To change the rear brake pads on a mountain bike, start by removing the wheel. Then, remove the retaining clip or pin that holds the brake pads in place. Push the brake piston back into the caliper using a brake piston tool or a flat-head screwdriver, making room for the new, thicker brake pads. Slide the new brake pads into place and reattach the retaining clip or pin. Finally, check the alignment and feel of the brake by squeezing the lever a few times before reinstalling the wheel.

First, loosen the stem cap bolt with an Allen wrench. Then use an adjustable wrench to loosen the stem bolts on both sides and remove the desired spacers. Adjust the stem level with the front wheel and retighten the bolts, making sure they are evenly tightened. Finally, retighten the stem cap bolt.

While mountain bikes can be used on roads, they might not be the best choice due to their heavy and durable build meant for off-road terrains. They also have wider tires and suspension systems, which tend to slow down the bike and could cause discomfort during long-distance road cycling. A road bike would be more suitable for smoother rides and longer distances on the road.

A medium size mountain bike is a bicycle designed for riding off-road on rough terrain, with a frame size that falls in the middle range of small and large sizes. It usually has suspension on the front and/or rear, knobby tires, and wider handlebars for better control. The specific size of a medium mountain bike can vary depending on the manufacturer and model, but it is generally recommended for people with a height between 5’6” and 5’10”.