Q:

Doubts about Tire compatibility on my wheels?

I want to get a pair of 26 x 2.1  tires for my Bicycle.
My wheels are compatible with these dimensions.
A reputable store near me offers 26x1.95 tires. I am pretty sure that 1.95s are compatible with my 2.1 wheel.
The issue is, these are marketed at tires for a single speed bicycle of theirs. Mine is a 21 (3 x 7) speed bike.
From what I can tell, the wheel matters in matters of compatibility with the gearing, and not the tires as long as it is compatible with my wheel. But still, to be extra sure, does it matter that these tires are marketed for single-speed cycles as long as they are compatible with my wheels ?

A:

The amount of gears has no bearing on the type of tyre. 
The 26" part refers to the wheel diameter, so this is the most important part. 
The 2.1" or 1.95", refer to the width of the tyre. The width of the rim determine which width tyres you should have. If your wheel is ok wth a 2.1 wide tyre, then a 1.95" wide tyre will be absolutely fine. 
What you should consider when changing a tyre is the terrain, the puncture protection level, the weight, the durability vs grip and the price. The bike gears alone shouldn't influence the tyre choice. 

