is there a surefire way to set the speed on a zero, when towing a sprayer behind. I've got a 30 gallon sprayer with a 6 foot boom that I tow with my toro zero. It supposed to be rated for 9.5 mph top ground speed which i think is a stretch. I'd like to be able to go about 3,4,or 5 mph so i can calibrate, kinda close, herbicides when spraying. any good tricks you guys know? it's mostly level area.