Ramps are too steep to stand on — you slide. Hold the strafe key toward the ramp (A if the ramp is on your left, D if it's on your right) and don't hold W. Look along the ramp; gravity pulls you down and the slope turns that into speed. In the air, strafe and turn the mouse together to steer. Falling off sends you back to your last checkpoint, still moving.

Auto-strafe (default on phones, pick it in Settings → Movement on desktop): the keys are pressed for you, so you only steer. On a ramp it holds A or D toward the ramp — and on a curve, the key the curve turns toward, so you carry your speed round the bend instead of up the face. It never presses W once you're on a ramp or in the air; W (or touch to run) only gets you off the start. In the air it strafes as you turn. Look a little away from the ramp to drop and gain speed, toward it to climb. Touch: auto-run + drag to look, or the classic stick layout.