| LIMITED SLIP DIFFERENTIAL TUNING FOR FORZA MOTORSPORT |
| Limited slip differential tuning in Forza Motorsport 4 is one of the more underrated elements of getting the most balanced performance out of your vehicles. Learning to tune the LSD will yield tremendous benefits in balancing your car. |
| Limited slip differentials have a greater effect on oversteer/understeer characteristics than you might think. We spend so much time tweaking our Spring Rates and ARBs that the LSD, at times, gets overlooked. But if you think about it, the LSD controls the split of rotational speed at the driven wheels, so needless to say, this variation between the inner and outer wheels will affect the vehicle's balance, both under deceleration, and when we start putting the power down on corner exit. |
| For the purposes of getting a feel for how your LSD settings affect cornering, let's break down a corner into three phases of transition: |
| 1- TURN ENTRY (OFF THROTTLE) 2- MID-CORNER TRANSITION: DECELERATION TO ACCELERATION 3- APPLICATION OF THROTTLE ON TURN EXIT |
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| A relatively low deceleration setting on the 2 way LSD is desirable. The default setting is 75% which, in my opinion is entirely too high. Before I even turn a single lap, i dial it down to 50% to start, knowing I'll probably lower it. As of right now, with the current Forza 4 tunes in my garage, I'm keeping it in the 20%-30% range with good results. You'll know it's too low if the back end starts to step out on you entering corners off-throttle. |
| FRONT WHEEL DRIVE and ALL WHEEL DRIVE CARS - Run a deceleration setting on the front differential of 0%. Between the amount of available traction needed for braking and turning, the car is going to understeer to begin with. Setting it to 0% will allow the front end of the car to turn in as sharply as possible. The default deceleration on AWD cars is 0% on the fornt, so just leave it there and don't concern yourself with it. |
| REAR WHEEL DRIVE CARS - Right now on my RWD cars (as stated above) I'm in the 20%-30% range, depending on the track. This also goes for the rear deceleration on AWD. Tracks with a lot of low speed, and/or late apexing turns like Road America, Laguna Seca, Bugatti, and Motegi, I'll run a lower % and tracks with more high speed sweepers and larger radius turns like Maple Valley, Suzuka, and Nurburgring I'll set the deceleration a little higher. |
| 2- MID-CORNER TRANSITION: DECELERATION TO ACCELERATION |
| There's a lot of stuff going on here, and what's happening will vary depending on the type of turn. Let's look at two different extremes, here: |
| 1- Tight radius, late apexing turn. 2- Sweeping turn. |
| A LATE APEXING turn can be a real pain in the ass. These types of turns can be identified, generally, by a radius of greater than 90 degrees. For a late apex, the key is to brake deeper into the corner before turing in. On a late apexing corner, a low % deceleration setting has the distinct benefit of a sharp turn in. A LOW DECEL and HIGH ACCEL setting lends well to transitioning from brake to throttle on tighter turns. A sharp turn-in, then a lot of rotation when you apply power as a higher accel setting lends to oversteer and gets the back end of the car to come around. |
| It would seem that the acceleration setting, represented as a percentage, determines how much of the available engine torque is applied to the outer driven wheel. Keep in mind, a regular differential distributes engine torque evenly to both driven wheels. Since the inside wheel has a lot less grip in a corner than the outside (laden) wheel, the 'path of least resistance' principle makes the engine want to apply power to the inside wheel, which is really bad news since we need the power to be distributed to the outside wheel for throttle steer (to rotate the car quickly), then pull us out of the corner. |
| This is why I am of the belief that we should run as much acceleration on the rear LSD as our set-up and driving skill can handle. |
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| A SWEEPING TURN is not as tight, has a larger radius, and has a longer duration. The distinct difference is the amount of steady state steering input needed to drive the corner. The optimal deceleration setting here is different than for a late apexing turn which presents a dilemma since many tracks have a mix of both. |
| If your car has a very low deceleration setting, (see above illustration) it will turn in sharply, but off-throttle as we approach mid corner it will also continue to oversteer while you're looking for the inner wheel to lock up and spin closer to the speed of the outer wheel to make the car 'push' a little bit. The slower the sweeper, the more twitchy and difficult the car will handle in mid corner if the deceleration is too low. This is mainly an issue with RWD rather than FWD or AWD cars. |
| I'll also include double apex turns here as well, which obligates you to turn in, unwind the steering wheel slightly for a brief moment, then turn in again. My favorite examples of this are Andretti Hairpin (turn 2) at Mazda Laguna Seca and turns 2&3 at Sunset Peninsula. If the car is getting loose on you in mid-corner and you like your ARB balance, try raising the deceleration setting a few clicks to dial it out. |
| 3 - APPLICATION OF THROTTLE ON TURN EXIT |
| This is the point of the corner where you're past the apex, you're gradually increasing the throttle to the point that it's wide open as you're unwinding the steering wheel. This is where your Acceleration setting is most noticeable. The higher your Acceleration setting, the more back end rotation you'll get to pull you through the exit of the corner and onto the straight. A high Acceleration setting will give you more on-throttle oversteer, especially in a Rear Wheel Drive car, where it will help get the back end to come around faster. |
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Generally speaking, set the Acceleration setting as high as you can without oversteer. In AWD cars or RWD cars that are tight and prone to understeer, don't be afraid to set your rear acceleration setting high to get a tighter rotation on corner exit. If you find the car is understeering when you get on the power on exit and you have to lift because you're running out of track, crank up the acceleration setting until you can run the car with a Wide Open Throttle on exit without having to lift. It should also be noted here, with AWD, that a rearward bias on the distribution of power from the center diff can also aid in getting the back end to rotate on power if the car is pushy. The reverse also applies here, especially when driving a high powered RWD car with no assists. If throttle application is troublesome coming out of corners, rather than playing around with the suspension to dial out the oversteer, sometimes it's a smart move to reduce the acceleration on the rear diff and call it a day. If the car otherwise feels balanced but you can't put down power (like the wheelspin is immediate when you apply throttle coming out of a corner), it's more likely too much accel rather than a swaybar or spring issue. |