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-   -   Unusual frame design- speculation encouraged (http://www.bikeforums.net/framebuilders/708799-unusual-frame-design-speculation-encouraged.html)

Velognome 01-22-11 08:38 PM

Unusual frame design- speculation encouraged
 
I'm intrigued by this 30's vintage frame, the wire stays to be exact. Any speculation on their function would be greatly apprciated.
http://www.classiclightweights.co.uk/dtwitchett6.jpg

The top tube wires and stay wires seem to be acting like the standing rigging on the mast of a sailboat to support the seatpost tube.

Not so sure about the bottom tube and rear fork wires. Are they two separate sets of wires or a continous wire begining from the headtube, rounding the bottom of the BB and terminating at the dropouts?

I have little information about the frame other than it was built by Fletcher-Kain and it appears to have been well used by the looks of the photo.

Any speculation on the configuration of the wires would be much appreciated.

mudboy 01-22-11 10:08 PM

The "down wires" are clearly two wires, crossed. My guess is that the wires are stranded.

Looks like the Slingshot's great-grandfather.

Velognome 01-22-11 10:37 PM

Quote:

The "down wires" are clearly two wires, crossed.
but do they terminate at the bb or continue to the dropouts?

Quote:

Looks like the Slingshot's great-grandfather.
Kinda, but the Slingshot was designed to flex, this appears to be rigid.

hillzofvalp 01-22-11 11:00 PM

Reminds me of an egg cutter if you get where I'm going---but it's a cool frame, nonetheless. If you used some of the lightweight steel of today, it could probably compete in weight with carbon frames.

mudboy 01-23-11 06:47 AM

Quote:

Originally Posted by Velognome (Post 12117504)
but do they terminate at the bb or continue to the dropouts?



Kinda, but the Slingshot was designed to flex, this appears to be rigid.

It would be far easier to manage the tension of the wires if they terminated at the BB, and then the lower "stays" were fixed at the BB and the dropouts. There would also need to be some sort of turnbuckle to adjust the tension of the wires.

I'd be really nervous having my man-candy that close to a couple of highly stressed wires/stranded cables.

Velognome 01-23-11 12:54 PM

Quote:

hillzofvalp

Reminds me of an egg cutter if you get where I'm going


<QUOTE]
mudboy http://www.bikeforums.net/images/yellow_jersey.gif


I'd be really nervous having my man-candy that close to a couple of highly stressed wires/stranded cables




[/QUOTE]

My son's immediate response also. In closer inspection, cheese slicers and Hardboiled egg cutter are single strand, this will have to be stranded, and if you fell hard enough to do any damage, I think a solid bar would be a more painful experience. Broken cable whip......that makes me nervous.

Quote:

There would also need to be some sort of turnbuckle to adjust the tension of the wires.

Got that sorted out with some threaded sleeves that will allow tension adjustment. The two prevailing ideas are to measure the frame untensioned, then tension evenly watching for movement; the other is to use a spoke tension guage to check for uniformity. I believe both systems will be employed in tuning the bike. A process that will have to be done before each ride I think to overcome cable stretch and changes due to temperture.











BryGuy 01-23-11 09:48 PM

All wires appear to be rigging wires to keep things in place with the weight born by the transverse "mixte" tube. They don't have to be stranded, could be heavy guage straight wire. Interesting concept.

repechage 01-23-11 10:04 PM

Quote:

Originally Posted by Velognome (Post 12116932)

That bike frame kind of reminds me of what the Swiss tried in the last Americas Cup, and lost.

This kind of structure works if you can keep the wires under tension, as they do not help in compression. I would like to watch this bike in action under hard acceleration. Think about how the "chain stay" wires would be behaving. Seat stay wires too.

An interesting feature is that the saddle clamp is reversed, bold enough to abandon convention, but just could not bear to make the seat tube steeper. A 72 degree seat tube would probably fit very well to catch things better.

Also note the bars and stem, that could well be one piece.

It appears to me that adjacent to the seat tube at the top are internal type turnbuckles for tension adjustment. In my view one would have to build it straight, then tension it and keep it in a jig "floating" to insure it stayed straight.

repechage 01-23-11 10:23 PM

Quote:

Originally Posted by BryGuy (Post 12121758)
All wires appear to be rigging wires to keep things in place with the weight born by the transverse "mixte" tube. They don't have to be stranded, could be heavy guage straight wire. Interesting concept.

Could be "rod rigging" used in the 12 meter racing sloops from the 1970's. Spokes are a form of rod rigging.

Allen 01-24-11 01:52 AM

Quote:

Originally Posted by repechage (Post 12121821)
An interesting feature is that the saddle clamp is reversed, bold enough to abandon convention, but just could not bear to make the seat tube steeper. A 72 degree seat tube would probably fit very well to catch things better.

That was the way saddles were mounted on race bikes back in the day.
Slack seat posts were the norm, and saddles were on stems.
http://cdn2-b.examiner.com/sites/def...%20Bicycle.jpg
Wright Brothers' bicycle

http://farm4.static.flickr.com/3465/...a7ea442036.jpg
1905 Motorpaced Stayer bike
PS. the fork is not backwards.

Velognome 01-24-11 07:59 AM

Quote:

It appears to me that adjacent to the seat tube at the top are internal type turnbuckles for tension adjustment. In my view one would have to build it straight, then tension it and keep it in a jig "floating" to insure it stayed straight.
I believe they are turnbuckles. Building it straight and getting it of the jig is the first step. Once it gets a few miles and the cables stretch a bit, re-tensioning will be a bit tricky.

Live Wire 01-24-11 08:56 AM

It's one of those classic examples of an engineer who knows a lot about a type of construction applying his designs in an area ill-suited to them. It's new, it's different, the engineer can talk for days about how superior it is, but once again the double diamond frame wins.
Came across this reinvention of the concept awhile ago:
http://s3images.coroflot.com/user_fi...ZLXlNebuGJ.jpg
Looks like the guy is good with computer imaging, but doesn't know a whole lot about bikes. Funny thing is that from the comments on his site, http://www.coroflot.com/ionutpredescu/City-Bike/2 he doesn't seem to know it was actually built before.

Velognome 01-24-11 12:50 PM

^^^ Ignorance is bliss??

[QUOTEIt's one of those classic examples of an engineer who knows a lot about a type of construction applying his designs in an area ill-suited to them.][/QUOTE]

Careful......just because it didn't catch on or work the first time doesn't mean the concept doesn't have merit. The Wright Brothers didn't fly out of the barn in their first airplane, the priciples and application were correct, the product needed tweeking. It's called R&D.

The idea's here, reduced weight through reduction of material and of micro adjusting a frame may have merit and application, the concept of feather weight and ride quality are not foriegn to bicycle design. What seems to be applied here are some techniques used in Sailing to handle large loads and stress with extremely light tackle.

cs1 01-24-11 02:29 PM

Looks a Slingshot bike. Here's a good intro:
http://mombat.org/Slingshot.htm
http://forums.mtbr.com/showthread.ph...ight=slingshot

Velognome 01-24-11 02:58 PM

Quote:

Looks a Slingshot bike.
Totally different concept.

This wired frame is designed around the concept of tensional integrety, "This can produce exceptionally rigid structures for their mass and for the cross section of the components."

This was a new concept in 1920's and here is a photo of a bike from that period or perhaps just a decade later!

repechage 01-24-11 04:20 PM

Quote:

Originally Posted by AllenG (Post 12122321)
That was the way saddles were mounted on race bikes back in the day.
Slack seat posts were the norm, and saddles were on stems.
http://cdn2-b.examiner.com/sites/def...%20Bicycle.jpg
Wright Brothers' bicycle

http://farm4.static.flickr.com/3465/...a7ea442036.jpg
1905 Motorpaced Stayer bike
PS. the fork is not backwards.

Indeed, but these designs are type conforming. The wire stay frame tossed out the blueprint and as such, since they were giving themselves such free reign, why not just go a bit farther?

Velognome 01-24-11 07:03 PM

^^^ Weren't the slack frame angles to help with tracking on rough pavement? If so, steeper angles would have only been seen as useful on prepared tracks, the slack angles would have been better on the rough roads of the period ( pure speculation on my part of course)

repechage 01-24-11 09:41 PM

Quote:

Originally Posted by Velognome (Post 12126402)
^^^ Weren't the slack frame angles to help with tracking on rough pavement? If so, steeper angles would have only been seen as useful on prepared tracks, the slack angles would have been better on the rough roads of the period ( pure speculation on my part of course)

For the head angle, I will accept that. For the seat angle, parts availability? The effort to place the seat forward of the seat tube by use of seat posts with forward extensions was common. I will even admit there must have been some suspension to doing that. But why on a track bike even? Granted there are some examples of machines with steeper angles, they seem to appear first on "6 day" bikes, but it seemed to take a long time to filter down to less specialized bikes.

Velognome 01-25-11 08:14 AM

So excluding the Head Tube angle, what advantage would there be to setting the Seat Tube at say 72 degrees in contrast to 68 degrees with a stem type post? And would having dissimular tube angles 68 head / 72 seat tube, adversely effect handling?

Doohickie 01-25-11 09:27 AM

Probably none, which is why you don't see this anymore. Designs in the old days were often based on nothing more than convention. Someone made it work with a certain angle, and a certain seat mounting configuration, and it was copied. Eventually it was optimized to increase stiffness, reduce weight, etc.


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