# Twin top tubes flexy?



## MDEnvEngr (Mar 11, 2004)

I've been thinking about a twin TT frmae for my next project. Have heard from a trusted source that the twin TT design is flexy as compared to a normal TT. I would have thought that the triangulation in the "Z" plane would make it more resistant to torsion...but that is not what I'm hearing.

Anyone have experience with the twin TT? I'm thinking twin 0.625" tubes, from the rear dropouts to the HT. Webs to the ST, and a couple of ladders between the ST and HT.

Thanks for any advice.

B


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## Blaster1200 (Feb 20, 2004)

Torker BMX bikes used that design back in the 80s. You can do a google search for more images.


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## Clockwork Bikes (Jun 17, 2006)

It really depends on how big the frame is. This guy is plenty stiff: http://www.clockworkbikes.com/urban.html









-Joel


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## shiggy (Dec 19, 1998)

Clockwork Bikes said:


> It really depends on how big the frame is. This guy is plenty stiff: http://www.clockworkbikes.com/urban.html
> 
> View attachment 452011
> 
> ...


Plus the tubing used and how you define "flexy."

There is good flex and bad flex and even those can depend on the rider's preferences.


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## toddre (Mar 1, 2004)

On a slight hi-jack here, anyone play around with twin downtubes?


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## Clockwork Bikes (Jun 17, 2006)

The DT takes quite bit of torsional force, which smaller twin tubes are terrible at resisting. Nothing beats a round profile for torsion.

-Joel


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## Schmitty (Sep 7, 2008)

Twin vert tubes is the way to go.. like the old work cargo bikes. Two top tubes of standard od would be mad stiff... and heavy.


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## wbarocsi (Jul 22, 2008)

Twin down tubes have been tried a few times recently. Alan/Guerciotti in and Carbon in the '80s and Colnago "Bititan" in the '90s. Also check out the Moulton space frame http://www.moultonbicycles.co.uk/ All good ideas, but not really an improvement over regular tubes.


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## Yogii (Jun 5, 2008)

If only moulton bicycles could make that a folder...
Thanks for the link.


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## ~martini~ (Dec 20, 2003)

I've got a Ti twin top(actually tri) tube bike. It flexes a crazy amount. The jury is still out on whether this is a good or bad thing. I thought it would lead to vagueness in the ride, but so far it really isn't the case. I'm STILL waiting to get it on trail. We got nearly 4" of rain here this w/e. Trails are going to be a bit....mushy for a few days yet.


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## Adam_M (Aug 8, 2008)

I had (since sold) a path racer built here in London in 1911 or so that had twin down tubes. Ain't nothin' new in the world.


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