Most modern vehicles’ engines are located to the front of the driver. However, some manufacturers placelocate the engine at some location point behind the driver. Due to the weight of the engine, its location can substantially impact a vehicle’s handling, behavior, and response characteristics. The goal of this article is to discuss the dynamic differences among front-, mid-, and rear-engine configurations.
Have you ever lifted the hood of a modern passenger car, only to find no motor? For most drivers, this has not occurred, as most vehicles’ engines are located up front. But if you drive a mid- or rear-engine vehicle, you would be accustomed to having only storage space up front under the hood. The goal of this article is to discuss the different engine locations and their impact on vehicle dynamics.

 

Front-Engine Vehicles

By far the most common engine location is at the front of the vehicle, ahead of the driver and the front axle line. While the earliest automobiles used a variety of engine locations, front-engine vehicles quickly became the norm for financial and engineering reasons. For example, most front-engine vehicles feature relatively easy access to the motor for maintenance and repair.

Positioning the engine ahead of the driver also impacts space considerations such as permitting permits a full-size interior. In addition, most front-engine vehicles feature large cabins, usually with seating for four or more occupants, including relatively spacious rear seating areas. Interior sound levels are also reduced because the engine is not directly adjacent to the cabin. The static weight distribution of front-engine vehicles (the weight of the front and rear of the automobile expressed in percentages) is generally favorable with between 50-66% of the vehicle’s weight over the front wheels (Bondurant ‘ Blakemore, 1998). Most front-engine vehicles feature relatively easy access to the motor for maintenance and repair.

Placing the engine up front also has some disadvantages. First, braking ability is somewhat diminished. Diminished braking occurs because weight transfers forward under braking (Karasa, 2001), leaving relatively little weight remaining over the rear wheels during braking and thus, limiting the ability of the rear tires to contribute the braking task. Second, accelerative ability is limited somewhat by the relative lack of static weight over the rear tires when, the weight of the vehicle shifts rearward upon acceleration (Scotti, 1995). Despite its relative drawbacks, the front-engine layout remains the most popular.

 

Mid-Engine Vehicles

In a mid-engine configuration the engine is located directly behind the cabin just ahead of the rear axle line. Essentially, the engine is located in the rear seat area. A rare configuration, the mid-engine vehicle is usually associated with high performance automobiles for several reasons. First, the static weight distribution tends to be close to the optimal 50/50 ratio , with the bias being slightly rearward, resulting in superior balance and handling characteristics (Bondurant ‘ Blakemore, 1998). Second, the vehicle’s mass (center of gravity) is The static weight distribution of front-engine vehicles (the weight of the front and rear of the automobile expressed in percentages) is generally favorable with between 50-66% of the vehicle’s weight over the front wheels (Bondurant ‘ Blakemore, 1998). Most front-engine vehicles feature relatively easy access to the motor for maintenance and repair.

Placing the engine up front also has some disadvantages. First, braking ability is somewhat diminished. Diminished braking occurs because weight transfers forward under braking (Karasa, 2001), leaving relatively little weight remaining over the rear wheels during braking and thus, limiting the ability of the rear tires to contribute the braking task. Second, accelerative ability is limited somewhat by the relative lack of static weight over the rear tires when, the weight of the vehicle shifts rearward upon acceleration (Scotti, 1995). Despite its relative drawbacks, the front-engine layout remains the most popular.

 

Rear-Engine Vehicles

In rear-engine vehicles, the motor is located in the rearmost portion, behind the rear axle line. Essentially, the engine is located in the trunk. Also a rare configuration, rear-engine automobiles tend to demonstrate exceptional braking ability due to a greater amount of weight from the engine remaining over the rear tires during braking. Thus, all four tires are heavily involved during braking instead of just the front tires. Acceleration is also enhanced, as the rearward transfer of weight and the engine weight combine to put maximum downward force on the rear tires (the tires responsible for acceleration in this configuration) resulting in a larger rear tire contact patch that enhances accelerative traction (Bentley, 1998).

While it may appear that rear-engine vehicles are the answer to all automotive needs, they do have drawbacks. First, the cabin generally has less room for rear passengers than does a front-engine vehicle. Some rear-engine cars do feature rear seats, but many do not offer enough room to carry rear passengers. Even in vehicles that do feature rear seats, the seats are often so smal that the only passengers able to sit comfortably in them are children.

erhaps even more disadvantageous is the rear-engine vehicle’s tendency to oversteer due to greater weight resident in the rear of the vehicle that results in greater momentum. Recall that oversteer (rear wheel) skids occur when the rear tires lose traction before the front tires, resulting in the rear of the car sliding out sideways or "fishtailing." (How To Drive, 2004). As oversteer skids are less easily corrected than understeer (front wheel) skids, this can be a problem for drivers not experienced and skilled in the driving dynamics of rear-engine cars" (Rich, 1998).

To help visualize this situation, imagine that you are playing a friendly game of darts. Instead of throwing your next dart normally, with the nose-heavy pointed end leading, you turn the dart around, throwing it fin-first toward the dartboard. Which end of the dart will eventually contact the dartboard? Indeed, the heavier end will spin in mid air during flight and contact the dartboard first. Under conditions of low traction or excessive speed, it’s the same with rear-engine vehicles; the rear of the vehicle will always want to "swap ends" with the front.

Front-engine vehicles can be either front or rear wheel drive, while all mid- and rear-engine vehicles are rear wheel drive. Table 1 displays a summary of the relative advantages and disadvantages of each engine location.

In dry conditions under normal driving conditions, the location of the engine does not make much of a difference in terms of driving dynamics. Aside from the mid-engine vehicle’s tendency to yield higher interior noise levels, most drivers will not detect a difference in the way these different vehicles respond to driver inputs. However, as the driving turns more spirited or involved emergency situations requiring abrupt driver inputs, these differences can surface, sometimes to the negative surprise of the driver. Generally, mid- and rear-engine vehicles will benefit the driver by offering shorter potential stopping distances and will disadvantage the driver to the degree that these layouts are more ends" with the front.

Front-engine vehicles can be either front or rear wheel drive, while all mid- and rear-engine vehicles are rear wheel drive. Table 1 displays a summary of the relative advantages and disadvantages of each engine location.

In dry conditions under normal driving conditions, the location of the engine does not make much of a difference in terms of driving dynamics. Aside from the mid-engine vehicle’s tendency to yield higher interior noise levels, most drivers will not detect a difference in the way these different vehicles respond to driver inputs. However, as the driving turns more spirited or involved emergency situations requiring abrupt driver inputs, these differences can surface, sometimes to the negative surprise of the driver. Generally, mid- and rear-engine vehicles will benefit the driver by offering shorter potential stopping distances and will disadvantage the driver to the degree that these layouts are more likely to oversteer than their front-engine counterparts.

As with front-, rear- and all-wheel-drive, modern traction maintenance systems tend to equalize the dynamic differences among front-, mid- and rear-engine vehicles (Wilson, 2005). Known generally as "dynamic stability conrol" systems, these computerized anti-skid systems help prevent negative events resulting from driving beyond these vehicles’ limits. These systems monitor the vehicle’s accelerative forces and very quickly adjust individual wheel speeds to reduce the chance of the driving losing control.

Maufacturers currently offer few mid- and rear-engine vehicles. The front-engine configuration remains the most popular layout. However, driving instructors may find themselves in a position to field questions about the difference among engine locations. It is hoped that this article contributes to preparing instructors to provide accurate information on this topic.

 

AAA, 2004. How to go on ice and snow. [Brochure].

Bentley, R. (1998).

Speed secrets. MBI Publishing Company, WI. Bondurant, B. ‘ Blakemore, J. (1998).

Bob Bondurant on high performance driving. MBI Publishing Company, WI.

 


Van Tassel, W.E. AAA National Office, Traffic Safety Programs; Manser, M.P. HumanFIRST Pprogram, University of Minnesota