Automotive Myths

[Guest keltik]

Il go out on a limb and say its a pretty poorly worded/written article if the main points are this unclear and so many people seem to have issues with it.

Or maybe we're all just idiots. Ive already confused backpressure with scavenging

[GC8E2DD]

 catsoup said:

explain with your reasoning how a porsche works with weight distribution having the motor behind the rear wheels.

A Porsche is also a compromise. Like a Fiat 850 Sport, a VW Beetle (original ) or even a Bambina, Porsches have been plagued from the outset with the 'backwards through a fence' syndrome. This is essentially an exagerrated tank slapper. Having your engine right at the back (behind the rear axle) gives a large lump of weight a huge turning moment along the vehicle's longitudinal axis, ie; chassis front to back. It works like a pendulum greatly amplifying weight shifts laterally across the chassis.

Because in this chassis layout you have virtually no weight over the front wheels, there is very little force in a neutral stance (carrying a constant speed on the flat) applied to the steering wheels. In an Bambina for instance, the difference between a full tank of gas and an empty one was reasonable steering, and flighty uncommunicative steering (the gas tank is over the front wheels, and a full tank of gas weighs a significant proportion of the car). The thing about tyre grip, is that it steadily increases as load is applied, to a point where it is overloaded, and grip swiftly decreases. Under hard acceleration followed by hard braking, this style chassis will go from hardly any front grip, to lots of front grip. You would find your steering come and go, and worst case scenario it goes when you need to turn, returns when you suddenly realise you aren't turning and hit the brakes, then lets that huge pendulum of an engine swing you backwards off the road as the inertia overcomes your rear tyre grip.

Porsche have the benefit (like Peugeot do with the 105/ 205 etc) of having developed effectively the same car for a very long time. This means they have slowly but surely engineered their way around the inherent compromises of this chassis design. Altering suspension and steering geometry as well as attempting to redress the weight imbalance by moving ancilliaries (and even the engine) further forward all help in this regard. It is no mistake that Porsches have inordinately large rear tyres! In later years they have also added (like most manufacturers of sports cars) sensor based technologies that measure things like pitch and yaw, steering and slip angles, as well as acceleration on these axis so as to be able to intervene when a driver gets it wrong. It is not so much that they have solved the inherent problems in the chassis, just that they have commendably worked their way around them.

Why not can it all together? As well as having inherent problems, a layout like this conversely has advantages, like all good compromises =]

For a start, having that weight over the rear wheels is excellent for traction (Assuming as mentioned you don't overload the rear tyres!). It is also good for braking in a straight line because you have a less violent (and chassis tunable) weight transfer from rear to front. This means the rear brakes on a Porsche are potentially much more useful than those on a front wheel drive front engined car where the lion's share of the weight is already over the front wheels (potentially overloading them), and further weight transfer from rear to front actually reduces rear traction. Sharing braking duties more evenly is also good for tyre life.

So really, a Porsche works very well because the engineers have invested 40 odd years in getting it to work. They were never going to give up on it, because there are advantages, and it is part of the vehicle's DNA. If they had stopped making them, and then resurrected the 911 20 years later as a front wheel drive front engined throwback like they did with the Beetle, it just wouldn't be a 911 - even if it was a great handling front wheel drive car.

[THUNDA]

f**k fwd tbh

Rear mounted engine + Rear wheel drive = the win

or 4WD

otherwise pssshhhht ya gaye

and also, the "back pressure" statement he made is a bit bullshite

but with turbo cars back pressure isnt nessesary at all, infact the shorter the path way to get fumes out the better (think of how the wastegate works)

back pressure is only needed for n/a cars for scavenging effect

(im my opinion)

[THUNDA]

this is the reply, explaining the previous preply, which should have actually said that i'm currently replying, but in past tense, but infact, this is the futureeee

ooooOOOoooOOOooo (ghost voice)

[Guest]

 funkytown']

[quote name='Qwerty said:

img]http://i220.photobucket.com/albums/dd226/phantom04xt/FWDsux.jpg[/img]

gold

lol i had that as my avatar a lil while ago.

[newsuba]

Fool's Gold.

A little Renaultsport Megane R26, FWD with a piddly 169kW is one of the finest driver's cars ever, easily out-handling most production AWD's, including the current STI and EVO.

[DPI]

Yeah, but to be fair Mike, the new STI and Evo are Big Fat Pigs...

The sales pitch for either should be:

Rally Bred, and then slowly killed by compromise and PC...

[Guest keltik]

Mike you are far too attached to Euros. Why is that?

[Joker]

cos they are better

[Guest keltik]

Go drive a passat for a month and say that...actually thinking about it - that thing was goooood

[NotAWhiteGTB]

Dont mock fwd, give me an ef9 civic and a small budget, i would be more than happy at the track driving around people who twice as much power.

Also, i would not say no to another Mini.... :'(

In saying that, fwd only works when it is in a small car, and i mean in a really small car. Anything that starts packing on the pounds and is still driven through the front is going to be a menace of a thing to control properly, then you definitely need to have something that is awd or rwd

This debate should be more along the lines of, in a small car, would you rather have fwd or rwd, and i would still answer fwd because you have less drive line, therefore less weight.

[newsuba]

 keltik']

Mike you are far too attached to Euros. Why is that?

I find most of them more aesthetically and philosophically attuned to my automotive needs.

;D

Japs usually win on VFM though.

cos they are better

Only half of them.

[quote name='keltik said:

Go drive a passat for a month and say that...actually thinking about it - that thing was goooood

Passat is a good, unexciting repmobile.

A (possibly) mutual acquaintance in the audio trade has used one for years.