russell hayward

Following this with interest.

So, because the front diff transfers the torque to the outside wheel (not spinning at this point), it then is more like to spin as well, causing the centre diff to direct more torque to the rear.

Presumably this also will happen in a car with an open front diff, if you get that outside wheel spinning too.

EvoRSX

Russell,
If you lift an inside wheel with an open front diff, you won't get any torque transferred to the outside wheel in order to make it spin at all.

Andy

russell hayward

Yes, but if you applied enough power to make the outside wheel spin as well, the end result is the same.

The front diff just makes this more likely and sudden.

sempers

I'm confused..

Surely below the limit of traction an open front diff will pull the car into the corner more - as most of the power goes to the outside wheel; an LSD is favouring the inside front with more of a share of the power than an open one? Or is this a traction circle type issue for the outside front? Or am I talking crap?

Out of interest, I've been experimenting with my std UK turbo in a nice open area of very slippery wet tarmac:

If you turn in too fast, it doesn't, and any application of power results in understeer.

If you get the car turning first, and apply power hard, the back comes round. Gently / less brutally results in understeer.

If you provoke lift off oversteer in, then hit the throttle, it comes around like nothing on earth.

If I understand correctly, the centre diff is between the drive and the rear wheels?

dowser

Diablo

Yep - I fitted the Quaife front diff. It totally transforms the handling...for the better, but with ability to bite-back

With hindsight, I wish I'd also fitted the 20kg/cm centre while the box was out. Only comment I could find while investigating the upgrade was that the uprated centre would be more suited to a gravel stage However, a stronger centre would bias torque rearwards quicker in the situations I have the problem with (p*ss poor entry speed judgement!).

Richard

DavidRB

http://www.howstuffworks.com/differential.htm
http://www.houseofthud.com/differentials.htm

scrappydoo

Guys this is worrying me now and im seriously considering not getting the sti that i set my heart on now. So you guys are saying that if i drive the sti like my MY01 wrx then i'll spin out on a corner or roundabout?

dowser

Scrappydoo - the front diff gives you much better traction at the front, improving the performance of the car considerably. Just means you have to learn to drive it carefully at first - especially it jumping straight from an open diff'ed car. Once mastered, corner exit speeds are much faster

Richard

roee

Hey guys, i'm new in here

I was wondering about lift-off oversteer - is it a common practice with AWD just like it is with FWD? can you safely use small amount of throttle to bring it back into line without drifting wide?

- roee

DavidRB

Different cars must be driven differently to get the best out of them. You don't drive a WRX the same way you drive a FWD Integra or RWD 200SX, you adjust to make the most of the 4WD. The change from WRX to STi is just the same.

Any car with over 250bhp must be driven with respect. If you are unsure about a car, then a few hundred quid on a day's performance driver training is money well-spent.

P1 Frog

good comment were can you get this training

mutant_matt

Well the 1st Lotus Performance Driving day is very good for type of training on an Airfield where you can afford to get it wrong. Very much recommended!!!!!!

Matt

Boxer

Firstly, I am happy to have generated a post that has lead to a wealth of information sharing on the STI's handling traits, thank you Diablo. Though to be honest, seeing as your a moderator, I would have expected a less scathing response on your part.
When I decided to buy this car in September '01 for Jan. delivery, I researched the hell out of it. I know all about the Suretrac front diff, perhaps with a less intricate knowledge of the exact mechanical forces at work than you, but I get the picture (it's alot clearer now I must say).
The post was intended to be a reader friendly STI experience sharing, for all newcomers to the STI (8,500km on mine, had it since Jan 15), and not a technical discussion on the mechanics of the diffs. I think most of us knew that the front diff. splits power L/R, and we know that the center diff is what splits power F/R.
(Quote)"No its not. Nor is any Scoob. They have fantastic traction in the wet, but no more grip in a given corner or "magical" handling prowess than many other cars."
Beg to differ on that quote from your first reply, the STI's suspension set up is awesome, combined with the traction of the 4WD, and it whups M3 butt, in the wet. Anyway.
Diablo, RT and Dowser thank you for the stimulating post, honestly, we've learned alot.
Cheers Y'all.
Represent.

PeterPerfect

Yep front LSDs are good under the right conditions as Diablo has pointed out.
I was initially disappointed a few years ago when I fitted an APRacing SureTrac diff to my GrpA 205. I had visions of it allowing me to use WOT through tight corners in the snow and rain. In fact the car tended to understeer big time Before the diff was fitted the inner wheel would pick up and spin, but the car would pretty well hold it's line. I did find a way round this problem though...called the handbrake....gets the front pointing in the right direction allowing both wheels to hook up with the LSD
Pete

Steve Whitehorn

iTrader: (13)

roee

Yes lift off overstear is the most common problem.
So therefore the correct entry speed in to a bend is vital in order to get the most out of my Scoob. I am totaly focused on this when I cane it down back roads as well as trying to be a smooth as I can.

The car is only fully under control when all 4 wheels are under power. Thats what 4WD is all about. So any engine braking or use of brake pedal combined with stearing makes the car less stable. weight transfer and all that. This is a bit of a clumbsy explanation so this web address explains all properly.

http://www.drivingtechniques.co.uk/

Cheers
Steve

my2009

In my opinion lift of oversteer is a beatiful thing I use it often to get into a tight corner and WOT -> shoot out from it. MY02 has raised back end COG for just that trick.

Steve Whitehorn

iTrader: (13)

my2009
O.K. 'Problem' is too strong a word for it - as you say it can be a lota fun if done in a controlled way ;-)

Cheers
Steve

[Edited by Steve Whitehorn - 4/17/2002 9:41:08 PM]

my2009

Right Steve, and I mainly did mean _tight_ corners as in a town accelerating from 10-> 40Mph

On track oversteer is somewhat a "problem" as you say.

Diablo

Boxer,

Sorry mate, wasn't meant to be scathing, but reading again it was perhaps a bit

Felt it needed to be said.

PS - being a moderator makes no difference...LOL....

scrappydoo

I suppose it would have to be driven with respect. As for the track day thing, im off to castle combe on tuesday for an all expenses paid dayout with subaru driving the sti. Cant wait. I should get a good comparison between the MY01 WRX and the STI.

RT

"(Quote)"No its not. Nor is any Scoob. They have fantastic traction in the wet, but no more grip in a given corner or "magical" handling prowess than many other cars."
Beg to differ on that quote from your first reply, the STI's suspension set up is awesome, combined with the traction of the 4WD, and it whups M3 butt, in the wet. Anyway.
Diablo, RT and Dowser thank you for the stimulating post, honestly, we've learned alot."


Interesting how this thread developed. Made me think thru things again...

However, I still can't reconcile the steady state cornering grip. I'll have to agree with D on this one. The max lateral G pulled in a steady state corner (not braking or accelerating) is dependant on the tyres, suspension setup (camber, caster etc), center of gravity etc.

I can't understand how 4wd comes into play here. My understanding is that 4wd only assists in the accelerative longitudinal plane, ie it allows you to get on the power sooner - not brake later or corner harder. Any differences between the style of driving a FrontWD/RearWD and a 4WD is to allow the latter to take max advantage of this trait.

Isn't this why rally drivers slide the car so much? To get the nose pointing in the desired direction before the apex so that they can be on WOT as soon as possible?

Diablo

Quote:

However, I still can't reconcile the steady state cornering grip. I'll have to agree with D on this one. The max lateral G pulled in a steady state corner (not braking or accelerating) is dependant on the tyres, suspension setup (camber, caster etc), center of gravity etc.

I can't understand how 4wd comes into play here. My understanding is that 4wd only assists in the accelerative longitudinal plane, ie it allows you to get on the power sooner - not brake later or corner harder. Any differences between the style of driving a FrontWD/RearWD and a 4WD is to allow the latter to take max advantage of this trait.

Isn't this why rally drivers slide the car so much? To get the nose pointing in the desired direction before the apex so that they can be on WOT as soon as possible?

Agree completely

ex-webby

Hi All

One thing to bare in mind is that true steady state cornering does not exist in the real world. Especially on a circuit where you are almost without exception accelerating or braking.

This is one of the reasons why drivetrain (espcially mechanical orientation and diffs) play such a large part in the overall performance of the car.

4WD does not necessarily mean you can get on the gas sooner, in fact RWD is more likely to allow you to get on the gas sooner on smooth tarmac.

Lift off oversteer if not the devil. It can cause a crash if not properly controlled, the same as any other handling trait. The problem is that famed benign handling of a scoob when on the throttle makes the transition between a fun blast on the throttle to the real world of limit handling mid-bend a stark contrast.

Why do rally drivers drive sideways?..

a few reasons.. one of which is definitely the ability to get on the gas sooner, but there are others..

for instance, being sideways allows you to have much more effective and accurate directional control over the car. You can change direction much quicker and with far higher precision than if you drove round depending solely on the front tyres.

On gravel this is even more important and it also creates further reasons for being sideways.

Gravel tyres are designed to take advantage of the fact that the tyres scrape into the gravel and drag gravel with them building up out side the tyres and providing a kind of lateral restance / force which can be converted into a cornering force by the use of the driver.

Gravel tyres are not restricted to the same laws of physics as those running on tarmac (slip angles, self aligning torque, percent slip, etc) they don't exhibit limits in that way. This is mainly due to the fact that the surface is moving and changing as well as there never being a consistent contact patch. A tyre can produce wildly different forces as it travels across each inch of a corner even if it is pointing in exactly the same direction.

All the best

Simon

Adam M

I wondered how long it would take for simon to add his bit to what is already a great thread.

RT

Great read Simon. Gimme a couple of hours to digest it, I'm sure I'll have questions!

RT

Quote:
"4WD does not necessarily mean you can get on the gas sooner, in fact RWD is more likely to allow you to get on the gas sooner on smooth tarmac."


...And the immediate question that springs to mind is: Why?


I agree with you that on the track, you're probably braking or accelerating while turning almost all the time. I was only using that example of pure lateral grip in a steady-state corner to try and reconcile the point of a 4wd not having more pure-lateral-G-generating-power than either a FrontWD or RearWD.

Do you agree with this statement? -or is there some other subtle point I have missed?

tks.

russell hayward

""Yes, but if you applied enough power to make the outside wheel spin as well, the end result is the same.

The front diff just makes this more likely and sudden. """

Will someone agree with me please ? or not as the case may be ?

EvoRSX

Russell,
With an open front diff, once you lift an inside wheel, you will not transfer any power to the outside wheel as all the power will be transferred to the path of least resistance i.e. the spinning in the air inside front.

Andy

sempers

Does that not then lead to the engine revs rising, and the inside wheel spinning ever faster, thus having the front side of the centre diff spinning fast, leading to the centre LSD locking up, and transfering torque rearward?

I'm not saying the inside front won't spin like hell, but that the rearward torque transfer must still happen.. Certainly the way I can loop out my MY97UK (open front diff) indicates that somehow the torque's going back in a hurry...

Edited to note that

1)I'm agreeing (I guess???) with russel that this still can happen on a open front diff?

In fact, looking at the above, I don't understand why it's not more common with an open front than a limited slip front. Anyone care to enlighten me?

2) Also (definately) with EvoRSX that the outside front is pretty much guaranteed not to spin with an open front diff.

- Mark.

[Edited by sempers - 4/18/2002 2:44:33 PM]

EvoRSX

Sempers,
The rearward transfer of torque will still happen it was just that AFAIK, Russell was talking about the transfer of power and torque to the outside front wheel with an open front diff which definitely won't happen.

Andy