In order to account for this, all racing games have to incorporate some smart buffers for the gamepad so that the gameplay feels more natural. When it comes to a wheel and pedal setup, we remove these buffers because players naturally use more analog or incremental inputs, thus giving them more direct control over the physics in the game. With the addition of tactile feedback such as rumble and Force Feedback, the wheel can be a superb way to experience a racing game.
Low Frequency Effects (LFE), such as Sub-woofers, can help communicate the state of the car. A powerful sub-woofer can shake the room. It can be great for stepping up the immersion of the game. LFE is really taken to the next level with the addition of a ButtKicker system. The ButtKicker is basically a sub-woofer that you bolt directly onto your chair so you can really “feel” the LFE. The ButtKicker system is an integrated aspect of the VRX racing chair we use at Turn 10 to test the immersion of the game. If you’ve had the opportunity to play the original Forza Motorsport on Xbox with a ButtKicker system, you’d know just how realistic it feels going over rumble strips in the game, or how devastating it feels flying into a wall at 100mph. Unfortunately, even with a ButtKicker, LFE can’t really provide adequate gradations of feedback -- simply put, it’s just not subtle enough.
Controller Rumble is also crucial for a racing simulator. While audio goes a long way towards communicating minute changes to the state of the physics model, we’ve found in testing that players can tactilely discern even the most subtle differences in controller rumble. Players can differentiate hundreds of levels of tactile gradation: from small amplitude, high frequency “buzz” to a full-on large amplitude, low frequency “shake”. In Forza Motorsport 2 we’ve taken great lengths to link this haptic interface with everything from subtle engine revs and gear shifts to tire friction and large scale collisions. It’s really cool to feel the rumble change as you approach and pass peak tire friction. This interface is indispensable for pushing your car to its the limits in a high-end simulator without the use of a wheel controller.
In car dynamics terms, aligning torque is the rotational force exerted around the up/down axis of a car wheel. The most commonly used example of aligning torque is the way in which the front wheels of a shopping cart self-center as you push it. The pivot at the top of the shopping cart wheel creates the up/down axis. As you push the cart, its front wheels self-center in the direction it’s moving by aligning the wheel where it contacts the ground (also called the wheel’s “contact patch”) behind the axis. The force exerted on the contact patch provides torque around this axis like a lever.
As with any lever, there are two primary ways of changing its torque. One way is to exert more or less force on the lever. In a car tire, this is done by changing the friction at the contact patch – usually through tire heat, pressure, or load. The second way is to increase or decrease the length of the lever arm. In a car tire, this is done by changing caster angle or wheel radius. Aligning torque in a car tire is also changed by the spring effect of contact patch deformation, but to get into that would require a whole new article.
Why We Need Aligning Torque
So why is aligning torque important and what does it have to do with Force Feedback in Forza Motorsport 2? When driving a car in real-life, aligning torque is what your hands “feel” in the steering wheel. Aligning torque wants to point the steering wheel in the direction of travel. It centers the steering wheel when you want to go straight. Aligning torque auto-corrects the steering wheel when you are over-steering or drifting. Aligning toque helps you find peak friction when you are under-steering. Basically, aligning torque is the primary language that your front tires use to talk to you.
Oversteer most commonly occurs when you’ve pushed your rear tires beyond their peak friction and the car yaw is greater than the direction of travel. This is what’s essentially known as drifting. The simplest way to recover from oversteer is to turn into the direction of travel. This technique is also called counter-steering. Because aligning torque wants to center the steering wheel in the direction of travel, it aids in counter-steering and recovery from a slide.
Meanwhile, understeer most commonly occurs when you’ve pushed your front tires beyond their peak friction by over rotating the wheel. The only way to recover from this is to back off the steering a bit until you’ve regained peak friction. This is somewhat counter-intuitive. In this situation, most drivers get themselves into a negative feedback loop. The tires are beyond peak friction and they want the car to turn more, so they rotate the wheels more or even get on the brake. This makes the car push more and turn less because the front tires are providing less and less proportional friction the more they deflect and load up. So they turn the wheel more, and so on and so forth until they are off the track.
The feeling of aligning torque falling away sharply tells your hands that you are under-steering and you should back off the steering to regain peak friction. This is critical for pushing your car to its limits. You need to be able to feel the minute changes in aligning torque as your tires approach and surpass peak friction. By sensing and reacting to this torque, you can keep the tires at peak friction. Maintaining peak friction is the key to speed through corners. Very few games simulate aligning torque understeer in Force Feedback at all. Considering that almost every production car in the world from a Ford Focus or a Mitsubishi Lancer to a Ferrari Enzo or Porsche 911 steady state understeers, this is a huge element of driving realism for racing sims to miss in Force Feedback implementation.
When aligning torque is properly simulated in Force Feedback, it helps you to recover from both understeer and oversteer situations more quickly and precisely without large input swings that can disrupt the car and hurt your lap time. It makes steering highly intuitive and ultimately more immersive. The wheel comes alive in your hands and you have incredibly direct tactile feedback. It makes car control easier by providing you with the feedback required to have a dynamic two way conversation with the physics in Forza Motorsport 2. Most games that enable Force Feedback simulate aligning torque in the over-steer case, but very few simulate aligning torque in the understeer case.
Hardware vs. Software
Up to now, I’ve talking primarily about the game software side of Force Feedback and not the physical hardware itself. In my experience, the Force Feedback Wheel is only a part of the overall experience. Most of what you feel, as you play a racing game with wheel in hand, comes down to game design and software. When Force Feedback is poorly implemented in a game, even the best Force Feedback wheel is often a less effective controller than a rubber-band wheel with a good deadzone. In some cases, because of the way Force Feedback is simulated in the software, a really good Force Feedback wheel is even less effective than a standard gamepad with rumble. If Force Feedback is not correctly simulated in the software, some of the features found on premium Force Feedback wheels actually detract from the experience and reduce your ability to communicate with the car.
For example, if a game does not simulate understeer aligning torque via Force Feedback (all too common even in premier racing games) and you are using a wheel with 900 degrees of rotation, then at any one time almost 800 degrees of that wheel rotation will give you incorrect or unrealistic feedback. Since the Force Feedback is not telling your hands to what degree the car is under-steering, you could be pushing straight off the course without any useful tactile information at all. You are left with what amounts to a huge outer dead-zone of useless steering play and inaccurate Force Feedback.
Delayed Impulses
There is another aspect of delivering good Force feedback that is hard to definitively pin on either the hardware or the game -- rather, it has more to do with how fast the game’s physics engine crunches its code. Often times, Force Feedback in some racing sims feel “jerky” or “stuttery” as a result of a poor update rate from the console to the hardware or a poor update rate in the physics simulation itself.
Some racing games only run their physics at 60 hertz – the same frequency as their graphics. This means that the in-game physics only update 60 times per second. 60 may sound pretty fast, but let me give a more concrete example. Let’s say a car is traveling at 200 mph or 98.4 meters per second. At 60 updates per second, that car travels almost 1.6 meters (5.38 feet) between each update of the physics engine. As you can imagine, a lot can happen in 1.6 meters of travel.
For example, the car could travel over several smaller bumps or even one huge bump in the track surface. Because of how these bumps are applied at the physics update, they can cause some big anomalies and even send the car flying. There are multiple ways to deal with this. The net effect usually results in a buffered and unresponsive physics system -- the real-life equivalent of driving in molasses. The higher the update rate, the more realistic your simulation is going to be and less susceptible to such anomalies.
Interestingly, though these physics system buffers are only a hack for inadequacy, some racing sim enthusiasts perceive this as a realistic representation of weight and understeer.
Rumble + Force Feedback = Immersion
It’s worth discussing rumble in conjunction with Force Feedback. In a perfect world, your wheel would feature both Rumble and Force Feedback. Unfortunately, very few Force Feedback wheels feature rumble motors. As a result, the game must transmit vibration from rear-tire slip, engine vibration or collisions using the Force Feedback motor. Often this means sending the Force Feedback motor conflicting signals. The primary signal may be front tire aligning torque. However, that feedback is then muddied by vibration forces. Ideally, you want one or two Force Feedback motors as well as at least two rumble motors in the wheel peripheral. This allows the game to send very clear signals about aligning torque in the front tires separately from the rear tire slip, collision and other vibration information.
Occasionally, a game or a console (such as the original Xbox) will not support Force Feedback at all. In this case, you are better off using a rubber-band wheel with a really small hardware dead-zone and rumble motors. You can even find wheels that use the rumble channels to cue steering wheel torque as even this hacked version of rumble is obviously better than driving with no feedback at all.
The worst of all worlds is using a high quality Force Feedback wheel, such as the Logitech G25 Racing Wheel or Driving Force Pro in “rubber-band” mode. In this mode, the Force Feedback motor is used to automatically center the wheel like a mechanical spring or a rubber-band. In my experience, even the best Force Feedback motors operate poorly as a rubber-band; they generally aren’t smooth enough and the gears in the motor can be unnecessarily loud.
Recently, it has been reported that the Playstation 3 will feature neither Rumble nor Force Feedback. I can say from personal experience that it’s very difficult to create a high end racing simulation experience without Force Feedback. I can’t even begin to imagine how difficult it would be to deliver an immersive racing experience without even rumble. Again, without Controller Rumble, even the casual racing gamer suffers.
More Feedback, More Realism
I’ve rambled through several Force Feedback issues in this article. In closing, why is Force Feedback such a critical issue to racing simulation? Racing in the real world is a truly multisensory experience. Cutting out Force Feedback (or rumble for that matter) is chopping out a piece of the experience. Yet, for Force Feedback to be useful, both under-steer and over-steer aligning torque must be accurately simulated in the game. Still, the best wheel in the world is powerless against bad software and game design. Though Force Feedback can be extremely useful, it’s even better when it’s combined with rumble. Hopefully you learned a thing or two in this article. I know we have in tuning Force Feedback for Forza Motorsport 2.