A: The connection of the seat to the seatpost is one of the most overlooked areas on the bike.  Saddle makers use everything from steel to carbon on their rails, and post makers all use different clamp mechanisms.  The good news is most seatpost clamps are designed to work with the standard seven-millimeter seat rails or the oversized eight-millimeter rails, which is good since there isn’t any set industry standard.  So basically seat selection comes down to comfort, price, and weight.

As for torque, it all depends on the material used and every manufacturer has their own spec.  If carbon, you better seek out this torque, but if it is a titanium or chromoly, then tightening enough so the seat won’t move (without over-tightening to the point where it is hard to get off) is the key.  Nuts and bolts tend to tighten even further when under stress so some anti-seize or grease will go a long way on the hardware (never use on carbon).

As for clamp design, two bolt systems tend to be more stable than single-bolt systems and require less torque.  If you buy quality parts, than slippage won’t be that big of a concern.  However, if it is a cheap bike/parts, than investing $1-2 at the local hardware store for some higher quality hardware will serve you well.

A: There are various pros and cons to running different length crank arms on a mountain bike.  There isn’t a clear “winner,” so rider body type, bike geometry, and style of riding should be the deciding factors.  Generally speaking, the longer your upper leg is, the longer your crank needs to be in order to feel comfortable riding and possibly avoid knee strain.

Longer cranks can be an asset for climbing, but a liability as they are more prone to bottom out when pedaling through rocky terrain or cornering.  Bikes with a low bottom bracket will probably want to utilize a shorter crank, while high bottom bracket bikes might want the extra leverage of a longer crank to help with climbs.

Factors to consider, when sizing your crank arms, include saddle position (fore/aft) and height, cleat position, and if any of the sizing is coming at a cost of other variables such as crank stiffness or crank weight.

The bottom line is comfort, so if you are in a position to try both sizes, do so, but if this if for a new purchase where you have to make a call, consider your upper leg size and bottom bracket height into the equation.