Re: Issues with Grubee GT2 Frame
This will make you cringe but it worked for me. I was in the same predicament as you, single speed rear wheel frame too wide at the drop outs. I opened my bench vice nearly all the way, put aluminum vice jaw blocks in, slid the GT2 frame rear wheel drop outs in-between the vice jaws, the frame in a vertical position (with the steer tube axis parallel to the ceiling of the garage), and proceeded to crank (tighten) on the vice pressing the drop outs toward each other until my single speed rear wheel fit as I wanted it to (drop out width inside to inside 4 1/4"). I had to squeeze it down to about 3 3/4" to allow for frame spring back, which brought it to 4 1/4" once the vice pressure was released. Pedal side sprocket aligns perfectly with the crank sprocket.
Like I said, it is cringe worthy but it worked and the frame looks like it was made to fit the single speed rear hub, no bends or kinks visible in the seat or chain stays. Something to think about.
I've done the same to two GT2 frames now.