Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

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tbessie
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Joined: 10 May 2014, 3:27am

Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby tbessie » 21 Mar 2018, 5:38pm

531colin wrote:As I posted originally, the small sizes have a dropped top tube. Look at the bike stood up against the green stone wall, I think its probably the second-smallest bike.


Got it - I was looking for that configuration regardless of size (and wasn't sure about the actual size of each of the bikes pictured).

So I take it you don't think there's anything sacrificed by lowering the top tube joint? No less strong of a bike, worse steering or anything?

- Tim

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531colin
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Location: North Yorkshire

Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby 531colin » 21 Mar 2018, 6:36pm

Dropping the top tube can't influence the steering.
As for structural failure at the top of the head tube......
I've seen 1930s/1940s lugless Higgins Ultralite head tubes "spread" where the headset fits.....because its lugless, and the way to make a steel frame light is to use less metal.......
But I can't think of anything else.....anybody?

tbessie
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Joined: 10 May 2014, 3:27am

Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby tbessie » 27 Mar 2018, 7:32pm

531colin wrote:Dropping the top tube can't influence the steering.
As for structural failure at the top of the head tube......
I've seen 1930s/1940s lugless Higgins Ultralite head tubes "spread" where the headset fits.....because its lugless, and the way to make a steel frame light is to use less metal.......
But I can't think of anything else.....anybody?


I asked the fellow who's building my frame about this, and he said something about increased stress at the joins, especially where the top tube meets the seat tube, if the joint at the head tube is lowered, and also that the closer the top tube/head tube joint is to the down tube/head tube joint, the more stress there is... something along those lines, I can't remember the terminology he used.

He said it wasn't very significant, but it was did change the stresses on the bike negatively.

- Tim

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531colin
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Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby 531colin » 28 Mar 2018, 2:48pm

Perhaps he just wants to build what he wants to build?
Just out of interest, was any advice forthcoming about 650 tyres?
If you worry about stressing the top tube/seat tube joint, look at all the frames with the latest rediscovered fashion for attaching the seat stays several centimetres below the top tube, so you get two lots of bending strain on the seat tube, from the rider's weight and from rear wheel loading.

petelucas
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Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby petelucas » 3 Apr 2018, 9:43pm

Hi

Take a look at the picture here:

viewtopic.php?f=32&t=121107&p=1222548#p1222548

Is this what you are referring to?

Pete