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Discussion Starter · #1 ·
The pigflu has kept me out of the garage and on the sofa watching movies for the past week but I did manage to get the braces done for the Seatstays and the disc brace the other night.

I was going to use Zip's program to do the miters but was too lazy to go inside and print it out so I just did it by hand. I'm enjoying doing miters like that now. It's easy just to stick a tube in the vise and start mitering it with the file.

Here's the seatstay brace (made out of the cut end of a scrapped seatstay):



And then I started on the disc brace (made out of the other end of a scrapped seatstay, note the taper going from the skinny tube to fat tube):




I finally cut the head tube so that I can face it and hit the rest of the frame with the wire wheel:



I have work to do on the hose guides on the seatstay tonight, need to chase and face the bb shell, need to face the HT, braze in the two braces, and then do some work on the seat tube/sleeve/binder before it can be ridden. I'm hoping the next couple of nights will let me get all of that work done. Of course, it's supposed to rain for the next three days so I may never get to actually ride it since our trails can't be ridden wet.
 

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Discussion Starter · #5 ·
Got my braces in last night along with my hose guides. We also faced the head tube and chased/faced the BB shell. Sorry, I don't have pictures of the frame prep stuff 'cause I was super stoked last night that it was getting done.

By the time I remembered to take pictures, it was in soak:


Here's the disc brace:


And of course the SS brace (and a preview of the hose guide):


More hose guide stuff, still have a lot of work to do on these but this is roughed in pretty nicely:

 

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Not be be an ass PVD, but as I've heard you ask "Where's the proof?"

I've not found anything that points to one way of the other being better. My take is it's more
heat in an area that really doesn't need it, and the bridge is so close to the bb as to add little to nothing as far as strength/stiffness.

I've heard of a study online that surmised as much, but have yet to find it. Anyone?

I'va also heard it put forth that cs braces orginally came about as a fender mount location. Speculation, but interesting none the less.

Worst case scenario, the op will notice nothing by adding one or leaving it out.

-Schmitty-
 

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I can feel the difference in the shop before and after doing the braces. I do not have any measurements, though. I'm sure a static calculation should show something if someone wants to take the time to do one. I would never build a bike without a chainstay bridge.
 

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The use if bridges has been experimented with quite bit over the years mostly in the '70s. Most of those experiments were on track bikes which helps eliminate a few of the variables. What seems to be concluded was that chainstay bridges stiffen up the rear quite a bit, but don't really affect longevity of the bike. My personal experience is along the same lines.

If you really care to know more I believe it was discussed in depth on the framebuilders listserve about 2 years ago. It included a bunch of posts by folks that actually did the experiment.
 

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Discussion Starter · #9 ·
Well, I'm riding it without it for sure (for now).

I actually had cut one (and still have it) assuming that I'd need to put it in. After some folks said that they didn't use them, I left it out. Now I have folks saying to put it in there....

If it feels too soft in the rear, I'll stick it in there before it goes out to powder (if in fact I do have it powdered, I'm mulling painting it myself). I'm planning on riding it naked for a while--and not putting paint/powder on the frame either ;)
 

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pvd said:
I can feel the difference in the shop before and after doing the braces. I do not have any measurements, though. I'm sure a static calculation should show something if someone wants to take the time to do one. I would never build a bike without a chainstay bridge.
I think a CS bridge is easy and quick enough to do that you can just go ahead and do one if you're on the fence. That said, we know that what you feel in the shop is not the same dynamic situation that is on the trail and is anecdotal at best. Hub/axle/dropout choice will play an important role. A squeeze test on the rear end doesn't really translate to anything (not implying that this was the test you did).
 

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themanmonkey said:
The use if bridges has been experimented with quite bit over the years mostly in the '70s. Most of those experiments were on track bikes which helps eliminate a few of the variables. What seems to be concluded was that chainstay bridges stiffen up the rear quite a bit, but don't really affect longevity of the bike. My personal experience is along the same lines.

If you really care to know more I believe it was discussed in depth on the framebuilders listserve about 2 years ago. It included a bunch of posts by folks that actually did the experiment.
That's one of the discussions I was thinking about and I seem to remember it falling on the other side.. need to do some digging.

Either way, how it 'feels' in the garage, and how it may or may not relate to high psi fixed wheel track machines are two different deals....

Even welding up two sets of stays and measuring 'stiffness' would prove little.

Whatever the truth, noobs shouldn't feel like they are leaving out something major, and it's even EASIER to leave it out if easy is your gig.

A debate for the ages....

-Schmitty-
 

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http://search.bikelist.org/?SearchString=chainstay bridge&Scope=framebuilders&pg=2

Interesting comments from builders of all ilks, most tending to say that cs bridges don't do much. There is talk in there of an '80's bike mag article that concluded the same somehow. Anyone seen it?

I searched a few of the easy phrases... someon else could probably glean some more from the phred by varying search phrases.

-Schmitty-
 

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Schmitty that's not the discussion I was thinking of, but it is the general consensus. The thread I was thinking of also discussed seatstay bridges. also there were engineers discussing twist. Here's another thread at Frameforum that may cloud things even more.

I could also be reading a lot of my personal bias into things. That said I don't use the chainstay bridges on bikes unless they want a fender, or some such. My bias is based on an experiment my co-workers and I did 15 years ago.

We each grabbed a basic road frame from the shop (we were a big used bike dealer in Seattle) from the bins and built them as commuters/around-town bikes. These became our personal project bikes. With these we tried various forks and rakes and other weird things with loads, etc. One of the last things a couple of us did was cut out the bridges. If you remove both bridges things get weird in the rear, and if you have canti-brakes your braking goes to hell. I would recommend this experiment to folks who are actually interested.
 

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themanmonkey said:
Schmitty

I could also be reading a lot of my personal bias into things.QUOTE]

I never do that!

Fine bikes can be built either way. Noobs need to understand that.. that their bikes won't fall apart or ride poorly one way or the other.

I built all my early frames with them, and then gradualy dispensed with the bridge with no discernable difference, and that was on exact same rears. Hell, I've even done a bunch of very over loaded BoB trailer pulling with one of the my first 'no bridge' bikes. I wish the thing would break somewhere so I could get rid of it!

Of course, this is all in regards to steel.

-Schmitty-
 

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A very basic, first pass engineeering analysis of chainstay bridges says the benefit of them has a positive correlation with ratios of chainstay length to distance from dropout to bridge further and further from one, so short chainstay bikes wouldn't benefit as much as longer chainstay bikes. Also, the smaller diameter the chainstays, the more the bridge helps with torsional stiffness. Modern tube sets use much larger diameter chainstays than many from the 70's.... None of this says anything to the magnitude of the effect, of course.


Personally, I will soon be adding a (massive, made from the top of a CX unicrown fork blade) chainstay bridge to a bike with short stays and big diameter chainstays, but seriously tortured stays for chainring/derailleur/tire/crank clearance. I've measured the lateral deflection of the drive side chainstay very precisely during climbing with a specific rider weight at a specific constant speed up a specific hill. The deflection was 2mm, which I feel represents enough power loss to justify the weight of the bridge in attempting to reduce it. I'll repeat the experiment after the bridge and report back (it will probably be months, but I will).
 

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There's no doubt that most bridges add 'stiffness'.

Is the stiffness needed/wanted? Does increased 'stiffness' mean less 'power loss'?

Does adding a bridge possibly shorten stay life? If so, is it worth the possible benefits od adding a stay?

These are the questions....

I don't think it comes down to the bridge personally. If it does, something else is lacking in the frame/design. I think a well designed/constructed frame will ride well/, ast a long time, etc etc with or without a bridge, with no discernable ride difference.

-Schmitty-
 
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