The Evolution of RWD

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GM's new Kappa (small RWD) platform is finally hitting showrooms late this year in the form of the Pontiac Solstice. With Kappa, GM has the ability to develop new RWD compact cars such as the Chevy Nomad concept. Will it happen? From what I've seen from GM as any car manufacturer, they will probably stay away from them because they aren't the norm in a small car anymore. But let's look at it from an engineering standpoint. Why? Why don't small cars get rear drive treatment? Is there significant drivetrain power loss in having a driveshaft? Is it the driveshaft taking space from trunks and hatch's? Is it just plain cheaper for them to manufacture FWD cars? Fuel Economy? Don't want to rock the small car boat? I personally love RWD and wonder why it is reserved for sports cars, sports sedans, roadsters and the like. I know RWD never left Germany, Sweden just resists change, America wants to change, and Japan is pretty split. What now?

posted by  VG30DE

Small cars USED to be all RWD, with few exceptions up utnil teh late '60s. At that point, however, everyone who had been watching the Mini realized that to package a small car and leave room inside for real adults, a transverse FWD layout was most logical. You didn't have a transmission tunnel taking up floorspace and seat space, and a differntial taking up cargo space.

Even on the luxury end, the Olds Toronado and Cadillack Eldorado in the late '60s picked up where the Cord 810 and Citroen Traction Avant did in the '30s, and showed that the FWD layout made for much more useable, luxrious floor space inside.

With the energy crunch of the '70s, manufacturers worldwide found that they could downsize the car on the outside, and still increase interior room with a FWD layout.

It certainly wasn't for saving costs because all new tooling had to be created that made the new FWD cars more expensive to initially build than the cheap RWD economy cars they replaced. But they provided more useable space and utility, as well as a little more all weather ability (again, proven by the Traction Avant, Mini, and Saabs). Once that ball was rolling, it went into every corner of the spectrum, including sports coupes. At the outer limits of performance, splitting the duties of the steering and drive wheels worked better, but until you were in a serious formula car or Sports racer, chassi sengineering allows FWD to work very well indeed.

Of course, the manufacturers are trying to go back to RWD, even with the packaging drawbacks, because buyers are demanding it, whether they understand the advantages or not. BMW and Mercedes still use it, so it MUST be better for getting groceries, right?

posted by  ChrisV

Thank you for that sweet post. I know all cars, even small cars used to be RWD, but I wonder if all those reasons for FWD like the space and room still hold true today. BMW is making their 1 series as all their 2WD cars RWD and it is a small car and a hatchback(an awesome exception to the rule). I guess they want to sacrifice some space for heritage and performance. Isn't it alot harder to work on those FWD cars and alot more expensive to maintain with everything all cluttered up in the front? I guess that is the price you pay for interior room.

posted by  VG30DE

Actually, all the reasons hold even more true today, as we try to pack more and more stuff into the cars, and make them larger and heavier. Micro cars and sub-compact cars are still a very important segment of the market (and probably mroeso as gas prices continue to rise) so amking cars smaller again on the outside while maximizing interor volume is still going to be a priority. It helps small station wagons and hatchbacks have much larger cargo areas without taking up as much space as, say, SUVs.

Funny thing about the new BMW 1 and 2 series... They are both larger and heavier than the old 2002 and first gen 320i...

As far as hard to work on and maintain, it's no different. Modern cars have a lot of stuff on their engine regardless of layout. Even some of the smallest engines on the market, the rotaries in the RX7 and RX8 are hard to get into a work on even with their RWD layout...

posted by  ChrisV

I kinda disagree. Looking under the hood of my mom's '02 miata, I know that RWD simplicity is bliss. I can't think of many if any FWD compacts where you have space to work. Maybe the Miata is just an exception, but I love how you can see the ground on both sides of the engine (just like old cars). I know the RX-8's rotary (and I think the RX-7's rotary) is way different because the engine is shoved under the dash (piston engines don't fit there :mrgreen: ) where noone but special mechanics with lifts can touch it for optimal weight distribution. That is just my opinion and I don't have tons of experience but from what I've seen, alot of FWD cars are just jam packed under the hood. Thanks for keeping this conversation alive :thumbs: .

posted by  VG30DE

Camaro engine compartment, jam packed:

http://www.streetrodsforever.com/car_images/94_chevy_camaro_z28/94_chevy_ca maro_engine.jpg

Supra engine:

http://www.cs.cmu.edu/~akj/supra/Supra_engine_bay.jpg

Supra engine:

http://www.fnsweet.com/pics/events/dfwstangs_041402/Supra_engine.jpg

BMW engine:

http://www.familycar.com/RoadTests/BMW-330/Images/Engine.jpg

All jam packed tightly, and hard to work on.

posted by  ChrisV

Civic engine (you can see the ground around it):

http://home.nc.rr.com/jaynesfamily/Civic_Engine.jpg[/img]

http://www.hansbezemer.nl/autos/foto/Honda/honda%20vtec%20engine.jpg

The engine doesn't take up much space in this Golf (they are quite easy to work on. i've had a couple)

http://www.vwgolf-mk2.com/Engine%20Room/Engine%20Room.jpg

The point is, the layout, FWD/RWD, has less to do with it than how much stuff the particular designer/engineers have tried to cram into the engine compartment. Some RWD cars are jam packed tight, as are some FWD cars. Some of each are easy to work around, and most fall somewhere in the middle.

Packaging, however, means [i]passenger space. And sadly, more and more FWD cars are trying to get that "cockpit"lok back, and taking up valuable floor space with consoles and the like, almost entirely negating the advantages in packaging (at least for pasengers). For cargo, the lack of differential can still make a larger cargo area in a smaller overall package. If the manufacturer uses a torsion beam axle, the space can be opened up even more.

In the case of the Miata, it's a 2 seat car with cargo space being way down the list of priorities, and overall balance and agility way up the list. As such, a small, light, front engine, RWD layout makes perfect sense. But it's not very practical. Combining more and more practicality with fun changes how the packaging requirements go.

posted by  ChrisV

So torsion beam on the front for FWD's you say? That is not the same thing as independent like most cars are today, correct? Isn't there a handling difference or is that the sacrifice you make for interior space?

posted by  VG30DE

No, torsion beam rear axle, for a low load floor. And there's a slight handling disadvantage at t elimits, I'd say, but considering there are stock and street prepared race cars with torsion beam axles that handle better than many street cars, I'd say for the role, it really doesn't hurt the car. I mean, my PT has a torsion beam rear axle to get a low load floor and lots of space, and there's nothing I'd do on the street that would tax the suspension, even under load. And it works quite well on the autocross track...

posted by  ChrisV

Lol, I have so much to learn about suspension.

posted by  VG30DE

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