Are front wheel drive vehicles inherently flawed?

Question

Perhaps similar to reasons for having a better braking system at the front of a vehicle as when braking, the weight shifts to the front, creating a greater downward force on the front wheels that further increases the traction.

When accelerating, the converse seems to be true (?), the weight must shift to the rear, pushing down on the rear wheels. Surely this

1. reduces the traction in general for the front wheels when accelerating
2. Would get only worse the greater the acceleration. I imagine with a rear wheel drive car, the traction would increase with greater acceleration.

I personally haven't driven a rear wheel car yet. However, it feels very uneasy when moving off in a front wheel drive where the weight seems to offload from the front and seem to make the wheels more likely to slip.

Aside from historical reasons, what are some good reasons that FWD cars are widely used today?

Answer 1

Do the math. Wheel slippage isn't a issue unless you are trying to accelerate exceptionally hard.

In practice, front wheel drive cars usually have better accelerating traction because the load on the front wheels is usually higher than on the back wheels. This is because the engine is heavy compared to other components, and when it's in front, there is more load on the front wheels than on the back. Accelerating does change this balance slightly, but in most cases not enough to make the load on the front wheels less than on the back.

Some cars have rear engines, which also feature rear drive for this reason. The old VW Beetle is a classic example. They were known to have good traction in snow, compared to other rear drive cars of the same era.

Answer 2

Most cars have the engine in the front. This is for two main reasons:

1. So that weight is over the front steering wheels and traction is maintained.
2. So that in a front-end collision the kinetic energy of the engine and heavy drive train parts smash into the brick wall (dissipating that energy) as opposed to crushing the passengers between the heavy engine and the brick wall.

A front engine car has superior traction with front wheel drive because there is more weight over the front tires.

Many classic sports cars are still rear wheel drive for the higher off-the-line traction you mentioned and lower weight(front wheel drive is more complex because the same wheels must both power and steer).

Regardless, your front wheels still must steer (You never want to steer with the rear wheels because you will lose traction during braking; a much more severe problem). So if you have enough acceleration for the front wheels to lose traction you will lose steering; again probably more severe than a lower high-end acceleration.

Answer 3

There is no real general answer to this as the drive and handling characteristics will vary from vehicle to vehicle, depending particularly on weight distribution and suspension design.

However the effect of weight transfer tends to be more significant under braking than acceleration as most cars are capable of generating higher braking loads than acceleration.

There are also some very important advantages to FWD cars

• Because there is no prop shaft to take drive to the rear you save space in the cabin. This goes hand in hand with a transverse engine layout (a logical consequence of FWD) and is a big factor in making cars more compact overall and with more usable internal space.
• FWD lends itself well to designing vehicles around a general purpose modular floor-pan. This allows manufacturers to make a lot of different models around one set of running gear and floor (a bit like a truck ladder chassis). While preserving the advantages of monocoque construction.
• For general everyday driving the handling of a FWD is generally safer as loss of grip through under-steer tends to me more progressive than overseer through loss of traction at the rear wheels and easier to correct as well as less likely to provoke a dangerously inappropriate reaction in an inexperienced driver.
• Driven steering wheels can improve handling in certain types of corner as the drive is pulling the vehicle in the desired direction as opposed to RWD which is acting at some tangent to the steering direction.
• Having the engine weight over the drive wheels improves traction in general driving, especially in slippery conditions. FWD cars generally handle better in snow, ice and mud.

RWD is generally only an advantage in cars with a very high power to weight ratio, especially mid engined cars where weight distribution is not biased towards the front. The main reason for this is that when cars are expected to handle steering and traction/braking loads simultaneously.

It is also worth noting that this only really matters in driving conditions where tyres are approaching the limit of grip eg in racing which is not what the majority of production cars are designed for.

Also bear in mind that up untill the point where the drive wheels actually lose traction/grip it make no difference and this is generally a lot more manageable (especially for non-expert drivers) in a FWD car where you just don't accelerate quite as quickly as opposed to a RWD car where it can end up swapping ends.

In summary for the vast majority of consumer cars FWD is just plain better and there are plenty of fairly large cars with pretty decent performance which are FWD.

Once you get into the realms of out and out sports cars things are a bit different but then again most proper sports cars are mid-engined in any case (note also that most 'front engined' performance cars have the mass of the engine well behind the front axle.

If anything the trend has been for larger and more powerful card to be FWD as time has gone on.

It is also worth noting that the Mini, one of the first mass produced FWD cars was extremely successful in rallying in the 1960s.

Answer 4

I think a point that has been passed over and really should be considered isn't related to the technical merits of FWD verses RWD but is economic. The emergence of the modern FWD automobile is directly related to the auto industry reducing the auto unit cost. It's just less expensive in materials, time and labor for the auto manufactures to produce FWD cars. The FWD configuration consists of engine, transmission, differential and drive shafts assembled into a single unit. It's typically installed in the vehicle with four bolts by one individual. It's analogous to the emergence of the uni-body construction eliminating the frame as a separate assembly. There are technical reasons for doing this but the economic aspects can't be overlooked.

Answer 5

FWD cars were created to save space, and create dealer income. In years past most people could and did service most of their vehicle. The industry didn't want people to service their own vehicles, so they decided to make them non-serviceable by the general public. Without specialized equipment much of the FWD car is non-serviceable by consumers. They are throw away vehicles. That's why you do not see many of them after they get much age on them. Their drive train is made of thin aluminum castings and are NOT nearly as durable as cast iron that is still used in most rear wheel drive cars and trucks today. Real Sports cars use rear wheel drive because FWD cars do not handle well if one wheel breaks traction. That includes driving on ice and snow. Handling and performance is what makes a sports car. If you know how to drive, a RWD vehicle is very unlikely to swap ends as was stated. It's to bad that so many people would rather open their wallet, rather than their toolbox. Or listen to people who have never worked on anything.

Answer 6

Traction is one thing. Understeer is another thing. Then there is torque steer. Most folks go buy a car and will maintain their car as it was when manufactured. That car was designed for optimal daily driving and for typical daily drivers. You likely won’t notice the understeer or torque steer in your day-to-day. More powerful FWD or modded FWD car owners will likely argue in favor of RWD cars as being the better of the two options.

Answer 7

midnightBlue - A vehicle is a power tool, and as such should be selected based on the intended application and operating conditions. A mismatch would suggest a "flawed" choice, but not an "inherently flawed" design. Also, your presumptive modelling of weight distribution would be greatly improved by furthering your understanding of chassis dynamics and how vehicle suspension systems operate.

That being said, here are my top 3 inherent detractors to FWD/transaxle vehicles.

1) They have a tendency to UNDERSTEER. Concentrating such a high percent of the vehicle's overall weight in the front causes its mass to resist changes in direction. You turn left but the car wants to continue going straight. 2) Due to spatial constraints they almost exclusively use unequal length drive axleshafts, inducing torque steer under heavy throttle. This causes a sensation that can feel like slipping or pulling to the left or right (towards the side with the shorter axle). 3) The CV axle boots have less service life, due to constant angular movement from steering input. One will rupture and tear every 60K miles, at least.

Any questions? Shoot!