Cosworth427

This is spawned off from the BMW 3 series thread made by tiggers. There is some misconceptions about FWD that should be cleared up and hopefully help some of you understand cars further. Here are some extracts regarding FWD and RWD from a member of another car enthusiasts board.


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"I never denied the fact that FWD cars can perform as well as RWD cars. But they have to COMPENSATE for the fact that they're front-wheel drive."


Actually, in most cases, they are compensating for the fact that the factory set them up as economy cars, by using soft shocks and small swaybars. Again, look at the last era of RWD economy cars to see that in action (from the original 510s and Corollas, to Pintos, Vegas, Chevettes, etc). Those cars are not set up very well from the factory either, and if you want to make them performance cars, you have to compensate for the fact that they were economy cars by changing the springs, etc. In handling situations, they usually had to compensate for the fact that they were front weight biased, vs mid engine, which is the ideal handling setup. JUST being RWD or FWD isn't the issue, otherwise all stock RWD cars would outperform ALL stock FWD cars.



"As far as he "weight transfer" goal of the suspention arms etc, you cannot defy the laws of physics. You cannot make the weight shift to the front wheels upon forward acceleration. "


You are kidding, right? You know that the physics of accelleration is identical whether it's forward accelleration, backwards acelleration or lateral alcelleration, right? Mass in motion. If you can transfer weight back to the opposite side with swaybars under lateral accelleration, you can transfer it forward under forward accelleration, and rearward under braking. In fact, that pretty much what anti-dive suspension does for braking. And FWD drag racers do the same to transfer weight forward under forward accelleration.


"Why don't you see any front-wheel drive BMWs or Porsches if it "doesn't matter"? Why are almost none of the performance models of the major manufacturers front-wheel drive?"


You're confusing cause and effect. The very FIRST car to bear the Porsche name was FWD. it was also electric, but that doesn't matter.
The Porsche BRAND started with the 356, which was originally concieved as a MID ENGINE car, which is teh ideal layout for handling. But it was based on the VW Beetle, a rugged, cheap car that had zero to do with performance. So the 356 became rear engine, RWD (though the race cars remained mid engine: as in 550 Spyder..)

Since Porsche's were designed to be able to compete in the top levels of motorsports, and in the late '40s and early '50s, there was very little knowledge of how to make FWD package very well in a small car, then they were RWD. They have stayed that way out of tradition. Why do you think they've retained rear engines? Not the best layout, but traditional for Porsche. they did go with water cooled front engine cars, with the engines set back for balance. Not condusive to FWD.

BMW is big on tradition, too. Look at the stink raised if they even LOOK slightly different than what BMW fans are used to... But in head to head competition, the Integra Type R runs with and beats the same class BMW 3 series, so obviously RWD isn't helping the "ultimate Driving machine" on the track.



"If it "doesn't matter" then at least 1/3 of the cars on this website would be front-wheel drive. And when you eliminate Civics, Integras, Neons, the Focus, and all other commuter cars (the performance versions there of), you're hard pressed to find even a couple."


Ever see a rear or mid engine car with only FWD? it's a packaging nightmare. Mid engine is know to be the best overall BALABCE for handling, which is why the ultimate race cars and ultimate road cars tend to have that layout (whether they are rear mid engine or front mid engine, like the Viper). But in all the cases you mention, are their suspensions tuned for soft ride and lots of travel? No. In order to make a RWD car work lik those cars, you HAVE TO CHANGE TEH SUSPENSION TO DEAL WITH THE FORCES OF HIGH SPEED USE. i.e. you have to compensate for stock tuning to make a RWD sedan or coupe work like an ultimate sports car.

And you have to tune a front engine RWD car different than a mid engine RWD car or a rear engine RWD car. In all cases, you aren't compensating or making changes due to drive wheels, but due to engine placement. And in all cases, it's different than a road car, so complaining about tuning a FWD car different yet is moot.

You'd have to do it with FWD, which is why the top FWD road racers chassis are set up different than the road car versions. But again, AS I'VE SAID, at the top levels of performance, you need mid engine layouts, and to package a mid engine layout and a driver (and regulated room for a passenger) you have to leave the car RWD.

No one has TRIED to make an ultimate supercar in FWD, I don't believe. Just like no one had tried to make an ultimate FWD drag racer until recently. But you'll notice that which was considered impossible just a few short years ago, is relatively common today.

Steve Whitehorn

iTrader: (13)

Thanks for that. That was an interesting read
Best wishes
Steve

chrisp

I thought FWD + RWD = AWD

MGJohn

There are other benefits to the Front Wheel Drive concept. As most cars steer with the front wheels power applied to them should by design be delivered in the same steered direction. That must be beneficial, particularly in poorer road conditions for the average ordinary car and its driver. There's another rarely mentioned FWD plus which comes into play and hear I speak from direct experience. Consider whereby most of the weight in FWD cars is on the front driven wheels than with the more 'perfect' front engine, rear driven wheels balanced arrangement .. no names no wossname ... With MORE weight over the front wheels in a conventional ordinary FWD concept, with that extra weight penetration on a rain soaked road there's obviously less chance of reaching the aquaplaning threshold than with a more balanced arrangement. Rear or mid-engined RWD cars are more likely to lose front wheel grip with a lower aquaplaning threshold ... all other things being equal. Won't go into details, but, some years ago, in heavy rain conditions when travelling in fast convoy with other cars, I was VERY glad I was in a pure FWD car ......

MGJohn

>>"As far as he "weight transfer" goal of the suspention arms etc, you cannot defy the laws of physics. You cannot make the weight shift to the front wheels upon forward acceleration. "<<

Older BMW motorcycless had forks (earles?) which worked in such a way that the front of the machine RAISED under braking.....

Funny thing Weight transfer..... Ever see a motor cycle stand on its front wheel alone with rear wheel well clear of the road under heavy braking ... under those conditions, that equals 100%+ weight on the front wheel only. I once jumped into auto-gearbox car, forgot and went to change gear manually and used my left foot on the large servo brake pedal with the same force as I would to depress the heavy clutch pedal I was used to. I swear I think that car stood briefly on its front wheels only ...

cletterridge

Can't agree more that mid-engine rear wheel drive is the ultimate set up.

However, the idea that FWD cars suffer no problems at all from weight transfer under acceleration is, to be frank, pants. I've driven some race prepared FWD cars round Knockhill and the one thing they drilled into us at the briefing was the problem of weight transfer under acceleration (weight goes to the rear) and braking (to the front). The British Touring Cars are another fine example. No-one can deny that these are anything less than 100% optimised for racing within the rules, but the BMW (RWD) always makes up 2-3 places from its grid slot at the start BECAUSE it is RWD and with weight transfer, the back (driven) wheels can just dig in and grip, while the FWD boys are busy feathering their clutches and accelerators and losing places.

FWD: Good for making cheap cars with plenty room in the back. Not so good for handling.

tiggers

Agreee on the traction front up to a point, but handling once the car is moving is not so simple. Some of the touring cars are good example of race prepared FWD vehicles and you've never seen any RWD manufacturer walking all over them - I know some of this may be down to levels of investment etc. etc., but you see what I'm saying.

As for road cars well there are some great handling FWD cars such as the Integra Type R. I currently drive an Integra and can honestly say that it can pretty much hold it's own in the handling department to many other RWD/4WD vehicles as long as you know how to drive it. Sure traction from a standing start is not good compared to a Scoob, but that isn't the whole story is it?

Also a lot of it comes down to driver competence and experience. In the last two years I have been lucky enough to own the Integra, a Scoob and an Elise. In the dry I'd take the Elise followed by the Integra followed by the Scoob, but in the wet the positions are reversed. The Elise was a handful in the wet (with me at the wheel anyway) and frankly had the ability to give me a scare which is not something I want on a public road.

None of this offers any conclusive proof about RWD/4WD/FWD, but simply illustrates the point that FWD can be damned good performance wise when engineered correctly. The fact that most "shopping trollies" are FWD and engineered to a completely different set of ideals simply blunts most enthusiast's opinion of FWD - it does not mean there is anything inherently wrong with it.

Regards,

tiggers.

ALi-B

iTrader: (1)

While everone is on about the weight on driven wheels etc. May I point out that the current BMW 3 series boast that it has "near 50/50 weight distribution" So its hardly you typical old fashion front-engine RWD set-up is it?

I'm just quoting here, so don't burn me

edited to add BMW..just incase you did'nt know what I was on about

[Edited by ALi-B - 9/23/2003 11:22:19 PM]

BOB.T

I agree that some FWD cars can live with some RWD and I agree that mid engined is the ideal but the rest is a crock of sh*t!

WTF is the weight transfer bit all about?! If I'm reading it correctly, it sounds like, said car has front to rear sway bars...eh?

ALi-B

iTrader: (1)

I could make a point on Cosworths explaination of FWD to RWD to mid engined set-up. It's just not a question of balance...
It's the polar moment of inertia. Mid engined is lower than that of front engined RWD etc.

In English...all the weight in the middle..Not just Balanced, basically gives better handling and steering response

edited...quote was irrelevant..whoops

[Edited by ALi-B - 9/23/2003 11:53:26 PM]

Paulo P

iTrader: (42)

I can't be fooked to read all that Rear wheel drive rules

cletterridge

Exactly! That's just why mid engined is best, NOT because it helps give a 50:50 balance (actually for racing 55rear:45front is often considered best as this evens to 50:50 on braking to have maximum possible grip, then 60:40 on acceleration for maximum traction at the rear).

The reason most Ferraris, Lamborghinis, Lotuses etc and all F1, F3 etc are mid-engined is to keep polar moment of inertia down. Why? So you can change direction as fast as possible. To explain this, imagine holding a bar with really heavy weights right at the ends, and imagine how difficult it is to twist round to face a different direction. Now move the weights right to the centre, and you can turn around to face a new direction much quicker. When you've got a 150kg lump of engine to put somewhere, the last place you want it is miles out in front of the centre of turning (in terms of steering response anyway).

However, this handling benefit is also what makes MR cars so twitchy over other types - if you start to slide it, it'll go much quicker to full spin for the same reasons. So, better layout for responsiveness, but more difficult (read rewarding!) to drive.

Merc_Cosworth

Too much generalisation here chaps.

Weight transfer is important, but only a very small part of the story.

There are plenty more things to take into consideration as to the effects on handling.

Like: RWD has to contend with being pushed through a corner, whilst FWD is pulled. Both have their relative merits and drawbacks according to the situation you place them in.

Comparing a Type-R Honda to a BMW three series isn't a fair fight. The Type-R is lighter, shorter geared, revvier and more attuned to a track environment than any modern BMW.

A BMW with its legendary 50:50 weight distribution isn't as great as the marketing hype created around it. 50:50 split only ensures one thing - it'll be a 50% chance that either end will break (I've had 4 E36 and E4? and driven them to and beyond the limit - I've always found it to be a lottery as to which end goes)

At least with a front bias RWD you can make an educated guess as to how it'll drive - plough on understeer if you go in too quick, and power oversteer if you jump on the gas too early.

But then this in itself can be changed by the addition of some fairly basic mechanical interference. LSD, Passive Rear Steer, geometry changes, different tyre sizes - all to influence, or change the characteristics of the car.

The geometry of the front and rear suspension can effect the handling to such a degree that it becomes irrelevant as to the layout and distribution of weight.

For years, Vauxhall/Opel saddled themselves with ET49mm offset on their FWD cars. Doesn't sound much does it? The sole reason for ET49mm offset was to induce 'Negative Scrub' as a way to prevent the wheels locking under braking and turning. This system works very well at the purpose it was designed for - but the resultant changes in suspension design to cope with the stress on other components culminated in a very strange front wishbone design. The rear bush on the front wishbone allows for passive flex in the system that negative scrub creates - which completely ***** up the handling on FWD Vauxhalls as the front geometry is never totally set.

The grip it gives is impressive, as the passive change in the geometry gives the tyre contact patch that little bit extra leeway to maintain optimum contact - but the simultaneously, the geometry changes creates an unpredictable slush of feedback.

Its doesn't matter if its FWD, 4WD or otherwise (Calibra Turbo as an example here) it just handles badly.

Which leads nicely onto tyre contact patch.

All suspension systems on road cars are inherently comprimised when compared with a track car for a reason. Driveability. An ideal suspension system will have no flex in it other than in the required plane of travel - giving a predictable and linear response to input on it - i.e. up and down for a wishbone. This works great on billard smooth roads where you don't need to go round corners.

As soon as the steering wheels turn then it screws this perfect equation up.

Camber, Castor, Toe, Scrub, Offset et al, all contribute to the steering characteristics of the vehicle, and to maintaining the optimum tyre contact patch.

This contact patch is the most important part of maintaining grip when you're driving at moderate speeds - which is how 90% of cars are driven 99% of the time.

How manufacturers configure geometry is dependant on many things, all of them a comprimise - average driver profile, tyre size, wheel size, steering rack ratio, PAS or no PAS, Spring and Shock characteristics, ride height, vehicle weight, driven wheels, steering wheels, ad infinatum.

Then the car has to engineered to be predicatable, stable at all speeds, easy to control, and kind on components. So everything is comprimised.

A theoritically ideal handling car will have 50:50 weight, rose jointed everything, no bodyroll, no passive geometry changes, low ride height, no body roll and neutral offset, scrub, camber etc.

In reality, any car set up like this will inherently handle like **** - it would be unpredictable, twitchy, unstable, and generally nasty to drive.

These cars exist (more or less) - they're called F1 cars.

And they need supermen to drive them flat out, need masses of downforce to keep them on the deck, and are totally irrelevant.

There is no natural conclusion as to the best layout and configuration of driven wheels and engine location - it depends on so many factors that it's not worth arguing about.

If that random collection makes any sense then great, if not - i've written it at work over the last half hour and I know what I'm going on about!

tiggers

Be careful - the BMW boys won't like you for that comment.

Another reason it's not a fair comparison is that Honda's variable timing doesn't go wrong Sorry I'm being naughty now

For the record I wasn't comparing a Honda Type R to a 3 series (God forbid ), I was simply using the Type R to illustrate that FWD cars can be made to handle rather well. I chose a Type R for the simple reason I have experience of one.

Regards,

tiggers.

Merc_Cosworth

No offence meant to the BMW fraternity

Having driven both E30, E36 and current M3 on the track, and Integra and Civic Type-R on the same track - there's no escaping the fact that the Type-R range is more focused on track driving.

I know which one I'd rather blast across Germany in though - horses for courses.

ALi-B

iTrader: (1)

If we're talking about suspension now Merc_Cosworth, yes your completely right EVERY SINGLE mass manufactured road-going car have very compromised suspension.

Mc-pherson struts for example are most certainly not the best type of front suspension, ok most car don't use the "true" mc-pherson design like the old VW Polo - which if you ever driven one...do not handle But it's not designed to, it's only designed for normal driving at normal speeds, comfort, space and cost. Ok the set-up can be tweeked to improve handling via geometry changes, seperate lower arms instead of using the anti-roll bars, and some upper link arms etc. And by changing the spring/damper rates. But it's at the expense of cost, predicatble handling and comfort.

In the end of the day a mass manfactured car has very compromised suspension, due space restrictions and cost (Mc-pherson front and beam rear being so common thanks to the compact and simple designs). Also that degree of predictability to the common mundane driver and comfort levels have to be included in the system, which all has a affect on the way a car handles.


[Edited by ALi-B - 9/24/2003 11:45:02 AM]

Skittles

[deleted to ensure offence is not caused - Cheers, Skittles ;-)]



[Edited by Skittles - 9/24/2003 12:28:15 PM]

sempers

Yup

YOU are kidding (whoever wrote that)? Please?

That demonstrates a fundamental lack of understanding - Sway bars (anti roll bars) INCREASE weight tansfer:

A car with no ARB will roll like a torpedoed battleship, and (in extremis) will have less grip as it's rolled way beyond the point where the suspension can keep the camber etc under control, but the chances of the inside wheel lifting clear are pretty small.

Stiff ARB's will stop the car rolling at the expense of loading up the outside tire. Chances of the inside wheel lifting are large as the compression of the outside strut is transfered to the inside strut by the arb.

ARBs can balance handling, however, stiffening an arb will reduce grip at that end of the car, softening it will gain grip (up to the point the suspension, aero etc can cope with the increased roll)

For a graphic example, look to race, or race inspired FWD cars; Massive ARBs at the back to control the roll, doesn't matter if this end looses some grip. At the front, much less (in some cases no) ARB to keep both fronts as much on the ground as possible, promoting traction and as much lateral grip as possible.

Typically they corner like a dog peeing on a lamp-post, inside rear in the air. Can't get much more weight transfer than that.
Road wise, the ITR is a great example of this philosophy.

In the example given, a car with a front rear (anti-pitch) bar (or anti squat suspension) will stay flatter, but will transfer weight off the fronts *far* faster than without.

Shocks (low freq end) also effect this: stiffening shocks will make the weight transfer faster, make the car feel sharper etc.

- Mark.

[edit to correct quote]

[Edited by sempers - 9/24/2003 1:44:07 PM]

[Edited by sempers - 9/24/2003 1:45:06 PM]

sempers

The *only* way weight can transfer forward on accel is if the centre of mass of the car is *below* the point through which the acceleration acts (i.e. the contact patch of the tires I think!)

jpmason33

where is good old MYCROFT when you need him

Merc_Cosworth

NOOOOOOOOO!!!!!

I do NOT need to know how stiff a Soarer shell is, or, how a Soarer can run with one tyre flat... (like a Citroen DS)

Cosworth427

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"YOU are kidding (whoever wrote that)? Please?

That demonstrates a fundamental lack of understanding - Sway bars (anti roll bars) INCREASE weight tansfer:"
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No, the real misunderstanding is that the front wheels are *always* completely unloaded under acceleration in FWD, because of the natural weight shift to the rears. But a stiffer bar, shock, spring at the front would increase rearward transfer, which would make your postulation correct. I haven't seen any FWD drag set up purposely used stiffer fronts. They'd ease weight transfer with softer fronts, control squat with stiffer rear set up.


-----------------------------------------------------------------
"For a graphic example, look to race, or race inspired FWD cars; Massive ARBs at the back to control the roll, doesn't matter if this end looses some grip. At the front, much less (in some cases no) ARB to keep both fronts as much on the ground as possible, promoting traction and as much lateral grip as possible.

Typically they corner like a dog peeing on a lamp-post, inside rear in the air. Can't get much more weight transfer than that."
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And a RWD set up would do the opposite. Induce understeer upon exit by having a more equally loaded rears than the fronts. The inside front wheel would be loaded the least, contary to the inside rear in a tuned FWD car.

jl123

MGJohn,

You bring up a grest point, aquaplaning. Why almost no one speaks about this is completly crazy. Its such an important aspect of the normal driving we all do- in fact as much as 50% of the time (depending on which town global warniimg has come to visit that/this year)We all experience it, often no matter how good the 'handling' of our cars is; no matter how great a time at the nurburgring our esteemed car can manage, if its raining and we are on a real road any smart driver would exchange his 'handling' (shuffling of over/understeer)for just plain and simple grip.

Though MG I might take issue with you that it is purly a FWD thing, Audi Quattro's (though their handling is only so-so) having been proving that extra front weight with 4 wheel drive is certainly no worse than extra weight with FrontWD for years. Note the pick of the old UrQ as 'most reassuring' car a few years back in a rally rep 4WD test in rainy Wales by Performance Car. Sometimes weight over handling can help when handling is less a factor.

"There are other benefits to the Front Wheel Drive concept. As most cars steer with the front wheels power applied to them should by design be delivered in the same steered direction. That must be beneficial, particularly in poorer road conditions for the average ordinary car and its driver. There's another rarely mentioned FWD plus which comes into play and hear I speak from direct experience. Consider whereby most of the weight in FWD cars is on the front driven wheels than with the more 'perfect' front engine, rear driven wheels balanced arrangement .. no names no wossname ... With MORE weight over the front wheels in a conventional ordinary FWD concept, with that extra weight penetration on a rain soaked road there's obviously less chance of reaching the aquaplaning threshold than with a more balanced arrangement. Rear or mid-engined RWD cars are more likely to lose front wheel grip with a lower aquaplaning threshold ... all other things being equal. Won't go into details, but, some years ago, in heavy rain conditions when travelling in fast convoy with other cars, I was VERY glad I was in a pure FWD car ......



[Edited by jl123 - 9/24/2003 6:42:38 PM]

Steve Whitehorn

iTrader: (13)

I know what you mean. I was driving a E36 M3, a fair few years back now, at a very low speed in very heavy rain and the front just went big time. It was quite amazing. I one point I was going at 45 degrees down the road. Fortunately it was at a low speed and I found some grip again. But must have been a combination of what you have just mentioned, Low profile wide tyres and a low front air dam and side skirts I suppose trapping alot of water as well.
Steve

Ridge Racer

that was like being back inschool , heeeeeelllpp !! please , if i press the right pedal car go , if i press the middle pedal car stop !!

Merc_Cosworth

Aquaplaning?

I thought we were arguing about weight transfer?

Steve Whitehorn

iTrader: (13)

The constantly evolving thread!

si325i

aquaplaning, did the thread tiggers start, say about the bmw crashing in the wet. and if it was aquaplaning it would not of mattered what car he was in aquaplaning= tyres not on road, cant stop till you start to slow down and brake through the water and find some tarmac.

tiggers

By my definition of aquaplaning the BMW in question in the thread you mention was not aquaplaning, there wasn't enough standing water for that.

No he simply overcooked it and then took totally the wrong course of action for an oversteering car.

Regards,

tiggers.

Merc_Cosworth

If its an evolving thread then Chain driven cams are better than belt driven.