Custom titanium frame questions...

Discuss light weight issues concerning road bikes & parts.
pdlpsher1
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by pdlpsher1

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pdlpsher1
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by pdlpsher1

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Last edited by pdlpsher1 on Fri Jun 15, 2018 10:33 pm, edited 1 time in total.

by Weenie


pdlpsher1
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by pdlpsher1

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Last edited by pdlpsher1 on Fri Jun 15, 2018 10:34 pm, edited 1 time in total.

pdlpsher1
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by pdlpsher1

I'm almost certain that all of the tubes on my bike with the exeption of the chainstays were locally ovalized by my builder. I don't know the reason why the DT is ovalized at the HT. I didn't ask for it. Maybe he did it for looks. I'm a small rider and there's really no need for any significant ovalization as the frame is already adequately stiff as is.

Many years ago I once owned a Litespeed Ultimate which had a tear-drop shaped top tube. I foudn the ride extremely stiff and unyielding. Litespeed is known for continuing this tradition in their latest T1SL. Can you think of a reason for such a stiff TT other than for looks?

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AndreLM
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Joined: Tue Feb 05, 2013 11:53 pm

by AndreLM

Specifically for the T1SL, the TT is made out of a rolled sheet of 6.4 Ti, that is supposedly very thin.

The T2 uses standard round & ovalized tube construction:

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Nixster
Posts: 62
Joined: Wed Oct 04, 2017 3:30 pm

by Nixster

So does the TT contribute to lateral stiffness?

Seems to me that it makes only a limited contribution to in plane stiffness if any, particularly on smaller frames. However it may contribute laterally. Hence me thinking oval all the way for the TT. Is the objection to this aesthetic, tradition or functional?

It could see some torsion on bigger frames but in smaller frames the DT would pick that up very quickly.
So why is the TT not usually smaller than the ST, which is limited by practical seat post sizes? :noidea:

Just trying to learn here, I am an engineer but definitely not a frame builder!

Nixster
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Joined: Wed Oct 04, 2017 3:30 pm

by Nixster

Oh and the Litespeed frames make no sense to me. Think how much lighter the super light T1SL could be with a sensible TT!

2lo8
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by 2lo8

Nixster wrote:
Fri Jun 15, 2018 10:52 pm
So does the TT contribute to lateral stiffness?

Seems to me that it makes only a limited contribution to in plane stiffness if any, particularly on smaller frames. However it may contribute laterally. Hence me thinking oval all the way for the TT. Is the objection to this aesthetic, tradition or functional?

It could see some torsion on bigger frames but in smaller frames the DT would pick that up very quickly.
So why is the TT not usually smaller than the ST, which is limited by practical seat post sizes? :noidea:

Just trying to learn here, I am an engineer but definitely not a frame builder!
I don't think any of the main frame tubes add signifigantly to in-plane stiffness unless you're talking about something like a 65cm trapezoid and how well they brace the headtube. For the front triangle on something that is actually somewhat triangular, the maintubes pretty much only need torsional and/or lateral stiffness. ST is mostly lateral because it is resisting being bent out of plane by the BB shell during the power stroke. DT is mostly torsional. TT is a mix.

You could ovalize a TT to be wider than taller, and/or taper it, which you see on a lot of carbon and aluminum frames. These are a lot less common steel and titanium. Sometimes you get things like vertical teardrop TTs which are even sillier than oval TTs. If you want to maximize torsional stiffness of a tube, you want to maximize the area inside the tube, meaning a circle, or the minimum amount of ovalization possible. To maximize lateral stiffness, you want the tube walls as far out to the sides as possible. Sometimes your tubes are already stiff enough. No one rides gaspipe hiten steel frames because they're a lot stiffer.
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pdlpsher1
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by pdlpsher1

I agree with 2lo8. I think the TT on the T1SL is overkill. Although I do find that bike to be very sexy! A large TT gives the frame an athletic and racy appearance.

Just for amusement here are some close-up shots of my titanium tandem. Note that the TT is larger than the ST but the TT was not ovalized at the miter. And note the coffee can sized boom tube which is severely ovalized. The ST is 34.9mm. The boom tube measures 80mm at the widest point, almost as wide as the BB386 EVO shell.

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RyanH
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by RyanH

What's curious to me is that my Litespeed Classic with relatively small diameter tubes is nearly as stiff (by feel) as my large tubed T3 which is as stiff as a lot of carbon bikes (of course, it helps that it is a small). So, if you're a small rider, unless you have a Ghisallo, I think most Ti frames will be sufficiently stiff. Larger riders is a different story. There's a thread on Paceline right now about the stiffness of Ti and steel for a larger rider. What I found interesting about that was that from my own experience, Ti was both more compliant and stiffer than steel (the indy fab) but opinions of larger riders is the opposite.
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Nixster
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Joined: Wed Oct 04, 2017 3:30 pm

by Nixster

I can't tell the difference in stiffness between my Lynskey and my SSix evo hi-mod. I get PBs on climbs on the Lynskey even though it's 1.5 kg heavier!

Curious RyanH what the main tube sizes on your Litespeeds?

pdlpsher1
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by pdlpsher1

RyanH wrote:What's curious to me is that my Litespeed Classic with relatively small diameter tubes is nearly as stiff (by feel) as my large tubed T3 which is as stiff as a lot of carbon bikes (of course, it helps that it is a small). So, if you're a small rider, unless you have a Ghisallo, I think most Ti frames will be sufficiently stiff. Larger riders is a different story. There's a thread on Paceline right now about the stiffness of Ti and steel for a larger rider. What I found interesting about that was that from my own experience, Ti was both more compliant and stiffer than steel (the indy fab) but opinions of larger riders is the opposite.
On the Classic and the T3, perhaps the answer is that once a bike is adequately stiff, any additional stiffness can’t be easily felt subjectively. Like you said small riders have an advantage in that most small frames will be adequately stiff even with small diameter tubing like your Classic.


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pdlpsher1
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Joined: Thu Jul 19, 2012 6:09 pm
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by pdlpsher1

Nixster wrote:
Sat Jun 16, 2018 7:06 am
I can't tell the difference in stiffness between my Lynskey and my SSix evo hi-mod. I get PBs on climbs on the Lynskey even though it's 1.5 kg heavier!

Curious RyanH what the main tube sizes on your Litespeeds?
Lynskeys are built to be very durable. They are not the lightest option when it comes to Ti but they are adequately stiff due to their higher weight and robust construction. If I was on a budget I would definitely get a Lynskey.

I think you mentioned you are thinking of a custom bike. What do you want that's missing on the Lynskey?

Nixster
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Joined: Wed Oct 04, 2017 3:30 pm

by Nixster

A good challenge!
I don't like the weight although that's not the biggest deal. The front end is a little high and the steering a little slow, mainly because the cstays are around 10mm longer than I would like at 425mm.
Mainly it's a feeling that it's over built and not the most elegant engineering solution, although I still like it. Also despite having long stays the brake bridge restricts clearance so it won't take guards/ fenders with wider tyres.
I can deal with all those points and include a few other details by going custom.

by Weenie


Berzin1
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Joined: Wed Jul 20, 2016 9:35 pm

by Berzin1

These are the photos of the frame that got me intrigued about a custom ti frame. It is a Litespeed Vortex, but I have no idea what year.

The tube shapes are what I like the most, except for the head tube. I think it would look better with an hourglass design, but that's just me.

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