The Limited Slip Differential Tuning Guide for Gran Turismo 5 (repost)
Wednesday, October 19, 2011 8:04:33 PM
Basically, once you purchase a car with the GT shop’s.. 2-way differential system, or reasonably close real-world equivalent. Or, more accurately, upgrade your car with a "limited slip differential", you are immediately encouraged to drive as if you had a front-wheel driven car. I.e., to keep all the wheels firmly and steadily on the road, and avoiding loss of grip both in and out of the corners.
So if you have some experience with.. speeding , and perhaps an amount of limited racing experience, then the default settings will work against you. The traction control (TCS) will stop you from increasing the throttle so much you lose grip. While the differential will try to compensate by applying more force on the wheel that is about to lose grip.
This is actually what you see in real life as well in a normally set up car. The wheels need to turn at different speeds, and that is what the differential allows. But - you pull into a corner too hard, and the car loses all force on the wheels if one of the wheels lose grip. While if you lose grip and need to counter a drift, you can't use the force from the drive-train to stabilise the car out of the turn. The reasoning for every car having this as a standard setup being all kinds of logical things in real life - such as that you shouldn't wear out the tires, break the car, kill the suspension, be on your way off on a potato-field if your concentration slips, or constantly fight the counter-force as the wheels turn in different speeds on the inside and the outside. Or speed that much anyway. None of which apply in GT5 (and in a limited sense on the racing track).
Luckily, you can tweak these settings a lot. But the tutorial doesn't quite explain what actually happens, or what sort of driving style will result in better or worse grip or lack of force from the wheels to the road, so here's a small pointer.
The best way to think about this is that you already have a differential system that will make the wheel slipping off the road spin (i.e., you're out driving in the snow, one wheel starts to spin, the other wheel stops - no force comes down on the road). And the limited slip system counters that effect to a higher or lower degree.
Practical example: if you're driving on snow, and one wheel slips, pushing a bit on the breaks to stop the wheel from spinning will make more force be applied to the other tire. This limits the differential.
If you're aiming to become a burnout champion, you will have to lock the wheels on the rear axle together. (A welding torch is not recommended).
This guide therefore suggests a strategy for limiting the slip-differential, and how much it should be limited to produce comfortable but fast and flexible racing.
The setting for the LSD goes from less "sensitivity" to more "sensitivity". What it means is that if the sensitivity is at the highest, the slip-differential will react instantly to uneven force on the wheels, and transfer force to the other side. When breaking down on a straight path, this will stop the wheels from skidding when the wheel jumps off the ground (something that happens to some extent all the time at high speeds). On the other hand, it also means that if you were breaking while turning, the force will be transferred to the outside very quickly, or the wheel that is in most heavy on the road, or in most contact with the road. So if you were breaking hard and expecting the inner wheel to be about to lose grip, you will instead lose force and transfer it to the outside. This then makes your car continue more or less straight ahead while leaving a trail of rubber on the outside wheel. This induces "understeer" - your front will start to drift towards the outside of the corner.
If on the other hand the "sensitivity" is low, the amount of force that transfer to the outside wheel is slower, making the inner wheel lock more easily. And cause "oversteer", making the front slip inwards(or the back drift out).
If you try to counter a drift while breaking (lightly), this will be obvious - if the back drifts out on a high sensitivity setting, the slip-differential will alternate between the wheels while breaking, making you have to stop, and regain stability before braking again. If the back drifts out on a low sensitivity setting, the breaking force on the wheels will be more even, and cause the outer wheel to slip more easily, pulling your back out again, or continuing the rotation.
Some sort of balance is probably a good idea here. A setting that allows you to break slowly while turning without losing grip is necessary on a technical race-track. But on some cars, you get a more predictable breaking behaviour if the back slips when breaking too hard. It only affects the rear, after all, and most of the force will go on the front wheels. So on certain cars, you can use this to induce oversteer on the way into a turn.
Short version - sensitivity all the way up, your car wants to go straight ahead (and counter drift). Sensitivity all the way down, rear wheels lock at the same time, causing you to slip out more easily.
So when racing, depending on what sort of turns you wish to make, adjust either way. The default settings seem to be in the middle betwen the two extremes - one that doesn't lock the wheels, but won't transfer all force to the free wheel.
2. Accelerating out of a turn.
The LSD settings have two settings here - the first is for initial torque. This is the amount of force before the LSD kicks in. (In a sports-car with a terrible stock setup, this could be relatively high, and you will feel the system kicking in. Exciting, but unpleasant and useless). One strategy would be to make the LSD kick in late, allowing you to be rescued by the system if you make a mistake. You get more sudden tweeks and shocks on the car then. But some cars will be difficult to control, and then a high initial torque limit will make the differential kick in and upset your driving. On the other hand, locking the wheels together more will make your car less easy to handle when going straight ahead, and when adjusting into corners.
The other setting is the acceleration sensitivity. Works in the same way as with the braking - the more "sensitivity", the more subtle the limitation will be. On a low-powered car a “high sensitivity” will force the car to move straight ahead and not spin when driving normally (the force will go towards the opposite end of the car, etc). But on a more powerful car, a "high sensitivity" will make the wheels spin and cause instability on even the smallest bump in the road. Or, on cars like the Zonda F, for example, it will make you able to push the throttle to the floor and spin off the road on any gear.
The lower the sensitivity, the more limitation will be kept on the slip.. Then, if you lose grip on the way out of a turn, or when pushing the engine, the force on the rear axle will be more even. This means that instead of being instantly trapped in a counter-drift because increased force will simply make the wheels spin on one side or the other, you will be able to force the wheels to pull you out. It makes you lose force, but if the force was more scientifically applied, you would have wasted it anyway.
So - all racing cars limit the slip in some way or other (just like all cars made now have a differential). The question is just how much the differential should be limited, and in what way.
Nevertheless, remember that constantly limiting the slip will pull on one of the wheels on the rear axle, meaning that it affects the steering also while driving normally - and before the wheels slip. In other words, there is no perfect setup, but understanding what the settings cause might help induce the car handling that feels most comfortable to you and your driving style.