RWD against FWD cars

[Mr. Inconspicuous]

Why are RWD cars better than FWD??

I don't understand what makes RWD superior when it comes to performance, especially straight line performance.What if the a bmw had FWD, what would it's weaknesses be?

Now, I'm not biased towards FWD cars, I just want to understand the physics involved. Perhaps, those who care to respond can compare/constrast the characteristics of FWD, RWD, and even AWD.

[Phil]

Originally posted by Mr. Inconspicuous
Why are RWD cars better than FWD??

I don't understand what makes RWD superior when it comes to performance, especially straight line performance.What if the a bmw had FWD, what would it's weaknesses be?



Under hard acceleration, the weight shifts to the rear wheels, so they have more traction. This lets RWD cars launch faster than FWD cars. AWD cars have an added advantage, but the added weight of the AWD system usually negates the advantage of the added grip (for drag racing).

For cornering, RWD cars have better yaw control, and the front wheels can be devoted to turning, without the added load of driving. FWD cars are more stable in slippery conditions, and can be made to yaw (though not as effectively as RWD.) AWD cars have very little yaw control, but retain their balance under power or in trailing throttle.

How's that.

[Junior]

Ok heres a bit for you even though I am up to my pretty tits.

How to you hit something to drive it forward normally ??
From behind

(No smutty ideas lads)

Rwd cars are steered by both wheel direction and power .. ie get the arse of the car out further to tighten the nose in. This allows them greater agility and more precise power and steering feedback.

[WhipLash]

Speaking of the FWD/RWD argument, its interesting to note that Ford have decided to go for FWD for its forthcoming Ford Focus RS, unlike its RWD rally conterpart. The expected BHP is around 200BHP. Also, the forthcoming (and similarly powered) Honda Civic R-Type will be FWD too.

So does that mean that advancements have been made that have pushed out the 200BHP FWD limit?

[SpyCamera]

For the ultimate in true sports car performance, RWD is much better, and AWD is the best. (But you pay the penalty with AWD drive of increased mechanical complexity and weight.) That is the reason why so many manufacturers, from Ferrari to Porsche to GM to Honda, have manufactured RWD or AWD cars when they wish to produce a true world class sports car.

At the same time, for real world driving like most of us do, FWD offers better performance, especially in inclement weather. FWD cars have the added advantage of being better able to make use of interior and boot space, due to the lack of a driveline hump and differential.

FWD does suffer from torque steer, which various manufacturers have tried to tame over the years. Torque steer occurs primarily when the two axle shafts from the transaxle to the wheels are of uneven lengths. The more sudden the acceleration, and the greater the horsepower, the worse torque steer tends to be. (Small, high revving four cylinders tend to have it the worst.)

FWD vehicles tend to be expensive to work on, becuase the lack of space caused by cramming many systems into the front end of a car makes them harder to work on. In addition, FWD cars tend to suffer worse from front end damage, because so many systems are clustered in one area.


Later Spy.

[BeCos]

Junior your argument is not quite true. "Getting the arse out to tighten the nose in" is not what normally happens with a rwd car. You merely change the attitude of the car and get the "shell" facing the right direction !!

Certain small fwd cars can easily out handle larger more powerful cars so IMO it's down to weight and design. If I was buying a high performance saloon I would obviously go for rwd. If there were such thing as a rwd hot hatch on the market today I doubt it would handle as well, or be as quick on the road, as a small fwd car.

Bear in mind that at Kirkistown the 155 understeered LESS than the Impreza Turbo and due to the lack of additional weight and the braking instability caused by 4wd, the 155 could easily outbrake the Subaru, not to mention every other car on the track!!

I'm not suggesting fwd is better, I'm not that foolish, but in the case of say a BMW 320i and a 155/156, I guarantee the Alfa would be faster across any given piece of tarmac.

When around 200BHP is reached fwd becomes foolish and is merely a hinderance!! All it does is show up defficiencies in chassis design!

AWD cars tend to feel quite numb at the helm and it's hard to have fun without travelling at mental speeds !!

[Junior]

I suppose to be perfectly correct you are right there Ben, I'm still only learning RWD driving style at the moment with the Bimmer we *purchased* off EOB.

Torque Steer has been elimanted to a great extent from FWD Cars ...

AWD V 4WD is a different story .. 4wd is great for 4 wheel drifts sliding in with a quick change of direction of the wheels and leave the diffs to keep her straight as you lay down some power ...

FWD is easier to drive as well .. lift off and it will save you ..

[Mr. Inconspicuous]

Thank you all for the information. I now have a better understanding of this subject.
If anyone would care to add any more info that might have been left out it would be greatly appreciated.

[BeCos]

I think also there are differences between various performance 4wd cars, their layouts and their behaviour.

The Subaru system is mainly front wheel drive with up to 50% torque available at the rear. The car mainly feels like a front wheel drive car, and understeers,until you can get all that torque to the rear for a "slingshot" out of a corner.

The Cosworth Sierras and Escorts were mainly rear wheel drive with a bias of roughly 35% front, 65% rear. They understeered in slow tight corners, but oversteered on nearly everything else allowing the front to "pull" them out of trouble.

Also the Mitsubishi lancer Evo is really a technological "Tour De Force" with various electronics and "Active Yaw Control" continuously varying the front/rear drive.

One thing about a lot of these systems is if you try to do a handbrake turn, you either can't or it will bugger up the 4wd system!!

[Toad]

Teh new 911 turbo is Rwd biased, the front drive only comes into play when you need it to pull the nose around.
Now if I win the lotto that's what I'm buying until I get my GTA

[Justin]

I don't know about the physics involved, but I have driven FWD, AWD and RWD cars and have had semi edge of envelope experiences with each. In a FWD car (Peugot 205 GTi) I found myself backwards in a hedge when the front wheels gave up the unequal struggle between their sidewalls and the massive g forces I was inflicting on them while trying also to control direction (I was young then and fully justified the insurance loading young people get)- up to that point in time I had been unaware of any particular distinction. In an AWD car (Subaru Impreza) the car scornfully reasserted control after I abdicated responsibility and administered last rites to myself (incident covered in previous post). In the Boxster, and in a 3 series, I found myself inexplicably and unintentionally suffering from massive oversteer and travelling sideways at quite modest speeds which would not have challenged a FWD or AWD car. The difference (IMHO) is that in the FWD car, if you lose it, you are a goner, because the wheels delivering direction are also suppposed to be delivering drive, but that makes the loss of directional stability less of a risk (no push/pull effect), in an AWD car, you are going to have to really cane the cobblers off it to lose control and if you do really lose control, it won't be fun, and in a non traction controlled RWD car, you will lose it at a lower speed, even if you aren't playing, if you aren't careful, particularly in the wet. This is because it is easy for the rear wheels to be pushed out if they are momentarily driving in a different direction to the steering direction. But, and this is a big but, (only) if it is dry, you can introduce a little hint of sideways fun in a RWD car and steer with the throttle which is heaps of fun.

In summary (IMHO), FWD cars are safer than RWD cars and the good ones are very nearly as much fun. AWD cars with a RWD bias can be the best compromise. RWD cars are probably the best fun but you develop a healthy respect for wet roads.

[Phil]

Here's some images showing FWD, RWD and AWD. This was taken from Howstuffworks (http://www.howstuffworks.com/)


http://www.howstuffworks.com/gif/differential-fwd.gif

http://www.howstuffworks.com/gif/differential-rwd.gif

http://www.howstuffworks.com/gif/differential-awd.gif

Hope this is of some help.