Originally Posted by Dave Moulton

By all means experiment with gussets in a frame, but think long and hard about what you wish to achieve. Often all you do when you strengthen a frame in one place, you weaken it somewhere else.

In the early days of frame building around the turn of the last century; frame lugs were heavy cast steel; nothing more than crude pipe fittings. As tubing manufacturers made tubes thinner wall and therefore lighter, frame builders found that frames would break at the edge of the lug. The lug was way too strong for the tube.

The answer was to in effect weaken the lug by filing it down to make it taper to a fine edge, and to sculpt the lug into intricate lacey patterns. Later pressed steel lugs made this unnecessary. We always think the main object when we build a frame is to make it as stiff as possible, but really it is a delicate balance between stiffness and flexibility.

A palm tree will survive a hurricane whereas other trees bigger and stronger will get their limbs ripped off. A good steel frame is like a very stiff spring; stiff but with just enough flexibility. Aluminum and carbon fiber frames do not have this asset.

On my 1985 MTB I left out the chainstay bridge, an old cyclo-cross trick so that mud will not collect but rather drop through between the chainstays. Often if you leave this bridge out; with the constant sideways flexing the bottom bracket shell will crack. So to compensate I took a piece of seatstay tube; 5/8 in dia. And about 5 inches long. I placed it diagonally from the seat tube; just below the front derailleur; to the left chainstay (Opposite the drive side.) just in front of the rear wheel.

This really stiffened up the bottom bracket area of the frame, but because I had done so with a tube rather than a solid steel gusset this tube had the same strength and flexibility as the rest of the frame. Also the tube was mitered to fit the other tubes so the brazing area was spread out. (Sorry I don’t have a picture.)

To sum up; if you are considering gussets: Don’t make them too stiff, in other words way stronger than the rest of the frame. And spread the area where the gusset attaches to the frame.