Pros and Cons of front and rear wheel drives
 

Dear friends,

Could you please list the pros and cons of front and rear wheel drives (basically a comparison between the 2 systems). Is it true
that ALL Mercedes cars (except some 4-wheel drive) have REAR wheel drive?

A newbie question: does front wheel drive have a differential like
that of real wheel drive?

Thank you in advance.

Eric

Eric,

I'll bite. To answer your MB question first - all MB's sold in the US with the exception of the ML and G series SUV's and some 4matic sedans, are rear wheel drive. I do believe that there are some small A series vehicles sold in europe that are front drivers but I may be wrong. (Can one of our European members answer this?)

As for the advantages or preference of one over the other - that is mostly a personal question. Many people who grew up driving rear wheel drive cars like myself much prefer them. Personally, I believe that if you take the time to understand how the vehicle behaves under different circumstances rear wheel drive is far superior. It offers much more predictible emergency handling, better traction on acceleration, and no interference between the acceleration and steering.

That said, I have come to realize that for the vast majority of people on American roads who aren't as keenly interested in driving, front wheel drive is less likely to cause problems. It provides 'easier' traction under most situations and is somewhat more forgiving of driver inattention and lack of care.

I think it is not an accident that most of the high performance cars the world over - MB, BMW, Jaguar, Lexus (at least the GS and LS) - are all rear drivers. These are all cars that are consistantly noted as having excellent driving characteristics and handeling.

jlc

With a high performance car, when you gun it the weight is shifted off of the front axle and onto the rear. This can lead to wheel hop in a FWD which is known to do some serious damage. Where as with a RWD, with a decent setup you would get the traction to launch.

In a more practical light though,
RWDs oversteer (rear comes loose in hard turn)
FWDs understeer (front tire 'plows' and fights the turn)
RWDs are dangerous on ice if you have to stay on the gas because the tires can come out from under you.
FWD are safer on ice, but if you hit the gas while turning you may not turn.

Jeff M.

my 2 cents
 

My experience has been primarily with rear wheel drive vehicles, although thru the years I have had 2 front drivers, a 94 escort gt, and a 97 taurus sho. For my driving style, the rear wheel drives are much more predictable, and I find them easier to control when the unexpected happens. When the unexpected happens, the initial reaction is to let off the throttle at which time a rear wheel drive slows down from the back of the car, essentially trying to keep the car straight (not always, but usually). A front driver slows down from the front, and the back end of the car sometimes trys to pivot around. Where I found this phenomenon was on uneven hard pack snow....or on highways that had snow patches... and some event happened requiring you to slow down suddenly. If a rear wheel drive steps sideways, you can control the slide with judicious application of the throttle, steer and motor on. I haven't found that (for me) same level of control (and predictability)on a front wheel drive.
As the other gentlemen indicated, front or rear wheel drive is primarily a personal choice based on driving style, cost of repairs/upkeep, and whether or not you like the vehicle.

Manufacturing Costs
 

FWD cars allow the drive train assembly to be built on a seperate assembly line, and installed as a single unit into the car body, allowing major cost savings for the manufacturer. They also save a bit of weight on the final product, which helps the companies with their product fuel efficiency and pollution requirements.

Good for them, but I much prefer RWD. My experience with FWD cars has been decreased brake and tire life in front from the poor weight distribution, and added upkeep in the form of CV joint replacement costs. I have owned 2 FWD, and won't be buying a third one!

ericnguyen,

Yes, it's a personal decision........

BUT one thing you can't get away from: FWD cars HAVE NO HANDLING REPERTOIRE !

They understeer, that's all.

Properly sorted RWD cars (like our MBs) have Understeer, neutral and Oversteer, all at the prod of the accelerator.

If you want to enjoy your driving, there is only one choice.:D

The main advantage of RWD is that the front tires do nothing but steer. Think of traction as a percentage. Ask your front tires to do two things (accelerate AND steer) and they get to 100% of available traction quick.

Look at the new crop of performance cars. Manufacturers are realizing their folly in pushing 250+hp into a FWD application. It sucks. Nissan is quickly changing all their high power chassis' into RWD. Even Honda is talking about RWD for their higher HP applications. They "broke the mold" already with the S2000 and NSX, so a RWD sedan line seems plausible.

RWD has some disadvantages. It "feels" different. For an unskilled driver, understeer plow feels safe. FWD cars naturally understeer, and it requires little tuning effort for makers to have an understeering FWD car. This conditioning makes RWD seem unsafe. RWD cars have less weight over their drive wheels. This makes acceleration traction in LOW TRACTION surfaces poorer than FWD.

However, a FWD car transfers weight away from it's drive wheels when dry pavement presents itself.

The main thing I don't like about FWD is drop-throttle oversteer. Oversteer is not a bad thing. Controlling a RWD on snow can be easy, and fun. Controlled four wheel drifts and moderate oversteer are not the out-of-control condition that most people think. However, FWD cars are trickier to drive at more than a slow pace on snow/ice. Understeer is very hard to correct, as it requires you to do the opposite to what you've been taught: turn more by steering less. You must turn the wheel stright to regain traction (remember, the front tires are trying to do two things at once, you've got to give them time off from one of their jobs) and brake, slowing the forward progress before you can try to alter the car's path again.

People 99.99% of the time turn the steering wheel MORE when plowing. Wrong. Then, realizing their mistake, they take their foot off the gas and stab for the brake. A FWD car is usually carrying only 35% of it's weight in the back. The rear tires unload dramatically, and completely lose traction. That 35% now acts as a pendulum. Oversteer! Lots of it, and very difficult to control.

AWD cars suffer some of the same problems as FWD, but have much less abrupt handling. It's a pretty good compromise between the "feel problem" of RWD and the potentially unsafe abrupt handling of FWD. Personally, I still prefer RWD.

I'm a RWD fan, but for all those saying FWD cars can't handle, drive a /good/ european hot hatch, say a VW Polo G40 or Peugeot 205 GTi. The way the cars just pull out of corners is incredible.

in addition to what may already have been mentioned:

* FWD introduces torque steer; some design and engineering effort is required to cancel this out.

* RWD allows the front wheels to be free from torque steer, and other associated effects of the driveshaft, resulting in potentially better steering feel and precision. That is the reason why BMWs have the best steering feel around. And steering feel and precision is one of the characteristics that inspires driver confidence.

* the unsprung mass of a RWD car's front wheels/suspension can potentially be made lower than that of a FWD car, because of the absence of the driveshaft and constant-velocity (CV) joint. This results in better frontend roadholding of a RWD car.

* the steering angle in a FWD car is invariably limited by the maximum angle of the CV joint. As such, the max steering angles of RWD cars are typically bigger that those of FWD cars.

JCE hit the MAIN advantage of FWD right square on the nose! The biggest advantage is to the manufacturer. That nice, neat package that contains, transmission, engine and drive axle comes down the line and drops right into place, saving beaucoup dollars for the manufacturers. They have done a great job over the years convincing many drivers that FWD somehow makes a car superior.

If I can think of a pro for the DRIVER of a FWD car, I'll let you know.

Have a great day,

Traction in slippery conditions is no contest between our '90 Accord and '91 190E. The Honda, driven carefully, will go through almost anything if it won't bottom out. The Merc likes it bone dry, no traction control, etc. On the other hand, our 5 ton RWD m'home with 4 of those on the big-lug duallies in the back can motor figure-8's around either on ice or through the fluffy - or most anything else on the road, regardless of drive geometry.

My late '88 Integra could out-handle either on a twisty, uneven road, and inspired confidence driven fast. Still, both FWD's had noticeable understeer under all conditions, and feel less nimble in tight turns than the 190E. Both bottom at the nose entering parking lots, and at times require 3-point maneuvers to park once in. The Merc has no problem.

Bottom line, though - I wouldn't make a decision on any car based on drive geometry - good choices come in both flavors for almost any criteria - as do bad. I wouldn't own a Benz because it is RWD. I would because it is a Benz.

Steve

Thank you very all your precious comments and opinions.

You guys rock!

Eric

How about...
 

...the FWD Saabs? I agree that generally FWD is not as performance-oriented as RWD, but what about Saabs? They've always been FWD and they are fairly good cars?

I know an indie mechanic that ears a VERY good living servicing Saabs. Saab-nuts swear by them, but they are not even close to Mercedes.

I've driven a few, and they're passable.

Guys,

Couldn't resist adding another 2 cents worth........

I'm prepared to say here that NO FWD CAR CAN BE A SPORTS CAR (at least not by any sane definition)

The amount of G that a FWD car can pull may be very impressive, but cornering is not handling.

If you go into a corner in a FWD car, it will understeer. Press a bit harder and it will understeer more. You have run out of options (pulling the handbrake is not an option on a public road). With a RWD car you have options: so long as you have sufficient power, you can neutralise the understeer or even have some oversteer fun.

This is what sets a sports car apart from a car which just looks sporting. It's nothing to do with 2 seats and a rag-top........

The old saying is worth repeating here: "cornering is what gets you there, but handling is what makes you enjoy the journey"


On the subject of Saabs; they are quite well made and seem to resist rust well. To call them sporting is completely misunderstand the definition of sporting.

All modern Saabs are just Opel Vectras vith a different body and a higher profit margin.

I'm sure I don't have to spell-out just how well an Opel Vectra handles.;)

As a parting shot, 4WD cars fall into the same dismal handling category IMHO, with the exception of those with a fixed torque-split, biased heavily to the rear. These include all the Ford 4WD saloons Sierra and Escort Cosworth, Lancia Integrale and of course the daddy of them all, Jensen FF.

That should provoke a bit of discussion ;)