If you are limiting the takeoff speed to prevent it bottoming out, then I suggest you lower the ramp. 45 degrees$45^\circ$ gives optimal range for a given takeoff speed (ignoring friction), but only if you don't care what the vertical component of the velocity is on landing.
At 30 mph$30\: \mathrm{mph}$, with a 45 degree$45^\circ$ jump, you say it doesn't bottom out. The vertical component of the velocity on landing has approximately the same magnitude as on take off (air resistance losses), which would be $30 \; cos(45)$$30 \; \cos(45^\circ)$ = about 26 mph$26\: \mathrm{mph}$.
To maximise the range, then, we need to keep this vertical component ($v_y = 26 \mathrm{mph}$$v_y = 26\: \mathrm{mph}$), whilst letting the overall speed ($v$) increase to 45 mph$45\: \mathrm{mph}$.
$v^2 = v_x^2 + v_y^2$
$v_x^2 = v^2 - v_y^2 = 45^2 - 26^2 = 1349$
$v_x = \sqrt{1349} = 36.7 \mathrm{mph} $
So we can calculate the angle from the $x$ and $y$ components of the velocity:
$\tan(\theta) = v_y / v_x = 26 / 36.7 = 0.71$
$\theta = \arctan(\theta) = \arctan(0.71) = 35^{\circ}$
So based on that information, try 35 degrees$35^\circ$, with a speed at the ramp of 45 mph$45\: \mathrm{mph}$.
