. Since the front tyres cannot provide any additional lateral force and the rear tyres can, the front of the vehicle will follow a path of greater radius than the rear
155:
Tyres transmit lateral (side to side) and longitudinal (front to back) forces to the ground. The total traction force (grip) available to the a tyre is the vector sum of the lateral and longitudinal forces, a function of the normal force and coefficient of friction. If the lateral and longitudinal
175:
In real-world driving, there are continuous changes in speed, acceleration (vehicle braking or accelerating), steering angle, etc. Those changes are all constantly altering the load distribution of the vehicle, which, along with changes in tyre temperatures and road surface conditions are is
286:
When an understeer vehicle is taken to the grip limit of the tyres, where it is no longer possible to increase lateral acceleration, the vehicle will follow a path with a radius larger than intended. Although the vehicle cannot increase lateral acceleration, it is dynamically stable.
110:, and it is normal for U to vary over the range of testing. It is possible for a vehicle to show understeer in some conditions and oversteer in others. Therefore, it is necessary to specify the speed and lateral acceleration whenever reporting understeer/oversteer characteristics.
41:
terms used to describe the sensitivity of the vehicle to changes in steering angle associated with changes in lateral acceleration. This sensitivity is defined for a level road for a given steady state operating condition by the
164:
is not changed, then the front wheels will trace out a smaller and smaller circle while the rear wheels continue to swing around the front of the car. This is what is happening when a car 'spins out'. A car susceptible to being
134:, and compliance in the steering system. Weight distribution affects the normal force on each tyre and therefore its grip. These individual contributions can be identified analytically or by measurement in a
176:
constantly changing the maximum traction force available at each tyre. Generally, though, it is changes to the center of mass which cause tyre saturation and inform limit handling characteristics.
156:
forces presented at the tyre during operations exceeds the tyre's available traction force then the tyre is said to be saturated and will loose its grip on the ground and start to slip.
103:
Results depend on the type of test, so simply giving a deg/g value is not sufficient; it is also necessary to indicate the type of procedure used to measure the gradient.
54:
is the amount of additional steering (at the road wheels, not the hand wheel) that must be added in any given steady-state maneuver beyond the
Ackermann steer angle. The
160:
and if there are no changes to the steering angle (i.e. the steering wheel stays in the same position), the vehicle's front will slide to the outside of the curve.
47:
86:
Car and motorsport enthusiasts often use the terminology informally in magazines and blogs to describe vehicle response to steering in a variety of manoueuvres.
401:
349:
International
Organization for Standardization, "Passenger cars – Steady-state circular driving behaviour – Open-loop test methods", ISO Standard 4138
340:
International
Organization for Standardization, "Road vehicles – Vehicle dynamics and road-holding ability – Vocabulary", ISO Standard 8855, Rev. 2010
186:
While weight distribution and suspension geometry have the greatest effect on measured understeer gradient in a steady-state test, power distribution,
1105:
221:
68:
is the rate of change of the understeer angle with respect to lateral acceleration on a level road for a given steady state operating condition.
61:
is the steer angle at which the vehicle would travel about a curve when there is no lateral acceleration required (at negligibly low speed).
684:
315:
gain (g's/deg), yaw velocity gain (1/s), and critical speed (the speed where an oversteer vehicle has infinite lateral acceleration gain).
800:
601:
394:
243:
50:(ISO) in document 8855. Whether the vehicle is understeer or oversteer depends on the rate of change of the understeer angle. The
294:. Although the vehicle is unstable in open-loop control, a skilled driver can maintain control past the point of instability with
810:
757:
225:
358:
T. D. Gillespie, "Fundamentals of
Vehicle Dynamics", Society of Automotive Engineers, Inc., Warrendale, PA, 1992. pp 226–230
835:
331:
SAE International
Surface Vehicle Recommended Practice, "Vehicle Dynamics Terminology", SAE Standard J670, Rev. 2008-01-24
442:
387:
910:
290:
When an oversteer vehicle is taken to the grip limit of the tyres, it becomes dynamically unstable with a tendency to
56:
1110:
747:
596:
578:
214:
1120:
1046:
935:
875:
840:
630:
306:
the front brakes. If this forward bias is too great, then the front tyres may lose traction, causing understeer.
825:
677:
190:
and front-rear weight transfer will also affect which wheels lose traction first in many real-world scenarios.
795:
767:
785:
775:
588:
168:
is sometimes known as 'tail happy', as in the way a dog wags its tail when happy and a common problem is
625:
437:
299:
180:
880:
815:
467:
127:
905:
885:
670:
608:
422:
118:
Many properties of the vehicle affect the understeer gradient, including tyre cornering stiffness,
1070:
1051:
956:
845:
732:
714:
645:
291:
273:
43:
920:
727:
613:
492:
261:
135:
107:
38:
940:
870:
507:
497:
298:
and/or correct use of the throttle or even brakes; this is done purposely in the sport of
131:
123:
179:
If the center of mass is moved forward, the understeer gradient tends to increase due to
1115:
1041:
855:
850:
741:
737:
541:
531:
526:
427:
1099:
1084:
1023:
1008:
988:
915:
752:
722:
618:
487:
452:
295:
119:
993:
930:
900:
895:
640:
562:
1074:
998:
971:
966:
830:
820:
780:
521:
516:
447:
203:
169:
1056:
1018:
860:
693:
635:
187:
1013:
1003:
925:
890:
557:
477:
432:
805:
462:
17:
228: in this section. Unsourced material may be challenged and removed.
379:
976:
790:
100:
Gillespie goes into some detail on two of the measurement methods.
961:
865:
983:
472:
666:
383:
704:
197:
662:
1034:
949:
766:
713:
587:
571:
550:
540:
506:
415:
368:Milliken, William F.; Milliken, Douglas L. (1994).
267:Spin: The car turns more sharply than intended.
48:International Organization for Standardization
678:
395:
8:
79:if the understeer gradient is negative, and
685:
671:
663:
547:
402:
388:
380:
244:Learn how and when to remove this message
83:if the understeer gradient is zero.
75:if the understeer gradient is positive,
324:
142:In contrast to limit handling behavior
95:Test to determine understeer gradient
7:
226:adding citations to reliable sources
114:Contributions to understeer gradient
279:Plow: The car does not turn enough.
801:Continuously variable transmission
46:(SAE) in document J670 and by the
25:
1106:Automotive steering technologies
1080:
1079:
1069:
272:
260:
202:
213:needs additional citations for
44:Society of Automotive Engineers
151:Limit handling characteristics
1:
836:Automated manual transmission
443:Electronic Stability Control
911:Semi-automatic transmission
1137:
748:Internal combustion engine
1065:
1047:Hybrid vehicle drivetrain
936:Transmission control unit
876:Limited-slip differential
841:Electrorheological clutch
700:
370:Race Car Vehicle Dynamics
826:Dual-clutch transmission
106:Vehicles are inherently
796:Constant-velocity joint
66:Understeer Gradient (U)
776:Automatic transmission
27:Vehicle dynamics terms
181:tyre load sensitivity
881:Locking differential
816:Direct-shift gearbox
372:. SAE International.
222:improve this article
128:self aligning torque
906:Preselector gearbox
886:Manual transmission
410:Automotive handling
1052:Electric generator
957:Wheel hub assembly
126:compliance steer,
1111:Automotive safety
1093:
1092:
846:Epicyclic gearing
715:Automotive engine
660:
659:
656:
655:
649:
646:Semi-trailing arm
622:
605:
254:
253:
246:
108:nonlinear systems
16:(Redirected from
1128:
1121:Vehicle dynamics
1083:
1082:
1073:
950:Wheels and tires
921:Torque converter
687:
680:
673:
664:
643:
616:
614:MacPherson strut
599:
572:Semi-independent
548:
493:Vehicle dynamics
404:
397:
390:
381:
374:
373:
365:
359:
356:
350:
347:
341:
338:
332:
329:
310:Related measures
276:
264:
249:
242:
238:
235:
229:
206:
198:
194:Limit conditions
136:Bundorf analysis
52:Understeer Angle
39:vehicle dynamics
21:
1136:
1135:
1131:
1130:
1129:
1127:
1126:
1125:
1096:
1095:
1094:
1089:
1061:
1030:
945:
941:Universal joint
871:Hotchkiss drive
762:
709:
696:
691:
661:
652:
597:Double wishbone
583:
567:
536:
502:
498:Weight transfer
411:
408:
378:
377:
367:
366:
362:
357:
353:
348:
344:
339:
335:
330:
326:
321:
312:
296:countersteering
284:
283:
282:
281:
280:
277:
269:
268:
265:
250:
239:
233:
230:
219:
207:
196:
153:
144:
132:weight transfer
116:
97:
92:
71:The vehicle is
57:Ackermann Steer
28:
23:
22:
15:
12:
11:
5:
1134:
1132:
1124:
1123:
1118:
1113:
1108:
1098:
1097:
1091:
1090:
1088:
1087:
1077:
1066:
1063:
1062:
1060:
1059:
1054:
1049:
1044:
1042:Electric motor
1038:
1036:
1032:
1031:
1029:
1028:
1027:
1026:
1021:
1016:
1011:
1006:
1001:
996:
991:
981:
980:
979:
974:
969:
959:
953:
951:
947:
946:
944:
943:
938:
933:
928:
923:
918:
913:
908:
903:
898:
893:
888:
883:
878:
873:
868:
863:
858:
856:Friction drive
853:
851:Fluid coupling
848:
843:
838:
833:
828:
823:
818:
813:
808:
803:
798:
793:
788:
783:
778:
772:
770:
764:
763:
761:
760:
755:
750:
745:
742:Plug-in hybrid
735:
730:
725:
719:
717:
711:
710:
701:
698:
697:
692:
690:
689:
682:
675:
667:
658:
657:
654:
653:
651:
650:
638:
633:
631:Sliding pillar
628:
623:
611:
606:
593:
591:
585:
584:
582:
581:
575:
573:
569:
568:
566:
565:
560:
554:
552:
545:
538:
537:
535:
534:
529:
524:
519:
513:
511:
504:
503:
501:
500:
495:
490:
485:
480:
475:
470:
465:
460:
455:
450:
445:
440:
435:
430:
428:Center of mass
425:
419:
417:
413:
412:
409:
407:
406:
399:
392:
384:
376:
375:
360:
351:
342:
333:
323:
322:
320:
317:
311:
308:
278:
271:
270:
266:
259:
258:
257:
256:
255:
252:
251:
210:
208:
201:
195:
192:
152:
149:
143:
140:
115:
112:
96:
93:
91:
88:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
1133:
1122:
1119:
1117:
1114:
1112:
1109:
1107:
1104:
1103:
1101:
1086:
1078:
1076:
1072:
1068:
1067:
1064:
1058:
1055:
1053:
1050:
1048:
1045:
1043:
1040:
1039:
1037:
1033:
1025:
1022:
1020:
1017:
1015:
1012:
1010:
1007:
1005:
1002:
1000:
997:
995:
992:
990:
987:
986:
985:
982:
978:
975:
973:
970:
968:
965:
964:
963:
960:
958:
955:
954:
952:
948:
942:
939:
937:
934:
932:
929:
927:
924:
922:
919:
917:
916:Shift-by-wire
914:
912:
909:
907:
904:
902:
899:
897:
894:
892:
889:
887:
884:
882:
879:
877:
874:
872:
869:
867:
864:
862:
859:
857:
854:
852:
849:
847:
844:
842:
839:
837:
834:
832:
829:
827:
824:
822:
819:
817:
814:
812:
809:
807:
804:
802:
799:
797:
794:
792:
789:
787:
784:
782:
779:
777:
774:
773:
771:
769:
765:
759:
756:
754:
753:Petrol engine
751:
749:
746:
743:
739:
736:
734:
731:
729:
726:
724:
723:Diesel engine
721:
720:
718:
716:
712:
708:
706:
699:
695:
688:
683:
681:
676:
674:
669:
668:
665:
647:
642:
639:
637:
634:
632:
629:
627:
624:
620:
619:Chapman strut
615:
612:
610:
607:
603:
598:
595:
594:
592:
590:
586:
580:
577:
576:
574:
570:
564:
561:
559:
556:
555:
553:
549:
546:
543:
539:
533:
530:
528:
525:
523:
520:
518:
515:
514:
512:
509:
505:
499:
496:
494:
491:
489:
488:Unsprung mass
486:
484:
481:
479:
476:
474:
471:
469:
466:
464:
461:
459:
456:
454:
453:Inboard brake
451:
449:
446:
444:
441:
439:
436:
434:
431:
429:
426:
424:
421:
420:
418:
414:
405:
400:
398:
393:
391:
386:
385:
382:
371:
364:
361:
355:
352:
346:
343:
337:
334:
328:
325:
318:
316:
309:
307:
303:
301:
297:
293:
288:
275:
263:
248:
245:
237:
227:
223:
217:
216:
211:This section
209:
205:
200:
199:
193:
191:
189:
184:
182:
177:
173:
171:
167:
161:
157:
150:
148:
141:
139:
137:
133:
129:
125:
124:lateral force
121:
120:camber thrust
113:
111:
109:
104:
101:
94:
89:
87:
84:
82:
81:Neutral steer
78:
74:
69:
67:
62:
60:
58:
53:
49:
45:
40:
36:
32:
19:
994:Racing slick
931:Transfer box
901:Park-by-wire
896:Parking pawl
811:Differential
786:Direct-drive
768:Transmission
758:Steam engine
703:Part of the
702:
641:Trailing arm
563:De Dion tube
482:
457:
423:Car handling
369:
363:
354:
345:
336:
327:
313:
304:
289:
285:
240:
234:October 2019
231:
220:Please help
215:verification
212:
185:
178:
174:
165:
162:
158:
154:
145:
117:
105:
102:
98:
85:
80:
76:
72:
70:
65:
63:
55:
51:
34:
30:
29:
972:Alloy wheel
831:Drive wheel
821:Drive shaft
781:Chain drive
589:Independent
473:Tire / Tyre
448:Fishtailing
416:Main topics
170:fishtailing
1100:Categories
1057:Alternator
705:Automobile
694:Powertrain
636:Swing axle
626:Multi-link
602:Jaguar IRS
579:Twist beam
542:Suspension
483:Understeer
468:Suspension
319:References
188:brake bias
130:, lateral
73:Understeer
31:Understeer
926:Transaxle
891:Manumatic
861:Gearshift
733:Fuel cell
558:Beam axle
551:Dependent
527:Pneumatic
478:Transaxle
458:Oversteer
433:Downforce
77:Oversteer
35:oversteer
18:Oversteer
1085:Category
1024:Tubeless
1009:Run-flat
989:Off-road
806:Coupling
728:Electric
609:Dubonnet
463:Steering
438:Drifting
300:drifting
90:Dynamics
532:Torsion
1075:Portal
1035:Hybrid
999:Radial
977:Hubcap
791:Clutch
738:Hybrid
707:series
508:Spring
1116:Tires
1019:Spare
962:Wheel
866:Giubo
544:types
510:types
166:loose
59:Angle
1014:Snow
1004:Rain
984:Tire
522:Leaf
517:Coil
292:spin
64:The
37:are
33:and
967:Rim
224:by
1102::
302:.
172:.
138:.
122:,
744:)
740:(
686:e
679:t
672:v
648:)
644:(
621:)
617:(
604:)
600:(
403:e
396:t
389:v
247:)
241:(
236:)
232:(
218:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
