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    Thread: FWD vs RWD vs AWD

    1. #1
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      FWD vs RWD vs AWD

      FWD vs RWD vs AWD

      Hello fellow Gearheads,
      This subject has been buzzing around in my head for a while but for one reason or another I have postponed it till now. I am taking the plunge here in the hope that I can put down what I have gathered in informal talks with other buffs who hold definite views on the subject, but have not really given much thought to it!

      Speaking for myself, I will confess that I am firmly in the RWD corner. And the reason is simple - I believe that from the 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 in this instance - should not be concentrated in one region, but distributed as much as possible in order to keep wear & tear low & prolong the life & durability of the system.

      FWD lay-out

      In a FWD set-up, the forces – (steering generated & engine torque generated) - are concentrated on the front wheels and its attached suspension, steering and drive-line components. And it doesn’t require too much imagination to visualise the cornering 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.
      While it is accepted that for good wheel articulation (in all three axes), universal couplings/CV couplings at both ends of each half-shaft to the front wheels are needed, the stresses (specially during adverse driving situations as mentioned above) due to steering forces & engine torque remains high in FWD vehicles. And the situation worsens as the wheel base keeps increasing and the vehicle wt approaches max. allowable GVW, the front wheels having to lug all the weight behind the front axle centerline.

      The peak (of this engineering folly?) 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 chassis-on-frame vehicles, were over 18 feet long, had the usual lazy V8s of 7 L displacement or thereabouts, & had kerb wts in excess of 2 tons! At the time they were the largest displacement engines in FWD cars, and despite their cumbersome handling & litany of niggles, they had long production runs.

      But the FWD trend continues globally today - Skoda Superb, Nissan Teana, Toyota Camry, Hyundai Sonata, Honda Accord, some Audi & Volvo sedans being large WB FWD examples sold in our market. The reason, as mentioned earlier, is the reduced manufacturing costs & compactness of the package. But one must concede the reason for this lay-out's commercial success - it is widely acknowledged that (for a WB < ~2.4 m & overall length < ~3.8 m, in other words, the small hatch-back!), the FWD layout, coupled with a monocoque structure, has distinct advantages in handling & agility.

      RWD lay-out

      On the other hand, in a RWD set-up, the same situation (stresses due to steering forces & engine torque) is more rationally resolved. The steering induced stresses are all focused on the front wheels and its accompanying suspension & steering components. The engine torque induced stresses are focused on the rear wheels and its associated sub-assemblies - the leading /trailing locating arms/linkages, 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 can be seen, the situation in a RWD set-up is much more in line (in my view!) with rational, practical engineering.

      AWD/4WD lay-out

      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 / torque sensing differentials of one kind or another, ESP and other similar software, etc. What some of us may not 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, while giving full steering lock. Thus it is clear that AWD is rather more complex & complicated (=higher maintenance & niggles issues!) than one would like in one's daily commuter. For the dedicated tourer - who also indulges in the occasional & necessary bits of off-roading in his travels - the investment in AWD may be worth the added expense and maintenance.

      I understand that the above expresses my views and therefore it would be worthwhile if members gave their valuable inputs/views/opinions to bring out any/many of the hitherto untouched aspects of this fascinating topic!

      Regards,
      Shashanka
      Last edited by shashanka; 29th Jun 2018 at 13:46.
      Anonymous cynic, possibly George Bernard Shaw, quoted frequently - "The more I see of some folks, the better I love my dogs"

    2. #2
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      I guess there is no doubt in this thing that RWD are the most fun to drive cars .

      As you have less of mechanical components on front axle and due to the arrangement of transmission , prop. shaft/drive shaft and differential in a RWD vehicle
      The weight of the car also gets distributed among the axles more evenly as compared to a FWD vehicle which makes it a more balanced .

      And rest i guess is specifically to the taste of individual .

      Sent from my Mi A1 using Tapatalk

    3. #3
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      I would love to drive a RWD car and probably most FTD. I am not sure which is the cheapest RWD car in India but not sure 40+ lakh INR is worth it. AWD too should be good on all surfaces with it grip levels

      But it is a myth that FWD cars cannot be fast or fun. Civic Type-R or CTR is considered the hottest hot hatch by most including motortrend:
      https://www.motortrend.com/cars/hond...ra-comparison/

    4. #4
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      Quote Originally Posted by KimiRaikkonen View Post
      I would love to drive a RWD car and probably most FTD. I am not sure which is the cheapest RWD car in India but not sure 40+ lakh INR is worth it. AWD too should be good on all surfaces with it grip levels

      But it is a myth that FWD cars cannot be fast or fun. Civic Type-R or CTR is considered the hottest hot hatch by most including motortrend:
      https://www.motortrend.com/cars/hond...ra-comparison/
      I agree entirely. I was reading a while back in another forum (in a reply to my post on the subject) where the member mentions Nissan (after they beat the pants off Porsche at Nurburgring with their GT-R) with their FWD track car delivering ~1000 bhp to the front wheels! So certainly, FWDers can be great fun too (one has only to see the original Italian Job with the fleet of Minis drawing circles around everything in sight!). My point was that extending the wheel base inordinately takes away the fun factor, apart from the other issues I have mentioned.
      Anonymous cynic, possibly George Bernard Shaw, quoted frequently - "The more I see of some folks, the better I love my dogs"

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