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Frame with no seatstay or chainstay bridge?

Old 04-27-12, 10:36 AM
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Airburst
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Frame with no seatstay or chainstay bridge?

I've found a rather nice-looking cyclocross frame on eBay which I'm considering buying to build into a wet-weather road bike. It's apparently a custom-built 531 steel frameset, but as the title says, there's no bridges on the seatstays and chainstays. The owner says this was done for better tyre clearance, he had the frame custom-built for him and the builder suggested it. I've never seen a bike built like that, but then again, I don't see many steel 'cross frames. Is that a legitimate thing to have done, or is something fishy going on?

Apart from durability, which I assume isn't a problem as the owner claims to have raced on the frame for several years without breaking it, my main concern would be outward flex of the frame when the rear brake (it has cantilever bosses) is applied, but I could presumeably fix that with a brake booster.
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Old 04-27-12, 10:50 AM
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That's wacked. Somebody hacked them off and repainted the frame- no builder would make a bike without a chainstay bridge or a seatstay bridge. The rear triangle would flop around with the greatest stress exactly where it's weakest at the BB joint and the brakes would bend the seatstays the second the pads hit the rim. If it were custom-built for larger tires, the builder could have easily accommodated the larger tires by adjusting (bending, lengthening, denting, choosing S-bent tubing) the stays or locating the bridges differently or any number of other methods. Run away from this one! Somebody with a torch and no brain was working on it.
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Old 04-27-12, 11:13 AM
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other than the baseless diatribe.. above ..

less places for sticky mud to gather is a concern for Actual cross racing..

you can always hire the services of a frame builder

and have them brazed in, and then get a repaint.

Bought New,
I have a '90's Pinarello Cross F&F, steel, no C/S bridge,
the S/S bridge is there, but a lot higher up.

Last edited by fietsbob; 04-27-12 at 11:58 AM.
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Old 04-27-12, 11:40 AM
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There are lots of frames without chainstay bridges. Here's my '97 Pinarello, for example:

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Old 04-27-12, 11:55 AM
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yea my RB1 has no chainstay bridge, a cast BB tangs do the job .

the other one TIG welded the BB in the frame ..
C/S tubes are ovalized where they are welded on
for more tire clearance..
& Back wheel in dirt will be a looser connection with the tire than on pavement any how.
so locking up the wheel to a skid is needing less force, anyhow..

Last edited by fietsbob; 04-27-12 at 12:42 PM.
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Old 04-27-12, 12:29 PM
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I've owned bikes without chainstay bridges but never seen one without a seatstay bridge (unless you count full-suspension MTBs)

I'd imagine the rear wheel would hold everything in place. Sort of like how an automobile frame is flexible and useless without a body and drivetrain mounted to it.
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Old 04-27-12, 12:49 PM
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I built a mountain bike frame years ago with no chainstay bridge to get the shortest possible chainstays, but I brazed-on gussets that wrapped around the front 2 1/2" of the inside of the Columbus Max OR chainstays, and then they were mitered and fillet brazed to the BB shell. I used SP seatstays with a bridge however because I was not confident that the ovalized Max seatstays would be stiff enough and I had plenty of room.

The bike was built for climbing concrete staircases at speed (The Rude Bike), to steer extremely quickly in sidewalk Gran Prix, and to accept being brutalized like a BMX frame. I had no noticable problems with flexing in the rear at all but I could power up 25-35' staircases easily, and I ended up with 16" chainstays if I remember correctly (or maybe even a little less because the rear triangle was hand-fitted around a 26x1.95 Specialized Ground Control tire....).

With appropriate stiffening of the BB/chainstay joint and an arched seatstay bridge, I see no problem at all, but the frame would have to have pretty short seatstays or a triple triangle configuration to justify leaving the seatstay bridge off, and I don't buy "mud clearance".

Last edited by Stealthammer; 04-27-12 at 12:59 PM.
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Old 04-27-12, 05:49 PM
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Hmm, I'll have to ask the seller for more details. I'll definitely use a brake booster if I do buy it, but you're saying there is at least the possibility that it's meant to be like that?
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Old 04-27-12, 06:12 PM
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trek mamba, for one
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Old 04-27-12, 10:24 PM
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Seatstay bridges don't have any structural function except as a place to mount a caliper brake. The tetrahedron formed by the double rear triangle is complete without the bridge. If there's no axle in the dropouts then the bridge may help the thing hold its shape which may be a factor in the factory - otherwise it is literally dead weight.

This is one of my favorite subjects just because it's so surprising to people.
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Old 04-27-12, 10:44 PM
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I have seen many bicycles with no seat stay / chain stay bridge... my Moulden XC racing bike has no true chain stay bridge which gives it that much more clearance to run the biggest and widest tyres possible.

Can tell you as a builder of these things that the bridges do not provide much in the way of structural support to the frame and are there for mounting brakes and fenders.
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Old 04-27-12, 11:18 PM
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I strongly disagree with the above two posts. When I am building frames the bridges are among the last things to go in. I can tell you that without the brake bridge, the rear triangle is MUCH more flexible regardless of whether the wheel is in the frame or not.

It may be different with OS and/or aluminum tubing, but with standard diameter steel it makes a very noticeable difference.
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Old 04-28-12, 01:23 AM
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Here's a pic of a Thorn Catalyst 853 frame. Very well known and regarded UK builder. Look Ma, no bridges.

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Old 04-28-12, 02:10 AM
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Originally Posted by Sixty Fiver View Post
Can tell you as a builder of these things that the bridges do not provide much in the way of structural support to the frame and are there for mounting brakes and fenders.
I'm going to listen to the actual framebuilder and assume it's fine.

Thanks guy!
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Old 04-28-12, 07:25 AM
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Originally Posted by Six jours View Post
I strongly disagree with the above two posts. When I am building frames the bridges are among the last things to go in. I can tell you that without the brake bridge, the rear triangle is MUCH more flexible regardless of whether the wheel is in the frame or not.

It may be different with OS and/or aluminum tubing, but with standard diameter steel it makes a very noticeable difference.
I had a steel frame that I converted to a fixed gear and I hacksawed the brake bridge off - I can tell you any difference was unnoticeable. It was my commuter bike and I rode off a lot of curbs with it - if there were a problem I would've found it. What possible forces do you think the bridge could be resisting? What direction would the seatstays move if the bridge weren't there? Have you ever seen a frame break at the brake bridge from being too weak?

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Old 04-28-12, 10:34 AM
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I wouldn't buy that bike. The lack of bridges may or may not be an issue but I wouldn't want to find out the hard way.

The only road frame that broke on me had no chainstay bridge. The driveside chainstay weld separated from the BB.
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Old 04-28-12, 10:39 AM
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That blue frame has a seat stay bridge.. I see a screw in it to mount a mudguard there.
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Old 04-29-12, 02:44 AM
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Well Fietsbob, your eyesight's better than mine, that's for sure. I looked at the website again, seems it is some kind of adapter for deep drop caliper brakes. So I take it all back.
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Old 04-29-12, 08:46 AM
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Originally Posted by DiabloScott View Post
Seatstay bridges don't have any structural function except as a place to mount a caliper brake. The tetrahedron formed by the double rear triangle is complete without the bridge. If there's no axle in the dropouts then the bridge may help the thing hold its shape which may be a factor in the factory - otherwise it is literally dead weight.

This is one of my favorite subjects just because it's so surprising to people.
Spoken like someone with absolutely no framebuilding experience whatsoever..... Thank you for the laugh.

In the real world seatstay/chainstay bridges stiffen up the rear triangle very noticably and they clearly reduce the torsional flexing of the rear end of the frame. Stating that "Seatstay bridges don't have any structural function except as a place to mount a caliper brake", is simply naive.


Originally Posted by Six jours View Post
I strongly disagree with the above two posts. When I am building frames the bridges are among the last things to go in. I can tell you that without the brake bridge, the rear triangle is MUCH more flexible regardless of whether the wheel is in the frame or not.

It may be different with OS and/or aluminum tubing, but with standard diameter steel it makes a very noticeable difference.
^^^^^ This. When I built bikes I would check and adjust the entire frame's alignment several times during the build process, and the addition of the seatstay/chainstay bridges would always make a very noticable difference in the force required to adjust the rear triangle's alignment on anything but fattest tubed aluminum.

Last edited by Stealthammer; 04-29-12 at 08:50 AM.
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Old 04-29-12, 08:53 AM
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Originally Posted by Six jours View Post
I strongly disagree with the above two posts. When I am building frames the bridges are among the last things to go in. I can tell you that without the brake bridge, the rear triangle is MUCH more flexible regardless of whether the wheel is in the frame or not.

It may be different with OS and/or aluminum tubing, but with standard diameter steel it makes a very noticeable difference.
This is a valid point in that if you are working with lightweight conventional tubes and are building a bike that requires caliper brakes, that the seat stay is rather important as it has to withstand a great deal of braking forces and although small, will lend some localized stiffness. Get down the stay and the stiffness is result of the tubing that is being used more than anything.

My touring bikes are insanely stiff due to the stays they use and do have bridges for brakes and mounts, my road bikes (with bridges) tend to have a little more flex in those stays as the tubing is lighter and thinner but once the wheel is in, these are also stiff bikes.

This topic was really speaking to bikes that use stay mounted brakes or discs and in these cases you are often working with OS tubing or Aluminium and newer steel alloys are about as good as we have ever seen and are much stronger and stiffer.

I have had some very old bicycles that were designed for fixed and coaster wheels and although they had a chain stay bridge, the seat stay bridge was no more than a hanger for the fender... they use some pretty heavy steel.

I would not be cutting the bridges out of bikes that have them... on a road bike any added stiffness is something that is desired so even if the bridge adds little in this respect, a little more stiffness at the saddle and bb is not a bad thing.
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Old 04-29-12, 09:03 AM
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The new Ritchey Swiss Cross has no chainstay bridge.
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Old 04-29-12, 09:11 AM
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Originally Posted by Stealthammer View Post
Spoken like someone with absolutely no framebuilding experience whatsoever..... Thank you for the laugh.

In the real world seatstay/chainstay bridges stiffen up the rear triangle very noticably and they clearly reduce the torsional flexing of the rear end of the frame. Stating that "Seatstay bridges don't have any structural function except as a place to mount a caliper brake", is simply naive.

^^^^^ This. When I built bikes I would check and adjust the entire frame's alignment several times during the build process, and the addition of the seatstay/chainstay bridges would always make a very noticable difference in the force required to adjust the rear triangle's alignment on anything but fattest tubed aluminum.
I think that to describe it best is that what happens when the bridges go in, they form a smaller triangle between the seat stay and the bottom bracket and effectively shorten the tube lengths between places where the bike experiences the most torsional flex and stress. A shorter tube will flex less than a longer one and when you are working on a frame and have the wheel out, you can usually flex the stays by hand on all but the stiffest of frames. The rear wheel is also a structural component.

We build tandems and touring bikes with OS tubes... the stays we use are custom drawn and are about as stiff and strong as they get and in some cases, longer than anything you have ever seen. The distance from the bridge to the rear axle is going to be as long as many conventional stays and re-spacing these by hand is immensely difficult once they are built due to the design of the stays.

These are the things I was speaking of.

Have built conventional frames and they have bridges because every little bit counts and I usually have to mount brakes and would prefer they don't tear themselves from the frame.
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Old 04-29-12, 10:08 AM
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Here's another of my road bikes...completely different animal, but no chainstay bridge on this one, either. The way bottom bracket areas on carbon frames are shaped and oversized these days, it's easy to see why they're super stiff when pedaling forces are applied. The chainstays are oversized and extremely stiff, too. If you look at the bottom bracket shell on my Pinarello above, there are some things going on with its shape that tell me it's meant to resist flexing and twisting from pedaling forces in the bb area as well. Does that bb shell help overcome any difference the bridgeless design makes? I don't know, but Pinarello introduced it as the "bridgeless bottom bracket shell" in the late '80's:



Pinarello's "bridgeless bottom bracket shell," introduced in the late '80's:

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Old 04-29-12, 10:32 AM
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I'm no framebuilder, but I seem to have a better intuitive grasp of engineering than most, and I find the suggestion that bridges contribute no structural rigidity absolutely laughable.

I also find the idea that a frame designed without them is inherently a bad idea equally silly.
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Old 04-29-12, 10:42 AM
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Originally Posted by Kimmo View Post
I'm no framebuilder, but I seem to have a better intuitive grasp of engineering than most, and I find the suggestion that bridges contribute no structural rigidity absolutely laughable.

I also find the idea that a frame designed without them is inherently a bad idea equally silly.
+1, personally I think that sums it up.
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