Alright, here is EXACTLY how you get this game working, with no fucking about.
Get the 2.08 JP version of Battle Gear 4.
Get JConfig for BG4
UNTICK High Resolution, Direct3D9 Wrapper, DX Window Mode
Keep DirectSound Wrapper ticked
On Joystick Type, select XInput, and turn the deadzone slider to about halfway, even if you won't be using deadzone, just follow along. Jconfig is a terrible program
Reopen JConfig, set your inputs. If you didn't set the deadzone earlier, Jconfig will shit the bed and think you're pushing sticks all the way when you're not.
If you want to have gas and brake on your triggers, you NEED to be using a DualShock 4 with DS4Windows, emulating a 360 pad. There's no other way to do this. In DS4Windows, set your right trigger to push the right stick up or down, and the left trigger to push the right stick to the left or right. Save this as a profile
In Jconfig you can now bind your brake and accel to their own axes. In Jconfig's extra settings menu, turn off "Fake Analog pedals"
Now put the deadzone back to 0, and save.
If there's a config.bin in your folder, delete it.
You will calibrate your gas and brake, this should work fine. In game, you press the service button to put a coin in, and start menu to start. In the test menu you can switch to freeplay, where you only need to push start
When you're playing, you'll find your steering is really sensitive. Get Xinput Plus. Direct it to your BG4 folder, where game.exe is
In the settings for left stick, set the linearity as far left as you prefer. I have it at -0.9 which also works well for other arcade games
Now you can play the fucking game.