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Double top tube, does it help?

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Double top tube, does it help?

Old 11-29-17, 09:32 PM
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calstar 
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Double top tube, does it help?

The Rivendell Homer Hilson has a double top tube on the large sizes, how does it help stiffen the frame. Seems like the lateral forces would not be effected in any appreciable manner. I get the smaller triangle idea, just don't see what it does. According to the Rivendell site there is an 8 month wait, business is good for them.

https://www.rivbike.com/collections/...a-homer-hilsen

thanks, Brian
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Old 11-29-17, 09:35 PM
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I think it makes the vaunted "vertically compliant" less vertically compliant. I suppose it could have an influence on BB sway just by making the front triangle smaller, in effect. I always thought it was mostly style
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Old 11-29-17, 09:42 PM
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Originally Posted by unterhausen View Post
I think it makes the vaunted "vertically compliant" less vertically compliant. I suppose it could have an influence on BB sway just by making the front triangle smaller, in effect. I always thought it was mostly style
Sorta what I'm thinking,

After my post I searched on this forum, there have been questions about this before, sorry for the redundancy. I still would like members thoughts on this

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Old 11-30-17, 05:01 AM
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I suspect it helps resist the torsional forces on the headtube when pulling on the handlebars. With a long headtube and the top and down tubes that far apart, there is a lot of leverage to twist the headtube. The second tube would assist in resisting that torsional force.
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Old 11-30-17, 06:50 AM
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I've built at least 15 frames with double TT's over the years, all 29" mtb's. It was for style but I was a little suprised to see that you can tell those frames are a little stiffer when you're standing up and really pulling on the bars. But it isn't enough to make any real difference in the overall ride. Do it for the cool points!
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Old 11-30-17, 10:44 AM
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I once said it was for style points on mtbr forum, and some rando took offense and negged my reputation. Apparently someone I never heard of and who has never posted about any of their frame builds thought it was a personal attack.
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Old 11-30-17, 01:22 PM
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Old Chinese/ Indian Bikes that people load their farm produce and briks on have double top tubes but that is not
seamless thin-wall chro-moly Tubing..





I have a one off frame with a double top tube , but its side by side, 2 tubes .049" wall 3/4" OD.. 4130
it is bent to form the rear triangle as well..

Used in Cargo bikes by the same builder..

as my 4 pannier loaded touring bike , because it has negligible top tube flex
with the rear rack top, & pannier, & front lowrider, and the bags rigidly fixed.

descents were solid and smooth.. belt and braces i got a hydraulic steering damper..
(Old Odyssey. MTB piece, miniature of a moto cross part )

perhaps a large diameter horizontally ovalized top tube (ala tandem boom tube) would do similar and use lighter materials...
use same stuff vertically oriented as a down tube ...






...

Last edited by fietsbob; 01-15-18 at 05:55 PM.
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Old 12-07-17, 09:57 AM
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Double top tubes (vertically or horizontally oriented) literally just double the torsional stiffness between the handlebar and the seat tube. Assuming round tubes, the same effect can be had by using a single tube that is 26% larger diameter.

I'm entertained by the quote on Riv's site:
"65-71cm: $2500. These sizes come with a second top tube (2tt).
The 2tt adds triangulation and the strength and anti-twisty stiffness that comes with it, to frames that could use that, due to their longer head tubes. Some people object to the unusual look, but there are hundreds of thousands of examples of 2tt bikes in the world, and it is a feature that came about to solve a problem. So if you're tall, embrace your gangliness and get the 2tt bike. If you're tall and light and will ne'er ride with any sort of weight on it, you can get a tall Homer with 1tt...but you don't save money doing that, and the bike is worse. So....?"
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Old 12-07-17, 03:42 PM
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Double top tube always seemed silly to me, since the top tube doesn't do much, compared to the rest of the bike.
Double, or oversize down tube would make more sense.
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Old 12-07-17, 04:49 PM
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Maybe Not, on a Gram conscious Road bike.. but a load bearing touring bike it made a lot of difference..

Rear rack With it's load, is a lever flexing the top tube...
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Old 01-15-18, 04:50 PM
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There are situations where more is needed, the question is more what. If a double top tube is a solution, why isn't it used on all frames? They could just then scale down the size of the other tubes? When someone like Riv talks about style and world wide use, I think we are talking about some unsophisticated builders who had only a few tubes available and just slapped an extra one on when they ran out of stiffness. They didn't have the option of many materials and configuration of tubing, or indeed, formed specialty tubes.
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Old 01-15-18, 05:50 PM
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Weight weenies have different priorities

Riv bikes have their own devotees.. cults happen..
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Old 01-15-18, 05:54 PM
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Originally Posted by fietsbob View Post
Maybe Not, on a Gram conscious Road bike.. but a load bearing touring bike it made a lot of difference..

Rear rack With it's load, is a lever flexing the top tube...
My thoughts as well.. Lacking a degree in engineering of course.
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Old 01-19-18, 06:41 PM
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I can see it with a really big frame, tall headtube....so big it makes the frame less of a triangle and more of a trapezoid.

I see a really tall guy on a really Rivendell with double top tubes, normally as he is passing me on the commute, so it doesn't slow anything down at any rate
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Old 01-19-18, 06:53 PM
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I cannot imagine what sort of extra degree of stiffness is needed as you pedal your 28 pound bike around with platform pedals, Earth Shoes and baggy shorts.

It is style for style on a modern bike.


Do smaller sizes get a price break because their buyers receive fewer tubes?
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Old 01-28-18, 04:35 PM
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if its a low wage low overhead country
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Old 01-28-18, 10:30 PM
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Even the old 25 1/2" CroMo Trek tour bike with its relatively longish wheelbase will be a bit whippy when loaded with paniers on the back, although... you can work with it if you even out the forces a bit with a good-size handlebar bag up front. A modern alloy frame with a tapered headbube, hydorformed tubing and comparatively shorter wheelbase -- that probably won't come in any bigger size than a ~s61 -- won't have these issues but they're not intended for touring. This tour bike which is about as big as any you'll ever see, I imagine is probably pretty stiff with the addition of a second top bar.
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Old 01-29-18, 02:59 PM
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my 56cm specialized expedition, from a Japanese factory, use a 1.125" top tube , and a 1.25" down tube ..

it flexed a little with every pedal stroke with my Touring load


VBQ cult Mag readers call that Plane-ing..
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Old 01-29-18, 07:45 PM
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Originally Posted by fietsbob View Post
my 56cm specialized expedition, from a Japanese factory, use a 1.125" top tube , and a 1.25" down tube ..

it flexed a little with every pedal stroke with my Touring load


VBQ cult Mag readers call that Plane-ing..

I think that Jan might quibble with your too simple explanation. As I understand it planning is when the frame's flex is perceived to be a help in powering the bike up the road. Not whenever it flexes. Andy
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Old 01-30-18, 09:42 AM
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just not in that Jan's cult
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