Framebuilders - The Chainstay Bridge
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09-05-08, 09:15 AM
So, I am putting the wood to an early 1980's Faggin (56cm-Campy Super Record) this morning on the way to work, and get a gnarly shudder on every stand-up downstroke.
Whaa? The entire back end is washing out, enough to engage the Modolo (mini red construction brick compound) brake pads.
looking down, I can detect the absence of a chainstay bridge, or gusseting to any degree rear of the bottom bracket. This might not be the total cause, but it is something to consider when building framesets.
My current build is using a Nova BB with the round chainstays and the little cast in joining web. I was considering whether or not to install a chainstay bridge. Not any more.
Something to consider, even though the bridge is typically very close to the BB, it really adds to the rigidity and takes a tremendous amount of strain away from the chainstay union, I don't know the percentage, but I suspect that it is considerable.
It triangulates the tubbing near the joints which reduces enormously the independant loading on the joints. Interestingly the proper way of adding strength to tubes in that situation is flat stock to the tangent points, just looks gross.
09-06-08, 10:05 PM
it sort of all comes down to the rider and the kind of riding. i ride a track frame (ture temper ox platnum) with honkin ovalized chain stays, and its more than stiff. i would say if your in doubt, put one in.
09-07-08, 09:12 AM
sounds like the frame may be broken. Some of the newer tubing sets should not have chainstay bridges. OP should check to see if that's the case with his tubing of choice.
09-07-08, 10:36 AM
that definitely sounds like more than not having a cs bridge. Unless of course it used to be there and was somehow detached. I learned that CS bridges are not necessary on some track bikes because of the short chainstays. sometimes there isn't much room for one. my track bike made from simple true temp heat treated has never been a problem without a bridge. I built a track bike with tt platinum cs a while back with no bridge and the owner has used it pretty hard on the street and velodrome with no complaints. in both cases the riders are sub 200lbs. I have heard about using them to take stress off the bb joint and may start adding them to every bike but I figure since Yamaguchi taught me to do bikes with sub 400mm stays without a bridge that they will probably hold up fine.
09-10-08, 05:36 PM
This topic has come up a few times on the framebuilders list and consensus is that CS bridges do not add significantly to the stiffness of the rear triangle. Sounds like something is wrong with the frame in question.
In terms of shoring up the rear end of the bike, round chain stays are stiffer laterally since they are 22mm wide where they attach to the bottom bracket shell verses tall oval chain stays that are only 16mm wide (steel bike tubing dimensions).
09-12-08, 10:30 AM
Nessism has it 100%. Do the research. bridges add very little if anything. Then take into account additional heating of tubes to put one in (assuming non integral w/ cast bb). Soemthing else is up wid your ride.
09-12-08, 12:37 PM
Speaking of heat distortion…on the first couple of frames I built the CS bridge was brazed in place without first constraining the stays at the dropouts – frame pulled in a goodly bit at the dropouts which had to be fixed by coldsetting the stays back to the proper width. Learned my lesson and spread the stays oversize from then on – after heat distortion, the stays pulled in and were just about right and didn’t need much tweaking after installing the bridge.
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