Editing Dynamometer (section)

===Chassis dynamometer (rolling road)===
{{main|Chassis dynamometer}}
[[Image:chassisdyno.jpg|thumb|right|[[Saab 96]] on chassis dynamometer]]

A [[chassis]] dynamometer, sometimes referred to as a rolling road,<ref>{{cite web |title=Rolling Road Dyno |url=http://www.tuningtools.co.uk/rolling-road-dyno-sales.html |work=Tuning Tools |access-date=3 August 2012 |archive-url=https://web.archive.org/web/20161203174940/http://www.tuningtools.co.uk/rolling-road-dyno-sales.html |archive-date=3 December 2016 |url-status=dead}}</ref> measures power delivered to the surface of the "drive roller" by the drive [[wheel]]s. The vehicle is often strapped down on the roller or rollers, which the car then turns, and the output measured thereby.

Modern roller-type chassis dyno systems use the "Salvisberg roller",<ref>{{cite web |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-bool.html&r=10&f=G&l=50&co1=AND&d=PTXT&s1=salvisberg&OS=salvisberg&RS=salvisberg |title=United States Patent: D798762 - Watch strap link |website=uspto.gov |access-date=7 April 2018}}</ref> which improves traction and repeatability, as compared to the use of smooth or [[Knurling|knurled]] drive rollers. Chassis dynamometers can be fixed or portable, and can do much more than display RPM, power, and torque. With modern electronics and quick reacting, low inertia dyno systems, it is now possible to tune to best power and the smoothest runs in real time.

Other types of chassis dynamometers are available that eliminate the potential for wheel slippage on old style drive rollers, attaching directly to the vehicle's [[Wheel hub assembly|hubs]] for direct torque measurement from the axle.

[[Motor vehicle emissions]] development and homologation dynamometer test systems often integrate emissions sampling, measurement, engine speed and load control, data acquisition, and safety monitoring into a complete test cell system. These test systems usually include complex emissions sampling equipment (such as constant volume samplers and raw [[exhaust gas]] sample preparation systems) and analyzers. These analyzers are much more sensitive and much faster than a typical portable exhaust gas analyzer. Response times of well under one second are common, and are required by many transient test cycles. In retail settings it is also common to tune the air-fuel ratio using a wideband [[oxygen sensor]] that is graphed along with the RPM.

Integration of the dynamometer control system with automatic calibration tools for engine system calibration is often found in development test cell systems. In these systems, the dynamometer load and engine speed are varied to many engine operating points, while selected engine management parameters are varied and the results recorded automatically. Later analysis of this data may then be used to generate engine calibration data used by the engine management software.

Because of frictional and mechanical losses in the various drivetrain components, the measured wheel brake horsepower is generally 15–20 percent less than the brake horsepower measured at the crankshaft or flywheel on an engine dynamometer.<ref>John Dinkel, "Chassis Dynamometer", ''Road and Track Illustrated Automotive Dictionary'', (Bentley Publishers, 2000) p. 46.</ref>