How to set up LSD: 4WD cars

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This is for 4 wheel drive cars only. LSD is most useful on a 4wd because it is on all four wheels.


entering low-speed corners:
---------------------------------------
Problem: Underseer
Solution:
Front Initial: low
Front Accel: --
Front Decel: low
Rear Initial: --
Rear Accel: --
Rear Decel: --


Problem: Oversteer
Solution:
NO SOLUTION: can not be fixed with LSD.
You need to set up other parts.


exiting low-speed corners:
---------------------------------------
Problem: Underseer
Solution:
Front Initial: low
Front Accel: low
Front Decel: --
Rear Initial: high
Rear Accel: high
Rear Decel: --


Problem: Oversteer
Solution:
Front Initial: high
Front Accel: high
Front Decel: --
Rear Initial: low
Rear Accel: low
Rear Decel: --


entering med/high-speed corners:
---------------------------------------
Problem: Underseer
Solution:
Front Initial: low
Front Accel: --
Front Decel: low
Rear Initial: slightly low
Rear Accel: --
Rear Decel: slightly low


Problem: Oversteer
Solution:
Front Initial: high
Front Accel: --
Front Decel: high
Rear Initial: slightly high
Rear Accel: --
Rear Decel: slightly high


exiting med/high speed corners:
---------------------------------------
Problem: Underseer
Solution:
Front Initial: low
Front Accel: slightly low
Front Decel: --
Rear Initial: high
Rear Accel: slightly high
Rear Decel: --


Problem: Oversteer
Solution:
Front Initial: high
Front Accel: slightly high
Front Decel: --
Rear Initial: low
Rear Accel: slightly low
Rear Decel: --
 
You can make a 4wd car handle like that of a front wheel drive by setting the front levels higher than the rear.

In contrast, setting the rear harder will make it handle like a FR.
 
well i got a skyline R34 all tuned up and i can't figure out how to fix my oversteer prob, i end up drifting after every corner or spining
 
Wouldn't you decrease the accel effect? I figure on a built Skyline, overpowering the rear traction is the real problem causing the oversteer. Increasing the accel would make that worse.

Are you thinking that increasing the accel effect will make the car more resistant to rotation? Is that what you're getting at?

I'd have to test and see which is more true. This is one of the reasons I'm not in love with Skylines to begin with.
 
Originally posted by neon_duke
Wouldn't you decrease the accel effect? I figure on a built Skyline, overpowering the rear traction is the real problem causing the oversteer. Increasing the accel would make that worse.

Are you thinking that increasing the accel effect will make the car more resistant to rotation? Is that what you're getting at?

I'd have to test and see which is more true. This is one of the reasons I'm not in love with Skylines to begin with.
Click to expand...

Hmmm...

That is what I was thinking, but I now recall that I previously conceded to your point about high power vehicles breaking loose with power going to both rear wheels relatively equally. :tapedshut ...At least high power FR cars. :sly:

I guess it really depends on the VCD balance, not to mention the TCS. I am going to have to take a break from the Complex String TT :banghead: and try this out tonight.

I know there are Skyline minions out there, but I have to share your sentiment toward them. :indiffere
 
Well, I ended up not doing a lot of testing with regard to :up: or :down: the rear LSD to settle the issue. Like I said, I think it really depends on the other settings.

What I tried to do was to find the best overall combination. For what it's worth, here's what I found.:2cents:

I used the Skyline GT-R V-spec II (R34, J),
1072 hp,
super-slick tires,
with the following settings:
(front/rear)

Springs: 17.6/18.6
Height: 86/88
Bound: 4/3
Rebound: 5/5
Camber: 3.0/1.0
Toe: 0/1.0
Stabilizers: 4/3

Brakes: 21/19

LSD Initial: 16/9
LSD Accel: 56/19
LSD Decel: 10/7
Gear Ratio (auto): 41 :Poke: (forgot to look at this)

Downforce: 0.29/0.40
ASM: 10
TCS: 6
VCD: 40% (wanted to keep it pretty true for 4WD)

I ran the car at Laguna Seca.

The car handled pretty well going into and coming out of the corners. The tricky thing about the Seca is that you have to account for fast corners as well as hairpins, and lest we forget, the corkscrew! :rscared:

I was pretty happy when I was consistently turning out lap times of 1:21.xxx. I even had a few 1:20.xxx times. I don't usually keep track of lap times, so I really didn't have much of a benchmark except the TT with the Viper. The time needed for first place in that TT is 1:22.716.

I will have to go back and try a more reasonable gear ratio and see if I can get any better (41 is almost as wide as you can get--42 is max.).
 
Thorough as ever Quattro!

On the LSD Accel value question, up to a certain point, increasing the LSD A will work to rein in power-on oversteer but there is a limit to how much it can do.

What happens is that as the throttle (and torque) inputs to the tyres increase, the LSD tries to keep them spinning at the same rate i.e. oversteer is decreased and straightline acceleration is improved. However, there is a threshold (determined to a large extent by the grip of the tyres) and if that boundary is passed then the wheels 'let go' all at once in catastrophic oversteer.

It's an effect that I term 'Grip Shear' and can be experienced in quite a few circumstances as forces build up on the tyres until they give up the unequal struggle. It's one of the main reason's I always recommend testing on T2's rather than anything grippier - grip shear will be much more obvious and allow you to tweak the chassis to minimise it.
 
OK.

Following the thorough advice here, I'm in the process of tweaking a car to run Laguna Seca in the Pro 4WD challenge. Ideally the car I'd like to run in this race is the WRX Impreza Wagon. Reason being, I can also run this car in the Boxer series shortly there after.

It is not a particularly powerful car, but one that I'd prefer to use.

For the first 4WD challenge I ran the Impreza LM car. Not really a close race. So...I switched over to the Impreza Wagon. Felt guilty, and a bit bored in the Impreza LM.

Had to go shopping and blow some cash.

Mods it already had are: Racing Transmission, Brakes and lightweight 1. I added Full suspension, Brake balance controller, Full LSD, Triple Clutch, Light weight Flywheel, Stage 2 turbo, racing intercooler, T2 Tires, and lightweight 2.

Settings:
Springs: 13.0/12.0
Ride Height: 105/105 (bottomed out)
Bound/Rebound = 5 (all)
Camber: 3.5/1.0
Toe: 0.0/-1.0
Stabilizers: 6/6
Brakes: 14/21
LSD (F): 10/8/20
LSD (R): 10/16/20
Auto Set gears: Level 27
Final Drive: 4.610
ASM = 0; TCS = 0
VCD: 35%

Yet I couldn't keep it running a decent line. The Skylines I was facing really didn't have a problem out-running me.

What suggestions would you have for me? Sukerkin? Quattro_bro? Neon_Duke? oosacker?

AO
 
Yet I couldn't keep it running a decent line.
Click to expand...

Two questions, Der Alta: :confused:

1. What type of a line was the car running? I am not at my PS2, so I need to try to visualize what sort of problems you're having.

2. With your mods and upgrades, what is the hp currently at?
 
to "ditto" your reply, I'm not at my PS2 either.

If I recall correctly, as I've played a full day of Golf in between, lumped in with a few late nights/early mornings...
The problems I was having, was a lack of oversteer. The car would follow a good line at moderate speed through the hairpins, and develop understeer before the rear end moved around. I've been experimenting with the LSD in the recent weeks, after reading all of these discussions. I've noticed better response with all of my cars.

Now in an FR making the adjustments to improve LSD reaction, it essentially makes the rear end of the car come around quicker, without breaking traction. This is the problem that I'm trying to modify the LSD to correct.

So it's not understeer that I'm getting, it's a lack of oversteer. I think.

I can check tonight to see what HP I'm running at, and add that info tomorrow. I'm fairly confident about the amount, as It is what I need to stay competitive in a straight line. Ideally, I'd like to boost the speed of the car through corners. I know that I need to enter the corner at the same speed as before, but by modifying the LSD, I can improve my exit speed.

Does this info help?

Thanks

AO
 
AO: I haven't done much to my WRX wagon except lighten it, but:

On any car I'm planning to race (seriously enough to drop the cash you have already) I always go Lightweight 3.

On my full-build Evo VI, I found I could mitigate that mid-corner FWD understeer by reducing the front diff accel value fairly substantially. That seemed to keep the front happily turning, without having to defeat the advantages of AWD by cutting the center diff down below 25-30%.

Call me silly, but I don't see much point in having an AWD car, and then cutting the front torque to 10% or something. It may be faster, but... I'd rather keep the torque bias around 30% and do my best with that.
 
I'd rather keep the torque bias around 30% and do my best with that.
Click to expand...

:embarrassed:uch: So much for my 13% VCD lap times in the WRL! :blackeye:

:D

Say neon_duke, this has been nagging at me for a while:
I tend to :up: the front LSD Accel substantially to get rid of mid-corner understeer on a 4WD car, while you find better results by substantially :down: the setting.

What is going on??? :reallyodd

My theory is that since I :up: LSD accel on FF cars to cut down on understeer, the same physics would apply to the front of a 4WD car.

My first question is 'do you agree with my FF method'?
If so, what am I missing on the 4WD setup? i.e. why is it different than FF?

:confused:
 
Hi OA

Mmm, tricky ... there are several things I think you could try but they're not to do with the LSD so they're not really relevant to the thread. Some of them might seem a little counter logical too but give them a try.

Raising the ride height (I said some might sound weird!) may well help. Particulary if you give about 5mm more to the rear than the front. The condition you're describing is of a car that is too stable in the turns and part of that is caused by not getting enough lateral thrust into the tyres because you have the centre of gravity as low as it will go.

Your front camber may be too high also. Beyond a certain point increasing the front camber will actually induce understeer rather than cure it because the contact patch becomes too small. This will be exacerbated by the very still anti-roll bar settings which are preventing the camber change that normally occurs during cornering (as a general rule of thumb, the stiffer the car, the less you need to modify camber).

A little positive front toe (-0.5 would do) can also help improve cornering performance because although initial turn in is slightly hampered by it, the absolute grip level increases (particularly on the inside wheel). Setting some negative rear toe could be of assistance too. +1.0 is not normally an excessive figure. What it does it enhance the straight line stability of the car and rein in power-on oversteer by countering the toe-out of drive wheels that occurs during acceleration.

Altering the stabilisers to something like 3/5 is a possibility, as making the rear stiffer than the front will encourage turning responsiveness and if the car is as stable as it sounds shouldn't encourage too much unwanted oversteer.

The spring rates at 13/12 are actually promoting understeer too. What's the weight of the car at present? A rule of thumb (another one!) is find out what the default spring rates are (this gives you a static snapshot of the general weight distribution of the car). Working from this you can adjust the ratio of the front/rear springs to move the centre of gravity fore or aft - you seem to want more oversteer so making the rear rate higher than the front is the option to go for (as it's a 4WD it shouldn't hurt acceleration all that much).

All the above said, the primary tool for adjusting the cornering balance of the car is the dampers. It sounds like you're suffering from Phase 2 and 3A understeer (there are 5 phases to a cornering manoever). The cure for this is to have your rear Bound and Rebound higher than the front. It is also generally good practice for cornering responsiveness for your rebound rates to be significantly higher than your bound at both front and rear (but for the difference to be larger at the rear). Fine tuning the dampers can take a while but the effects can be quite marked - I've improved lap times by a second with just 3 clicks of change to the dampers.

If I get chance tomorrow, I'll take an Imprezza Wagon (I'm sure there's one lurking in my garage somewhere!), tune it up to your current stats (assuming you don't take the Dukes good advice and shell out for Stage 3 weight reduction) and fettle with it for a while.

To give me a benchmark, what lap times were you making around 'Seca?

Windbaggy as ever

Sukerkin
 
And the story goes....

this is what I did last night after following all the advice I had at 5:30pm. Sukerkin, I'll address your thoughts at the end of the post, as I still have to race Deep Forest tonight.

Total mods:
Racing Transmission, Brakes and lightweight 1. also Full suspension, Brake balance controller, Full LSD, Triple Clutch, Light weight Flywheel, Stage 2 turbo, racing intercooler, T2 Tires, and lightweight 2. For a total of 409 Hp. I don't usually note the weight of the car, so I don't have that handy.

Settings:
Springs: 9.5/10.5
Ride Height: 102/102 (bottomed out)
Bound/Rebound = 6 (all)
Camber: 3.4/1.0
Toe: 0.0/-1.0
Stabilizers: 3/3
Brakes: 14/19
LSD (F): 5/5/10
LSD (R): 30/40/10
Auto Set gears: Level 27
Final Drive: 4.610
ASM = 0; TCS = 0
VCD: 35%

This set up gave me the win. The car felt very stable, although it could have used a higher LSD on the front. Instead I may take Sukerkin's thoughts to mind on this one.

Results:
S4: + 1.882 (pitted on lap 7)
Skyline (R34): + 2.894 ( pitted on lap 8)
Lancer Evo VI: + 21.666 pitted on lap 6
3000 GT VR-4: 32.581 pitted on lap 6
Celica GT4: 36.804 pitted on lap 5

Best lap: 1’28.107
Total time: 15’16.099

This was a very close race. Including the S4 bumping me in the first hairpin in the last lap. Once tires warmed up, the lead cars were very well matched. I was able to keep very close to the pace of the lead cars, but tended to loose time on the straights. Usually a tenth of a second. I did note that I could take the first and last hairpin, as well as the Corksrew faster than the AI could. That was a positive note.

Sukerkin:
I think I hit nearly all of your points in the setting changes that I did make. I always have about -0.5 or -1.0 on the rear toe. You may have miss read the first post. I did a test run on Deep Forest last night, and can keep with the field once my tires have warmed up, but by then I'm usually 8 seconds down from first place. So...tonight I'll try adjusting ride height, lessening the front camber, tune the stabilizers and set the bound rebound at 4/5 and 5/7 for the rear.

Yes, this thread has come way off topic, but it delves into the subtleties of 4WD tuning and what can affect it beyond the LSD.

A wee bit windbaggy myself...

AO
 
Hi again Ao

If I'm reading this right the mods on your Wagon don't include Chip, Exhaust, Port Polish or Engine Balance, so I didn't use them whilst having a bit of a play with the settings.

I only tweaked with it for about an hour so my conclusions aren't solid and although the settings I ended up with don't resemble yours, the times around 'Seca are about the same. Another example of the fact that there is no such thing as a perfect set-up in GT3, only one which suits the driver!

I wont clutter up this thread with exactly what my settings were (if you'd like to see them I'll PM them to you).

One comment - as far as I know, negative numbers for toe in GT3 mean toe-out and positive ones toe-in. My own experience gels with this and a 'stock' toe adjustment for me is -5 Front and +10 Rear.

I'm assuming you've toe'd out the rear as a deliberate ploy to encourage rapid turn-in and don't find the augemented power-on oversteer a problem?

I think for any further discussions on this we should start a new thread about dialing in the Wagon (unless we focus on the LSD aspects of the tuning). What do you think?
 
this made my EVO VI RS in GT4 handle a lot better

it doesn't snap anymore during late braking and it understeers a lot less during cornering

well done
 
I used to have major understeer probs with my FTO LM Edition, until I dropped the LSD effect down to its minimum on the front and rear Initial, Accel, and Deccel and a 10% front distribution on the VCD and it now handles beautifully, more like an FR and managed to knock 7 seconds off my Complex String time.
 
I find that for most 4-wheel drive racing, you don't actually need limited-slip action. All it does is induce understeer..even light LSD tuning. :nervous: Personally, i'd rather have a more flexible 4WD car that occasionally oversteers and "steps out" than one that just understeers all the time.

One huge exception is in rally races, of course.
 
Agreed, i don't use LS on my awd's unless its for rally. Even at the low settings they tend to have a front heavy feel to them.
 
breakpoint
Agreed, i don't use LS on my awd's unless its for rally. Even at the low settings they tend to have a front heavy feel to them.
Click to expand...

Some people just try and confuse themselves i guess. For road racing, i really only use limted-slip (when low-powered) for some front engine/rear-drive cars and front-drives (but not mid-engine cars or 4WD's since they have superior traction). As the power gets raised, you'll eventually need LSd for mid-engine cars, too, but i have yet to use it on a 4WD unless the power is reaching insane levels. :D
 

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