Forza 4 - Your Questions Answered

Development chief Dan Greenawalt tells it like it is

A while back we asked you to submit your questions to Mr Dan Greenawalt, development chief behind the latest Forza 4 game, and question him you did. We sent Dan the thread, and we are pleased to be able to publish his answers today.

Before we get to that, don't forget that you can still win a GT40 replica with PistonHeads and Forza 4 simply by voting on what parts we should fit to the car as we build it in the measured and sterile conditions of, erm, a shopping centre.

To view the video and register to vote just visit this link. The winner of the GT40 will be announced at 19.00 tomorrow. Good luck.

Right, back to the questions. Over to you Dan the floor is yours:

PH - Why is Forza not available to play on PC as the sales would beat any Need for Speed game?

Dan - Forza Motorsport is highly optimized for the Xbox 360 architecture. Porting it over to PC would require a considerable amount of time and resources from the core team. Thus far, we’ve elected to apply our best and brightest towards innovating and incubating new experiences on the Xbox 360.

PH - What suspension kinematics do you have programmed in?

Dan - We’ve modelled the movement found in multi-link (double wishbone), McPherson, solid axle, and swing arm architectures. This has a big impact on how the tyre stays in contact with the road (and changes camber) as the car pitches and rolls. For Forza Motorsport 4, we took another look at how we had these suspension types mathematically modelled. We didn’t like the way the solid axle in particular was moving (one of the simplest architectures), so we took a car apart and studied the movement. After that, we figured we should reuse the measuring rig to better investigate a larger range of suspension types. This had a considerable impact on the perception of roll in both classic cars as well as the rest of the cars in the game.

PH - Is a live axle car really simulated with a live axle, is a McP strut really reacting like a McP?

Dan - Yes. But honestly, this isn’t the hardest math. Tire simulation is far more difficult and far more critical to making a good simulation. That’s why we’ve focused so much time and energy on improving our tyre simulation every release. The industry’s understanding of the science of tyres is advancing every year. Every year the tire manufacturers learn more. It’s not good enough to follow the text books regarding tyre models from two years ago. We want to use the data that will write the text books two years in the future.

PH - How much of car electronics are simulated? Ie, the McLaren MP4 12C brake steer? Do you program in a system similar in action to the real one with manufacturer feedback?

Dan - It’s a blend. Some proprietary systems are modelled with regards to torque vectoring. However, we’ve generalized the TCS, STM and ABS systems so that they can layer across all the cars in a consistent way.

PH - Or the F458 Italia e-diff, again, do you know how it reacts in different modes and copy it, or just make up what 'feels' ok?

Dan - As you know, the E-Diff does many things. It does torque vectoring as well as assist TCS and STM. It’s also highly proprietary. As mentioned before, we replicate some aspects of proprietary torque vectoring systems, but generalize TCS.

PH - Will we see the end of the 4WD dominance that plagued Forza 3?

Dan - Performance Index (PI) and car classification changed dramatically in Forza Motorsport 4. The AWD cars now generally scored higher. This means they have less headroom for upgrades before they are to the top of the class. Now, of course, we didn’t just add extra PI for AWD. We changed the simulation that drives PI. The two largest changes were:

1. We changed the PI sim track to include more complex corner types and some longer straights. One of the new corners in particular is increasing radius. This corner type naturally favours AWD cars-- as they can really apply their power as they unwind the steering and accelerate through the corner.

2. We changed the simulation code itself to more effectively use understeer on corner exit. This increased the exit speeds of the AWD cars in the PI simulation, therefore giving them a higher PI (and thus less headroom to the top of class). In short, we believe we’ve addressed the issue of AWD dominance at the top of each class.

PH - Tyre wear, will the tyres act in real time, or accelerated wear? Will it include marbles?

Dan - Tyres wear in real-time. Tyres heat in real-time. The tyre carcass flexes and heats up regionally. The tyre gasses heat up as a result of carcass heat and the gas pressure increases as a result of the gas heat. All of the systems are related. All of this data was brought in with all of the other data from our partnership with Pirelli. The tyre data in Forza Motorsport 4 is completely unadulterated. Pirelli performed custom tyre tests for us across hundreds of tyre combinations and conditions. They delivered reams of data and we changed our system so that it could be inserted directly into our simulation without any changes. This approach means that the tyre model in Forza 4 is the most cutting-edge available. Getting this level of partnership from a tyre manufacturer just isn’t possible most companies. This is the same approach that McLaren uses for the simulation they use to train their Formula 1 drivers.

PH - We know that a lot of effort goes in to simulate the varied range of cars in the game, but what about the tracks? One of the biggest differences for me is that some of the tracks have a static feel, there are bumps and ripples in certain tracks that do not appear in the game. What level of detail has gone into improving the tracks for Forza Motorsport 4 over Forza Motorsport 3?

Dan - The tracks have bumps and ripples. These were honed using the experience of professional race car drivers we bring into the studio. If you play Forza Motorsport 3 and watch the replays, you’ll see that there are lots of bumps. The biggest issue is that the suspension of the car absorbs the perception of bumps and ripples. In the real-world you feel the bumps. Some games increase the perception of the bumps by unrealistically adding huge (3+ inches or more) bumps where they don’t exist on the real track. That’s great for making hyper-action, but it isn’t our way.

For Forza Motorsport 4, we did two things:

1. We re-evaluated the different concrete and tarmac surface types on all of the tracks. We looked at the age of the surface and gave each of them a general smoothness score. This variety of surface types and corresponding scores translate into far more bumps and grooves than in Forza 3--but at realistic levels.

2. Of course, the car’s suspension still obfuscates much of the perception of these bumps, because our suspension modelling is realistic. So, we also added more player camera layers to help the bumps make it past the suspension and into the drivers view. This increases the perception of the bumps without sacrificing the simulation.

PH - On some of the cars I felt there wasn't a big difference in sound when upgrading the exhaust will Forza 4 be different?

Dan - We worked with many partners in the creation of Forza Motorsport 4. We partnered with TopGear to bring more levity and humor. We partnered with Pirelli to bring more accuracy to the simulation. We also partnered with Warner Brothers (in Hollywood) to help us get more impact out of our audio. In Forza Motorsport 3, we optimized the audio for 5.1 systems, but many players use their basic television speakers. In Forza 4, we have multiple mixes that are optimized for different speaker setup qualities.

It’s also worth noting that a petrol burning race car is so much louder than even a relatively loud production car. Furthermore, adding aftermarket parts like exhausts change not only the note, but the loudness of a car. However, your speakers are only turned up so loud based on your preference. We have to normalize volumes so that all cars can be heard, while still maintaining authenticity and impact. This means the mix has to be well-architected. This is what Hollywood does so well. We still use real samples to construct and position each car’s audio, but, thanks to our work with Warner Brothers, the mix has been designed to bring out the nuances from each car and its current state.

PH - Also when upgrading the cars will there be the choice of being able to put an engine from another manufacturer into a car e.g a LS3 into a Nissan etc ?