Instant steering - PC only. This trick requires either a gamepad that supports Dinput (usually Logitech) or a steering wheel that you plug into your computer before starting the game. You can also just install vJoy program and it should work as well. Once you're in the game, go to controls and restore default settings. You should now see that all of the movement keys are bound to your gamepad/wheel. Start any race, open up main menu via ESC and bind your steering keys to digital inputs on your keyboard. You should get a warning message about switching from analog to digital, but you can just ignore it. From now on, whenever you press a steering key, the wheels will instantly steer to maximum lock, which allows you to attack corners more agressively, but it makes the car a bit sensitive and twitchy, especially with traction on. The trick works till you exit the game.
Manual transmission - You always want to use manual transmission as you will get better control over the speed during cornering. Automatic often doesn't downshift and if it does so when you're going out of a corner, it's too late and you loose time.
Gearing - Some cars have "broken" gears, which means that the upper gear is actually faster, even though it doesn't make sense, so it's actually faster to just skip that broken gear when upshifting. I have prepared a document with details: https://docs.google.com/spreadsheets/d/1j59AAOQTIO6OxO_gh-gy5g2dPAPSr3CvKIZfTly0K-g
Brake steering - In NFSIV, you almost never want to let go of gas. It's unreliable and you'll only loose speed. Instead, use brakes to steer! That's right. When you brake and accelerate at the same time, the car slightly drifts (with brake balance set to -100%) and loses a bit of speed. So if you're attacking a corner and you see you won't make it without crashing, you just slightly tap your brakes a bit and you should go through that corner at maximum speed unless you're going too fast in which case you have to either tap the brakes more or use downshift braking.
"Wiggle glitch" - If you're using the instant steering trick, you can use this glitch to accelerate faster in a straight line. What you do is to rapidly press left and right steering keys between each other to make the car "wiggle". You need to have consistent timing, otherwise the car will just steer off the track.
Jumps - You always want to avoid jumping, especially on PC, because for some reason you're losing speed when you're flying AND you lose another 10-20kph when you land. This is not the case on PS, however. You can avoid some of the jumps by simply avoiding them, but some you can't, so what can you do? If you steer over some of the small jumps, you fool the game into thinking you're actually on the ground and it lets you go over that jump without actually jumping. You can sometimes notice the car sort of hovers over the jump, but it won't jump. This trick is unfortunately quite random and not useful at every small jump, because you need space and you also loose some speed since you have to slightly steer. Also, unlike in NFSIII, you loose more speed during jumps if you hold accelerate midair, so always let go of it. Your landing speed also depends on with which gear you land, the higher is usually better.
Perfect landing - Perfect landing is when your car doesn't "stumble" upon landing. If this happens, you don't lose 10-20kph in the process. It's quite rare, random and only works on some jumps, usually those that are not perfectly horizontal. The chance of getting it in NFSIV is even smaller than in NFSIII.
"S" technique - Not sure if guys over HOSS have different name for this trick, but this is how I call it. The idea is to rapidly change your direction to quickly slow down the car while driving over a jump OR slow down the car as fast as possible if you have enough space to do so. This trick is used in only several specific places and what you do looks like "S". Drive straight, do a hard brakesteer to one side, then quickly to the other. The trick itself is not that hard, it's hard to time it correctly.
Surface - Compared to NFSIII, snow and grass doesn't seem to affect car's handling that much, so you can drive on these surfaces just fine.
Curbs - Unlike in NFSIII, curbs have much bigger impact on car's suspension. Even just a small curb slows you down a lot, so you have to know exactly which racing line to take in order to avoid them.
Software - I am not sure if this is just placebo or if this is really true, but from my testing, I was always a bit faster in software mode and it felt like the car is a little bit less sensitive to steering inputs.
Traction - You can find this setting in Driving Assists. It basically increases your grip, so the car steers better and faster. The downside is that it will be harder to precisely control the car. It's recommended not to use this with combination of Gofast/tuning as the car will have so much grip that it will spin out during hard brakesteering or just steering on a lose surface.
