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SCHMEELENDORF!
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Discussion Starter #1 (Edited)
Post your Forza tuning tips here. Please keep extraneous comments to a minimum so this may remain a quick reference guide.

Some of the topics that should be included are: chassis, differentials, purpose-built engines, and gearing.

Keep in mind, what works for one person may not work for another. Ultimately, you must tune for your own driving style and controller setup.


If possible, I would like to request this thread be made a sticky.
 

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Discussion Starter #2 (Edited)
Re: Forza Tuning

Let's start with CHASSIS TUNING FOR CIRCUIT RACING:

I have been researching the nuances of suspension tuning since I starting playing Forza 2. Some of my information has come from forums, some from online guides, some from sites such as DIY Race Tuning, some from tuning calculators, and some from trial-and-error. I hope what I post does not lead anyone astray and that we all become better tuners with the discussion that will inevitably result. Here we go...

I'll start by saying that I always keep everything in proportion to the weight of the car. Let's say we have a FR car with a weight ratio of 52% Front. If you divide 48 by 52, you get .92. I would then adjust all of the rear settings to equal 92% of the front settings. Following this format, you should get an equal amount of roll from both ends of the car.

SPRINGS: I've found that the stock coilover settings are tailored for what would be 1" of static spring compression. If we use the weight ratio above on a 2945 lb. vehicle, the stock front spring rates will be about 765.7 lbs/in. This figure is found by taking 2945 lbs. (total curb weight) times 52% (weight of front of the car) divided by 2 (weight each spring supports). I've recently made the following change to the rest of the "formula": I divide by 2 for racecars and prototypes, divide by 2.5 for production cars with slicks or excessive weight (3,500 lbs +), divide by 3 for production cars with Sport tires, divide by 3.5 for cars with Street or stock tires. This will at least get you close to where you need to be to properly transfer weight and have the suspension not be too stiff. If your car continually slides out mid-corner and your tires are overheating, you should lower the spring rates.

SHOCKS: I've done a lot of trial and error with shock tuning and the following description is what is working for me at the moment. I adjust the bump settings, keeping the numbers in proper ratio (rear = 92% of front), until the understeer and oversteer are in balance (the front end dives in without plowing or spinning the car). I then adjust the rebound setting so that the damping ratio (DR = bump/rebound) is about 70% for racecars/prototypes and 65% for production cars to start. I usually end up with a damping ratio of 60-70% (I have read that great handling production-type track cars will have a 65% ratio and prototypes can have 75% and above due to less overall travel). It's at this point that I am tuning based on how the car feels. The goal is for the car to turn in smoothly without understeering and feel like it is carving the corners as opposed to pushing. The side-to-side transition should feel like the car is low and wide. The car should glide over bumps and most curbs.

ANTI-ROLL BARS: If using the FR example above, I would start with the front at 20.0 and the rear at 18.5. I've run with them as high as 25.0 in the past, but found I could never quite get the car to dive into the corners the way I wanted without dropping the spring rates lower than they should be. When tuning, I don't usually tweak these too much even though, in real-world racing, sway bars play a much more important role in fine-tuning cornering characteristics. I will certainly, however, use these when other suspension components are not adjustable (i.e. - running Sport shocks).

RIDE HEIGHT: I set this as low as possible while making sure the suspension does not bottom out under "normal" conditions, including riding along banked turns. I generally increase the ride height when I decrease the spring rate. The idea is to gain the maximum compliance with the lowest center of gravity.

There are a few nasty corners on certain tracks that the car will bottom out unless you significantly raise the spring rate or ride height. This category includes such corners as Turn 5 of Road Atlanta (after the essesses) and the dip right before/after the start/finish line at Camino Viejo. Whenever you bottom out the suspension, you increase the chances of losing control of your car. I should also add that ride height can work to your advantage. Raising the rear will increase rotation, which can help in tight corners or with cars that understeer. It can also help with weight transfer in a straight line.

TIRE PRESSURE/TEMPERATURE: I always aim to have the racing pressures between 32 and 33 psi and have them the same front and rear. I have searched for tips on how to set up the car to maintain proper tire temps and I basically just aim to keep the telemetry reading dark green (180°-200°) during normal race conditions. If your tires are overheating (yellow/red on telemetry), you should lower the spring rate to reduce weight transfer. There will be instances where the tires will overheat regardless of what you do, such as running the Mulsanne straight at top speed.

CAMBER/CASTER/TOE: Anyone that I have sent a tune to will realize that I don't play around with these settings a lot. I keep both front and rear toe at 0°, the caster at 5°, and a relatively low camber setting. I can get away with this because I use higher ARB and spring rates, so the car doesn't roll very much. Overall, I want to make sure that the outside tire temperature never goes higher than the inside temperature and that the tire is heating evenly. That way you know you are getting the widest contact patch possible instead of riding on the edges of the tire.

BRAKING: I decided to add this as part of the "chassis tuning" due to the effect the suspension can have on braking. Adding race brakes to your car grants the ability to change front-rear bias. In Forza 3, I was able to trail-brake like a mofo, which meant I could push way into a corner and, with the help of the brakes and decel setting on the diff, pull through the corner without decorating the wall. I haven't experienced quite the same success in Forza 4. Anyways, I tune braking based almost entirely on feel. I usually go with a slight rearward bias (48% Front) and soften the pressure to about 98%. This makes straightline braking sketchy sometimes, but I can still hit the brakes mid-corner without spinning.


While some of the above may conflict with real-world race tuning practices, it is as close as I have come to creating a tuning "formula" in an attempt to avoid a random crap-shoot of trial-and-error. One final thing to keep in mind is that when you change one setting, it has an effect on the balance of the car and will likely require you to change another setting to regain equilibrium.
 

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SCHMEELENDORF!
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Discussion Starter #3 (Edited)
Re: Forza Tuning

TROUBLESHOOTING HANDLING ISSUES:

In order to figure out what changes need to be made to improve handling, you need to figure out at what point in the turn the issue is occurring. To begin with, I only make changes to the suspension to affect off-throttle handling. If the car is stable in off-throttle instances, the differential can be used to tweak how it handles when accelerating and braking, including entering and exiting corners under throttle.

TURN-IN: While all the suspension settings combined have an effect on this, I tackle issues with off-throttle turn-in by primarily adjusting damping settings. However, you do need to be careful because if you set the overall damping too high, the car will be non-compliant over bumps and curbing. To improve turn-in, you can also adjust toe settings, but I have found that creates problems elsewhere, such as sluggish transition or instability under braking.

NOTE: Be careful not to mess up a balanced suspension when the problem is actually lift-throttle oversteer (you can check this by going into a corner partially on-throttle, getting the car near its grip limit, and lifting half way through; if the back end kicks out or the car spins, change your differential settings not your suspension settings).

STEADY-STATE CORNERING: The setting most heavily affecting this is ARB. If your car feels like it is sliding out mid-corner after a smooth entry, you should lower your ARB setting. If this does not work, try reducing your spring rate or increasing ride height. Your car may be pushing due to lack of suspension travel.

CORNER EXIT: If your turn-in is balanced, then corner exit should be as well, for the most part. Since you are normally on-throttle while exiting a corner, you would fix issues with this by changing the differential settings. It is possible to lower the rear spring rate or damping settings to make the back end more stable, but this will have an effect on weight transfer and turn-in response.


A good place to test this theory is the Carousel at Road America. To maintain momentum throughout the corner, you need a smooth turn-in and good steady-state grip. I know I'm preaching to the choir as I'm sure many of us have experienced oversteer going into the turn and/or pushed to the outside mid-corner.


Please feel free to add any suspension tuning strategies that you use. In a week or so, we can change to another area of tuning, such as differential settings.
 

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Discussion Starter #4 (Edited)
I put together a build to help illustrate some of my tuning techniques. The specs are as follows:

CAR: 2009 BMW 135i Coupe
CLASS: A600

POWER: 450 hp @ 6900 rpm
TORQUE: 395 lb-ft @ 2000 rpm
REDLINE: 7600 rpm
WEIGHT: 2945 lbs/52% Front

If you want to build the same car to mess around with, add the following parts (if it is not listed keep it stock):

RACE: ignition, exhaust, cams, displacement, flywheel, brakes, suspension, front and rear swaybars, clutch, transmission, differential

SPORT: air filter, weight reduction, driveline, tires (front - 235/35R18 and rear - 255/35R18)

WHEELS: Advan RGII

AERO: Hamann front, BMW rear, BMW wing


I placed the car in the FJ garage and will be resyncing it when needed. I'm still playing with the suspension settings, but the setup already demonstrates the on-throttle/off-throttle issue discussed above. Following are the initial tuning settings:

TIRE PRESSURE: Front - 29.5 psi/Rear - 29.5 psi
GEARING: Final - 3.20, 1st - 2.65, 2nd - 1.90, 3rd - 1.45, 4th - 1.17, 5th - 0.98, 6th - 0.85
CAMBER: Front - -1.2°/Rear - -1.0°
TOE: Front - 0°/Rear - 0°
CASTER: 5.0°
ARB: Front - 20.00/Rear - 18.5
SPRING RATE: Front - 600.0 lb/in/Rear - 554 lb/in
RIDE HEIGHT: Front - 5.5 in/Rear - 5.5 in
REBOUND: Front - 7.6/Rear - 7.0
BUMP: Front - 5.0/Rear - 4.6
BRAKE BALANCE: 47% Front
BRAKE PRESSURE: 110%
DIFFERENTIAL: Acceleration - 75%/Deceleration - 75%

At this point, the car will maneuver corners fairly well, but can still be pushed past its grip threshold. The differential deceleration setting is too high to help rotate the car into a corner and getting back on the throttle after the apex will cause the back end to slip out.
 

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Discussion Starter #5 (Edited)
DIFFERENTIAL TUNING FOR CIRCUIT RACING:

I'll start by saying that I got most of my information regarding differential tuning in Forza 4 from DIY Race Tuning and the rest through trial-and-error. Tuning the differential will change how the car reacts when letting off of and applying the throttle. In my opinion, diff settings can make or break your tune since you will transition on/off throttle at nearly every corner you encounter.

When you are maneuvering a corner, the inside must rotate fewer revolutions than the outside. To accomplish this, a differential works to allow the wheels to spin at different rates. Some vehicles come from the factory with an "open" differential while others come fitted with a "limited slip differential". Well, what's the difference?




With an Open Differential torque will follow the path of least resistance. This can be problematic for your track car if your suspension settings are stiff and the inside wheel lifts off the ground. The differential will send all of the torque to the lifted wheel while the planted wheel receives none. Your car slows down and you lose precious seconds.



With a Limited Slip Differential the opposite is true. Torque is directed to the wheel with the most grip. This is why a race differential is such an important upgrade. Time and time again I have purchased cars off the Auction House "maxed out" in the power category but they still sport the stock differential. LSDs are key in planting the power on a 1,000hp+ beast.


Moving on we need to look at the "slip" part of limited slip differential. The slip setting, simply put, will determine how much of a difference in rotation between the two wheels is allowed before the diff locks and the wheels are forced to spin at the same rate. Changing this setting can drastically alter the way your car enters and exits corners.

DECELERATION SETTING: I've had the most success running the decel setting at around 25% based on the stiffness of my suspension settings. I know the decel is set right when I can let off the throttle close to the corner and the car feels like it is pulling itself around the curve smoothly without a bunch of tire noise. If your setting is too low, the car will plow through the turn and head off track when you release the throttle. If your setting is too high, the car will over-rotate/spin going into the turn.

ACCELERATION SETTING: I typically start the accel setting about double what the decel is set at and adjust from there. If your setting is too low, the car will want to straighten out and head off track when you get back on the throttle. If the setting is too high, the car will over-rotate and the tires will overheat.

CENTER DIFFERENTIAL SETTING: I usually set this between 70-80%. This gives my AWD cars more of a RWD feel. While it can result in more oversteer, the front wheels will typically pull you out of a spin.

Once you have a suspension setup you are happy with, try tuning the differential to dial in the turn-in and corner exit.

NOTE: The best way to really test how differential changes affect handling is to add a race differential to a car with stock suspension and observe the results of each adjustment by viewing the individual tire speeds on the telemetry screen. I learned this from our Forza 3 GT3RS series.
 

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SCHMEELENDORF!
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Discussion Starter #6 (Edited)
Unfortunately, I haven't found FWD and AWD differential tuning quite so straight-forward.

With FWD, I have tried somewhat high settings (around 60%) and really low settings (about 8%). I've noticed that too low a setting results in a lot of lift-throttle oversteer while too high a setting tends to make the wheels lock and pull the car straight off track, especially in high-power vehicles. My most current theory is that, since the setting determines how much difference in rotation will result in lock, a higher setting is better for tighter corners and a lower setting for wider corners.

With AWD tuning, I set the rear up like a normal RWD car and just move the front acceleration setting down 1% at a time until it handles the way I want. The stock settings for the race differential put the front acceleration at about 2/3 of the rear acceleration, so I've been using that as my starting point.

UPDATE: I have added my 1,000 hp Aventador to the FJ garage. The differential settings are as follows:
FRONT - Acceleration - 35/Deceleration - 0
REAR - Accleration - 50/Deceleration - 25
BIAS - 70% Rear

The car cuts around corners whether on-throttle or off with a smooth transition in between. It does slide out from time to time, but only because it's on stock tires.


Please feel free to add any differential tuning strategies that you use. In a week or so, we can change to another area of tuning, such as engine builds and gearing.
 

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SCHMEELENDORF!
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Discussion Starter #7 (Edited)
I've gone ahead and made further adjustments to the 135i. The new tuning settings are as follows:

TIRE PRESSURE: Front - 29.5 psi/Rear - 29.0 psi
GEARING: Final - 3.20, 1st - 2.65, 2nd - 1.90, 3rd - 1.45, 4th - 1.17, 5th - 0.98, 6th - 0.85
CAMBER: Front - -1.2°/Rear - -1.0°
TOE: Front - 0°/Rear - 0°
CASTER: 5.0°
ARB: Front - 22.00/Rear - 20.3
SPRING RATE: Front - 550.0 lb/in/Rear - 507.5 lb/in
RIDE HEIGHT: Front - 5.6 in/Rear - 5.6 in
REBOUND: Front - 7.7/Rear - 7.1 (66% Damping Ratio Front and Rear)
BUMP: Front - 5.1/Rear - 4.7
BRAKE BALANCE: 48% Front
BRAKE PRESSURE: 98%
DIFFERENTIAL: Acceleration - 52%/Deceleration - 26%

I lowered the spring rate and increased the ARBs/damping for better weight transfer and quicker response on turn-in (and to get rid of slight rear end cycling during acceleration). I also increased the ride height to improve tire compliance and lowered the rear tire pressure to reduce response (in this case traction loss).

With these changes in place, the front end dives into corners, the suspension absorbs most bumps easily, and the car will slide out when driven at 10/10ths. The back end can still get a little squirrely if you jam on the throttle exiting a corner, but, keep in mind, it's trying to put 395 lb-ft of torque down on 255 tires.


FINAL THOUGHTS ON SUSPENSION/DIFFERENTIAL TUNING:

1. You will almost always have to compromise when tuning for any specific track. The car will not handle the same in high-speed sweeping turns as it does in low-speed hairpins. Tune your suspension/differential for whichever part of the track is most crucial to lower lap times.

2. I encourage you to tune so that your car is at its limit at 9/10ths driving. The car is fastest at its grip threshold. Anything more or less and you are wasting the car's potential.

3. AERO: You'll notice that a majority of my tunes do not include aero pieces. I generally view them as a hindrance because they add weight (both the parts and the increase in downforce) and only help part of the time (above 60 mph). Top circuit racing teams, like Ganassi, trim out their aero to reduce drag and increase straight-line speed, so aero can hurt as much as it can help. If I do add a wing and/or splitter, I make sure to either increase the ride height or add spring rate to compensate for the additional suspension compression that will occur at higher speeds.

4. Whenever possible, drive the stock version of the car you plan on tuning. That way, you will know if your changes have improved the handling or made it worse. I've found this particularly helpful with my Aventador and 458 builds since these cars handle really well stock and it's easy to mess them up.
 

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Discussion Starter #8 (Edited)
ENGINE BUILDING FOR CIRCUIT RACING:

It's very tempting in Forza to slap a bunch of parts on a motor and make huge horsepower numbers believing it will make the car faster. It's also one of the more frustrating aspects of the game because it seems to work more often than not. Leaderboard cars end up being ridiculously over-powered, under-tired turds with excessively-narrow gearing (rant concluded).

Realistically, the shape of the power curve, the area under the curve, the powerband range, and the gearing determine how fast a car is. DSport Magazine published an article called Learning Curves written by Allan Lockheed, Jr., who developed a race engine design program called Engine Expert. Engine builders use it to design parts with manipulating the power band in mind. I'm going to try to relay the relevant information as it pertains to Forza tuning.

PARTS: There are different trains of thought when it comes to parts choice. For a while, I was only picking engine parts that also reduced weight thinking power-weight ratio was the most important thing. Then, I came across an article on dyno graphs and began to change the way I build engines.

As noted in the article, the first thing you need to figure out is "what is the engine going to be used for?". Since ours is for circuit racing (and not drifting or rallying), we want good low-end torque for acceleration and good top-end horsepower for overall speed. Basically, cake and eat it. Many engines will have one or the other covered, requiring you to build the other end up.

Here are some of the parts you can add to change each end of the power curve:

LOW-END TORQUE: increased displacement, pistons, superchargers, intake and exhaust
TOP-END HORSEPOWER: race cams, turbochargers

While it is easier to pick a car that already has a good powerband, it is possible to take a car with poor characteristics and make it better.
 

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Discussion Starter #9 (Edited)
ENGINE BUILDING FOR CIRCUIT RACING (CONTINUED):

To make this explanation as coherent as possible, I have created a .jpg drawing with some labels that I will reference in subsequent engine (and some gearing) posts.

POWER CURVE/POWERBAND: Below is the power curve for the BMW 135i. The orange horizontal line connecting points B and C highlights the powerband. When adding parts to an engine, you want create a wide powerband (as much space between points B and C as possible).

So, how do you use a dyno chart for tuning? Well, when you shift from one gear to another, there is potential to upset the balance of the car. To maintain stability when shifting, two key ideas (both found on the dyno chart) should be observed:

1. Always keep the engine speed above peak torque (POINT A).

2. Time the shifts so that power at the up-shift recovery point (B) is the same as the shift point (C).

Although it is sometimes incredibly difficult in Forza, I try to follow this advice when building engines and adjusting gearing.

Following the guidelines above, I should never let the revs drop below 2000 rpm (no problem in the BMW 135i) and always shift at redline. However, this puts me below the ideal up-shift recovery point (5800 rpm) due to the rev drop experienced during shifting.

I have 3 options to remedy this rev drop:
1. I can extend the rpm range with cams (race cams already installed).
2. I can add parts to make the car change gears faster (race clutch already installed).
3. Or, I can shorten the gearing (will be discussed in the gearing post).

AREA UNDER THE CURVE: A car with more area under the power curve within the powerband will put down faster lap times than a car that is peaky or one with maladjusted shift points. Some of my high-horsepower builds have had somewhat peaky power curves because I was adamant that they have exactly 1,000 hp. This makes them fun to drive in a straight line at high rpm, but not-so-fun while going around a curve at lower rpm. In the end your goal should be to have the widest powerband possible (i.e. - the greatest distance between points B and C).
 

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Discussion Starter #10 (Edited)
GEARING FOR CIRCUIT RACING:

I would imagine that most of us have played around with individual gear settings to see what effect it had. The following is the result of a bunch of reading and some good ol' fashioned messing around.

I always start gear tuning by optimizing the gears to maintain engine speeds within the powerband. Below is another MS Paint drawing to help make sense of the transmission tuning screen.

We are used to seeing the yellow lines on our tuning screen. Moving the sliders left or right will shorten or lengthen the yellow lines. But what does it mean?

If you move the slider for 1st gear, you will notice that Point 1b will move side-to-side along the redline marker. If you were to finish tracing the dotted purple line all the way down to the MPH axis, you would know what speed the car will achieve at the end of 1st gear. I personally adjust first gear not for final speed, but to control wheelspin on launch or to help with a low-speed hairpin.

When you adjust the slider for 2nd gear, you see Point 2a moves vertically along the dotted purple line while Point 2b moves side-to-side along the redline. Just like with 1st gear, the vertical purple line shows you what speed you will be going at the end of the gear. However, the horizontal pink dotted line, when traced to the RPM axis, denotes the rev drop when up-shifting. By shortening the gear, you reduce the rpm drop (i.e. - shorten the distance between 1b and 2a, 2b and 3a, etc.). I should also add that shorter gears will allow your car to stop in a shorter distance. It can also affect your turn-in response/stability.

FINAL GEAR RATIO: Once you have individual gears set properly, you can use the slider on the final gear ratio to determine the top speed/acceleration. I tend to just set the final ratio so that I can reach maximum speed and still have a few rpm left for drafting. In other words, I try to never hit the rev limiter.

One difficult part of gear tuning is when you enter a corner and are "between gears" on the exit. "Between gears" means if you use the gear below you hit the rev limiter and if you try the gear above the car bogs down. Not only can this affect your initial turn-in (the car doesn't respond as sharply if you are in too high a gear), but it also affects your exit speed (an immediate shift or being out of the power band will slow you down). You may need to lengthen/shorten individual gears for specific corners of a track. This is another reason race transmissions are a good upgrade.

REALITY CHECK: The challenge of tuning gear ratios as described above is that the RPM axis is not labeled accurately. To help, you can use the first telemetry screen. While it is harder to tell what RPM you are at as compared to the analog tachometer, you can see the shift point and recovery horsepower figures.


CLUTCH/FLYWHEEL: Unfortunately, because of the points involved, I usually end up using these to level a car's performance index. Realistically, these two items can have a huge effect on shifting and rev drop. Lightweight flywheels are good because they help the engine rev faster, which improves acceleration. But, they also allow the rpm to drop faster because of less rotating mass. When you upgrade your clutch, it not only reduces weight, but it also increases shift speed. This can be a life-saver if you have an engine with a quick rpm drop.
 

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Discussion Starter #12 (Edited)
I've made some changes to the "Chassis Tuning" section, specifically regarding spring rates. This is what is working for me at the moment and it has made dramatic improvements to some of my favorite tunes.

I have also reworked the "Differential" section as the DIY Tuning images are no longer hosted. Much of the information is new including a brief explanation of how a differential works.

I hope this new information as well as the old will translate well to Forza 5/6, Project CARS, or any other racing simulator.
 
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