I just installed Marathon Plus tires on my Scorpion FX-20. I am new to trikes and have not used these tires before. I have a 3 day tour coming up in a couple weeks that is mostly on pavement, but there will be 7 miles of fairly rough dirt roads. I will be loaded with gear with most of it on a trailer (also never pulled a trailer before). What would be the best tire pressure for these tires. Also, the trailer, which is borrowed from a friend, has 16" tires. what pressure for trailer tires?

sounds like a blast! ask this guy!

Let me ask this another way. The Marathon Plus tires are marked 50 to 70 PSI. Is it best to run near the low or high? Does it matter?

I can only speak of road & hybrid bikes w any first hand knowledge. in general, it's usually a trial & error kind of thing. safe to start higher & let a little air out if the ride feels harsh or if you're sinking in soft, sandy dirt. so use max for the road then let a cpl lbs out for the rougher dirt. they hold less air than tires I'm used to, so when you let the air out go slow. counting to 1 might be all you need to do from max. if they aren't bulging & you feel they are still too hard & narrow, count to 1 again. but that would probably be it. again just guessing here. when you hit the pavement again you're gonna wanna pump them back up. but that's a lot of tires to be pumping even w CO2

if the trailer is light & bouncing a lot, it would probably be more stable with slightly softer pressures

It’s been recommended to me to run the rear tire 5 psi higher than the front, since a lot of weight is carried there. Tire pressure recommendations are also influenced by your weight. I run Schwalbe Marathon Racer tires (20” front & 26” rear) and I like 55 psi front & 60 psi rear. I agree, though to experiment to see what you like best given the surfaces you ride.

For gravel or mud rides, or even ice lower both tires to less than what you’d usually run.

The Marathon Plus tires aren't all that flexible, so I think you won't find much difference by varying pressure. Run 'em at 60psi and enjoy the scenery.