I am here. But I am working on a tight schedule. My semester report is due in 12 days. So I don't have time to type up a lot of stuff. But I can still help.
Try this link:
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www.sportplanet.com]
Despite being for GP2, it is still one (if not THE) best setup guide available on the net. There are actually 3 guides, so check the links one the right side of the page:
Eric Côté's setup guide (the best one)
SimRacingNews' setup guide (very good)
Themis' Guide (also of value)
I know that none of them really covers differentials, but they aren't that hard to figure out. Basically the diff links the two driveshafts to the rear wheels. The driveshafts transmit the power from the engine to the wheels, and since there are two of them, each wheel (in theory) can spin independant each the other. So one wheel could have 55 rotations per second and the other only 5. As you can imagine, that would be a major spin. This is what the diff affects.
By linking the two wheels, you make sure that you do not spin off the track each time you apply power or brake. The tighter the coupling, the less amount of wheelspin difference will be allowed.
You have 4 settings:
NOTE: The wheel seldom LEAVES the tarmac, unless you are really keen on riding the curbs, but it can have very little contact, and thats what I am refering to both here and later in the text. Generally try and minimize this with the spring, roll bar and damper settings before setting the diff. Otherwise you are just masking poor mechanical grip.
Speed shaft difference (acceleration) - This helps when you are accelerating and one wheel becomes unloaded. A wheel becomes unloaded when you turn. So if you accelerate through a right-hander, the right rear wheel tends to lift into the air. Without the diff, it will spin up much faster than the other wheel, and when it makes contact with the tarmac again, you take a big spin. So this is useful when turning and accelerating.
Torque input (acceleration) - This is connected to acceleration in general. When you accelerate, the rear wheels will not have the same level of traction, because of the suspension being in motion and because the tarmac is never excatly the same in two spots. Thus without the diff, you would always experience varying levels of oversteer while accelerating, so you would be flicking the steering wheel from side to side, until you reached the point where the aerodynamics provide the majority of the grip (at about 130 kph depending on wing settings and undercar downforce). So this catches a low speed slidy rear. Beware that the coupling is done to the torque of the engine, so the harder you accelerate, the tighter the rear wheels will be linked together.
Speed shaft difference (decceleration) - This is almost the same as for acceleration. This setting prevents one wheel from locking up when it becomes unloaded. Again unloading of a wheel happens when you turn. Also, take note that this diff setting only kicks in, when you use the engine as a brake. So if you are going through the nice tricky Maggots/Becketts section at Silverstone, this setting kicks in and prevents one of the wheels from locking up will unloaded. If it didn't, then when the wheel returned to the tarmac, then it would be locked and send you into a spin.
Torque input (decceleration) - Again this setting only works when you use the engine as a brake. This links the wheelspin difference allowed with the amount of torque provided by the engine, which means that the harder you let the engine brake, the tighter the rear wheels will be linked. This adds to your braking stability, since the harder you let the engine brake, the more the rear wheels will spin in unison (Good for Hockenheim!!). However this is a disadvantage if you get several places where you need the engine as to brake heavily while turning, since the diff will try and prevent your rears to turn at different speeds (Bad for Maggots/Becketts).
Generally you will set the diff very late in the setup proces, and it induces quite a lot of understeer, especially in the 0-175 kph range. I usually try and keep fair amounts of oversteer in both the aero and mechanical grip while still setting good laptimes. Then increase the diff settings to acheive more stability and hence more confidence in your car.
Happy tinkering!
It's only after we've lost everything, that we are free to do anything.