page_title: Differential (mechanical device)
section_title: Loss of traction
hierarchical_section_title: Differential (mechanical device) / Loss of traction
caption_attribution_description: ARB, Air Locking Rear Differential.
context_page_description: A differential is a gear train with three shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others, or a fixed multiple of that average.
context_section_description: One undesirable side effect of an open differential is that it can limit traction under less than ideal conditions. The amount of traction required to propel the vehicle at any given moment depends on the load at that instant—how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum, and so on.
  The torque applied to each driving wheel is the result of the engine, transmission and drive axle applying a twisting force against the resistance of the traction at that roadwheel. In lower gears, and thus at lower speeds, and unless the load is exceptionally high, the drivetrain can supply as much torque as necessary, so the limiting factor becomes the traction under each wheel. It is therefore convenient to define traction as the amount of force that can be transmitted between the tire and the road surface before the wheel starts to slip. If the torque applied to one of the drive wheels exceeds the threshold of traction, then that wheel will spin, and thus provide torque only at the other driven wheel equal to the sliding friction at the slipping wheel. The reduced net traction may still be enough to propel the vehicle slowly.
  An open (non-locking or otherwise traction-aided) differential always supplies close to equal torque to each side. To illustrate how this can limit torque applied to the driving wheels, imagine a simple rear-wheel drive vehicle, with one rear roadwheel on asphalt with good grip, and the other on a patch of slippery ice. It takes very little torque to spin the side on slippery ice, and because a differential splits torque equally to each side, the torque that is applied to the side that is on asphalt is limited to this amount.
  Based on the load, gradient, etc., the vehicle requires a certain amount of torque applied to the drive wheels to move forward. Since an open differential limits total torque applied to both drive wheels to the amount used by the lower traction wheel multiplied by two, when one wheel is on a slippery surface, the total torque applied to the driving wheels may be lower than the minimum torque required for vehicle propulsion.
  A proposed alternate way to distribute power to the wheels, is to use the concept of a gearless differential, about which a review has been reported by Provatidis, but the various configurations seem to correspond either to the "sliding pins and cams" type, such as the ZF B-70 available on early Volkswagens, or are a variation of the ball differential.
  Many newer vehicles feature traction control, which partially mitigates the poor traction characteristics of an open differential by using the anti-lock braking system to limit or stop the slippage of the low traction wheel, increasing the torque that can be applied to the opposite wheel. While not as effective as a traction-aided differential, it is better than a simple mechanical open differential with no traction assistance.
caption: ARB, air-locking differential
exif: {"Image Make": "FUJIFILM", "Image Model": "FinePix S9600", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Digital Camera FinePix S9600   Ver1.00", "Image DateTime": "2007:09:29 16:24:36", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "", "Image ExifOffset": "294", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 50, 53, 48, 0, 0, 2, 0, 2, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail Orientation": "Horizontal (normal)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1342", "Thumbnail JPEGInterchangeFormatLength": "8808", "Thumbnail YCbCrPositioning": "Co-sited", "EXIF ExposureTime": "1/70", "EXIF FNumber": "29/10", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "400", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2007:09:29 16:24:36", "EXIF DateTimeDigitized": "2007:09:29 16:24:36", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "4", "EXIF ShutterSpeedValue": "613/100", "EXIF ApertureValue": "31/10", "EXIF BrightnessValue": "47/20", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "3", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash fired, compulsory flash mode", "EXIF FocalLength": "34/5", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3488", "EXIF ExifImageLength": "2616", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "1194", "EXIF FocalPlaneXResolution": "4482", "EXIF FocalPlaneYResolution": "4482", "EXIF FocalPlaneResolutionUnit": "3", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "2"}