RWD > AWD or FWD? Why?

[bbman]

I am curious: Why is RWD considered better for racing than FWD and even AWD?

I mean, it is said that FWD can turn faster than RWD and can accelerate earlier out of the turn (or am I totally wrong)? Also, somebody told me that it is impossible to accelerate through a turn with RWD (which I really don't believe, but how comes somebody thinks that?)...

In addition, how comes AWD is considered better only on loose underground and drag? I know, this two really need all the traction you can possibly have, but I think the same rules apply to track racing, don't they? I always though an AWD not only accelerates faster because it has more traction, but it also corners faster of the same reason... So why are there almost no AWDs on the track? :scratchch

[Shotglass]

fwd - light, uneven weight distribution, understeer at corner exit
4wd - heavy, even weight distribution, best acceleration, huge drivetrain losses
rwd - light, even weight distribution, oversteer at corner exit

basically fwd is the worst concept for acceleration especially out of corners
4wd is (by far - caution subjective opinion) the best concept but its weight penalty and drivetrain losses effectively ban it for any racing series with limits on power other than rallying where the road conditions pronounce the traction advantages of 4wd more
with an rwd concept you give up some traction making the car harder to control at the corner exit (not that much of a problem with wide slicks downforce and good tarmac) for a (huge) efficiency and weight advantage

[himself]

It is known that FWD can not have more power than 200 - 220 bhp.
Second of all while accelerating cars weight center is being moved to the back of the car. You can see that clearly after pressing F in LFS. Rear wheels have more grip and therefore can handle more torge without wheelspin. This is also the reason why power distribution in 4WD is 60-40 / 70-30 (rear - front).

I dont know why AWD are not that popular maybe because steering wheels without propulsion give more information through the steering wheel about the car behaviour :scratchch

I think that powerloss in AWD is still to high and the weight of 4WD chasis is bigger than RWD one. However electronic differential is making a terrific job on power distribution for example in Lancer EVO VIII or IX and this system is soon to be used in racing.

There is also driving technique of power-turning or whatever you call it.

Furthermore RWD cars are classic. Sport cars have always been RWD and its the way it will remain for long time.

RWD is more challanging and sport can not be too easy or it will be too boring.

[Hyperactive]

Awd would be a good racing solution but it can only help you to put the power down better on corner exits for a short period of time. And that time period is the time there is the danger of wheel spin in a rwd vehicle. When not on that time period, awd cars lose to fwd and rwd cars because of the bigger losses between engine and tires in the drivetrain. Also the higher weight in awd versus rwd/fwd does not do enough to be justified. And fwd can't put the power down and steer efficiently at the same time.

In rallying awd can accelerate out of the corners better because the period of oversteer is longer for rwd. So awd can gain more there.

That's how I see it :shy:

EDIT: After reading my own post...maybe I should start posting in finnish :shrug:

[Funnybear]

Most racing cars are mid engined. That's where the engine sits behind the driver but in front of the rear axle. This gives the car much better handling characturistics. Due to this the weight distribution of a racing car rests on the rear axle. Thus that is where you want the power to go. More weight = more traction. You will never see a rear engined front wheel drive race car, no weight on the axle means no drive. Also one axle one job. It simplifies the manufacturing of components and therefor the racing reliability if you simplify everything. Rear wheel drive enables this by keeping the steering and the drive seperate. Simple components mean lighter components. FWD/Front engined allows for a safer drive, which is why many raod cars use this lay out. The engine gives weight to the front axle allowing it have traction, but this is not actually the fastest method in racing as the engine will tend to lead a car into a corner producing understeer and torque steer on the exit when you are trying to apply maximum power. Rear engined cars being more balanced can produce a more nuetral handling whilst cornering. FWD cars are generally used for small twisty circuits where the need for quick manouvable attributes favour the FWD cars.

AWD cars obviously generate more traction, but the weight penalty induced by carrying a heavier drive train renders it wholy impractical in circuit racing. It has been tryed, Audi use it effectily in Touring Cars, but it is not the generally accepted pratice. In rallying the wieght is less of an issue, can can sometimes be an asset when traction is more important than overall speed.

It's not a simple matter.

[bbman]

Hmm... I knew some things you've said, but never put 1+1 together... :doh:

I see the reasons now, thanks @ll... :)

[danowat]

Also depending on the setup an AWD car can give very pronouced understeer on corner exit.

Dan,

[Madman_CZ]

yep... common prob with the fxr gtr and my sets... but a fun car to drive none the less....

mad

[Shotglass]

just load more torque onto the rear wheels and the understeer will be gone

[ajp71]

FWD really need not be considered for racing purposes.

RWD cars make up the vast majority of racing cars and are the logical choice in mid engined cars, with the gearbox and diff all bolted onto the engine.

4WD cars tend to be heavier although they do give better traction, particuarly useful on slow courses.

A RWD car does not have to oversteer on corner exit, a lot of racing cars are setup to understeer slighty, especially in high power cars, something missing from LFS's setups.

4WD single seaters could be groundbreaking in hillclimbing, the Hepworth special (a 1970s 4WD chevy smallblock V8 hillclimbing single seater) still leaves the line faster than any of the Pillbeams or Goulds (big single seaters, built purely for short runs and as fast as F1 cars over them). Also Nick Mann's new car is an impressive Mallock style front engined clubmans style car, with 4WD and a 2 litre BDA, which uses a helicopter starter motor to give a constant boost turbo, is almost as fast as the big single seaters up Shelsley.

[richy]

i remember BTCC a while back with the audi 4WD vs the others and in the wet the 4WD had a significant advantage.

[Jakg]

It is known that FWD can not have more power than 200 - 220 bhp.for a ROAD car the limit is 250 with proper suspension...

[Blowtus]

says who? how heavy is the car? how hard does the power come on?

[sinbad]

says who? how heavy is the car? how hard does the power come on?

That's just a figure TopGear and other motoring press are using at the moment. Not too long ago they were all saying 200bhp so I wouldn't take what they say as fact and I fully expect Clarkson to say at some point in the future: "so you thought the most power a fwd car could manage without ripping itself to pieces was 250bhp.......well.......you were wrong" :cue tyre smoking hot hatch being punished, background rock music, and nice filters on the camera.

[ajp71]

for a ROAD car the limit is 250 with proper suspension...

What are you talking about, you can have a 500 bhp FWD road or race car it will just be horrible to drive, there's no limit to how powerful you can make a FWD car :shrug:

[Shotglass]

A RWD car does not have to oversteer on corner exit, a lot of racing cars are setup to understeer slighty, especially in high power cars, something missing from LFS's setups.

a lot of cars in lfs have massive understeer at the exit ... especially the fz5 and the fzr

[ajp71]

a lot of cars in lfs have massive understeer at the exit ... especially the fz5 and the fzr

Yes but the LXs and FOX tend to be setup towards oversteer.

[Shotglass]

Yes but the LXs and FOX tend to be setup towards oversteer.

yes because its faster at the expense of less driveability

[ajp71]

yes because its faster at the expense of less driveability

Thats bollocks a small single seater should be faster set towards a slight understeer. Don't use the arguement that these cars should be setup like historic single seaters, these are modern cars with modern materials and construction.

[tinvek]

every tyre has a finite amount of grip to be shared between any actions its asked to do, slowing the car, accelerating the car, holding the car round corners or turning the car.

traditionally rwd was used because it spread this load, then, ignoring ferdinand porsche's rather strange effort for racing in argentina after ww2, when f1 went from 1.5 to 3 lt in 1967 people started worrying that 2 tryes couldnt cope, hence all the top teams , and cosworth for some reason, decided to try 4wd. all discovered that it didnt really work as either the fronts couldnt cope with power or the car was very unwieldy on a track, the result being that the lotus ended up with as little as 10% power to the front wheels which didnt really justify the added weight / complexity.

at the same time tyres improved by a huge amount and someone had the idea of tying an upside down plane to a car and so the problem was gone till the era of qualifying 1.5 turbo grenade engines but by then 4wd was banned in f1.

4wd has been competative in saloon racing but in most of the catagories the raced the power could be coped with by 2wd in the dry so no real advantage and weight penalties, both from running gear and rules, rendered then popintless.

fwd currently dominates uk saloon racing due to rules requiring cars to follow road versions and also the power / tyre grip figure being too low, in germany were power in the dtm is higher a fwd would be a major challenge to drive.

when you factor weight distribution in, both static and actuall, fwd has no chance at high power. assuming you can build a fwd and rwd with same weight dist then when you acelerate weight is being taken off a fwds driving wheels just when it needs it the most. of course when its slippy and acceleration is less, the extra front weight a fwd has in real life stays more over front and so in such conditions they can have an advantage. of course if youve a 911 then the weight is ove real wheels and they just stick and go till the corner.

could go on more but just realised im supposed to be in work in 20 mins

[96 GTS]

That's just a figure TopGear and other motoring press are using at the moment. Not too long ago they were all saying 200bhp so I wouldn't take what they say as fact and I fully expect Clarkson to say at some point in the future: "so you thought the most power a fwd car could manage without ripping itself to pieces was 250bhp.......well.......you were wrong" :cue tyre smoking hot hatch being punished, background rock music, and nice filters on the camera.
The Nissan Maxima has 265hp if I recall. My friend's dad has one with a 6-speed and it's a blast to drive. Sure it can cook the front tires if you want, but if you're easy on the throttle on corner exits, man does it go! Driving the Maxima, I can pretty easily keep up with his AWD Audi S4 on twisty backroads.

[Gentlefoot]

I don't believe RWD is considered superior for racing than AWD. Who says that?

If F1 was allowed AWD don't you think they'd use it? Ofcourse they would but they can't because its banned.

[tristancliffe]

An F1 team, perhaps Brabham under the ownership of Bernard Eccelstone, tried AWD on their cars, and the added weight and complexity at the time made it absolutely awful. The drivers hated the way it drove. In fact, if I remember correctly, it was only better out of very slow corners. RWD was quicker off the line (controlled wheel slip), faster through corners, better at braking and lighter.

I think the same would be true today, even with 'clever' 4WD.

[Blowtus]

awd would wipe the floor if it was allowed, with no 'penalties', is the impression I got from reading a few bits and pieces. If it were a disadvantage, would there be a need to ban it?
awd is a little more advanced now than 30 (more?) years ago...

[nikimere]

RWD > AWD or FWD? Why?

I dont think it is in LFS, the RWD cars aren't as realistic as the FWD cars imo. Physics are just too wrong, mainly because of the low speed buy, RWD is a pain in the ass on the slow stuff in LFS.

my 2c

[Gentlefoot]

I agree Niki - I only ever use FWD in LFS because its so much more realistic.

Tris - In 1969 a number of F1 teams experimented with AWD. Mclaren, Lotus and Matra. The reason they wanted to develop AWD was because these systems had been so successful in Indy Oval racing in 68. Successful enough to be banned in 1970!

However, I don't believe these attempts failed because of inherent floors in the 4WD concept. Yes they had problems with weight and understeer but they never really had resource to address these problems. Matra and Lotus were both title contenders in 69 anyway and Mclaren were coming on strong. For this reason, resource was diverted away from the 4WD projects as developers were requried to work directly for the teams title challenges.

This coupled with significant aero and tyres developments at the time meant the benefits of 4WD were being negated anyway and the teams abandoned their projects.

[ajp71]

The reason why RWD tends to be used more is because it is lighter and more compact, both very important things in a racing car.

An F1 team, perhaps Brabham under the ownership of Bernard Eccelstone, tried AWD on their cars, and the added weight and complexity at the time made it absolutely awful. The drivers hated the way it drove. In fact, if I remember correctly, it was only better out of very slow corners. RWD was quicker off the line (controlled wheel slip), faster through corners, better at braking and lighter.

Lotus tried it with the Lotus 63, which was one of Chapman's disasters, as it happened it came shortly after slicks and wings, before these there was a huge problem with putting power down so had a well sorted 4WD car been ready for the '67 season the next decade of F1 could have been very different.

RWD was quicker off the line

Where'd you get that from? Maybe true for the Lotus 63 but certainly not for all 4WD single seaters. The Hepworth Special was a 1970s hillclimb 4WD special powered by a smallblock V8, it can still get faster split times off the line (it matters a lot on a 30 second hillclimb) than any of the 700+ bhp conventional modern 3.5 litre Goulds/Pillbeams.

http://www.hillclimbandsprint.co.uk/images/speedscene.jpg

http://www.ferrariownersclub.co.uk/happenings/2005/september/shelsley_postcard/popup/10.asp

I think the same would be true today, even with 'clever' 4WD.

Most likely with the current wide tracks and move towards lower power cars that will remain true, however, if we moved back to another generation of turbo cars with silly power outputs then 4WD could well be the way forward.

4WD would also be the way to go in hillclimbing today, I can't find more photos or more than this little snippet on it but Nick Mann's front engined clubmans style special really shows the potential for 4WD in hillclimbing.

I had been chatting to Nick Mann earlier, and luckily I had the chance to watch his home made four wheel drive single seater perform two practice runs. The car features a Ford BDA Turbo engine, only 1700cc, but it punches out between 400 and 500 BHP. The Turbo isn't spun by the exhaust gasses though. Its spun by a Helicopter gas turbine engine which is started by his helper after he's coaxed the BDA in to life. Nick went on to set FTD in his Mannic/Beattie car

http://www.shelsley-walsh.co.uk/images/photos/gallery/100/thumb3a.jpg

[Hyperactive]

In F1 they started experimenting with awd because the engines were powerful enough so they were having difficulties putting all the power to the road. But the tires got better and aerodynamics got better so there wasn't actual need for such system anymore. Putting an awd system on modern F1 car just makes it too heavy. The TCS does it better than awd. And less parts to break = less worries = less problems.

EDIT: I just read ajp's post and he already said the same thing, d'oh.

[Gentlefoot]

This coupled with significant aero and tyres developments at the time meant the benefits of 4WD were being negated anyway and the teams abandoned their projects.

As did I.

[Gentlefoot]

In relation to the last point - in most forms of motorsport, power, weight, aoreodynamics, tyre dimensions and other technical specifications are limited in some way. So I would say, in order to fully understand the benefits of AWD you would need to test the configuration in an un restricted form of motorsport.

Does anyone know of such a series?

My guess is that in such a series AWD would dominate. I know, I'm asking for it. :schwitz:

[Blowtus]

f1 cars currently have a minimum weight specified, yes? so awd is unlikely to increase the weight at all, just means the weight balance is not as adjustable.

[ajp71]

In relation to the last point - in most forms of motorsport, power, weight, aoreodynamics, tyre dimensions and other technical specifications are limited in some way. So I would say, in order to fully understand the benefits of AWD you would need to test the configuration in an un restricted form of motorsport.

Does anyone know of such a series?

Hillclimbing/sprinting has very few rules, I think fuel is restricted to normal safe racing fuels (none of the old highly canceragenic special brews) and nitrous is now banned.

f1 cars currently have a minimum weight specified, yes? so awd is unlikely to increase the weight at all, just means the weight balance is not as adjustable.

You can't make a 4WD F1 car, or do much at all due to the restrictive rules. As for weight yes it is specified but racing cars are always built as light as possible and then ballasted up to acheive a low centre of gravity, you'll probably find that around 200kg of a 600kg F1 car is ballast.

[tristancliffe]

Ferrari have about 105kg ballast from what I read (Mr Piola, the clever journalist).

[Blowtus]

You can't make a 4WD F1 car, or do much at all due to the restrictive rules. As for weight yes it is specified but racing cars are always built as light as possible and then ballasted up to acheive a low centre of gravity, you'll probably find that around 200kg of a 600kg F1 car is ballast.

Yes... that was my point :thumb:

[Gentlefoot]

Hillclimbing/sprinting has very few rules, I think fuel is restricted to normal safe racing fuels (none of the old highly canceragenic special brews) and nitrous is now banned.


That's not actually true. Hillclimb and sprint events in the UK are goverened by MSA regs. Also, there are several classes all subject to various restrictions. Eg Road Going Production Modified under 2000cc. In this class, you must have all interior in place, the engine and transmission must be a derivative of the original. i.e. you can't switch a 2WD to 4WD or 16 valves from 8 valves, or put a 3.5 litre Rover v8 in a mkII Golf.

However, the sports libre classes are designed as a catch all for cars that are not eligible for other classes. Even this class is restricted to some extent though. Cars are subject to minimum weight and size, tyre softening compounds and warmers are banned and there are many other rules I am unaware of I'm sure.

[Fordman]

250bhp Limited on FWD, not quite right. Late 90's early 2000's the BTCC cars ( Vectra's and Mondeo's ) had 300bhp they was all FWD. Same as todays BTCC, all FWD except 1 new entry, the new BMW and thats RWD.

4WD Racing ( not Rally ) cars do benefit. Look at Audi and Frank Biela. Audi Dominated the BTCC, and thus 4WD got banned.

Whether its FWD or RWD or AWD. It all depends on the driver and what they prefer. I prefer FWD, but thats just me. Regarding LFS, Niki hit the note. FWD is more realistic due to the bugs, but once these bugs are removed, then I think we might see from dedicated FWD drivers converted :scratchch

[sinbad]

250bhp Limited on FWD, not quite right. Late 90's early 2000's the BTCC cars ( Vectra's and Mondeo's ) had 300bhp they was all FWD.

The motoring press's 250bhp "limit" figure (not that I agree with it particularly) is for road cars, there are, have been and always will be fwd race cars with more power than the most powerful fwd road cars. But put 300bhp through the front wheels of a road-spec Cavalier SRi and the result would not be as pretty as it was with Cleland's championship winning car :)


Same as todays BTCC, all FWD except 1 new entry, the new BMW and thats RWD.

That's only down to rules. If the allowed amount of power rose to 500bhp then the fwd field would have no hope and fade right away. Similarly, if the field could modify the configuration of their cars without penalty, few (if any) would keep them fwd, but with just 250bhp, I doubt any would bother with 4wd.


FWD is more realistic due to the bugs, but once these bugs are removed, then I think we might see from dedicated FWD drivers converted :scratchch

Just different bugs. Doesn't the essential locked-diff and bizarre slight power-oversteer bother you at all? FWD cars certainly are no more realistic in LFS, but perhaps because they're much easier to drive their deficiencies are less obvious.

[ajp71]

Just different bugs. Doesn't the essential locked-diff and bizarre slight power-oversteer bother you at all? FWD cars certainly are no more realistic in LFS, but perhaps because they're much easier to drive their deficiencies are less obvious.

As Sinbad said FWD cars are not realistic in LFS, with a locked diff you would be unable to go round corners IRL because they'd simply rip themselves to pieces (assuming you were strong enough to turn the wheel in the first place).

[ajp71]

However, the sports libre classes are designed as a catch all for cars that are not eligible for other classes. Even this class is restricted to some extent though. Cars are subject to minimum weight and size, tyre softening compounds and warmers are banned and there are many other rules I am unaware of I'm sure.

What I was trying to say was that there are free single seater classes (which is unusual as normally open wheeled cars don't race in all comers races like closed wheeled cars do) obviously they still have to follow the MSA safety requirements and the odd specific rule set by the hillclimb club.

As for a Rover V8 Nick Mann competed his Morris Minor in the modified production car class as did Hannu Mikola in his Audi, although the rules may have been tightened since then.

[Niels Heusinkveld]

Well, BTCC had them all IIRC some years ago.. 4WD audis, RWD beemers and loads of FWD cars. I seem to recall the audis being good in the rain but 'close but not quite there' on dry stuff, and slower on the straight.

FWD and RWD is close in speed but if you are a bit like Tiff Needel, i.e. enjoy controlling cars near the limit, you'll curse everything that is front wheel drive as you can't play with them. And even racing, you don't get that 'balance the nose direction with throttle' with front wheel drive.

If racing was all FWD, I wouldn't be into simracing. The pure challenge of car control imo is only possible with RWD. FWD is more about being very clean and precise. Of course RWD is that as well but sooooo much more interesting. The right foot steers the car :) (well.. ish)

[Blowtus]

if you're going to judge the capability of drivetrain layouts, you really need to use something other than parity modified racing :)

[tinvek]

i once experience quite savage oversteer in a customers mg metro turbo once due to a faulty rear suspension bush giving an unwelcome rear wheel steer effect. quite terrifying as it wasnt expected, he had just said it felt funny when driving reasonably fast and asked me to go for drive in it. i ended up on a long left hander with the rear end out being unable to lift off in case it went round on me and with a right hander coming up straight after the bend. fortunatly i had a 100 meters or so of straight to slow it down

[bavor]

It is known that FWD can not have more power than 200 - 220 bhp.


for a ROAD car the limit is 250 with proper suspension...

Where do people get these strange ideas? Have they not driven FWD cars before or do they read somethign that someone wrote 30 years ago based on false assumptions and assume it to be true today?

There are plenty of production FWD cars that have been available over the past 15 years with 250-300 HP. There are a lot of daily driven, modified FWD cars that have more than that. Even back in the 1960's Oldsmobile had a 425 cubic inch displacement(7.0 liter) FWD V8 car with 385 bhp (287 kW) and 475 ft·lbf (644 N·m) of torque.

I've driven modified FWD cars that put down 300 to 400 HP at the wheels acordign to a dynojet dyno and not a single one of them was difficult to drive or a problem to drive in an autocross or tight road course. They also behaved very well on the street and some weren't much different in daily driving than the same car with stock horsepower.

One of the high horsepower FWD cars I helped build won 1st place in Car & Driver's superfour challenge and about the same lap times as a forced induction lotus elise.
http://www.caranddriver.com/article.asp?section_id=35&article_id=10165&page_number=8

As the article says, "With all that locomotive torque, we expected a wrestling match at the steering wheel every time we tramped on the gas. But that wasn't the case. There was a little tugging in the first three gears, but nothing to rival the antics of the two boosted Civics, and no worse than a stock SRT4."

[bavor]

FWD and RWD is close in speed but if you are a bit like Tiff Needel, i.e. enjoy controlling cars near the limit, you'll curse everything that is front wheel drive as you can't play with them. And even racing, you don't get that 'balance the nose direction with throttle' with front wheel drive.


You can set up a FWD car's suspenstion to be steerable with the throttle at the limit. You can also get FWD cars to behave like RWD cars. My FWD daily driven car that I also use for autocross has lift throttle oversteer and also can be guided with the throttle aorund turns depending on how I drive it. The suspension is 100% stock except for th rear sway bar, which is thicker than stock. FWD cars can be played with on the track, you just have to know how to set them up.

[Blowtus]

sorry, but the bit about fwd cars behaving like rwd is as much misguided rubbish as the first poster :)

[bavor]

sorry, but the bit about fwd cars behaving like rwd is as much misguided rubbish as the first poster :)

I didn't say they behave 100% exactly liek RWD cars, but if you disagree, you have not messed around with the suspension on a FWD car.

[Blowtus]

if you think oversteer is what defines 'behaving like a rwd' then you lack an understanding of vehicle dynamics in general :)

[skiingman]

An F1 team, perhaps Brabham under the ownership of Bernard Eccelstone, tried AWD on their cars, and the added weight and complexity at the time made it absolutely awful. The drivers hated the way it drove. In fact, if I remember correctly, it was only better out of very slow corners. RWD was quicker off the line (controlled wheel slip), faster through corners, better at braking and lighter.

I think the same would be true today, even with 'clever' 4WD.

Yet even in its awful, unrefined form it won a race, IIRC.

Also, I do believe they were using either a locked center or locked front diff. Obviously that would explain the unpleasant handling bits. To say that modern traction control and modern differentials offer much more is an understatement.

Whether or not "clever" 4wd will be faster depends entirely on the set of regulations. Mandated low power makes it less viable, mandated small grooved tires makes it more viable. It would be rather fun to see. Its really unfortunate that the golden days of competition for the technical sake of it have been more or less replaced by spectator sport with controlled costs and huge rules packages.

[bubbles]

But what sort of sport are we talking about people?
If it's circuit racing,
I have seen ff cars have a good run, the problem is they use their front tires to accelerate, brake and corner so their front tires wear quicker and understeer gets worse. Also they don't handle very well with too much horsepower. This is the main issue with ff cars even if their tuned to oversteer.
AWD cars have a lot of traction thus it's the fastest to take off at start, doesn't require much skill to drive especially the current evo's and sti's with their star wars technology, they can handle a lot of horsepower.
4WD's have come along way since the audi quattro, however due to current car manufacturer safety regulations these cars have gotten heavier and heavier(I mean the gallant vr4 was heavy, but these days the evo9 is just or heavier) Thats the only downside I can think off really besides power losses, but they are a really good platform for someone thats not experience with RWD cars. The Skyline GTR isn't a full time 4WD, I'll cover that later.
Sorry but like the FR AWD Lamborguini and others I don't no much about.

I'll cover FR and MR cars when I have the time, I have to go .

[Gentlefoot]

if you think oversteer is what defines 'behaving like a rwd' then you lack an understanding of vehicle dynamics in general :)

Any car be it 4WD, FWD or RWD can have understeer or oversteer.

In most caes, only cars with power to the rear wheels can produce 'power oversteer'. However, even front wheel drive cars can experience power oversteer with certain setups and a diff under some circumstances.

[der_jackal]

Where do people get these strange ideas? Have they not driven FWD cars before or do they read somethign that someone wrote 30 years ago based on false assumptions and assume it to be true today?

There are plenty of production FWD cars that have been available over the past 15 years with 250-300 HP. There are a lot of daily driven, modified FWD cars that have more than that. Even back in the 1960's Oldsmobile had a 425 cubic inch displacement(7.0 liter) FWD V8 car with 385 bhp (287 kW) and 475 ft·lbf (644 N·m) of torque.


God forbid you ever tried to turn that thing at speed....wow what a nightmare. But then again it is / was a 60's-90's American car. Not meant for the twisty bits back then.

And those numbers are kind of skewed, the Nm was to the crank, I believe it actually lost a considerable amount by the time it got to the wheels.



One of the high horsepower FWD cars I helped build won 1st place in Car & Driver's superfour challenge and about the same lap times as a forced induction lotus elise.
http://www.caranddriver.com/article.asp?section_id=35&article_id=10165&page_number=8


It took first in the FW class, they never did an overall winner between FW & AWD/RW IIRC.

The ridiculously overpriced HKS EVO took first in the AWD /RW segment.

http://www.caranddriver.com/article.asp?section_id=15&article_id=10165&page_number=16

Preface:

Sure some of the times on the road course can come down to the driver (IIRC they weren't driven by the same person around the track, each one was driven by somebody from that company / team), but surely that car should have been able to make up some of the difference by sheer brute force. It wasn't even .50 a second within reach of the best time of the Audi, and > 1 second off the times of the Hondata Lotus.

The SRT-4 had blistering straight line speeds, but pretty slow on the road course considering the weight, power and torque numbers IMO.

Power (mfr's claim): 452 bhp @ 5500 rpm
Torque (mfr's claim): 476 lb-ft @ 4000 rpm
Curb weight: 2934 lb

Road-course time, sec
60.25
54.60
DNF
51.95
52.45

Best in class FW road course was the Mini;

Power (mfr's claim): 265 bhp @ 7200 rpm
Torque (mfr's claim): 225 lb-ft @ 6600 rpm
Curb weight: 2634 lb

Road-course time, sec
52.60
51.80
51.15
51.70
51.55

Nearly 1/2 the HP and well under 1/2 the torque and at its best still ~.80" faster than the SRT-4. Sure it's 300lbs lighter, but again, 1/2 the total grunt numbers of the Dodge.

For comparison from the other classes:

The Hondata Lotus (RW);

Power (mfr's claim): 320 bhp @ 8500 rpm
Torque (mfr's claim): 220 lb-ft @ 7200 rpm
Curb weight: 1935 lb

Road-course time, sec
49.95
50.65
48.65
50.20
50.75

And the thoroughly disappointing, heavier and last place in class, A4 (AWD);

Power (mfr's claim): 340 bhp @ 6100 rpm
Torque (mfr's claim): 332 lb-ft @ 4100 rpm
Curb weight: 3581 lb

Road-course time, sec
52.60
52.25
51.80
51.50
51.25

I would have liked to see them get an independent driver for all the road course times because after all is said and done, those values really only serve to show AWD / RWD cars are easier at being driven around a track.

But still at the end of the day, you can put as much power in a FW car as you can any AWD or RW car, problem is using that power on, in or around corners is lost. FW tuners are getting better at curing that, but there's only so far it can go before ol' Mr. Physics rears his head again and shows that fundamental flaw w/ FW cars.

[ajp71]

Also, I do believe they were using either a locked center or locked front diff.

It would not have been a locked front diff, you cannot run a locked diff on on any car that has to go around corners on a fixed surface, this is a common misconception in the LFS community, most likely caused because LFS allows you to set the car up with locked diffs, which is totally inaccurate.

[Blowtus]

In most caes, only cars with power to the rear wheels can produce 'power oversteer'. However, even front wheel drive cars can experience power oversteer with certain setups and a diff under some circumstances.

Mind describing some of those circumstances?

[Shotglass]

It would not have been a locked front diff, you cannot run a locked diff on on any car that has to go around corners on a fixed surface, this is a common misconception in the LFS community, most likely caused because LFS allows you to set the car up with locked diffs, which is totally inaccurate.

how often do we have to tell you that this is utter nonsense ?

[der_jackal]

You can run a locked front diff on FW cars, it just handles like total sh**e.

It will cause a sizeable change in steering; damn near impossible to turn in under braking and it produces higher understeer because of it, but does allow all the power to be put down on exit better.

[Blowtus]

so why can't you correct for the understeer with a bigger rear roll bar, damper tuning, or any of the other usual options...?

[der_jackal]

The outside front tire is more heavily loaded under braking in this situation, so it will always pull you out. When you are able to turn in and get to the entry of the corner you're going to have an outside front tire that is; trying to steer, and put power down equal to its inside and much lighter brother and in doing so, voila, added understeer. You compound that with the natural tendencies of FWD cars to understeer and fun times ensue! It shifts the whole balance of the car to push out even more.

It's inherent nature on a locked front diff which is why people tend to stay away from locking front diffs on anything but off road vehicles.

You can offset it to a degree with car setup, but it's still prominent.

[Gentlefoot]

It would not have been a locked front diff, you cannot run a locked diff on on any car that has to go around corners on a fixed surface, this is a common misconception in the LFS community, most likely caused because LFS allows you to set the car up with locked diffs, which is totally inaccurate.

Wrong! Oval Racers run locked diffs but with larger rolling radius on the outside wheels.

[Gentlefoot]

Mind describing some of those circumstances?

Sure. I have a MkII Golf. It is set up to lift off oversteer (big rear bar and appropriate spring rates). It has a Quaiffe ATB LSD. As the LSD begins to lock in a corner it allows the inside wheel to pull the front round the corner. This pulls the front towards the inside of the corner.

Now, in wet conditions the oversteering characteristics of the car are magnified. I would normally soften off the rear bar in these circumstances.

However, at Donnington in November I decided to have some fun and left the rear bar set to hard. I noticed power on oversteer coming out of Coppice. It occurred as the diff began to lock. Coppice is a fast right hander, slightly up hill with some helpful camber and opening up onto the straight. The power oversteer occurred under full throttle on the exit of this corner.

[Blowtus]

ok, but you're hardly initiating the rear wheels sliding with power. you're just getting a bit of extra bite from the front once the rear is hanging out...

[Gentlefoot]

This is power oversteer though mate - oversteer brought on by the application of throttle.

You don't have to be spinning the rear wheels for it to be power oversteer. You just need to be on the power and steering the rear of the car, as was the case coming out of Coppice.

[Blowtus]

seems we have a fairly different idea of power oversteer. obviously you could put some maccas trays under your fwd hatchback's rear wheels, get on the power, and call it power oversteer if you wanted, but that's hardly behaving like a rwd :)

[Gentlefoot]

I never have and never will say a FWD handles like a RWD. That is nonsense. They do handle differently but the difference is not to do with lift off or power oversteer, its to do with the forces these different configurations experience during transistional states.

Power oversteer is called such because it is oversteer caused by the application of power. Conversely, lift off oversteer is caused by lifting off.

Whether it is the rear wheels or front wheels spinning is compeletely irrelevant.

Just so we're clear:

Oversteer - the car turns more than the steering input
Understeer - the car turns less than the steering input

Power Oversteer - the car turns more than the steering input and the throttle is open.

Lift Off Oversteer - the car turns more than the steering input and the throttle is closed.

To my knowledge there is no such thing as 'rear wheel spinning oversteer', which I believe is what you are referring to.

[Blowtus]

you can play definition god all you like if you really want :)
to my mind, the forces involved in your fwd 'power oversteer' are very similar to the forces involved in lift off oversteer. weight shift is the sole contributor to the oversteer, whereas 'power oversteer' to me implies that power is the main contributor.

[ajp71]

You can run a locked front diff on FW cars, it just handles like total sh**e.

It will cause a sizeable change in steering; damn near impossible to turn in under braking and it produces higher understeer because of it, but does allow all the power to be put down on exit better.

Even if you were able to turn the car you'd find that with the torsional forces on the differential it would simply rip it apart. Running a car with a locked rear differential on an aesymetric oval car has about as much relevance as the fact they are used in drag racing, ice racing or off roading.

You can run a FWD car with a locked diff but (on fixed surfaces) you will not be able to go round corners under power, so whilst it may be possible to build a car that could cope with road loads and maybe racing loads it still defeats the point as it would be slower than a car with an LSD because it could not be driven hard enough.

Even running an LSD a racing Mini (UFR) made them extremely heavy to drive and fragile due to the huge forces. I remember hearing somewhere that in a Car & Car Conversions report of testing a selection of BTCC cars in the '70s the Mini with an LSD was heavier to drive than an unpower assisted big block Camaro (when they really did handle like a dog despite what some here may argue).




I like to think of the locked diff as having 'zero slip'. By definition, a locked diff is rather poorly suited to normal roadgoing situations on 2WD cars because of the increased tyre wear created by both wheels being forced to rotate at the same speed. However, a locked differential can be put to very good use as the centre differential in a 4WD vehicle... as proven by umpteen rally wins around the globe by the legendary UR quattro and its three world championship titles to prove it. The rally quattros always ran with a locked centre differential because of the predictable handling on the limit - especially on mud, gravel and snow.

The biggest disadvantage of a locked differential is that the car always 'wants' to go in a straight line. This gives rise to severe tyre wear and bizarre handling on sealed surfaces - especially at low speeds when turning tight corners.

http://s2central.net/tranny_intro_p2.html

Locked diffs can be run at the centre of a 4WD system on fixed surfaces but are not ideal, this maybe where the confusion arose from, I have know idea whether the the 63 ran a locked centre diff.


Whilst I've heard enough shit about locked diffs being used IRL I've never actually heard of one example of a car running a permenantly locked diff (except in the centre of a 4WD system) on a fixed surface in any form of motorsport which involves turning both left and right, can anyone actually find an example?

[GT Touring]

I find you can adjust the driving style for a FWD car with a locked diff and make it frighteningly fast. True a proper set up differential would work best but it is the braking (coast) setting of a diff in a front driver which make it a bear if wrong- the car lifts the rear and woooop
spin.
the lockeddiff simplifies much of the racing, as the driven wheel now are very predictable the behavior is no longer variable. in LFS it certainly works for me.
Turn in later than usual and hammer down through the apex out and you will be cookin around the circuit.

in real life it seems that a locked front diff is madness- but i know of a few front drivers (outside of drag racing who do this)
the car in the attached pic runs a locked front diff- it does the FIA border series (a weak touring car series on the mexico/california border cities- mostly street races and some mexican cicuits)

Different drivers can get away with much, and rules can allow for FWD AWD and 4WD compete equally (WTCC alfas vs. BMW- the Alfas certainly do the right job quickly) Ford Mondeo any one BTCC? fast as any comer for sure.

[ajp71]

^^ Do you know how he sets that car up? I guess a very heavy rear brake bias and turning it under braking, or even disengaging the power through the corners?

[bavor]

if you think oversteer is what defines 'behaving like a rwd' then you lack an understanding of vehicle dynamics in general :)

I never said that. Thanks for putting words in my mouth.

[bavor]

God forbid you ever tried to turn that thing at speed....wow what a nightmare. But then again it is / was a 60's-90's American car. Not meant for the twisty bits back then.
And those numbers are kind of skewed, the Nm was to the crank, I believe it actually lost a considerable amount by the time it got to the wheels.

However, there are still many peole that seem to think that high power FWD cars are undriveable.

It took first in the FW class, they never did an overall winner between FW & AWD/RW IIRC.
The ridiculously overpriced HKS EVO took first in the AWD /RW segment.
http://www.caranddriver.com/article.asp?section_id=15&article_id=10165&page_number=16
Preface:
Sure some of the times on the road course can come down to the driver (IIRC they weren't driven by the same person around the track, each one was driven by somebody from that company / team),

Actually, msot of the cars, including the SRT-4 were driver by Larry Webster form Car & Driver.

but surely that car should have been able to make up some of the difference by sheer brute force. It wasn't even .50 a second within reach of the best time of the Audi, and > 1 second off the times of the Hondata Lotus.
The SRT-4 had blistering straight line speeds, but pretty slow on the road course considering the weight, power and torque numbers IMO.

Actually, the car had no brakes. Well almost no brakes. Wilwood sent us the wrong brake pads and we didn't find out about it until the first run through the course. The pads were completely glazed over during the stop from the first part of the course, the acceleration run. Larry Webster from Car & Driver said the road course lap times in the car could easily be 5 seconds faster with properly functioning brakes. If you could see the magazine article with the comparison chart, you can see the car obviously had some brake problems.

Best in class FW road course was the Mini;
Nearly 1/2 the HP and well under 1/2 the torque and at its best still ~.80" faster than the SRT-4. Sure it's 300lbs lighter, but again, 1/2 the total grunt numbers of the Dodge.
And it also had functional brakes.
For comparison from the other classes:
....
Also look at the results for the Forcefed Lotus Elise. It ran about the same lap times as the SRT-4.
I would have liked to see them get an independent driver for all the road course times because after all is said and done, those values really only serve to show AWD / RWD cars are easier at being driven around a track.

Most of the cars were driven with the same driver. Larry Webster form Car & Driver.

But still at the end of the day, you can put as much power in a FW car as you can any AWD or RW car, problem is using that power on, in or around corners is lost. FW tuners are getting better at curing that, but there's only so far it can go before ol' Mr. Physics rears his head again and shows that fundamental flaw w/ FW cars.

True, but FWD cars aren't the poor handling pigs that a lot of people think they are. They can handle quite well. In some racing classes, they run the same lap times as the RWD cars with similar power levels and weights.

[ajp71]

True, but FWD cars aren't the poor handling pigs that a lot of people think they are. They can handle quite well. In some racing classes, they run the same lap times as the RWD cars with similar power levels and weights.

Any properly production based car will have serious flaws in them and the chances are with relatively low amounts of power and limited fundamental re-designs of cars in club racing a FWD car can keep up with a RWD one, however, that doesn't mean to say that you'd ever think of making a FWD racing car when designing a car from scratch, and in an ideal world you wouldn't select a RWD car either. However much people bullshit about what config is best nothing will ever actually be able to beat an AWD with modern active diff technology in an unregulated formula.

[Blowtus]

I never said that. Thanks for putting words in my mouth.

that's why I said 'if' - it sounded like you were probably lining up to tell me that fwd and rwd can be similar because they oversteer. Still interested in what you were actually meaning...

[george_tsiros]

apples, oranges...

[Viper93]

True, but FWD cars aren't the poor handling pigs that a lot of people think they are. They can handle quite well. In some racing classes, they run the same lap times as the RWD cars with similar power levels and weights.

No they are not. Dodge ran the SRT-4 in the runoffs last year in SCCA and did a final place of 9th overall. There was over 100 entries I believe, all of them either being RWD or 4WD dodge being the only FWD allowed from what I understood. These included everything from porshe, viper, vette, caddy ect ect.

I have driven a camaro and trans-am, both late 90's models. They dont even compaire to what the SRT-4 has in handling. Power is quicker in them(due to the turbo14PSI in the srt-4) but the power levels are the same. 230HP factory, at the wheels. or brake horse =P ( it does have a 400 pound difference in weight, but it also has 70 less HP)


But I feel that racing, especally long races if for RWD, AWD eats tires, and FWD is trying to do too many things with the front wheels.