Hi, Sleepkirby6472. I suspect the reason you are going slow is because you are using manual transmission. You can change the transmission to automatic in the menu or shift with the N and M keys. Keep in mind that Automatic isn't fully implemented and if you use it, you wont be able to reverse, so abort if you get stuck on a wall.
The game is best played with a controller or wheel, keyboard really isn't ideal as it makes the cars very hard to control.
All of the invisible walls have been removed, so you'll need to jump carefully or use your cars brakes to keep from flying off the track! This is a change I most likely won't be reverting to keep this version of the game different from Project R.
Tires are really just an experimental feature that aren't working out how I'd like and will be temporarily removed in the next patch.
Thanks for playing! If you have further questions, There's a lot more info in the readme included in the game's download folder.