Thanks for the guidelines 350Z - it will help me get going!
This subject has been buzzing around in my head for a while but for one reason or another I have postponed it. I am taking another plunge in the hope that I can start a real debate/discussion on the subject. In informal talks with other buffs I have often found that people do
hold views on the subject but have not given much thought to it!
For myself, I will confess that I am firmly in the RWD corner. And the reason is simple - I believe that from an engineer's point of view, a FWD arrangement is a bean-counter's solution and not the engineer's. A FWD set-up is easy to manufacture. The engine, clutch, G/B and undercarriage sub-assembly can be made very compact and the set-up lends itself perfectly for volume production! But - it is not an engineer's solution.
Good engineering practice warrants that the stresses and strains in a mechanical system - a car - should not be concentrated in one region, but distributed as much as possible to keep wear & tear low & prolong life & durability. In a FWD set-up
both steering forces & engine torque forces are concentrated on the front wheels and its attached suspension, steering and drive-line components. And one can imagine the stresses built-up when the car is being driven at full steering lock and at max allowable torque (= throttle) - a situation common enough for me when climbing the steep hairpins of Uttaranchal. It is understood that for wheel articulation (in all 3 axes) universal couplings/CV couplings at both ends of each half-shaft to the front wheels are needed. But the stress concentration (during adverse driving situations as outlined above) due to steering & engine torque remains high in FWD vehicles. And the situation becomes worse as the wheel base keeps increasing. The peak of this engineering joke was reached by the Americans in the 70's when they decided to follow the European lead in FWD application. GM installed FWD on their full sized goliaths - the Cadillac Eldorado & the Oldsmobile Tornado - both of which were over 18 feet long & had the usual lazy V8s of 7 L displacement! Needless to add that both these died a mercifully quick death due to their impractical lay-out. But the FWD trend continues globally today (Skoda Superb, Nissan Teana, Toyota Camry, Hyundai Sonata and Honda Accord being large WB examples sold in our market). The reason as mentioned earlier is the reduced manufacturing costs & compactness of the package.
But as a concession to this design's commercial success, it is generally acknowledged that (for a WB < ~2.4 mtrs & overall length < ~3.8 mtrs), the FWD layout, coupled with a monocoque structure, has distinct advantages in handling & agility.
On the other hand, in a RWD set-up
, the same situation (stresses due to steering forces & engine torque) is more simply resolved. The steering stresses are all acting on the front wheels and its accompanying suspension & steering components. The engine torque generated stresses are concentrated on the rear wheels and its associated sub-assemblies - the locating arms, the suspension components, & in case of IRS, the half-shafts & their associated bits & pieces. The transmission & drive-line(prop shaft) losses are usually ignored as they are minor in comparison. As one can see, the situation in a RWD set-up is much more in line (in my view!
) with engineering integrity.
And finally, the AWD/4WD set-up
, for tackling the difficulties faced in driving over bad terrain - mud, slush, ice & snow and of course off-road "kaccha" surfaces. We have all seen AWD rally cars in WRC events with their stupendous ability to tackle dangerous surfaces. We also know that most of them are equipped with add-ons - limited slip or torque sensing differentials of one kind or another, ESP and other similar software, etc. What fewer people know is that full-time AWD (the Audi Quattro models, eg) requires a central/3rd differential or a viscous coupling (like the AWD version of our home-grown XUV500) to prevent torque wind-up or "chirping" on smooth tarmac with AWD engaged. So, as can be seen, AWD is rather more complex & complicated (=higher maintenance & niggles issues!) than one would like in one's daily commuter. But for the dedicated tourer (who also indulges in occasional & necessary bits of off-roading in his travels!) the investment in AWD may be worth the added expense and - occasional! - maintenance.
I feel the foregoing is an adequate introduction (obviously, the views/opinions expressed are mine only!) and I now hope that our forum members will join in with their own views/opinions/inputs and we can get a lively discussion/debate going!