RWD versus FWD

[Satch]

An old chestnut.

Per BMW (no vested interest of course!):

Acceleration
Accelerate with near full power in a front-wheel drive car and you'll quickly notice the resulting effect of rearward weight shift. The front tyres will likely lose traction and spin – even on clean, dry road. By contrast, hard acceleration in rear-wheel drive cars will tend to increases the rear wheel grip on good road surface because of the rearward weight shift.

Braking
Stopping ability is enhanced by the superior weight distribution of RWD. With the rear wheels carrying a greater percentage of the car's weight load than on a front-wheel drive car, they can apply more braking force to the road and help shorten stopping distances. Since RWD contributes to even tyre wear, it is more likely that tyres on a RWD car will have greater tread depth. Unless tyres on a FWD car are rotated religiously, the fronts may become worn and less effective in braking.

Responsive Cornering
Near equal weight distribution helps give front and rear wheels more balanced traction. This balance gives neutral handling characteristics that make cornering maneuvers easier. Rear-wheel drive's more equal weight distribution also aids handling agility through a lower moment of inertia. FWD cars usually have higher moments of inertia, contributing to understeer and sluggishness in cornering. As a result, RWD cars feel more responsive, lighter, and more nimble.


Balanced Force Distribution
With FWD, both steering and propulsion forces tax the front tyres' slip-resistance during cornering. That's part of the reason why FWD cars tend to understeer, changing directions less quickly than the turning angle of the front wheels. Since RWD separates the tasks of cornering (front wheels) and propulsion (rear wheels), it more equally distributes the traction-threatening forces to all four wheels.

Torque Steering
Torque steering is a negative side-effect of FWD caused by the delivery of power to the wheels that steer the car, especially if teh vehicle has drive shafts on unequal length. During acceleration in a curve or from a standstill, the force of torque steering can pose a hazard by changing the direction of the front wheels unless the driver is alert and can exert counteractive force on the steering wheel. RWD does not exhibit torque effect because the engine is isolated from the steering gear.

Longer Wheelbase
RWD allows a longer wheelbase and a more forward positioning of the front wheels. The longer wheelbase provides better handling while the forward position of the wheels reduces the possibility of the front spoiler scraping on dips.



No CV Joints
FWD cars have four CV (constant velocity) joints connecting the engine to the front wheels. In comparison, RWD cars use universal joints which wear out much slower than CV joints.



Summary
RWD pros:
Fore-aft weight distribution more balanced. Braking performance enhanced. Tire wear more even. Cornering easier, more responsive. Lighter than AWD configuration for better acceleration and cornering performance and better fuel-efficiency. Better hard acceleration performance on good surfaces than with FWD. Better cornering ability because steering and propulsion are applied at separate axles. Greater agility because of lower resistance to changes in direction (lower moment of inertia). Longer wheelbase for smoother ride. Absence of torque steering effect common with FWD. No CV joints to replace.

FWD pros:
Good traction during mild acceleration on slippery surfaces. Lighter weight helps fuel-efficiency. Interior room enhanced by lack of longitudinal driveshaft. Less expensive to manufacture.

AWD pros:
Traction enhanced on all road surfaces under all weather conditions. Faster acceleration "off the line" due to all wheels driving. Better road grip during cornering in adverse weather or slippery road conditions.

Oddly they do not mention the important perception effect caused by FWD cars wanting to turn around their centre of mass which is usually forward of the driver. In many RWD cars this, and the actual centre of turning thanks to a longer wheelbase, is much closer to where the driver sits so the effect is for a given lateral G force a RWD car will tend to be felt as rotating around the driver (which feels quite natural) whereas in Fwd cars the driver tends to get more of a sense of sideways movement around a turning point forward of the seating position. Often hard for drivers to put in words, but held to be one reason why many people just feel more comfortable with a RWD car

 

[janner]

Front wheels are for steering, rear wheels are for driving...anything else is for shopping.

 

[W210 Fan]

Rear wheel drive cars also have better turning circles as their front wheels can be turned to a greater anglr because there are no drive shafts at the front stopping the angle of turn.

Longer wheelbase gives better high speed stbility and more warning of rear end breakaway, short wheelbase cars will handle better through twisty parts but tend to "snap" with less warning.

AWD will give better traction but cars have to rolled from the start under hard acceleration because all the revs will cook the clutch.

thats my 2 pence worth

 

[RichieRuss2000]

Agreed RWD or AWD is dynamically better athough sometimes a FWD car comes out that handles very well... note Mk 1 Golf GTI or 205 GTI...

 

[jeremytaylor]

Agreed RWD or AWD is dynamically better athough sometimes a FWD car comes out that handles very well... note Mk 1 Golf GTI or 205 GTI...

They do handle very well, but they are pretty low powered compared to today's hot hatches. Just look at the reported torque steer on the Astra VXR, and note that the Golf R32 is 4x4, along with other performance VAG cars, rather than fwd like the run of the mill models.

My C270 was my first RWD since a Hilman Hunter over 20 years ago. IMHO FWD is best for smaller, lower powered cars, but RWD is best for bigger and/or performance cars. 4x4 on cars is, I think, a bit of an unecessary compromise, only practised by those who generally otherwise produce FWD.

 

[Howard]

Agreed RWD or AWD is dynamically better athough sometimes a FWD car comes out that handles very well... note Mk 1 Golf GTI or 205 GTI...

CRX VTEC (wedge shaped one, not the hairdresser one with the lift off roof) also comes to mind !

 

[prprandall51]

Whilst I am also a RWD fan, there are plus points for FWD (that justified its development in the first place). Off the top of my head:

Increased cabin room - no large gearbox intrusion between the front seats or propeller shaft tunnel along the length of the car.

Substantially increased grip in very slippery conditions (with all of the engine's weight over the driven wheels).

Substantially safer handling in very slippery conditions (no outrageous fishtailing, unfortunately - aah! happy days in a Capri 2.8 on an icy car park!).

Better front end packaging (for smaller engine capacities) - allows the engine to be mounted east-west, reducing the bonnet line.

Although it wasn't the first FWD car, I believe the above reasons (well the packaging ones, anyway) were what motivated Issigonis to make the Mini FWD.

Can anyone think of any others?

Philip

 

[prprandall51]

And, of course, safer handling generally. Understeer is fixed mostly by lifting off the throttle, which is what people do naturally when a car starts to slide. So FWD cars are naturally self-fixing in a slide. RWD cars (before the advent of ESP et al) required precise amounts of opposite lock to catch the slide. Unless you are born in Finland or Sweden, this is a difficult skill to acquire.

Philip

PS: Peugeot 205 excepted. Brilliant handling until it let go, at which point you were merely along for the ride (usually viewed through the passenger door window) until something solid got in the way.

 

[BTB 500]

Substantially safer handling in very slippery conditions (no outrageous fishtailing, unfortunately - aah! happy days in a Capri 2.8 on an icy car park!).

You didn't need a 2.8 V6 or ice - as a novice driver I spun my puny 1100cc Vauxhall Viva several times (once in a damp Safeway car park doing all of 5 mph!).

 

[prprandall51]

You didn't need a 2.8 V6 or ice - as a novice driver I spun my puny 1100cc Vauxhall Viva several times (once in a damp Safeway car park doing all of 5 mph!).

An HB? Now there's a real example of "they don't make them like they used to"!

 

[BTB 500]

An HB?

Sadly no, it was an HC (although it had an HB diff. in it!).

 

[jeremytaylor]

Whilst I am also a RWD fan, there are plus points for FWD (that justified its development in the first place). Off the top of my head:

Substantially increased grip in very slippery conditions (with all of the engine's weight over the driven wheels).

Philip

Last winter on a trip to the Swiss Alps I was amazed at how many (FWD)2CVs were still trundling around in what is after all a very affluent country.

Despite having no thermal insulation (canvas roof, drafty doors etc.) they are ideal cars for snowy conditions - not only is all the weight over the front wheels but the tyres are VERY skinny, so the weight of the car cuts through the snow and grips the road below.

 

[W210 Fan]

And, of course, safer handling generally. Understeer is fixed mostly by lifting off the throttle, which is what people do naturally when a car starts to slide. So FWD cars are naturally self-fixing in a slide. RWD cars (before the advent of ESP et al) required precise amounts of opposite lock to catch the slide. Unless you are born in Finland or Sweden, this is a difficult skill to acquire.

Philip

PS: Peugeot 205 excepted. Brilliant handling until it let go, at which point you were merely along for the ride (usually viewed through the passenger door window) until something solid got in the way.

I have just thrashed a mates 309 GTI (same car, bit longer) and it was very fun, very very fun, I know a lot of people in motorsport who still drive 205 GTI`s in varian states of tuning and track day setups and they swear by them.

 

[Bobby Dazzler]

Just look at the reported torque steer on the Astra VXR, and note that the Golf R32 is 4x4, along with other performance VAG cars, rather than fwd like the run of the mill models.

Torque steer is an intrinsic part of the charm of driving a high-powered 4WD!!

I have a Astra Coupe Turbo, the engine from which has evolved into the Astra VXR engine, with main differences being a more aggressive turbo and different map to make the most of the turbo - gives an extra 30bhp.

I have ever experienced any torque steer at all. The suspension on the new VXR is a lot more aggressive than mine, and it does have a touch more power, but I'm sure it's not that bad!!

I have a few friends pushing 300bhp plus in Astras, and whilst torque steer is there, it's not uncontrollable. There are lots of 280bhp cars, and there are two 340bhp cars about to be released by different tuners. Mental in a FWD car!!

 

[Bobby Dazzler]

Last winter on a trip to the Swiss Alps I was amazed at how many (FWD)2CVs were still trundling around in what is after all a very affluent country.

Despite having no thermal insulation (canvas roof, drafty doors etc.) they are ideal cars for snowy conditions - not only is all the weight over the front wheels but the tyres are VERY skinny, so the weight of the car cuts through the snow and grips the road below.

Visited a quarry before Christmas. Apparently very old Renault 4 were the vehicles of choice in quarries until very recently when they switched to Land Cruisers.

Spoke to a chap who'd worked in the quarry over 40 years, and he said the Renault 4 would go anywhere in any weather, regardless of the incline and the snow/ice/mud on the ground. He described them as climbing better than a mountain goat!!

He did say that the staff were happier to see them go when they saw what happens when a dumper with a 100ton payload reverses over one - did it for a safety video when they were being decommissioned!! That said I can't imagine a Land Cruiser would put up much of a fight!!