Forza Motorsport 4 Tuning Guide and Car Upgrades

By   /   Oct 12, 2011


Turn 10 Studios have introduced quite a few changes in Forza Motorsport 4 physics especially how tires react to real world situations, how track bumpiness affects the driving, steering has been overhauled, and how suspension works in the game.

The goal of tuning your car is to make the right trade offs for right scenarios and this guide will help you do just that. It is really important that you only upgrade the right components of your car and you may end having to adjust all these components again just to make it drive-able.

Our goal is to walk you through each tuning option, give you the pros and cons, and give you insight how that specific part will hold under different conditions.

For this reason, we have taken the suggestions of the pro’s and have written them in a precise way to help you understand the basics of tuning and upgrading your engine parts in Forza Motorsport 4.

Table of Content

Forza 4 Car Tuning

Forza 4 Car Upgrades

Forza Motorsport 4 Car Tuning

Advanced Tuning tips by Manual Clutch, CerebralColton, and KTLR.

Tire Pressure

I have already explained why having good tires is important to get the best out of your engine. Tire pressure affects a tire’s grip, responsiveness and wear so adjusting front and rear tire pressures under different circumstances is important to keep that grip. You need to adjust the front tire pressure when the tires are cold so that they can reach their grip potential after they heat up to race temperatures.

Maximum grip potential of a tire ranges from 180 to 200 degrees. You can use the telemetry to get an idea about the grip potential of your tires and what setup you would need in race.

Peak friction of the tires is generally 32 psi but, you are doing even if you are somewhere between 30-34 degrees. You will still have necessary grip. You will know the tire temperatures and PSI once you have raced through few laps and tires have heated up.

When your tires heat up, you may need to do some adjustments to keep them in good grip range. The general rule is if the tire center is hotter than edges, tire pressure is too high and you need to reduce 1 psi for each 5 degree temperature difference.

If tire edge are hotter than center, tire pressure is too and you need to add 1 psi for each 5 degrees of temperature difference. If inner edge of the tire is hotter than outer edge, your tires have too much camber so you need to decrease negative camber.

If outer edge is hotter than inner edge, there is too much toe or not enough negative camber so you need to increase negative camber or decrease toe-in. If the tire is below peak temperature range, tire pressure is too high or tire is too wide or springs are too soft at the axle. In this case, you need to decrease tire pressure or reduce the tire width or stiffen up the springs and sway bars on the axle.

If the tires are above peak temperature range, tire pressure is too low or tire is too narrow or springs and sway bars are too stiff at the axle. In this case, you need to increase tire pressure, increase tire width or soften up springs and sway bars on the axle.

If front tires are hotter than rear tires, your car will under steer. This is because, too much front spring/sway bar, not enough rear spring/sway bar, or front pressure is too high or front tires are too narrow or rear tires are too wide. In this case, soften up front spring and sway bar, stiffen up rear spring and sway bar, decrease front pressure or increase rear pressure.

If rear tires are hotter than front tires, your car will over steer. This is because, too much rear spring/sway bar, not enough front spring/sway bar, rear pressure is too high, front pressure is too low, rear tires are too narrow or front tires are too wide. In this case, soften up rear springs and sway bar, stiffen up front spring and sway bar, decrease rear pressure or increase front pressure.

Your best shot to help you adjust these settings appropriately is Telemetry. Instead of following your guts when adjusting the tire pressure, do a quick 3 lap session in quick race and find out your tire pressures and other variables that will help you adjust your tires’ pressure for that track.

Alignment

Camber, Toe, and Caster are the three major alignment parameters. Let’s first see why these alignment parameters are important to adjust.

Camber is the inward or outward tilt of the wheel, which makes it the most important alignment adjustment for a street car. If you want maximum cornering force, set camber of the outside wheels on the ground to about -0.5 degrees.

It is good to have some negative camber as it increase cornering force but the important question is, how you would know how much negative camber you need for a particular track ?

You will find this out in a quick session before the race by measuring the temperature profile across the tire immediately after completing few laps. You want the inboard edge of the tire slightly hotter than the outboard edge.

Toe affects three major aspects of car performance. Tire Wear – excessive toe-in or toe-out can cause the tires to scrub, since they are always rotating relative to the direction of the travel.

If you set too much toe-in, it will cause accelerated wear a the outboard edges of the tires and if you set too much toe-out, it causes wear at the inboard edges of the tires.

Straight-line Speed – When the steering wheel is centered, toe-in causes the wheels to tend to roll along the paths that intersect each other. Under this condition, even with slight steering input, the rolling paths of the wheels don’t make any turn so toe enhances the straight-line stability and helps you keep the speed.

Corners Entry – If the car is set up with toe-out on the front tires, any small steering angle will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Under this condition, the car will always be trying to enter a turn, rather than maintaining a straight line speed.

Now we are left with Caster. It’s tricky, and difficult to grasp but let’s try. Caster is your angle to which the steering pivot axis is tilted forward or backward from vertical, as viewed from the side. In a car, ball joints connect your wheels and steering column. The angle between the joint and the steering is called the caster angle.

You have positive and negative settings for the caster. It’s your low and high settings in Forza Motorsport 4. High caster setting is good for straights but makes it harder to turn, low caster is good for turns but makes it harder to keep the straights.

Tuning these settings depends on your style of driving. Do you understeer or oversteer through turns ? This will decide how you should go about tuning the alignment in Forza Motorsport 4. Remember, it will need great deal of trial and testing before you will finally fine tune the alignment of your car.

Tuning Camber
To adjust Camber, stop the car on a straight road with no elevation and go to telemetry to note the camber angle the car makes with the road. If it matches the setting you have tuned then you are on a flat surface.

Do a quick race and after three laps, watch the replay. Launch Telemetry and go to ‘Tires Misc’ to get what you need. You need to note the several times you see a positive camber for your front and rear tires by looking at the camber angle.

Once you have noted down these values, go back to tuning adjust these settings as follows:

  • Positive camber on straights – Decrease camber by .1
  • Positive camber on turns – Decrease camber by .1
  • No Positive camber on straights – Increase camber by .1
  • No Positive camber on turns – Increase camber by .1

We can conclude that positive camber reduces traction and stability. Now, let’s tune for cornering:

For Left Turn

  • The right Tire must be less than or equal to 0.0 degrees.

For Right Turn

  • The left Tire must be less than or equal to 0.0 degrees.

We can conclude that close to 0 better the handling and anything that’s above 0 means that the tire is not helping you. You must have negative camber and if you are tuning for drag racing, set camber and toe at 0.

Toe
Toe improves the handling of the car for corner entry.

Front Toe + Rear Toe 0

  • Better Corner Entry Any Car.

Front Toe – Rear Toe 0

  • Reduce Steer Sensitivity Bad Corner Entry.

Front Toe 0 Rear Toe +

  • Under steer tendencies but Better Corner Exit in any Car and stability under braking.

Front Toe 0 Rear Toe –

  • Slow Corner Exit.

Front Toe + Rear Toe +

  • Provides stability under braking and creates over steer tendencies in cornering.

Front Toe + Rear Toe –

  • Amazing Handling on any car but can cause under steer.

Front Toe – Rear Toe +

  • Amazing Handling on any car but can cause over steer.

Front Toe – Rear Toe –

  • Oval track.

Brakes

Brake Bias maintains the balance between the front and rear brakes. It is represented by a percentage such as, a brake bias of 65/35 means that the front brakes get 65% of the braking power, and the rear brakes get 35% of the braking power. It’s an important setting that you would need to adjust subjected to how you go into the corner and get out of it.

Now to the tuning part – When you move brake bias toward the front brakes, the car is tight and more stable while braking and entering a turn. When you move the brake bias toward the rear, the car is loose while braking and entering a turn.

Be careful though, excessive front braking can lock up the tires and decrease overall effectiveness of your brakes since you are not slowing down the car by using the rear brakes.

It is recommended that your car always have more front braking power than the rear because the weight transfer during braking loads the front tires only. If you set brake bias toward rear, the rear tires will lock as weight transfers forward and makes the rear of the car lighter.

Set the brake bias between 70/30 and move from there to fine tune your car. Don’t forget to ‘Turn ABS OFF’. How would you fine tune the brake bias ? Replay and Telemetry combo… read the telemetry for friction.

How Should You Read Telemetry For Friction ?
Red Circles is a visual of the grip available at each tire, and the blue lines inside them are the amount of grip you are actually asking the tire to produce. This displays a more detailed brake down of the “Friction Circle” type telemetry from the “Body Acceleration” telemetry screen.

If you watch the red circles off the start line, the front ones will get slightly smaller and the back ones will grow. That is because a tire’s grip is related to the amount of weight on that tire more weight = more grip, to an extent. So as you jump on the gas, weight shifts backward, and the rear circles grow because your rear tires have more grip.

When you go into a corner, you will also see the circles change size as weight shifts side-to-side. jump over a curb, and the circles disappear if the tire leaves the ground! The blue line shows how much you are asking of the tire – if it is outside the red circle, it means you are pushing that tire too hard and it has lost grip, so it is sliding. If you look at the telemetry during a spin, the blue lines will be well outside the red circles.

If the blue line is inside the circle, it means that there is more grip available, since the circle is the limit. You are using your tires most effectively when the blue line is touching the red circle.

Notice while Braking which circles are getting bigger, usually the front will get bigger than the rear with the bias > that 50% Front. Keep moving 1% Front till you have lost grip completely skidded out as a result of understeer when braking. Move back 1% to be in the safe zone.

Tuning Brake Pressure
Once you have found the ideal setting for brake bias, the brake pressure will increase your stopping power. To fine tune brake pressure, look at the brake indicator and notice if you are at 100% or 70%.

Subjected to your braking style, you may do one of these:

  • On Demand (Pull the trigger all the way back)
  • On Power (Pull the trigger all the way back with acceleration)
  • Off Throttle Down Shift Half Brake (Pull the trigger half way)

On Demand
Go for less brake pressure as you want the tires to skid only when the trigger is pulled all the way back. Start at 100% and keep going down 5% till you have the perfect brake. Using the Telemetry, make sure you have 4 big red circles when skidding to show good brake bias.

On Power
Similar to On Demand but make sure you get into a race-brake situation you are locking the front tires and burning the rear tires.

Off Throttle
Squeezing the brakes coming out of the corner is similar to squeezing the throttle, you will learn it over time and it comes natural afterwards.

Differential

Differential controls how your car transfers its power and torque to the road. Differential sends the power to the wheels with least grip and because of the way your car transfers power to the wheels, it is prone to wasting it and losing traction.

Similarly, when the differential sends the uneven amount of torque to the wheels, the limited slip kicks in, and locks the wheel together. Though, it evenly locks both wheels still one wheel is receiving more torque.

Differential has two settings, Acceleration and Deceleration. Acceleration controls at what point the differential locks while on gas. Having a higher percentage of acceleration will prevent each wheel from slipping, which will allow you to harness more power when exiting a corner but if you are driving an RWD car, it is easier to spin out a drift.

Having a lower percentage will make it easier for each wheel to slip, resulting in power loss when exiting a corner but if you are driving a RWD car, it is hard to spin out and drift.

Use the high-slip rate, even in front wheels because it usually creates a less sloppy feeling when you exit a corner and it allows you to leave the corner with higher speeds but if back-end of your car slides out more than you should stick to lower rate.

Deceleration controls at what point the differential locks when you let off the gas, usually when entering the corner. The high the rate, the more stable your car will be.

It will make your car less agile, and can cause under steer. Having the higher rate while accelerating, makes it harder to stop the skid, so be careful with whatever setting you choose. Use the low-slip rate here, because it will make your car more agile. If your car tends to over steer, increase the slip-rate a bit.

The central differential of AWD cars control how the torque is divided between the front and back wheels. It sends more power to wherever there is least amount of grip, just like any other differential. Rear biased central differential gets the most performance out of AWD, so give it a try.

Damping

It controls the suspension’s stiffness and compression between wheel and wheel-well. Rebound and Bump work in ‘reverse-way’ like having the Front Rebound higher than rear increases grip on rear, because more weight is concentrated in the front tires under spring compression, so rear wheel con work more freely.

Rebound Stiffness

Increasing Front Rebound

  • More grip in the rear.

Decreasing Front Rebound

  • Reduces transitional under steer.

Increasing Rear Rebound

  • More grip in the front.

Decreasing Rear Rebound

  • Reduces transitional over steer.

Front biased Rebound

  • Increases under steer & increases grip in RWD cars, sacrificing turn-in slightly.

Rear biased Rebound

  • Increases over steer & highly recommended for FWD & AWD cars.

How high rebound setups you can have depends on the Bump stiffness that you have set. If you are using high Rebound with low Bump, your car may get upset by curbs etc. This is modified by ride height and suspension stiffness.

Higher Rebound than Bump is must but the Bump Stiffness should be 75% of the Rebound’s stiffness at maximum. Low Bump Stiffness goes great so don’t limit yourself with officially given tip that 50% of the Rebound’s stiffness should be a minimum.

Bump Stiffness
It fine tunes damping and suspension.

Increasing Front Bump

  • Increases under steer and slightly increases rear grip + modifies the effectiveness of Damping and Spring setups.

Increasing Rear Bump

  • Increases over steer and slightly increases front grip + modifies the effectiveness of Damping and Spring setups.

Decreasing Front Bump

  • Improves bump absorption + modifies the effectiveness of Damping & Springs.

Decreasing Rear Bump

  • Improves bump absorption + modifies the effectiveness of Damping & Springs.

Front biased Bump

  • Increases under steer + slightly increases grip in RWD cars.

Rear biased Bump

  • Increases over steer & highly recommended for FWD & AWD cars.

To test the excessive Bump Stiffness, let your car take a mild curb aggressively and then see if your car rolls. If it rolls, your setup is too stiff. If you already had your bump

Forza Motorsport 4 Car Upgrades

Upgrade engine parts of your Car to increase its efficiency and performance on the track.

Engine and Power

Air Filters
You can equip your car with better performance air filters to increase the horse power of the car to a certain degree. Once equipped with good filters, your car will also give out sporty sound. Air Filters protect the engine from dust impurities and in turn increase its efficiency hence you can get more out of your basic.

Intake Manifold & Throttle Body
Intake Manifold is another key part of the car in determining its horsepower. It basically provides the energy needed for other engine parts to work properly.

Intake Manifold can greatly reduce the efficiency of car if it isn’t working properly or mixing fuel mixtures properly, which reduces the horsepower drastically.

Throttle Body is another part of the engine which increases/decreases the power supplied by the car engine. As, it increases/decreases the amount of air that enters the engine. In turn increasing/decreasing the amount of horse power.

Fuel System
Engines requires the efficient flow of fuel so that can convert that fuel to energy for maximum horsepower. Upgrading your engine’s fuel system will definitely bring few horsepower and efficiency to the car while racing.

Ignition
Ignition is important aspect of the car engine, which dictates when the spark will ignite the air and fuel. When upgraded, it improves efficiency and timing.

When your car Ignition system, Ignites the air and fuel a bit earlier, it allows more combustion, and in turn creates more horse power out of the same engine.

Exhaust
It not only changes the sound of your car and increase horsepower but also facilitates smoke ejection properly. In turn giving you an overall boost at straights when your car is at max speed.

Camshaft
This is a critical upgrade for any car. While an upgraded camshaft does add horsepower to your engine but is it really necessary ? The answer lies in your style of driving.

If you can keep the RPM up in turns, you should use a bigger camshaft. If you are someone who drops the RPM, then you should go for a smaller camshaft. Bigger camshaft in a car with lower turn speed will not have enough torque at the turn exit because it will be below the maximum power band. Go for trial and error to find out what works best for you.

Valves
The valves springs and Camshafts go side by side. You can’t have too strong Valves because it would result in excessive wear on camshaft and you also can’t have too weak vales, because if the valve doesn’t fully close when it needs to, it would result in engine damage or at least loss of power. Upgrading these will improve handling of the car and of course engine efficiency.

Displacement
One of the easiest ways to increase the horsepower of the engine is to upgrade its capacity/displacement.

Pistons and Compression
Again, it’s a critical choice whether you should go for High Compression Pistons for high-compression ratio or Low Compression Pistons for low compression ratio.

High compression ratio will give you more horsepower but come at a price of reduced engine efficiency. Low Compression Pistons prevent ignition problems and reduce turbo lag at the cost of HP.

Oil & Cooling
Upgrading Oil and Cooling add reasonable horsepower to your car.

Flywheel
You have two choices, either choose a heavy Flywheel or a lightened Flywheel. Heavy Flywheel gives you steady speed but sucks when you need good acceleration or fast engine response which would require Horse Power. Lightened Flywheel gives you more acceleration and Horse Power at the expanse of reduced engine momentum.

Platform & Handling

Brakes
Brakes with good stopping can make the racing easier. These upgrades are excellent choice for a racing car as they allow you to carry your speed further into the turn and brake later. This allows for faster lap times.

Springs and Dampers
Adding power to your car engine is all well and good! but it has its own consequences. More power to your engine will ask for upgraded suspension to maintain car handling and stability during the corners.

Upgrading Springs should be your first step to tune suspension after the upgrade. These reduce the height of the car and which ensures load capacity and lowers the car’s center of gravity for added stability. It also allows the tires to work more effectively when performing at their limits.

Dampers and Shock upgrades give more stability to the car by keeping it in contact with road surface for a longer time period. Upgrading Dampers will result in more stability and responsive steering, ultimately giving you more control over your tuned-high performance car.

Anti-Roll Bars
Anti-Roll Bars support the balance of the car at cornering or stop it from rolling over at corners. There are two types of Anti-Roll Bars – Front Anti-Roll Bars and Rear Anti-Roll Bars.

Upgrading Anti-Front Roll Bar will decrease front chassis roll while giving your more rear grip, while upgrading Anti-Rear Roll bar will decrease rear chassis roll and give your more front grip.

You can choose between Soft and Stiffer Bars and benefits are:
Softer Front Anti-Roll Bar

  • Increases front chassis roll.
  • Increases front grip or traction, while decreasing rear grip or traction.
  • Slower steering response.
  • Increases off-power steering at corner entry.

Stiffer Front Anti-Roll Bar

  • Decreases front chassis roll.
  • Decreases front grip or traction, while increasing rear grip or traction.
  • Faster steering response.
  • Decreases off-power steering at corner entry.

Softer Rear Anti-Roll Bar

  • Increases rear chassis roll
  • Increases rear grip or traction, while decreasing front grip or traction.
  • Less on-power steering.

Stiffer Rear Anti-Roll Bar

  • Decreases rear chassis roll.
  • Decreases rear traction, while increasing front grip or traction.
  • Faster steering response in high-speed corners and chicane.
  • Increases on-power steering.

If the track is bumpy, don’t use Anti-Roll Bars because they would make it harder for you to drive.

Chassis Reinforcement & Roll Cage
Chassis Reinforcement increase the handling of the car during tight corners. When you reinforce the body, the car becomes rigid, increases grip and becomes more stable.

Stiffening the body of the car will reduce the car body twisting during the hard turns and accelerations at high speeds, adding stability and helping to keep your wheels planted.

Though it would increase the weight but the performance gain is more. By upgrading Roll Cages you can see a sharp increase in the handling of the car. It reduces car body roll and provides much-needed rigidity.

Weight Reduction
If you want more acceleration, turn speed, and brake stopping power then go for weight reduction upgrade. It will make your car accelerate, turn and brake faster.

Drive-train

Clutch
If you have upgraded your car to extract more power out of it. You need a powerful clutch to take the engine power and smoothly transfer it to the wheels. If you want to make the best out of your car, upgrade your Clutch with respect to all your engine upgrades.

Transmission
You can make a significant different in how fast your car runs on the track just by upgrading its transmission box or adjust it. You can make your engine powerful but you also need a transmission system good enough to send that power to the wheels.

You can alter your gears either manually for more acceleration or alternately for more speed. Transmission upgrades adjust your gears in such a way that would either increase speed or acceleration.

Your choice should be dependent on the track you would be driving your car on – like you should go for speed on relatively straighter tracks.

Driveline

With efficient drive-line, you can take full advantage of your engine’s power.

Differential
The role of differential is to distribute equal amount of torque to both wheels. Allow the wheel with more resistance to rotate less and wheel with less resistance rotate faster – needed in turns where the inside wheel has to rotate less than the outside wheel.

If you are driving a FWD Car, stiffen up the front different acceleration to force more power to the outside wheel but it can result in understeer if you put too much power to the front wheel. Soften up the front differential acceleration to let inside wheel spin.

If you have RWD car – stiffen up your front differential acceleration to force more power to the outside wheel but it can result in oversteer if you put too much power.

Tires and Rims

Tires
Turn 10 has completely overhauled the tires in Forza Motorsport 4 so you will a lot more nuance in model than ever before.

Rims
You can use custom Rims to make your car look the way you want.

AERO Dynamics and Appearance

Front and Rear Bumper
The front and rear bumpers allow the car to sustain an impact without damage or at least reducing the damage that it would normally take. They also enhance the look and feel of your car.

Airfoils beneath these bumper direct the air flow of the car. Airfoils create a downforce that enhance the grip of the front tires while optimizing the flow of air.

Rear Wing
Rear Wings in racing cars are used to generate downforce on an automobile. Rear end of the car requires twice as much downforce compared to front end of the car to maintain balance.

The angle of rear wing can be adjusted to increase downforce on rear wheels, but it will increase the drag. Before deciding to play with aerodynamics of your car, take a look at the track and its requirements and your goal.

Side Skirts
They reduce the damage of the impact. You can also change the look of your car by introducing side skirts.

Hood
The hinged cover of the car that allows access to engine for repair and maintenance. You can change the look of your car by changing its hood.

Conversion

Aspiration Conversion and Engine Swap
Want raw horse power ? go for engine swap. Be careful with your decision though, an overpowered car would require all transmission and suspension upgrades before you will be able to drive it.

There is a trade-off between Aspiration Conversion and Engine Swap. If you are tuning for Short/Twisty tracks, go for aspiration conversion. If you are tuning for straight speed, go for turbo super charge.

Go for Aspiration conversion if the engine swap adds more weight to the car and that’s the last thing you want. Pick Aspiration Conversion when engine swap has a lower amount of low-end torque because of a turbo already installed.

Drivetrain Swap
You can convert your RWD vehicle to AWD/FWD or vice verse. Depending on the vehicle, you will notice a change in performance and sometimes, it’s a drastic change.

Like the weight increase/decrease after the Drivetrain Swap can increase/decrease your overall handling of the car. You can use the Drivetrain Swap to make your powerful car more manageable.

If you want to contribute in any way, don’t hold back – comment and we will add your suggestion in the guide. Don’t forget to share your tunes, they may come in handy for other novice racers.

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