My car (almost) doesn't turn

I’ve made a car via watching the tutorials on Ue’s channel, but i’ve run into a problem:
Everything was working great until i got to the part when you’re gonna set it so the back wheels doesn’t turn, i did it just like in the tutorial but the outcome was rather dissapointing, the car can’t turn if im not accelerating and it goes completely straight after achiveing a “Normal” speed, Any way to fix this without letting the back wheels turn?