Should work with update 1.0.678.1, and up to the Doomsday update. Might work all the way back to update 1.0.335.2, but it is not tested.
**You MUST run GTA 5 as Administrator or you will get an error when changing drive modes!**

Check out @ikt's Real Time Handling Editor for a more serious and fulfilling handling editor experience :)

Requirements
ScripthookV
ScripthookV.NET

Installation
Place the "scripts" folder in your GTA V directory where GTA5.exe is located.

What does this mod do?
- This mod allows you to create, edit, and switch between unlimited handling presets as you drive.
- You can choose which vehicles you would like to use the mod with; each vehicle will have their own unique settings file that you can share with others.
- These are the values you can edit to your liking thus far:
fMass
fInitialDragCoeff
vecCentreOfMass
vecInertiaMultiplier
fPercentSubmerged
fDriveBiasFront
nInitialGears
fDriveInertia
fClutchChangeRateScaleUpShift
fClutchChangeRateScaleDownShift
fInitialDriveForce
fInitialDriveMaxFlatVel
fBrakeForce
fBrakeBiasFront
fHandBrakeForce
fSteeringLock
fTractionCurveMax
fTractionCurveMin
fTractionCurveLateral
fTractionSprintDeltaMax
fLowSpeedTractionLossMult
fCamberStiffness
fTractionBiasFront
fTractionLossMult
fSuspensionForce
fSuspensionCompDamp
fSuspensionReboundDamp
fSuspensionUpperLimit
fSuspensionLowerLimit
fSuspensionBiasFront
fAntiRollBarForce
fAntiRollBarBiasFront
fRollCentreHeightFront
fRollCentreHeightRear
fCollisionDamageMult
fWeaponDamageMult
fDeformationDamageMult
fEngineDamageMult
Each value has a description of what it does in the handling editor menu.
- Each vehicle can have 3 custom vehicle cameras of the following types:
1. First-Person camera
2. Bonnet/Fixed camera
3. Third-Person camera
Each camera can be edited directly through the menu in real-time.
- If you don't want to set up cameras for each vehicle, just don't create a config for it, it will use the Global Camera Settings instead.
- No camera roll for bikes in the First-Person cam.
- No camera limits; you can look straight up, down, left, right, all around. Only for 1st person and fixed cameras.
- In first person, you can press a configurable key (default is VehicleAim key) to move your head to the left or right (amount is also configurable) depending on the direction your camera is facing, allowing you to stick your head out of the window for example.

Changelog:
2.0.5
- added fMass, fInitialDragCoeff, fPercentSubmerged, fCollisionDamageMult, fWeaponDamageMult, fDeformationDamageMult, and fEngineDamageMult
- Using Unknown_Modder's pattern, with examples from CamxxCore, sollaholla, and ikt, this script shouldn't need updating every time there is a major game update.

2.0.4
- Fixed for Smugger's Run (1.0.1180.2) update
- Vehicles should no longer stay persistent after switching drive modes
- Camera settings should automatically load when entering a new vehicle
- In the vehicle editor, your vehicle will automatically and immediately respawn whenever you change a value, to ensure that all values are applied.

2.0.3c
- Fixed for Steam users for Gunrunning (1.0.1103.2) update

2.0.3b
- Updated for Gunrunning (1.0.1103.2) update

2.0.2
- Should fix issues with fdrivebiasfront getting the wrong value, seems to work great on my end now
- Fix crashing when no configs are found while in the vehicle editor menu

2.0.1
- Should fix issues with creating initial configs
- Added vecCentreOfMass and vecInertiaMultiplier

2.0
- No longer uses NativeUI. Uses a new menu that shouldn't cause any noticeable frame drops.
- You can now use an unlimited amount of handling configs, with their own names, which you can navigate through and activate as you drive.
- Added more handling values you can edit. Drifting presets are now easier to make. alex20121981 has kindly provided some of his handling edits, which I've assigned to the Banshee2 for you to test right away.
- You can now make copies of handling presets directly through the menu, giving them their own name, without ever having to minimize the game.
- You can also delete configs directly through the menu.
- Removed camera limits for 1st person and fixed cameras.
- Vehicle cameras don't need to be edited separately, they now use global settings. You can still create a config if you want special settings for a specific vehicle.
- You can now enable/disable any of the three custom cameras.
- Added camera movement sensitivity options in the camera menu.

1.2
- Some quick fixes based on feedback from alex20121981 and Rstein that I forgot to upload a week ago
- Added Auto-Center camera toggle for First-Person and Bonnet type cameras. Sorry to those waiting for more updates, I have been working on an update for another one of my mods and it's been taking a lot of my time!

1.1
- Support for the latest GTA V update. Please be sure you update to the latest ScriptHookV.Net
- 9 more handling values you can edit (still working on adding more!)
- Ability to select the number of modes you would like to use
- A bunch of other stuff I am forgetting (sorry, it's been a while that I worked on this)
- Every time you change modes, your vehicle will quickly respawn so that all handling values are applied to the vehicle. Note, the radio can be quite annoying due to this (you'll see what I mean), but it's a side affect that I don't think I can overcome.
- For those waiting for updates to the camera part of this mod, I haven't forgotten!!

Default Controls:
Note: Keyboard and Gamepad controls can be edited in the Controls.ini file.
Keyboard:
Menu key: F10
Drive Mode display key: 0 (not the numpad, but the number 0 under the F keys). Use W and S to go up/down the menu.
Camera switch key: 9 (again, not the numpad)
Additional offset in 1st person: Hold Right-Click while looking 90 degrees to the left or right.

Gamepad:
Xbox-type controllers
Switch drive mode: Press DPAD Down multiple times while holding X to navigate through each handling preset
Switch camera: X + Vehicle Horn button
Additional offset in 1st person: Hold LB while looking 90 degrees to the left or right.

Playstation-type controllers
Switch drive mode: Press DPAD Down multiple times while holding Square (☐) to navigate through each handling preset
Switch camera: Square (☐) + Vehicle Horn button
Additional offset in 1st person: Hold L1 while looking 90 degrees to the left or right.

Credits to Senator3211 for this idea. Credits to ikt for his Real Time Handling Editor source (and for personally helping me!) and to leftas for his vehicle struct research. Last but not least, credits to LeeC2202 for sharing his solution to the camera issues I was having.

Sourcecode
Click here.