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A speed limiter is a governor used to limit the top speed of a vehicle. For some classes of vehicle and in some jurisdictions they are a statutory requirement, for some other vehicles the manufacturer provides a non-statutory system which may be fixed or programmable by the driver.
The legal definition of a Moped in the United Kingdom was revised in 1977 to include a maximum design speed of 30 mph (48 km/h). This was further revised to 50 km/h (31 mph) in the 1990s, then 45 km/h (28 mph) in the late 2000s to fall in line with unified European Union licensing regulations.[n 1][better source needed]
To comply with this, mopeds typically include some method of onboard speed restriction to prevent the machine exceeding the prescribed speed (on a flat road, in still air, with a rider of standard height and weight). Older models such as the Honda C50 used a simple centrifugal governor as part of the transmission, which progressively and severely advanced the ignition as speed rose past a set point, causing engine power to fall off rapidly at higher rpm and road speed, but maintaining the low- and moderate-speed hill climbing ability of the unrestricted version. Other systems achieved a similar result with simple restrictor flaps in the air intake, much like those used to restrict the power output of full-size motorcycles. Modern mopeds use electronic systems with speed sensors that can cut the ignition spark (and, where fitted, interrupt fuel injection) once measured speed reaches or exceeds the set point, maintaining full power right up to the limited speed.
Early restriction methods could be defeated by simple physical modifications (e.g. cutting out the restriction plate). Modern electronic limiters at the very least require replacing the friction rollers in a scooter's CVT transmission, or even changing wheel size and/or reprogramming the engine management system, all in an effort to fool the sensors into detecting a lower than actual road speed.
Public services vehicles
Public service vehicles often have a legislated top speed. Scheduled coach services in the United kingdom (and also bus services) are limited to either 65 mph or 100 km/h (62 mph) depending on their age (newer coaches have the lower speed version installed, in line with harmonised EU regulations), though for city buses the use of limiters is to satisfy regulatory requirements, as many city buses cannot achieve these speeds even on an open roadway.
Heavy goods vehicles
HGVs in the UK have been subject to mandatory 60 mph (97 km/h) limiters since the early 1990s, which was subsequently revised to 56 mph (90 km/h) during EU harmonisation. Certain classes of heavy truck are subject to a further reduced 53 mph (85 km/h) limiter.
Many Citroën, Mercedes Benz, Peugeot, Renault as well as some Ford car and van models have driver-controlled speed limiters fitted or available as an optional accessory which can be set by the driver to any desired speed; the limiter can be overridden if required by pressing hard on the accelerator. The limiter may be considered as setting the maximum speed (with throttle kickdown to override it) easing the throttle to reduce speed, whereas cruise control sets the minimum speed (with the brake pedal to override it) pressing on the throttle to increase speed. The limiter may shift down through automatic gears to hold the maximum speed.
In European markets, General Motors Europe sometimes allow certain high-powered Opel or Vauxhall cars to exceed the 250 kilometres per hour (155 mph) mark, whereas their Cadillacs do not. The Chrysler 300C SRT8 is limited to 270 km/h. Most Japanese domestic market vehicles are limited to only 180 kilometres per hour (112 mph) or 190 kilometres per hour (118 mph).
BMW and Mercedes will 'unhook' their speed limited cars in Europe and Mercedes will provide some vehicles in the USA without limiters for an additional price. There are also third-party companies who will re-flash vehicle computers with new software which will remove the speed limits and improve overall performance.
Many small and medium sized commercial vehicles are now routinely fitted with speed limiters as a manufacturer option, with a mind towards reducing fuel bills, maintenance costs and insurance premiums, as well as discouraging employees from abusing company vehicles, attracting speeding fines and attracting bad publicity. These limiters are set somewhat lower than for sports cars, typically at 56, 62, 68 or 70 mph (90, 100, 110 or 113 km/h) in the UK, with options for 75 and 81 mph (120 and 130 km/h) listed in countries where these speeds are legal. Often the fitting of a limiter is combined with a small warning sticker on the rear of the vehicle, stating its maximum speed, to discourage drivers who may themselves be delayed by having to follow it from tailgating or other aggressive driving intended to intimidate the lead driver into accelerating.
Similarly, most electric cars and vans which are not inherently limited by a low power output or "short" gearing tend to implement a maximum speed cap via their power controllers, to prevent the rapid loss of battery charge and corresponding reduction in range caused by the much greater power demands of high speeds; for example, the Smart ED, Nissan Leaf, Mitsubishi MiEV, and the Citroen Berlingo EV. The limits are typically in line with those of other deliberately limited vehicles, for a balance that does not overly compromise either range or travel time; e.g. 90 km/h for the Berlingo, 100~120 km/h for the Smart (depending on version). The Leaf is an unusual case, being instead limited to a much higher 145 km/h (90 mph).
Some small economy cars feature limiters, because of stability and other safety concerns (short crumple zones, etc.), and to safeguard their small engines from the prolonged overrevving required to produce the power to achieve higher speeds. The first generation Smart was limited to 135 km/h (84 mph) (later generations were unlimited), and the Mitsubishi i to 130 km/h (81 mph).
Some heavy goods vehicle operators (typically big-name retailers, rather than haulage contractors) further reduce their HGV limiters from 90 km/h to a lower speed, typically 85 or 80 km/h (53 or 50 mph), in a claimed bid to reduce fuel consumption and emissions. This is again often highlighted by a warning sticker on the truck's tailgate.
- Department for Transport (2008), p.179 "Mopeds redefined to 30 mph maximum design speed"
- Documents referenced from 'Notes' section
- Department for Transport (2008). "Reported Road Casualties Great Britain: 2008 Annual Report". Retrieved 2010-01-09.
- Other references for article
- "History of British road safety". Retrieved 2010-01-20.
- "Overspeed warning, speed limiter and cruise control". Ateco Automotive. Retrieved 2010-04-28.
- "Speed limiter". Automobiles MERCEDES BENZ. Retrieved 2011-04-03.
- "Speed limiter, cruise control and overspeed warning". Automobiles PEUGEOT. Retrieved 2010-04-28.
- "New Clio brochure including mention of Cruise Control/Speed Limiter function". Automobiles RENAULT. Retrieved 2012-05-16.
- "Ford Speed Limiter technology". Ford. Retrieved 2011-05-13.
- "Why Japan finally got its foot off the brake". Japan Times. 2008-04-13.
- "So Long Guv'nor: Mercedes Will Unlock Top Speed on AMG Models in the US, for a Price". Jalopink. 2006-02-11.