Please help, Tube sizing problem for my Univega Sport

[mrb1974]

Hi all,
Please forgive me if this has been covered somewhere on this site, if it has, I can't find it.

I have 26 x 1.50 rims with 26 x 1.75 tires
needed two new inner tubes.

The bike shop sells me a 26 x 1.50/1.75 with Schrader valve and a 26 x 1.9/2.125 also with Schrader valve.
They didn't have anymore of the 1.50/1.75 with Schrader valve and said the 1.9/2.125 would fit especially since it's a mountain/city bike.
The problem is that the 26 x 1.9/2.2.125 is too "big" for the wheel.
The width seems OK but when I put the tube on the rim there's space between the rim and the tube.
I don't understand this. If "26" is the size and 1.9/2.2.125 is the width why the space?
My other question, with this tube size, should I inflate the tube based on the psi figures from the 26 x 1.75 tire?

Any help would be greatly appreciated.

I've just moved to a town where it's easier to get around on a bike. Walking is too slow and driving can be even slower. My bike is the perfect solution.
Again, any help would be greatly appreciated.

[DaveM]

The 1.95 tubes should be OK (though 1.5's would be preferable just because they're a little easier to mount.)
First thing to remember is that when you put air in a tube outside of the tire, it will get much larger so that doesn't really tell you anything about the fit.

The best way to install the tube is to put just a bit of air into it so it takes it's donut shape. Then put it into the tire first. If you can fit it in the tire so it sits straight and doesn't have any kinks, you should be fine. If it is too big, try letting a little air out.

Once it's in the tire straight, then install the tire on the rim. As long as you can get the tire mounted without the tube getting pinched between the tire and rim, everything will be fine. You can pump it up to the pressure listed on the side of the tire.