Schwalbe Marathon Plus PSI?
 

What PSI are folks running with 26x1.75 Schwalbe Marathon Plus? (Front & rear.)

Having 3 sets of SMPs, though all 700x 25 or 28mm I run mine consistantly 10-20 psi over recommended specs because of the rolling resistance the tire thickness creates. No probs, so far. If your tires call for 75 psi max, running them at 90 shouldn't present any significant problems. They're very tough tires and the sidewalls are made to standup to alot of abuse. You can always back down the pressure if the ride seems a little too stiff.

I had 26 x 1.75 Marathon + on my old commuter rig, and I ran 70psi front and rear. I'm 250 pounds, if that makes any difference.

I usually run about 80, a bit less in the winter time.
700x28 SMPs

I have that exact size MP's. I found that they rode a little rough, so I lowed the psi to 45 or 50. On my Big Dummy, I increased the psi a little to maybe 60 psi. I also run them tubeless with homemade sealant. I won't jinx myself by bragging about how few flats I've gotten.

I have 700x32s and I pumped them to 90psi for my test drive around my neighborhood and they felt great. Today I took a ride that is part of my work commute that took me over some chip seal and other rough surfaces, and it was harsh at times. Of course, I just switched some from 26x1.95s that I ran around 55, so it's not surprising I noticed a difference. I think I'm going to drop the pressure some but I don't want to go far enough to bring pinch flats into play.

Going from 26x1.95 (f 40psi, b 55psi) to SMP 26x1.75, both at 70psi, was a bit of a bone-shaker. Looks like I'll be experimenting for a while!

10psi over the max on the rear...so about 80psi. around 70-80psi in the front to take a bit of harshness out, although not much. i like to compensate for all the gear i'm carrying plus my own weight. the tires roll so smooth over the rough stuff, even at 80psi that i don't really notice their weight or rolling resistance.

As a representative at Schwalbe, the official line is follow the guidelines on the sidewall of the tire. As a cyclist, I highly recommend reading about tire "Width and Pressure" on Sheldon Brown's website (RIP Sheldon).

If you go to Sheldon Brown's website, make sure you have some time to kill.... a lot of time (especially if you've never been to the site before). No man or woman or other beast has ever put so much good information in one place for cyclists... and for life.