Question: Why do so many FWD cars tend to have such long overhangs?

[Turbo]

This is something that I've been noticing more and more recently and it's driving me curious. FWD vehicles, usually mid and full sized cars, not compacts, visually have longer overhangs than cars that are RWD. Many FWD designs, both retro and contemporary, would look much better if their wheelbases were a few inches longer; many of them appear too tall, crammed together, or just plain awkward. Is this merely a coincidence, or is there a reason why FWD vehicles generally have wheelbases shorter than RWD cars? I'm guessing, if it's not a coincidence, it has to do with the placement of the drivetrain.

Here are a few examples of what I'm talking about.

Chevrolet Impala: overhangs are too long



Lincoln MKZ: too tall and "blobby" looking.


Lancia Kappa: combination of appearing too tall and overhangs being too long



Chevrolet Monte Carlo: unaesthetically pleasing design, too "crammed".


Here's a comparison of FWD and RWD:

Lexus ES: 111.0 inch wheelbase, 193 inches long, 57.1 inches high.


Lexus GS: 112.2 inch wheelbase, 190 inches long, 57.3 inches high.



See the difference? It's very easy to tell which is FWD and which is RWD. The ES is three inches longer than the GS, yet rides on a wheelbase over an inch shorter. The heights of the cars are almost identical, yet the ES appears taller while the GS looks lower. ES design is fussy and condensed, while the GS's lines are smoother and sleeker.

 

[TexRex]

Packaging differences between FWD and RWD vehicles are considerable.

The overwhelming majority of FWD cars have all of the engine's mass, not including manifolds or ancillaries, positioned transversely (sideways) ahead of the front axles. V6s and V8s are the exception, as the rear cylinder head tends to sit above the axles, but in those examples there tends to be mass positioned even farther away from the axles, in the form of the front cylinder head.

Things get even worse with unconventional layouts, such as longitudinal examples from Subaru and Audi primarily (there have been others, of course, but these two are the primary culprits), where, take a manual car as an example, the flywheel and clutch assembly are positioned ahead of the final drive's ring gear.

These layouts aren't new, but with increasingly strict safety regulations, there's more and more going on between the bumper and the engine in modern cars. This isn't lost on a number, and we've seen transverse engines tilt backwards and longitudinal drivetrains narrow the gap between the engine and axles through clever engineering.

RWD cars are a great deal simpler. Because the final drive is in the rear, the engine can be positioned virtually anywhere between the front wheels. As more is necessary in front of the engine, the engine can be moved rearward instead of doing unusual things with the drivetrain. Bonus, the engine tends to weigh more than crumple zones, so when you move it back, the weight balance moves back with it allowing for more responsive handling characteristics. All that really changes is the shape of the oil pan to allow for steering gear to pass beneath the engine block.

 

[Turbo]

Packaging differences between FWD and RWD vehicles are considerable.

The overwhelming majority of FWD cars have all of the engine's mass, not including manifolds or ancillaries, positioned transversely (sideways) ahead of the front axles. V6s and V8s are the exception, as the rear cylinder head tends to sit above the axles, but in those examples there tends to be mass positioned even farther away from the axles, in the form of the front cylinder head.

Things get even worse with unconventional layouts, such as longitudinal examples from Subaru and Audi primarily (there have been others, of course, but these two are the primary culprits), where, take a manual car as an example, the flywheel and clutch assembly are positioned ahead of the final drive's ring gear.

These layouts aren't new, but with increasingly strict safety regulations, there's more and more going on between the bumper and the engine in modern cars. This isn't lost on a number, and we've seen transverse engines tilt backwards and longitudinal drivetrains narrow the gap between the engine and axles through clever engineering.

RWD cars are a great deal simpler. Because the final drive is in the rear, the engine can be positioned virtually anywhere between the front wheels. As more is necessary in front of the engine, the engine can be moved rearward instead of doing unusual things with the drivetrain. Bonus, the engine tends to weigh more than crumple zones, so when you move it back, the weight balance moves back with it allowing for more responsive handling characteristics. All that really changes is the shape of the oil pan to allow for steering gear to pass beneath the engine block.

That's the type of answer I was looking for, thanks.

 

[Beeblebrox237]

Mainly because the engine is in front of the front wheels, as TexRex mentioned. I've attached a pair of Road & Track data panels, they used to have these great drawings on them which showed, among other things, the powertrain and the space it occupies in the car. Compare the Maxima and the 335i: the Maxima has a V6 mounted in front of the front wheels, and so it requires a long overhang to house the engine peripherals, and crash structures. The 335's engine is mostly behind the front axle, so much less room is needed in front of it. In practice this gives much better weight distribution, in exchange for less interior space.

 

[TexRex]

Road & Track data panels

I was looking for exactly those, but couldn't remember which publication was reponsible for them.

 

[Beeblebrox237]

I was looking for exactly those, but couldn't remember which publication was reponsible for them.

It's a shame they've declined so much in quality recently. I had to use the wayback machine to even access their data panel archive, it's like they're actively removing all the good content from their site in exchange for the usual clickbait. [/grumpy ex-subscriber]

 

[MatskiMonk]

One thing I've pondered briefly in the past, is why FWD cars have the engines infront of the front wheels?

 

[TexRex]

One thing I've pondered briefly in the past, is why FWD cars have the engines infront of the front wheels?

Not all have, but those that do have similarly done so for packaging.

Placing the engine behind the front axle reduces occupant capacity with comparable distance between the front and rear axle centerlines. Steering gear also tends to go behind the axle in FWD cars and having the engine there complicates matters.

Edit: The Toyota iQ is the most recent exception I'm aware of:

Citroën's DS and SM are longitudinal FWD with the entire transaxle aheard of the engine. The company's Traction Avant from the '30s started the convention for them. Here's a cutaway of the SM:

Cord utilized a similar layout in the '30s, as did some Miller Indy cars.

R. Buckminster Fuller's "car of the future" Dymaxion had a conventional RWD drivetrain flipped 180° with the driven wheels in front, but behind the driver:

Oldsmobile's original Toronado placed the engine conventionally for the period, directly on the front axle centerline, but utilized a 180° drivetrain with the axles crossing under it:

 

[MatskiMonk]

Not all have, but those that do have similarly done so for packaging.

Placing the engine behind the front axle reduces occupant capacity with comparable distance between thefront and rear axle centerlines. Steering gear also tends to go behind the axle in FWD cars and having the engine there complicates matters.

Nothing a slightly longer wheelbase and shorter front overhang wouldn't rectify though (in other words RWD proportions), surely?

 

[TexRex]

Nothing a slightly longer wheelbase and shorter front overhang wouldn't rectify though (in other words RWD proportions), surely?

Surely, but with FWD, the name of the game is efficiency in packaging and drivetrain simplicity. See the edit to my above post.

Edit: Also, the "distance between front and rear axle centerlines" indeed refers to the wheelbase. My intent was to make all things equal in the comparison.

 

[Beeblebrox237]

Nothing a slightly longer wheelbase and shorter front overhang wouldn't rectify though (in other words RWD proportions), surely?

At that point I think the thought process is that you may as well just make a RWD car. Engineering very rarely will make such fundamental compromises for a minor aesthetic benefit, if nothing else it would yield a car that simply isn't competitive with other cars in its class. Either they're RWD and handle better or they're conventional transverse FF cars with more space in a shorter, smaller package which is lighter, easier to park, and probably cheaper.

 

[Tornado]

In a front wheel drive car, any wheelbase in front of the passenger compartment is essentially wasted, since the reason the car is FWD in the first place is probably heavily based on packaging concerns anyway.

So whatever, dump the engine there. Most manufacturers don't have airs of chasing BMW with their FWD cars anyway, and it can help with crash tests.

 

[MatskiMonk]

Surely, but with FWD, the name of the game is efficiency in packaging and drivetrain simplicity. See the edit to my above post.

Yeah, I kind of thought that would be the case, as that's where we've ended up. However, I don't see why it would be a more complex drivetrain, and the packaging doesn't seem to be affected if the front wheels are further forward, as is demonstrated by the iQ diagram.

At that point I think the thought process is that you may as well just make a RWD car. Engineering very rarely will make such fundamental compromises for a minor aesthetic benefit, if nothing else it would yield a car that simply isn't competitive with other cars in its class. Either they're RWD and handle better or they're conventional transverse FF cars with more space in a shorter, smaller package which is lighter, easier to park, and probably cheaper.

I get it if you're trying to use a longitudinal engine or using an existing platform. But with effectively the same three elements to consider I don't get where one way would be fundamentally compromised?

 

[TexRex]

I don't see why it would be a more complex drivetrain, and the packaging doesn't seem to be affected if the front wheels are further forward, as is demonstrated by the iQ diagram.

The iQ's engine is particularly diminutive, which is fine for the segment, but start throwing in more substantial lumps and packaging concerns become more complicated. The decision to arrange things in the manner they did was influenced greatly by the overall package they wanted to have and the want for FWD.

A Fiat 500 may seem equally small, but its conventional FWD layout fits in a compartment considerably larger than that of the Toyota.

Also, the engine and drivetrain isn't really more complex with the engine behind the axles and tilted forward, but packaging ancillaries and other systems within the same vicinity becomes more complicated since conventions are thrown to the wind. I'm not sure the sea change was worthwhile and I'm not aware that Toyota has implemented the configuration anywhere else in the line, including where the same engine is utilized (Aygo and Yaris).

 

[Wolfe]

Things get even worse with unconventional layouts, such as longitudinal examples from Subaru and Audi primarily (there have been others, of course, but these two are the primary culprits), where, take a manual car as an example, the flywheel and clutch assembly are positioned ahead of the final drive's ring gear.

The tight turning radius is worth it though. For an engine that points its cylinder heads straight out towards the wheels, I was surprised how tightly Subarus (especially our Forester!) can make a U-turn.

 

[DesertPenguin]

Forgive me for not knowing but what's an overhang? I'm not sure what I'm looking for

 

[TexRex]

The tight turning radius is worth it though. For an engine that points its cylinder heads straight out towards the wheels, I was surprised how tightly Subarus (especially our Forester!) can make a U-turn.

The longitudinal layout is of considerable benefit to steering angle over transverse engines. Unlike in a classic Mini with its engine on top of the gearbox, contemporary transverse engines have the transmission tacked onto the end necessitating a considerably offset engine to allow space. While the boxer is quite wide, its heads may not encounter rubber as soon as a transverse engine's accessories or drive belt might.

 

[Wolfe]

Forgive me for not knowing but what's an overhang? I'm not sure what I'm looking for

Distance between the wheels and bumper. Here's a side-by-side example between a BMW E30 and Audi 80:

 

[DesertPenguin]

Gotcha

 

[TexRex]

Missed that one.

It also applies to the rear, but I gathered by the OP that an explanation for what's going on in the front is what was requested.

Unless the engine is in the rear, what's going on there is largely an aesthetic balancing act, seeking to ensure one end doesn't look significantly out of place when compared to the other. Of course there are also storage capacity concerns.

 

[Beeblebrox237]

I get it if you're trying to use a longitudinal engine or using an existing platform. But with effectively the same three elements to consider I don't get where one way would be fundamentally compromised?

As TexRex explained, packaging becomes a major concern. You've got to remember that the footwells are going to mean that the rear of the engine bay has much more room at the top than at the bottom and isn't just a box, and that combined with having to put things like the brake master cylinder, power steering, steering column, pedal box, etc. in front of the driver near the firewall means there's not really space for an engine there unless you push the front wheels really far forward. What happens then is that you have a lot of space in front of the front wheels that's wasted and empty, since you still have to have some space, but the engine MUST be significantly offset from the axle centreline because you've also got the gearbox inbetween it and the wheels. It's a careful balance of packaging, and automakers pretty quickly figured out that a FF layout with the engine behind the front wheels doesn't make any sense, which is why they're virtually nonexistent. It's not competitive because it results in a more expensive car with less space, similar dynamics, and slightly better proportions. Ever wonder why the Toyota iQ was a sales flop? It was too cramped and too expensive compared to its rivals.

 

[homeforsummer]

The iQ's engine is particularly diminutive, which is fine for the segment, but start throwing in more substantial lumps and packaging concerns become more complicated. The decision to arrange things in the manner they did was influenced greatly by the overall package they wanted to have and the want for FWD.

It's notable in that technical image that the iQ's engine is canted forwards too, presumably to free up space for the bulkhead in such a short platform. The most extreme example I can think of for such a thing is with the first-generation, A168 A-class, where the engine was nearly horizontal and mounted towards a sandwich floor, with the passenger compartment raised (I can't find a cutaway image showing its location in the car itself, but this is a good image showing the engine and its ancillaries as they would be in-situ):

Nobody else has gone quite so extreme with that but it shows why the A-class was able to have such a short bonnet and short overhangs and still have huge cabin space (better than the contemporary E-class, IIRC). Also it was tall - which helps in smaller cars.

Small engines do help with overhangs though. I imagine at least one reason for the larger front-drive cars having larger overhangs, other than engine size, are the requirements for using larger engines too - more cooling, more crash structure before the large, incompressible engine block, larger ancillaries etc.

I'm certainly struggling to find images of large front-drive cars that don't have disproportionately large front overhangs. There's less excuse for a large rear overhang though the front is certainly more styling-sensitive.

Distance between the wheels and bumper. Here's a side-by-side example between a BMW E30 and Audi 80:

View attachment 738111

Apropos of nothing, that's a great pic. I like the shape of the E30 but that particular Audi looks excellent...