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Encyclopedia > FF layout
Sketch of FF layout
Sketch of FF layout

In automotive design, a FF, or Front-engine, Front-wheel drive layout places both the engine and driven wheels at the front of the vehicle. This layout is typically chosen for its compact packaging, allowing the rest of the vehicle to be designed more flexibly. In contrast with the FR layout, the FF layout eliminates the need for a central tunnel or a higher chassis clearance to accommodate a driveshaft providing power to the rear wheels. Like the RR and RMR layouts, it places the engine over the drive wheels which aids traction. As the steered wheels are also the driven wheels, FF cars are generally considered superior to FR cars in conditions where there is low traction such as snow, mud, gravel or wet tarmac. However, powerful cars rarely use the FF layout because weight is transferred to the rear wheels under acceleration, while unloading the front wheels and sharply reducing their grip, effectively putting a cap on the amount of horsepower which could realistically be utilized. Electronic traction control can avoid wheelspin but largely negates the benefit of extra power. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Designers at work in 1961. ... A front-mounted engine describes the placement of an automobile engine in front of or on the front axle. ... Front-wheel drive is the most common form of engine/transmission layout used in modern passenger cars, where the engine drives the front wheels. ... The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. ... Sketch of FR layout In automobile design, an FR, or front-engine, rear wheel drive means a layout where the engine is in the front of the vehicle and drive wheels at the rear. ... This article is about the mechanical device. ... This article does not cite any references or sources. ... Sketch of RMR layout In automobile design, an RMR or Rear Mid-engine, Rear-wheel drive layout is one in which the rear wheels are driven by an engine placed just in front of them, behind the passenger compartment. ... Traction usually refers to friction between a drive member and the surface it runs on, where friction is used to provide motion. ...


Early cars using the FF layout include the 1948 Citroën 2CV, 1949 Saab 92 and the 1959 Mini. In the 1980s, the traction and packaging advantages of this layout caused many compact and mid-sized vehicles to adopt it. Because the transversely-mounted engine does not require a bevel gear to change the direction of the final drive, coastdown losses are reduced by approximately 2-3% of flywheel power and hence overall efficiency is slightly higher than with a FR design. First generation Ripple Bonnet Citroën 2CV built from 1948 to 1960 The Citroën 2CV (French: deux chevaux, literally two horses, from the tax horsepower rating) was an economy car produced by the French automaker Citroën from 1948 to 1990. ... Saab 92 Saab 92 is an automobile from Saab. ... For the new MINI, see MINI (BMW). ...


There are four quite different particular arrangements for this basic layout, according to the location of the engine, which is the heaviest component of the drivetrain, with respect to the front wheels:

  1. The earliest such arrangement was not technically FF, but rather MF and had the engine mounted longitudinally (fore-and-aft, or north-south) behind the wheels, with the transmission and differential in front. It was designed by Walter Miller, who had the drivetrain double back to put the differential in the middle, with brakes mounted inboard. E. L. Cord took the easier method of putting the differential in front. With the engine so far back, the weight balance of the L-29 Cord was unwieldy; the driven wheels did not have enough weight upon them. His later 810 and 812 cars were similar. The Citroën Traction Avant used the same MF layout, but solved the weight distribution issue with a new, low slung unibody design, resulting in remarkable handling for the era.
  1. The Grégoire Sport, amongst other cars by that firm, had the engine longitudinally in front of the front wheels, with the differential in the middle. This became quite popular, as the German Ford Taunus 12M and the Lancia Flavia used it as well.
  1. Issigonis's Mini and a few successor cars had the engine laterally mounted (east-west), with the transmission in the sump below the crankshaft. This was as near as possible to putting the entire weight of the drivetrain on the front wheels.
  1. Dante Giacosa put the transmission on one side of the laterally mounted engine, and doubled back the drivetrain to put the differential just behind it, but offset to one side. Hence the driveshafts to the wheels are longer on one side than the other, something which was avoided in the past. This located the weight just a bit in front of the wheels. This arrangement was first tried out on the Autobianchi Primula, next on the Fiat 128, and finally on the Fiat 127, which became car of the year. It is this system which dominates worldwide at present.

Vehicles with the Giacosa arrangement tend to suffer from torque steer under heavy acceleration. The shorter drive shaft, being stiffer than the longer drive shaft, transmits the motion to the wheels immediately instead of 'winding' up due to the drive torque[citation needed]. The net result is more tractive force at the wheel with the shorter drive shaft and the car tends to pull to the opposite side. For this reason, the Issigonis design (in which the two driveshafts are equal in length) is still preferred by many performance drivers and accounts for much of the Mini's success in rally and short-track circuit racing. In automobile design, an MF or Mid-engine, Front wheel drive layout is one in which the front wheels are driven by an engine placed just behind them, in front of the passenger compartment. ... A 1929 Cord L-29 Phaeton on display at the 2005 United States Grand Prix Cord L-29. ... It has been suggested that this article or section be merged with Citroën Traction Avant 22CV. (Discuss) The rear of a Citroën Traction Avant The Citroën Traction Avant was an automobile produced by the French manufacturer Citroën. ... Monocoque (French for single shell) or unibody is a construction technique that uses the external skin of an object to support some or most of the load on the structure. ... Ford Taunus was a large family car sold by Ford in Germany. ... Lancia Flavia coupé Lancia Flavia Zagato A Lancia Flavia 2000 The Lancia Flavia was developed by Professor Fessia in the late 1950s, and introduced for sale in 1961. ... The machine factory (shown here in a company letter of 1910) founded by Demosthenis Issigonis, Alecs grandfather, was one of the thriving Greek businesses in Smyrna (now Izmir). ... For the new MINI, see MINI (BMW). ... Danti Giacosa Autobianchi Primula Dante Giacosa (January 3, 1905 Rome - March 31, 1996 Turin) was one of the greatest light car designers of all time. ... These cars were produced between 1964 and 1970. ... The 128 was a subcompact automobile manufactured by the Italian manufacturer Fiat from 1969 to 1985. ... The Fiat 127 was a supermini automobile produced by the Italian manufacturer Fiat between 1971 and 1987. ... Front wheel drive is the most common form of engine/transmission layout used in modern automobiles, where the engine drives the front wheels. ...


References

Sedgwick, Michael Cars of the 50s and 60s. Gotherburg, Sweden: A B Nordbok, 1983. Has pictures of the engine layouts of the Traction Avant and the modern designs as in No. 4 above.


  Results from FactBites:
 
FF layout - Wikicars (754 words)
In contrast with the FR layout, the FF layout eliminates the need for a central tunnel or a higher chassis clearance to accommodate a driveshaft providing power to the rear wheels.
However, powerful cars rarely use the FF layout because weight transference under acceleration unloads the front wheels and sharply reduces their grip, effectively putting a cap on the amount of horsepower which could realistically be utilized.
The earliest such arrangement was not technically FF, but rather MF and had the engine mounted longitudinally (fore-and-aft, or north-south) behind the wheels, with the transmission and differential in front.
Tony Foale Designs, article on feetforward motorcycles. (3065 words)
For directional stability it is desirable to have the sideways centre of pressure behind the C of G. and fortunately the FF.
Any lowering of the sideways centre of pressure will probably be approximately proportional to the lowering of the C of G., whereas the roll moment-of-inertia will vary approximately as the square of the C of G. height.
This layout gives rise to a very long wheelbase, 100 inches in this case for just a single occupant, this length can be shortened if the front wheel is mounted between the legs.
  More results at FactBites »

 
 

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