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Chain stay bridge musings

Old 08-12-22, 08:58 PM
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Chain stay bridge musings

When I worked at the Schwinn store, I had a 60 cm Paramount, and the owner’s son, slightly shorter than me, had a 58, or maybe smaller. My frame had a chain stay bridge; his didn’t. I always resented that little bit of extra weight/metal on my bike. When I got my more-appropriately sized Cinelli, it didn’t have a chain stay bridge either.

Are these bits of metal superfluous? Necessary? Thoughts?
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Old 08-12-22, 09:37 PM
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Mistakes happen.
the '72 US Olympic track bikes had no bridges, chain or seat stays.
a builder in Germany added the seat stay bridges.
ooops

if the smaller bike was all chrome, better chance of a nice finish there
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Old 08-13-22, 04:56 AM
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My first thought is they add value by ensuring the stiffness of the stays and BB lateral stiffness, provide a place for mounting a brake (seat stay), reducing the forces on the seat lug and BB shell, add a place for a fender mount. I can see the value of any or all of that for larger frames with longer WB.
The chain stay bridge must be of some value if, when not using one, the BB is often buttressed. Not being a frame builder or have experience in structure or force analysis of bicycle frames, it is just an educated opinion.
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Old 08-13-22, 06:00 AM
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Gitane Defi's don't have one, and they have an otherwise pedestrian bb shell.
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Old 08-13-22, 10:26 AM
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Chain Stay Bridge

OK, I just checked and both my 1974 Mercian and 2004 Waterford have a chain stay bridge. You must be awfully sensitive to let that extra weight bother you..
Bill
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Old 08-13-22, 10:44 AM
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Originally Posted by SJX426 View Post
My first thought is they add value by ensuring the stiffness of the stays and BB lateral stiffness, provide a place for mounting a brake (seat stay), reducing the forces on the seat lug and BB shell, add a place for a fender mount. I can see the value of any or all of that for larger frames with longer WB.
The chain stay bridge must be of some value if, when not using one, the BB is often buttressed. Not being a frame builder or have experience in structure or force analysis of bicycle frames, it is just an educated opinion.
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think tradition and momentum.
with investment cast bottom bracket shells, creators experimented to move away from them.
it was not mentioned the year of the bridgeless paramount.
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Old 08-13-22, 11:05 AM
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Originally Posted by BillRS22 View Post
OK, I just checked and both my 1974 Mercian and 2004 Waterford have a chain stay bridge. You must be awfully sensitive to let that extra weight bother you..
Bill
I think it's like any thing that you're passionate about- something that you'd NEVER notice if you didn't know it was there/not there- but once you know it- it's the difference between life and death. Or something.

Whether it's a chainstay bridge, a cm here or there in the geometry, a degree in angle or it's unoxygenated copper wires, Brazilian rosewood...

Or maybe it's a variation on the whole "grass is greener" concept.
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Old 08-13-22, 11:17 AM
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Chain Stay Bridge

Of course you are right about being passionate regarding areas of interest. If an item you collect has a flaw, then that is all you see. Other people wouldn’t notice it. My neighbor thinks I’m nuts for working on my bike all the time. I think he’s nuts working in his yard all the time. But hey, to each his own. Bill
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Old 08-13-22, 11:20 AM
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Originally Posted by The Golden Boy View Post
I think it's like any thing that you're passionate about- something that you'd NEVER notice if you didn't know it was there/not there- but once you know it- it's the difference between life and death. Or something.

Whether it's a chainstay bridge, a cm here or there in the geometry, a degree in angle or it's unoxygenated copper wires, Brazilian rosewood...

Or maybe it's a variation on the whole "grass is greener" concept.
Ain't that the truth. As a guitarist with lousy ears I can hear all kinds of bad stuff in a signal chain that no one cares anything about.
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Old 08-13-22, 11:24 AM
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If you're that worried about the extra weight, you could cut your shoelaces shorter or not take that last bite of sandwich at lunch.
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Old 08-13-22, 12:00 PM
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I’m not an engineer. That said, just by looking at a frame it seems CS bridges have some utility in added strength to the / lateral rigidity in acceleration and strengthening the bottom bracket area. The webbed buttresses surely help some, too (only applicable to under the BB cable routing which seemed to have been introduced to save cash). Just looking at the basic geometry..

I also read somewhere that the CS bridges were helpful when used in conjunction with horizontal dropouts as a ‘limiter’ to keep the rear tire from jamming between the chain stays on some bikes during fast tire changes.
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Old 08-13-22, 12:19 PM
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Originally Posted by BillRS22 View Post
Of course you are right about being passionate regarding areas of interest. If an item you collect has a flaw, then that is all you see. Other people wouldn’t notice it. My neighbor thinks I’m nuts for working on my bike all the time. I think he’s nuts working in his yard all the time. But hey, to each his own. Bill
+ a million on the yard thing, he is nuts.

I keep mine up just enough to keep ahead of the folks who don't.
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Old 08-13-22, 04:33 PM
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I am not sure that presence or lack of a bridge really matters from a lateral rigidity perspective, but if it does, it seems like it would matter more for longer chain stays; racing frames not so much.

But if you don't have a bridge, how would you mount your fender?
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Old 08-13-22, 04:35 PM
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Originally Posted by davester View Post
If you're that worried about the extra weight, you could cut your shoelaces shorter or not take that last bite of sandwich at lunch.
Not worried. My Cinelli doesn’t have a CS bridge, as I noted in the first post. But thanks for the suggestions.
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Old 08-13-22, 04:39 PM
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I like this design for adding rigidity


DiNucci
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Old 08-13-22, 04:40 PM
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Originally Posted by BillRS22 View Post
OK, I just checked and both my 1974 Mercian and 2004 Waterford have a chain stay bridge. You must be awfully sensitive to let that extra weight bother you..
Bill
So…you didn’t know whether or not your frames had chain stay bridges until you looked?
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Old 08-13-22, 04:54 PM
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Originally Posted by repechage View Post
I like this design for adding rigidity


DiNucci
Yeah that might add back some of the rigidity "thrown away" by using oval stays. I bet round stays with no bridge will be stiffer than oval stays with bridge, all else equal.
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Old 08-13-22, 05:00 PM
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Stop me if I've told this one before... OK I know I've told it and you can't stop me, bwah-ha-ha

Specialized Allez Epic lugged-carbon frames were a decent value, but a lot of them got warrantied for cracking where the chainstay bridge was glued in. It was the only (or one of the few) places that were just a glued butt-joint, no lug or fiber lay-up across the joint. They came up with a brilliant fix: They deleted the bridge. Epics with no bridge had the same ride as far as I could tell, and zero warranty returns for cracked bridge joints. And lighter weight too! win-win-win

Mark B
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Old 08-13-22, 05:57 PM
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Fun story on the chainstay bridge of the bike of my avatar. TiCycles built me a rather unusual fix gear based on a trashed Peugeot I saved from the dumpster. That circa 1990 sport Peugeot was a blast to ride fixed but the drop, while horizontal, was very short. I could ride a double sided hub if I kept the cogs to within 2 teeth of each other, 3 with a half link and the right chainring. So I designed this new bike to have a really long horizontal dropout (not a rear facing track end which I despise for road bikes). Dropout opens to the front, then a right angle turn down. This allows the wheel to be slid all the way forward with the biggest fix gear cog made, almost touching the seattube and still make for easy and fast wheel removals for gear change flips.

Fine and dandy, except the builder didn't quite think through what happens at wheel changes with the biggest planned tire size. Tire hit the bridge before the axle was far enough forward to reach the opening, Deflate tire to do anything. Oops! Gave him a call. He admitted his mistake, then thought up a rather neat idea. Ti frame so the bridge was a ti tube rather larger diameter than a typical steel tube. So he cut a "fishmouth" out of the tube and welded in an oval piece cut out of a larger diameter tube. And drilled a hole through for the fender with a countersink for a FH thead screw on the back/wheel side. Ingenious, looks like it was planned that way from the start and for the fender, works really well. Fender comes down forward of the bridge. I had to trim for both bridge and chainstay. I run a SS steel strap down from the fender and the FH screw from the tires side, through the bridge, strap and a nut. The area forward is just big enough to get one finger in to start the nut easily and slide in a skinny open end wrench. 3mm Allen form the rear does all the work.

And while I am on chainstay bridges - their effect structurally is to move chainstay failures to right behind the bridge. My UO-8 broke there (at 19,000 miles and way into double digits on crashes). The sport Peugeot I picked up 20 years later had been hit from the side by I'm guessing an SUV. Took it to the coop to straighten out the rear triangle and reset from who knows what to 120 OLD. Way to easy! Both chainstays were about to break. Cracks 2/3rds DS and 1/3 NDS right behind that bridge. But first ride "this bike is fun! In fact, I haven't had this kind of fun since my racing bike long ago." What do I do?

Well, I am Ben, a former boatbuiled with real fiberglass skills. And someone long ago gave me a couple of feet of carbon fiber boat hull material. I always have boat builder grade epoxy resin on hand. So, time t dive in and get messy! I did and learned the this CF stuff didn't wet out and go soft and piable like fiberglass cloth. Instead, it sprung away from all the tight turns of the ST, DT, BB, chainstay and bridge junction. No gentle curves there at all. So, disaster ready to set up and become permanent! Instant thought: Wrap it with innertube! Working lightening speed, I cut innertube strips and wrapped the whole mess tight. Resin squeezed out everywhere. Well, damage ios done. There's nothing more I can do so I cleaned and washed up and left the bike to die of epoxy in the garage. Came back the next morning knowing all that innertube was now solidly bonded to that sweet riding frame. Oh well.

Start peeling the innertube off and it all came off clean! The confounded CF had laid back down, had ll its excess resin squeezed out, all the weave showcased beautifully and looked for al the world like a high quality vacuum bag job. OMG! And the bike went from a cracked wet noodle (stiff is an adjective never applied to any Peugeot I am pretty sure) to probably the stiffest Peugeot ever.

That wrap started an inch or so up the DT, maybe a half inch up the ST, around the whole BB, chainstays and bridge to about 4 inches behind the bridge on the DS and 2" NDS. (I had to file a little off the DS to clear the chainring but there is so much excess strength and stiffness, hardly an issue.

So chainstay bridges - they are another thing to get wrong, they save chainstay/BB stress crack issues (probably the main reason they are there) but push those failures a little further back. And yet another place inventive DIYers can get creative. All in addition to being a nice place to land a fender.

Now, in this world of declining mental health, we are seeing that bridges are tempting suicides like never before. Bicycle manufactures are taking heed and eliminating them before the lawsuits happen.
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Old 08-13-22, 06:08 PM
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As far as I can tell the only real value that a chainstay bridge adds is a place to attach a fender. On fendered 650b conversions I typically remove them and braze a new one in for a nice, even fenderline without using anything more than a single leather washer.

My Ritchey Breakaway didn't come with a chainstay bridge.
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Old 08-13-22, 07:27 PM
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Originally Posted by bulgie View Post
Stop me if I've told this one before... OK I know I've told it and you can't stop me, bwah-ha-ha

Specialized Allez Epic lugged-carbon frames were a decent value, but a lot of them got warrantied for cracking where the chainstay bridge was glued in. It was the only (or one of the few) places that were just a glued butt-joint, no lug or fiber lay-up across the joint. They came up with a brilliant fix: They deleted the bridge. Epics with no bridge had the same ride as far as I could tell, and zero warranty returns for cracked bridge joints. And lighter weight too! win-win-win

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Old 08-13-22, 07:34 PM
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Originally Posted by 79pmooney View Post
Fun story on the chainstay bridge of the bike of my avatar. TiCycles built me a rather unusual fix gear based on a trashed Peugeot I saved from the dumpster. That circa 1990 sport Peugeot was a blast to ride fixed but the drop, while horizontal, was very short. I could ride a double sided hub if I kept the cogs to within 2 teeth of each other, 3 with a half link and the right chainring. So I designed this new bike to have a really long horizontal dropout (not a rear facing track end which I despise for road bikes). Dropout opens to the front, then a right angle turn down. This allows the wheel to be slid all the way forward with the biggest fix gear cog made, almost touching the seattube and still make for easy and fast wheel removals for gear change flips.

Fine and dandy, except the builder didn't quite think through what happens at wheel changes with the biggest planned tire size. Tire hit the bridge before the axle was far enough forward to reach the opening, Deflate tire to do anything. Oops! Gave him a call. He admitted his mistake, then thought up a rather neat idea. Ti frame so the bridge was a ti tube rather larger diameter than a typical steel tube. So he cut a "fishmouth" out of the tube and welded in an oval piece cut out of a larger diameter tube. And drilled a hole through for the fender with a countersink for a FH thead screw on the back/wheel side. Ingenious, looks like it was planned that way from the start and for the fender, works really well. Fender comes down forward of the bridge. I had to trim for both bridge and chainstay. I run a SS steel strap down from the fender and the FH screw from the tires side, through the bridge, strap and a nut. The area forward is just big enough to get one finger in to start the nut easily and slide in a skinny open end wrench. 3mm Allen form the rear does all the work.

And while I am on chainstay bridges - their effect structurally is to move chainstay failures to right behind the bridge. My UO-8 broke there (at 19,000 miles and way into double digits on crashes). The sport Peugeot I picked up 20 years later had been hit from the side by I'm guessing an SUV. Took it to the coop to straighten out the rear triangle and reset from who knows what to 120 OLD. Way to easy! Both chainstays were about to break. Cracks 2/3rds DS and 1/3 NDS right behind that bridge. But first ride "this bike is fun! In fact, I haven't had this kind of fun since my racing bike long ago." What do I do?

Well, I am Ben, a former boatbuiled with real fiberglass skills. And someone long ago gave me a couple of feet of carbon fiber boat hull material. I always have boat builder grade epoxy resin on hand. So, time t dive in and get messy! I did and learned the this CF stuff didn't wet out and go soft and piable like fiberglass cloth. Instead, it sprung away from all the tight turns of the ST, DT, BB, chainstay and bridge junction. No gentle curves there at all. So, disaster ready to set up and become permanent! Instant thought: Wrap it with innertube! Working lightening speed, I cut innertube strips and wrapped the whole mess tight. Resin squeezed out everywhere. Well, damage ios done. There's nothing more I can do so I cleaned and washed up and left the bike to die of epoxy in the garage. Came back the next morning knowing all that innertube was now solidly bonded to that sweet riding frame. Oh well.

Start peeling the innertube off and it all came off clean! The confounded CF had laid back down, had ll its excess resin squeezed out, all the weave showcased beautifully and looked for al the world like a high quality vacuum bag job. OMG! And the bike went from a cracked wet noodle (stiff is an adjective never applied to any Peugeot I am pretty sure) to probably the stiffest Peugeot ever.

That wrap started an inch or so up the DT, maybe a half inch up the ST, around the whole BB, chainstays and bridge to about 4 inches behind the bridge on the DS and 2" NDS. (I had to file a little off the DS to clear the chainring but there is so much excess strength and stiffness, hardly an issue.

So chainstay bridges - they are another thing to get wrong, they save chainstay/BB stress crack issues (probably the main reason they are there) but push those failures a little further back. And yet another place inventive DIYers can get creative. All in addition to being a nice place to land a fender.

Now, in this world of declining mental health, we are seeing that bridges are tempting suicides like never before. Bicycle manufactures are taking heed and eliminating them before the lawsuits happen.
Carbon does not like to bend.
makes one wonder about those all Carbon forks.
West System ?
system 3 ? ( are they still around?)
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Old 08-13-22, 07:51 PM
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I can't believe that none of you mentioned the vital role that the chain stay bridge plays in squaring up the kickstands on your Paramounts, Pinarellos, Allezii, and Titanium whatevers.
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Old 08-13-22, 09:23 PM
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Originally Posted by repechage View Post
Carbon does not like to bend.
makes one wonder about those all Carbon forks.
West System ?
system 3 ? ( are they still around?)
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.
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Old 08-13-22, 11:07 PM
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Bridge or buttress? buttbridge?

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