Yikes - the slackest seat tube in the world? ….

[2manyoranges]

https://www.ebay.co.uk/itm/17641833...OcRkYagJQcP0IRH3LDnrm4egfQRz|tkp:BFBMiq3H9tpk

 

[ChromeChainstay]

my eyes hurt looking at that •

 

[bikeworkshop]

Surprisingly common
@bagpuss was offering a nice one a few years ago

https://www.retrobike.co.uk/threads/sun-manx-tt.420387/

 

[2manyoranges]

interesting

quite an uncommon price though ...

gulp

but always interesting to see the innovation which was actually there in the culture during the 30's-60's

 

[bikeworkshop]

Iirc you weren't allowed to have the frame manufacturer on prominent display on a professional race bike at this point in time, so manufacturers were encouraged to make distinct frame shapes that couldn't be copied, but could easily be spotted from afar.
The curly, the flying gate, the manxman, the saxon twintube, the rensch...


No doubt they all explained the unusual shapes in terms of sporting advantage...

I love them all, and once harboured a desire to collect these unusual shaped lightweights.

 

[bagpuss]

From information I have read online 200 Sun Manx tt short wheel frames were built. Production started just after WW2 although the design was earlier. All the ones I have seen had forward facing drop outs . The one I have has track style ones . I have seen a fillet brazed frame , which I understand to be very rare .


Fillet brazed Sun Manx tt .

https://flic.kr/p/bJgBjz

https://flic.kr/p/bvmQQ9

https://flic.kr/p/bvmTDw

 

[2manyoranges]

And some of the designs such as the twin tube, allowed a very steep seat angle - something I liked at the time (70s) and have always strongly advocated for, and has now come to pass with West Coast geometry on Transitions etc. A current trend. Or, it turns out, not new at all....

https://www.transitionbikes.com/Bikes_Spire.cfm?

 

[bikeworkshop]

There was a keen interest in an ultra short wheelbase - several of these designs address that.

It allows a stiffer rear triangle for acceleration whilst using superlight steel stays.

Materials, and framebuilders choices improved though rendering the designs obsolete...

 

[2manyoranges]

hmmmm .... I am interested in this. I wantred steeper STAs in the 80s, knowing that this improved climbing DESPITE what most people claimed.

But with a straight seat tube there's only so far you can steepen things without the tyre interfering with the lower section of the seat tube. Bendy seat tubes (eg Stanton) were and are a way around this, but obviously with increased cost. The Saxon Twintube was a reknowned climber, and had a very steep (virtual) seat tube angle, since the tyre overlapped the actual line of the seat tube. Climbing was a special part of this debate and design field.

 

[bikeworkshop]

The modern bent seat tube though is really to allow an oversize tyre.
There are quite a few tt frames nowdays with almost vertical seattube,
although as you neither climb nor sprint, it's back to "riding on the rivet"

I think there's a rule about how far forward the saddle can be?