Originally Posted by biketony
The tires I had were 26 x 1 3/8, with an equivalent psi of 50-60.
I think the psi is the culprit. I'm still in the testing phase with mine (27 x 1 3/8 from airfree.com). First I tried 90 psi but they felt slow and mushy like they were 60 psi. They said on the website that rider/load weight is a factor with the ride of tires from this material and that the psi equivalence ratings were for people weighing up to 180 lbs. I'm right around that, so I asked to upgrade to 120 psi and they sent 130 psi no charge as an exchange. While I haven't been able to put many miles on them yet, the initial tests feel like exactly what I was hoping for.
I'd recommend that before giving up, try a higher psi if available - max it out if you're carrying an additional load besides yourself. Personally, I'd expect a slow & mushy ride on 50 psi of any tire, period.