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

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

Postby tbessie » 20 Mar 2018, 12:37am

Hey again folks...

So as mentioned elsewhere, I'm having a custom touring bike built for me.

The builder is making it with a quite long head tube and about 13 degrees of slope in the top tube, so that I can have the handlebars high for comfort, but still be able to stand over the bike.

On another discussion on another site of handlebar height and sloping top tubes (which I can't find anymore), the topic came around to bikes built with long head tubes, but with quite a bit of head tube extending above the top tube/head tube joint; this way, you could have something close to a horizontal top tube, but still have handlebars mounted high up without a lot of spacers, tall quill stem, or extreme-angled threadless stem. Someone even posted a picture of such a bike (I think it was also a custom job).

It's too late to ask the builder to do that (he didn't seem to want to do that to the extent I wanted; he lowered the joint about a cm, but not much more).

Has anyone here ridden such a bike? Are there disadvantages (besides it looking kind of funny) to that design?

- Tim

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

Postby pwa » 20 Mar 2018, 6:16am

The most mechanically satisfactory join will always have the tubes meet close to their ends, leaving only a little bit of head tube sticking out beyond that. And to my eye it would look a little odd with more than a small bit sticking up. But I am one of those who find gently sloping top tubes easier on the eye than horizontal, and others don't agree with me on that.

I'd be happiest if I felt the person joining the tubes together was happy with the design and enthusiastic about what he/she is doing. I'd not push them to create a detail that they were not convinced about.

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

Postby tatanab » 20 Mar 2018, 6:56am

I think it probably depends how much of the head tube is above the top tube. I have both Roberts and Longstaff with horizontal top tubes and extended head tubes, but in each case the head tube extends only about an inch.
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foxyrider
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Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby foxyrider » 20 Mar 2018, 8:48am

tatanab wrote:I think it probably depends how much of the head tube is above the top tube. I have both Roberts and Longstaff with horizontal top tubes and extended head tubes, but in each case the head tube extends only about an inch.
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The design of this owes as much to availability of lugs for brazed frames as to an actual desire to be built this way. As soon as materials designed for welding came along and we stopped having to use lugs we could build stronger, better designs.

A good design will have the tubes supported towards the end, any unsupported length of tube is susceptible to flex and potential failure.
Convention? what's that then?
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tatanab
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Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby tatanab » 20 Mar 2018, 8:49am

foxyrider wrote:The design of this owes as much to availability of lugs for brazed frames as to an actual desire to be built this way.
Agreed. here's the lugless Longstaff.

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

Postby pwa » 20 Mar 2018, 9:14am

tatanab wrote:I think it probably depends how much of the head tube is above the top tube. I have both Roberts and Longstaff with horizontal top tubes and extended head tubes, but in each case the head tube extends only about an inch.
small.JPG


While an unsupported length of tube must be more susceptible to flex, such a short extension can't be a problem. So it becomes a personal aesthetic choice between that and the alternative sloping top tube. No right or wrong choice there, just what you like or don't like.

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

Postby 531colin » 20 Mar 2018, 12:09pm

1. With the exception of the bottom bracket shell, the head tube is the biggest diameter and thickest walled tube in the frame.
2. The head tube above the top tube is one of the least loaded/stressed bits of the frame. (the bottom of the head tube sees greater loadings than the top)

Its perfectly acceptable to extend the head tube above the top tube, many people find this "looks better" than a big stack of spacers. (It also gives a bigger distance between top and bottom headset bearings, with a largely theoretical benefit in bearing life.)

These bikes are steel, welded construction...https://www.flickr.com/photos/52358536@N06/24518630264/sizes/z/
With a lugged/brazed construction, it looks a bit odd to see the top head lug with more head tube above it. It looks much neater with the head tube above the lug sleeved to make up the diameter the same as the lug, so what you see is a smooth tube. Alternatively the top head lug can be cut back to remove the part that normally encircles the top of the head tube, so you just see a lug making the joint between top and head tube, with the head tube continuing above the lug....the top of the head tube is normally fitted with a "reinforcing" ring in these frames, although its purpose is more decorative than mechanical.

edit...one I found ....https://www.bing.com/images/search?view=detailV2&ccid=7pSHcb7X&id=7D52C794FBBA139870F0749086DCEC0BBF2D1528&thid=OIP.7pSHcb7X2_o0Y2qOt15PZAHaFj&mediaurl=http%3A%2F%2Fwww.renehersebicycles.com%2FIMG_5978.JPG&exph=1200&expw=1600&q=bicycle+frame+lugs+picture&simid=608047103597154053&selectedindex=234&ajaxhist=0

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

Postby amediasatex » 20 Mar 2018, 12:33pm

One of my Mercians is like the latter example from Colins post above, with the top lug tall/extended. It's not by much, but it does make a small difference. you could achieve the same with a longer quill or positive rise stem of course.

I'm not a huge fan of it aesthetically but it's not awful. Some frames look better horizontal, others look better with a bit of slope, all in the eye of the beholder though so largely irrelevant what other people think of it.

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

Postby peetee » 20 Mar 2018, 4:34pm

I think most builders of steel bikes avoid sloping top tubes on lugged frames because of the difficulty of sourcing lugs with the required angles.
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tbessie
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Re: Custom Touring Bike : Top/Head Tube joint way lower to avoid slope?

Postby tbessie » 20 Mar 2018, 4:48pm

peetee wrote:I think most builders of steel bikes avoid sloping top tubes on lugged frames because of the difficulty of sourcing lugs with the required angles.


Just for the record, the bike I'm having built is titanium, so I couldn't have lugs on it even if I wanted to (unless they've found a new technique for adding lugs to titanium frames - at least, my builder doesn't do that). So that's not a concern.

- 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 » 20 Mar 2018, 9:22pm

Go to Spa Cycles website and look at Elan....that's a Ti frame.....the small sizes have both seat tubes and head tubes extended above the top tube.....you can call that a dropped top tube, if you like, and its for standover for short legs.
Just to show alls fair in love and bicycles, the biggest size is limited by the available length of steerer in carbon forks.

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

Postby tbessie » 20 Mar 2018, 10:07pm

531colin wrote:Go to Spa Cycles website and look at Elan....that's a Ti frame.....the small sizes have both seat tubes and head tubes extended above the top tube.....you can call that a dropped top tube, if you like, and its for standover for short legs.
Just to show alls fair in love and bicycles, the biggest size is limited by the available length of steerer in carbon forks.


I took a look - this? https://www.spacycles.co.uk/m1b0s21p355 ... -triple%29

I doesn't look like what we're talking about, that I can see - it seems to have a bunch of spacers. The "Ti Tourer" looks more like what you're describing, but that, too, looks like it has a bunch of spacers:

https://www.spacycles.co.uk/m1b0s21p255 ... -Ti-Tourer

Do you have a link for what you're describing?

- Tim

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

Postby the snail » 20 Mar 2018, 10:20pm

The image of the elan at top left under the main pic looks like the head tube extends above the top tube

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

Postby tbessie » 20 Mar 2018, 10:52pm

the snail wrote:The image of the elan at top left under the main pic looks like the head tube extends above the top tube


Weird, some of them do and some of them don't; I wonder if that is related to the official bike "size".

- 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 » 21 Mar 2018, 8:38am

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.
This is because (weirdly :wink: ) standover clearance is a problem for people with short legs. For riders approaching "average male height" there shouldn't be any problems getting a bike to fit, unless the rider requires an unusual riding position. **
So the smallest Elan has a significantly dropped top tube with quite an obvious slope. The biggest bike has a slightly sloping top tube which isn't dropped at all.
The titanium tourer was the first bike I designed for Spa, and so is fairly conventional, relying on a steel steerer and a big stack of spacers to get the bars up, like Thorn do. Elan is designed around using a full carbon fork, so you can't use a big spacer stack.

Why would you make bikes for tall and short riders to exactly the same design, and just scale the drawing up and down? Wheels and bars don't scale

**In general, riders about 5'4" tall and upwards are easy to fit for a bike. Riders 5' tall are difficult to fit, because wheels and stuff don't scale.