Chain stay bridge musings
08-13-22, 11:29 PM
#26
Crawlin' up, flyin' down
Join Date: Jan 2006
Location: Democratic Peoples' Republic of Berkeley
Posts: 5,653
Bikes: 1967 Paramount; 1982-ish Ron Cooper; 1978 Eisentraut "A"; two mid-1960s Cinelli Speciale Corsas; and others in various stages of non-rideability.
Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 1025 Post(s)
Liked 2,526 Times
in
1,056 Posts
Other than for attaching fenders, does CS bridge vs. no brake bridge matter? Probably not at all, and certainly not a lot. My take: either way, if it was good enough for Cino and Luigi, it's good enough for me.
__________________
"I'm in shape -- round is a shape." Andy Rooney
"I'm in shape -- round is a shape." Andy Rooney
08-14-22, 05:47 AM
#27
Senior Member
Join Date: Jan 2005
Location: Baltimore, MD
Posts: 5,373
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 2482 Post(s)
Liked 2,954 Times
in
1,678 Posts
I remember looking at photos of European pros in races back in the '60s and '70s and wondering why so many of them were wearing bulky-looking wristwatches. Your bike is as light as possible: why drag around the weight of that wristwatch when the guy holding the chalkboard (or whatever was) on the back of the motorcycle keeps showing you the time to the breakaway group?
08-14-22, 09:07 AM
#28
Senior Member
Thread Starter
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 5,790
Bikes: 1989 Cinelli Supercorsa
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 3511 Post(s)
Liked 2,926 Times
in
1,775 Posts
The absence of a chain stay bridge looks much more elegant to me. And it was good enough for Mario…
08-14-22, 09:54 AM
#29
Bike Butcher of Portland
Join Date: Jul 2014
Location: Portland, OR
Posts: 11,639
Bikes: It's complicated.
Mentioned: 1299 Post(s)
Tagged: 0 Thread(s)
Quoted: 4681 Post(s)
Liked 5,799 Times
in
2,284 Posts
I've done a couple of chain and brake bridge repairs. Obviously a brake bridge is a necessity. Even if you're using cantilevers or brazed on centerpull posts it mitigates twisting of the small diameter seat stays when braking. @RustyJames brought this frame in to repair a brake bridge that was only held in place from one side.
Proud of my work, I posted it to a thread somewhere that I can't find. What I didn't notice, but @bulgie did was that the right side chainstay bridge didn't appear to be quite as attached to the stay as one would like. Sure enough, same issue. While heating the other side up to liquify the silver based filler I contemplated just leaving it off. I've always wondered what structural improvement it might give. I'm sure the extra triangulation stiffens the rear triangle a bit. Somebody with a finite element analysis (FEA) package could model this and answer that question, but this may well be a "yes, it does, but not significantly".
So, I still don't know if a chainstay bridge is worth brazing onto a frame, but I did learn that crowd sourcing quality control by posting pics to Flickr is a smart thing to do (thanks again, Mark B.!)
__________________
If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.
If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.
08-14-22, 10:31 AM
#30
Senior Member
Join Date: Mar 2021
Location: Beaverton, OR
Posts: 1,435
Bikes: You had me at rusty and Italian!!
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 566 Post(s)
Liked 1,048 Times
in
543 Posts
"Less is more." I like it.
I've done a couple of chain and brake bridge repairs. Obviously a brake bridge is a necessity. Even if you're using cantilevers or brazed on centerpull posts it mitigates twisting of the small diameter seat stays when braking. @RustyJames brought this frame in to repair a brake bridge that was only held in place from one side.
Proud of my work, I posted it to a thread somewhere that I can't find. What I didn't notice, but @bulgie did was that the right side chainstay bridge didn't appear to be quite as attached to the stay as one would like. Sure enough, same issue. While heating the other side up to liquify the silver based filler I contemplated just leaving it off. I've always wondered what structural improvement it might give. I'm sure the extra triangulation stiffens the rear triangle a bit. Somebody with a finite element analysis (FEA) package could model this and answer that question, but this may well be a "yes, it does, but not significantly".
So, I still don't know if a chainstay bridge is worth brazing onto a frame, but I did learn that crowd sourcing quality control by posting pics to Flickr is a smart thing to do (thanks again, Mark B.!)
I've done a couple of chain and brake bridge repairs. Obviously a brake bridge is a necessity. Even if you're using cantilevers or brazed on centerpull posts it mitigates twisting of the small diameter seat stays when braking. @RustyJames brought this frame in to repair a brake bridge that was only held in place from one side.
Proud of my work, I posted it to a thread somewhere that I can't find. What I didn't notice, but @bulgie did was that the right side chainstay bridge didn't appear to be quite as attached to the stay as one would like. Sure enough, same issue. While heating the other side up to liquify the silver based filler I contemplated just leaving it off. I've always wondered what structural improvement it might give. I'm sure the extra triangulation stiffens the rear triangle a bit. Somebody with a finite element analysis (FEA) package could model this and answer that question, but this may well be a "yes, it does, but not significantly".
So, I still don't know if a chainstay bridge is worth brazing onto a frame, but I did learn that crowd sourcing quality control by posting pics to Flickr is a smart thing to do (thanks again, Mark B.!)
Interesting discussion, this. I was rattle canning my fillet brazed SuperSport, looking at the integrated kickstand doodad and wondering if I could cut that off. I isn’t no genius regarding frame structural integrity so I left it in situ. Also, there’s something quaint about it that I like.
08-15-22, 07:48 PM
#31
Senior Member
Join Date: Jun 2006
Posts: 20,305
Mentioned: 130 Post(s)
Tagged: 0 Thread(s)
Quoted: 3464 Post(s)
Liked 2,829 Times
in
1,995 Posts
West System. The issue I had was that the scrap was a roving-like material with plastic "threads" holding it together that did not break down like fiberglass mat when exposed to polyester resin. Also the roving-like coarse CF strands.
Carbon forks are vacuum bagged which squeezed the fabric against the fork mold; much like my inner tube wrap did manually. What CF forks don't get that my repair did was human eyes on the finished laminate. Flaws. little and big, are never seen until the fork breaks, is cut apart for forensics or is X-rayed or scanned. I could see all of my work after. Nothing hidden until 18 months later when I had the bike painted.
Carbon forks are vacuum bagged which squeezed the fabric against the fork mold; much like my inner tube wrap did manually. What CF forks don't get that my repair did was human eyes on the finished laminate. Flaws. little and big, are never seen until the fork breaks, is cut apart for forensics or is X-rayed or scanned. I could see all of my work after. Nothing hidden until 18 months later when I had the bike painted.
Sonograms and infrared are the decent non destructive tests today.
Binding up the layup with innertube will improve the compaction, but nowhere near vacuum. Might get a nice surface between the binding laps.
I don't like all carbon forks. The industry has marketed the 1.125 to 1.5" tapered steerer as a stiffness thing, sure, but also reduces the deflection the carbon has to make at the crown race, that can be cheated by having the strands spiral at the turn vs meeting the corner head on.
The bike industry has jumped the shark in design there and the assembly schemes to route internal cables.
One brand has gone another way and placed the structural element of the fork IN FRONT of the frame headtube/steering axis. might be more aero to boot. first seen on TT machines, now on road bikes.
