Clicking the customize tab will give you 3 drop down menu choices.
Player - Settings - Vehicle
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Lets look at the Player Screen..
This will be defaulted to the Player you created during initial setup.
Here you can create a new player profile
Here is also where you can adjust and make changes to your current profile.
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Lets look at the Settings tab..
At the Bottom of the screen are the "Basic" settings controls.
Difficulty, Rules, Controls, Display, Audio.
These can be adjusted by clicking the arrows next to the desired selection.
You can adjust your settings do pre-defined values by using the arrow keys

To open the advanced settings at the top of the screen click the window button to the left of the settings you wish to adjust.

Highlighted is the DIFFICULTY tab, with the advanced difficulty settings showing at in the top portion of the screen.

Here you can adjust individual difficulty setting to your liking and or skill level.
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Next is the RULES tab:
This page allows you to customize options for race sessions.
Note that similar options exist when setting up race seasons or multiplayer races.
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Controls screen
Within the controls settings screens you will setup or "map" your controllers definitions and rates.
To map a "action" to your controller, simply click on the action you wish to assign.
For example, to setup steering, click on "Brake", then step on the brake pedal.
You should take care to set up your basic driving controls - steering, brakes, and throttle. It is also recommended that you review your Controller Rates, especially Speed Sensitive Steering. For the most realistic setting using a steering wheel, we recommended a Speed Sensitive Steering value near 0%. However, inexperienced users or those driving with the joystick or keyboard should try something in the range of 50-100%.
Note there are some Presets that can be used with different wheel/pedal/joystick setups. Try using one of the Presets and then customizing if necessary. You can save your current settings as a new Preset and then share them with other users using the same input devices. The file is saved to UserData/Controller/<preset name>.ini.
Similarly, you should review your Difficulty settings, as these will affect your driving. Driving aids such as steering help and braking help cause the game to partially control your steering and braking input. They are only recommended for novice users who do not know the track layout. Other aids such as Traction Control, Stability Control, and Antilock Brakes won't guide you around the track, but may help prevent erratic inputs from destabilizing your vehicle.
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Display settings:
Here is where you can customize your graphics display levels and cockpit display options.
Note that while higher settings produce a better look in-game, they are also more system intensive.
If you notice low frame rates or "jitter" try turning down some of there options to increase system performance.
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Audio setting tab:
Allows for detailed adjustment of your audio (sound) within rFactor.
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VEHICLE TAB:
The vehicle tab displays all the
cars allowed for the current mod. The purchase, selling, and upgrading of your car collection is accomplished here.
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