This has been bugging me to no end. It was fine, then one day started pulling. The wheel will re-center itself a few degrees left, or pull against me if I keep it straight.
So far I've:
Swapped tires from my del sol
Put in new axles
Checked the caliper slides for sticking (lubed everything)
Checked ball joint, tie-rod, and wheel bearing play
Made sure tie-rods use the same amount of thread per side
Checked the rack for autonomous movement
Checked alignment, also tried adjusting both tie-rods for more toe-in and out
The only prob I can think of is the caliper piston isn't retracting (collapsed hose or bad prop valve?), or the brakes are just shot. They still have lots of meat on them, and the rotors are smooth. FYI I put on a GSR rack with low miles months before it started doing this.