Question about the differential adjustment scale
This?
There's only one differential in the drivetrain, linked to the rear axle. The "on" and "off" are two sets of parameters for its functionality, aiming at two different scenarios: when you're on-throttle and when you're off-throttle – crudely speaking, the of rotation offered by the rear axle on corner exits (on-throttle diff behavior) and the rotation offered by the rear axle on corner entry (off-throttle).
The scale is always the same: it's how much locking force the differential will present.
When fully locked (100%), the axle functions as a single rod and one full rotation of a wheel is matched by a full rotation of the opposite wheel. As you progressively open the differential, you allow the wheels to spin freely and this is key for your cornering ability. When turning, the inside wheel has a much shorter path to take than the outside wheel as it is practically following a circumference of a shorter radius.
Talking differential mechanisms in general terms, with a locked axle the inside wheel will be forced to spin at a higher rate, effectively scrubbing the rubber across the tarmac and creating resistance. With the outside wheel spinning firmly and the inside wheel dragging, the rear end of the car will shift outside (oversteer) and you’ll end up with lots of wear on the inside tires.
It is not as simple as just unlocking the differential though. When you’re on throttle, the engine power will be put down on the tarmac through the easier route – meaning the corner of the car with the least resistance, the one with least traction. That is, the inside wheel, or the wheel that goes through a patch of grass, or the wheel that goes over a puddle of water.
In summation, an open differential will channel the engine power through the corner of the car with the least resistance.
You want a somewhat open diff when entering a corner so that each wheel spins in accordance with the path it has to take – longer on the outside and shorter on the inside. However, you’ll want a fairly locked diff when exiting a corner so that the power won’t be “sapped” from the grippier corner of the car by the wheel with least resistance – you want to make both wheels spin in tandem to straighten up the car and put the pedal to the metal properly.
It is to cope with such diverse scenarios that marvelous engineering machines like F1 cars have quite complex differential system. And it is to compensate for our lack of engineering knowledge that Codemasters boils things down to two different mechanisms, a on-throttle (or power) diff and an off-throttle (or coast) one.
When cornering we have these 5 phases:
- Deaccelerating in a straight line
- Deaccelerating while rotating
- Turning
- Accelerating while rotating
- Accelerating in a straight line.
We can straight up drop #1 and #5 out of our consideration as no differential has any affect on these two stages.
The on-throttle differential will influence the car behavior on curved acceleration stretches. The diff has no bearing on straight line acceleration. So only stage #4.
The off-throttle differential will influence the car rotation when braking and turning simultaneously or when simply turning. So scenarios #2 and 3.
When accelerating on corner exit, an over locked on-throttle diff will sway the handling to an oversteery car as the system forces the power to be planted through the outside wheel.
Opening up the acceleration diff too much though will result in an understeery car as the power will be channeled to the inside wheel (lesser load thus less grip thus less traction thus less resistance), making it harder to complete the car rotation as the inside wheel will push to increase the radius of your trajectory – understeering.
If you need to come off the throttle on corner exit to avoid the car going wide, increase the on-throttle differential to lock up the axle, delivering more power to the outside wheel.
If you are losing your rear too rapidly when accelerating out of a corner, decrease the on-throttle differential to unlock the driven axle, enabling the power to be distributed more evenly to the wheels.
That tidbit we all carry around in a scrap of paper in our back pockets about how differential works is a tad misleading. Yes, opening up the on-throttle diff will hurt your acceleration potential in curved acceleration zones. However, overshoot your mark and lock it too much and bam, you’re facing the wrong way in a heartbeat! It is a balance game, not an on-off switch.
And balance geared towards your preference, to your driving style. There are drivers that will perform better with a firm, stable, predictable rear end – Vettel. Then there will be drivers with a liking towards a loose, lively, spirited tail to aid them on completing the car’s rotation – Alonso. Admittedly there are more dominant variables dictating the balance between over and understeering, but you get the gist.
Now with the off-throttle differential. It is all about corner entry, your cornering ability before getting back on accelerating.
Over lock your rear axle when coasting will bound the wheels towards a single spinning rate, inducing understeer as the inside wheel insists on spinning too much, widening your trajectory by trying to increase the radius of the turn.
Now if you exceed the grip available to your rear tires as you enter a corner with a coasting differential that is too opened up, either by carrying too much speed or by over braking when turning in, your car will most likely oversteer as each wheel spins unfetteredly and the inside wheel, content to slack on the job given the shorter path ahead, will not sap the outside wheel’s energy. Your outside tire will dominate the turning, pushing for a shorter radius with not much to counteract it.
If you are understeering on corner entry, unlock your off-throttle differential so that the inside wheel is enabled to spin at a lower rate, decreasing the radius of your curve. Opening the coast diff will supplement your car ability to rotate.
If you are oversteering on corner entry too easily or cannot trail brake properly, lock up your off-throttle differential so that your inside wheel is forced to spin more, sapping the energy of the outside wheel. Closing the coasting diff will reduce your car ability to rotate.
I’d suggest starting with as low an off-throttle setting as you’re able to manage. Lock it up only if the track calls for a lot of trail-braking and your car is too unstable under it or if you are simply oversteering all the while confident that your suspension setup is adequate.
In summation and to put it bluntly:
Oh, you’re fonder of the other way of memorizing this dataset? No problemo, *:
The best setting is a rear axle unlocked just enough so that each wheel is enabled to spin at a rate matching the longer (outside wheel) or shorter (inside wheel) path it needs to take to hug the apex just right.
Nonetheless, bear in mind that the differentials are there really to optimize your cornering rate, your corner speed. It is a fine tuning of your turnability. One should not really try to address handling issues by changing the diffs setup first. If we were to rate the influence all these mechanisms have on over- and understeering, the differentials slot in on the lower end of the list. To proper balance the car to your liking here, you should look at wing, springs, and anti-roll bars first.
Most of the above is from an old post of mine back in the original forums. I should probably update it, but that's the gist.
