Doubts about Tire compatibility on my wheels?
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.