on 4/3/10 5:22 PM, cyclotourist at cyclotour...@gmail.com wrote: I question how many Bombadil frames are cracking in half due to lack of stiffness.
Well.... arguably, "stiffness" is what would cause things to crack in half - an inability to transfer force so it gets concentrated to one specific area. In short, a materials introduced "stress riser". If I understand GP's comments and thought process correctly, the reasoning for the second top tube is to create two trusses where there is one. That stiffens the structure, but doesn't necessarily make an unyielding - i.e. "stiff" structure - it passes the stresses along the structure. Even if you use thicker, stiffer tubing, you still join a traditional bicycle frame at discrete points - the headtube, seat cluster and bottom bracket - six points to be exact. The stiffer and less yielding the tubes are, the more stresses are on the connection points. I would _suspect_ that adding a second top tube lets you use lighter top tubes so they can flex and disperse stress, while at the same time you are stiffening the structure without adding stresses to the joints. Since any force is distributed through the frame, then force "X" would be distritbuted over a greater number of tubes _and_ joints, it would seem to end up with less stress on each. Just thinking out loud here... - Jim -- Jim Edgar cyclofi...@earthlink.net Cyclofiend Bicycle Photo Galleries - http://www.cyclofiend.com Current Classics - Cross Bikes Singlespeed - Working Bikes Workshops of the iBob's Send In Your Photos! - Here's how: http://www.cyclofiend.com/guidelines "My nighttime attitude is anyone can run you down and get away with it. That's why I don't even own a bike light or one of those godawful reflective suits. Because if you've put yourself in a position where someone has to see you in order for you to be safe...you've already blown it." -- Neal Stephenson, "Zodiac" -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bu...@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
