Reddit mentions of Intercomp (360067 2.5" 0-60 PSI Liquid Filled Deluxe Air Pressure Gauge

I'm serious about the rear tire pressure. It's probably around 35-40lbs of pressure right now. Get a really good tire pressure gauge... because you need one anyway. I could build a nice house for what you have invested in that bike, so don't be cheap and get a good one. Hell, even if you don't change the tire pressure like I'm suggesting, you still need a good tire pressure gauge.

There's a ton of $10 gauges floating around, but I've never found two that read the same, so all of them can be counted on to be inaccurate. But there are good, relatively inexpensive gauges out there. Avoid the digital ones unless you into the >$200 product lines. Not necessary unless you work on a racing team and 1/10lb differences are going to be appropriate and necessary for track condition changes. But GOOD dial-gauges with flexible hoses can be had for about $40-50. Intercomp and Joe's Racing both make reliable, accurate gauges, and they're almost as good as the ones for professional racing teams. Make sure these are 60lb gauges, because you can use them on your car and truck, too. Buy a good one once and you'll never need to buy another. I know you understand this idea.

You probably don't have an inner tube in that rear tire so don't go below 20lbs ever, although I've limped my Road King home on a tire going flat that had about 15lbs in it (an 800lb bike is NOT the same as the 475lb bikes that Harley recommended 15lbs of pressure for). but 22-25lbs is more than enough for the tire to retain its bead on the rim under almost all conditions (except drag racing, unless you're rolling on the throttle instead of dumping the clutch) and hitting a hard curb straight on at 50+mph, and then you'e already got other problems. But running 22-25lbs may make the difference between enjoying every minute of your ride and having to buy a football mouth guard to keep from breaking teeth. OK, you probably don't need the mouth guard, but the difference between 35-40lbs and 22-25lbs will be night and day. Give it a try?