Trying to figure out which tires/tubes I can use I have a road bike tire with the following markings:
50-559 

26x1.95

K935-001

I weigh about 200lbs and will probably carry a pannier holding 40lbs. Some research said that my tire should inflate to about 110 PSI. This tire reads that it doesn't support a PSI over 65 (bought the bike used). So I figure I need a new tire.
However, from here it’s been hard to research what I should get.  When I search Amazon I don’t find a lot of tubes that describe the width as 28mm.  Instead I see a lot of measurements like 26x1.95, which is the dimension my current bike has.  I figured maybe the 1.95 represent the width in inches, but when I convert it to millimeters it’s about 44 millimeters, way bigger than what I found recommended.
So I’m just not clear one how to reconcile all these incomplete and contradictory-seeming sources of info.  All I really want to know is:  When I go on Amazon to get the tubes for my bike, which measurement (or ranges) do I need to search for to be sure it fits and won’t explode under me?
50-559 means 50mm wide tire, for a rim that measures &quot;ERTO 559mm&quot; in diameter. This is a very common size.
The &quot;inch&quot; equivalent is a tire for a 26&quot; wheel, with a width of about 2 inches. Any &quot;26 inch&quot; tire that's about 2 inches (or 50mm) wide will fit your bike, such a 26x1.95. The difference between 1.85, 1.95 and 2 widths is not large.
You could potentially get a wider tire, like 60mm / 26x2.4 inch, and it will fit your rim, but you would have to check if the wider tire will rub on your frame or fenders. Wider tires will ride better, but be heavier.
You could also get a narrower tire like 35mm / 26x1.5, and if should fit too, but the current trend is towards wider tires. Narrow tires will ride worse but be lighter.
Tire pressure that you should use is relative and will depend on your weight and the tire size. The number printed on the tire is the maximum tire pressure not to exceed. Usually, you will run less pressure than the max. On my cargo bike I run 26x2.5 tires with a max of 60psi. I actually run 35-40psi.
Tubes will work for a range of tires and you don't need to be exact. Practically any 26 inch tube between 1.5 and 2.5 inches will work for that whole range of tire widths. So you can use a 26x1.95 tube for a 26x2.25 tire, for example. The important thing is the correct wheel size (26&quot;) and a width that is reasonably close to rhe tire width.