This is extremely simple: Just drive through it. Make sure not to turn slightly to the left or right or this will greatly affect your speed. If you feel like you messed up, just wait until it respawns you after you drove through the trigger (0.5 seconds) and then try again. Most of my cars with suspension are hard to steer, so I try hard to drive straight and I do this 3 times, until I get a speed thats higher than my last.

When testing modded vehicles double check and see if it has more than one core block on it. (It could be shrunk or transformed into a different shape) The extra core blocks should be removed because if they are kept on and you go through the trigger it will produce highly innacurate results, because the multiple core blocks will send multiple signals, causing the speedometer to fly off the chart. So make sure your modded vehicle only has 1 core block on it.