LSD Tuning
Ok, I'll skip the basic theory stuff and try to explain how to set it up rather than how it works, you can read about that
here if you would like 👍
(*This will be mostly describing a RWD chassis as they are the easiest to explain)
There are two separate functions:
Accel - Activated by torque being delivered from the engine to the wheels. It controls the amount of differential rotation possible while accelerating
Decel - Activated by resistive torque coming from the brakes/rolling resistance of the car. It controls the amount of differential rotation while braking (and to a lesser extent coasting)
And one that controls the transition between the two:
Initial - Controls how smooth or aggressive the change in state is
What do the numbers represent?
We have a sliding scale for each of the functions that ranges from 5-60
.
5 Represents an open differential - An open differential means that the inside/outside wheels can rotate separately of each other at any speed.
Pros:-
Accel: Can turn more tightly/maintain rotation while accelerating
Decel: Can turn more tightly/maintain rotation while braking/coasting
Cons:-
Accel: Inefficient power transfer and has a tendency to spin the unloaded inside wheel under acceleration or suddenly lose traction on outside wheel if traction is broken.
Decel: Instability during braking or over rotation when coasting
60 Represents a locked differential - A locked differential means that the inside/outside wheels are forced to rotate at the same speed.
Pros:-
Accel: Maximum acceleration force in a straight line and predictability when traction is broken
Decel: Increased stability/predictability during braking
Cons:-
Accel: Greatly reduced rotational ability when accelerating
Decel: Greatly reduced rotational ability when braking/coasting
What about the Initial?
The Initial should be looked at as a way of controlling how fast/aggressive the transition between the Accel/Decel functions is.
-The lower the number, the faster and more aggressive the transition will be.
-The higher the number the smoother the transfer will be.
Low number:-
Pros: The car will be more responsive to throttle/brake input
Cons: Harder to control/predict and more likely to become unstable
High number:-
Pros: The switch will be more consistent and predictable enhancing stability
Cons: Less responsive to throttle/brake input
What should I be aiming for when tuning?
In the most basic terms, efficiency. The LSD needs to enable enough rotation to allow you to follow the fastest lines in and out of corners without inducing instability or being inefficient during power delivery.
How do I achieve this?
The best way as with all other tuning processes is trial and error and looking out for indicators. Indicators will come in the form of visual cues from the tyre temperature displays so keep your eye on this and feedback cues from driving feel.
Accel: This is the easiest to diagnose, it basically comes down to which wheel goes red first when traction is lost. If the outside wheel is lighting up then the Accel is too high, if the inside wheel is lighting up then the Accel is too low.
Decel: This one comes down to feel more than anything so trial and error will be the best approach here. If the car feels unresponsive to steering input when braking then the Decel is too high, if the car tends to over rotate when braking and turning then the Decel is too low.
Initial: This one is a little harder to explain as the symptoms can masquerade as other problems with the Accel/Decel. Sudden negative reactions to either acceleration (snap oversteer) or braking (sudden ploughing or diving in the direction of rotation) are generally a sign that the Initial is too low. If the car feels a bit numb/sluggish when responding to acceleration or brake application/release then this can be indicative of the Initial being set too high, this often leads to understeer.
Where Should I begin?
Most cars have a preset, greyed-out value for the stock LSD, this is generally where I start when fitting the full custom unit. I will then test the car and try to analyse how the LSD is performing. This is my thought process as I approach that first conventional corner (Brake-Turn in-Throttle) -
(Brake)
Does it over rotate when braking?
Yes: Increase Decel
No: Leave it alone
Does it under rotate when braking?
Yes: Decrease Decel
No: Leave it alone
(Turn in)
How does the car respond when the brake is released while rotating?
Understeer: Decrease Initial
Oversteer: Increase Initial
Neutral: Leave it alone
(Throttle)
Does the inside wheel or outside wheel go red under acceleration while rotating?
Inside: Increase Accel
Outside: Decrease Accel
Both (gradual): Decrease Accel
Both (sudden): Decrease Accel + Increase Initial
Does the car understeer under acceleration?
Yes: Decrease Accel
No: Leave it alone
Ok, now I have it basically set up how do I refine it?
Well, this all comes down to what you're driving, where and how you're driving it.
Accel: Lowering Accel numbers will allow you to get on the throttle much earlier while rotating but the downside of this is that you will not get as much acceleration force. This approach will suit tracks with flowing complex corners where getting on the thottle early and sustaining pace is more important than raw acceleration. Increasing Accel numbers will give you much more efficient drive out of the corners but at the cost of exit rotation. This approach will suit tracks with a lot of slow tight corners where getting on the thottle early is less important than drive out of the corner.
Decel: This is dictated by track type and driver preference. Increasing Decel numbers will give you much more stable and firm braking in a straight line which will suit fast straights with tight turns at the end, this will also suit drivers who prefer conventional straight line braking. Decreasing Decel numbers will help to maintain/increase rotation during braking which will suit tighter, twisty tracks where trail braking is more efficient or preferred.
Initial: If you want the car to be as sharp and nimble as possible then you will want to try decreasing the Initial as far as you can without making it twitchy, this will suit cars and tracks that need an aggressive approach and consistency is less important. Increasing the Initial will make the car much more predictable and consistent but the risk of increasing this too far is inducing understeer, this may suit more difficult cars or situations where consistency is more important than raw speed.