So after my first custom Ti frame, I am having second thought about the material. Ti is branded (and priced accordingly) as the wonder material for rigid and hardtail bikes. There is just one problem - FLEX.
My beautiful frame is close to ideal in every aspect except lateral stiffness. I can noticablly flex the frame by twisting the bars and seatpost while standing. Compared to my steel bikes, such as Honzo, there is much less torsion in this test.
Ti is something like 60% less stiff than cromolly steel, so this is not totally a surprise, and yet...
The $1,000+ question is, can a Ti frame be made as stiff as a steel frame, without giving up the weight advantage?
That looks like your bringing back the hardcore hardtail. What grade Ti was used and what is i.d. and o.d. of the tubing. Depending on diameter and grade, a ti frame can be made stiff or flexy. A friend of mine welded Ti frames at Serotta for a few years and on his personal hardcore frame he added a small brace near the headtube to give it more latteral rigidity, it was designed around a judy xl(back when 100mm fork needed a dual crown). Before yours that was the only "freeride" hardtail frame I had seen.
You were ill-served. A Ti frame can be easily made stiff and still kept light. Tube diameter and wall thickness will profoundly affect the aforementioned. I have a Black sheep and a Kish, and had a Lynskey. All were stiffer than my steel Waltworks (which was an excellent bike).
Last edited by Climber999; 08-24-2012 at 07:53 AM.
You're not going to find many frames that flex less than a Honzo. You have picked that frame up, right? What's the weight differential... 30% in the frame alone? Of stiffer material?
Not surprising.
The answer to your $1,000 question is: "without a doubt."
Originally Posted by pvd
Time to stop believing the hype and start doing some science.
So after my first custom Ti frame, I am having second thought about the material. Ti is branded (and priced accordingly) as the wonder material for rigid and hardtail bikes. There is just one problem - FLEX.
My beautiful frame is close to ideal in every aspect except lateral stiffness. I can noticablly flex the frame by twisting the bars and seatpost while standing. Compared to my steel bikes, such as Honzo, there is much less torsion in this test.
Ti is something like 60% less stiff than cromolly steel, so this is not totally a surprise, and yet...
The $1,000+ question is, can a Ti frame be made as stiff as a steel frame, without giving up the weight advantage?
Flex is one of the things Ti is know for. A frame can be designed to be stiffer, at the expense of weight and and reduction of the signature smooth ride quality.
mtbtires.com
The trouble with common sense is it is no longer common
there are a lot of levels of execution when it comes to Titanium. As with all frame materials.
At the lower end there can be compromises in reliability.
I have thrown about 100,000 km at a Moots Ybb and its as good as new. Especially after a factory refinish.
Lots of good builders out there but it costs a bit more.. Sourcing of Titanium and welding skills are important.. Also the use of machined hard points like seatpost section, BB, Headset and drop outs. It costs more but machined from Paragon or comparable are really durable.
Honzo is a very heavy and strong frame. Build a 3Kg Titanium frame and you wouldn't hear any complaint about it being flexy.
I've got a book on material strengths (at work), and it states that all metals, with the exception of a few exotic things like gold/platinum, have the same strength to weigh ratio give or take 2%
I didn't believe it when I first read it, and had to create a speadsheet to prove it to myself.
If you don't have a size limitation, there is no real advantage to titanium, that can't be overcome with a proper redesign.
As already pointed out, Flex can be good. You can also specify the type of titanium, and the gauge (wall) thickness on some tubes to increase stiffness.
Additionally if you want a stiffer feeling you can always add more material such as a head-tube gusset. Ti isn't painted and doesn't require heat treatment, so you can always take it back to your framebuilder and ask/tell him what you want. They should be able to add more gussets / stiffening material. See the gusset at the tt, dt, ht junction on this bike:
My ti Seven is WAY more stiff & responsive than my steel Niner. It's not punishing though - not as smmoth as the Niner but it rides way smoother than my 2011 Canondale Alloy Flash without giving up any responsivesness. It's all about the build quality.
2013 Cannondale Scalpel 29er 1x10
2012 Seven ti 29er SS rigid
2012 Seven steel 29er SS rigid Southern Maryland Crew
What is the weight of a Honzo compared to your Ti frame? I tested a Honzo before I got my El Mar, and was blown away by how heavy it was.
Stock build was it? Those are well over 30 lbs, close approaching 35 lbs. The frame weight itself is on par with other All-Mountain cromoly frames out there.
I've got a book on material strengths (at work), and it states that all metals, with the exception of a few exotic things like gold/platinum, have the same strength to weigh ratio give or take 2%
I didn't believe it when I first read it, and had to create a speadsheet to prove it to myself.
I know for a fact that is not true. I'd love to see what you got, though.
Strength-to-weight (or specific strength) as it is defined does not give a complete picture of a material's performance. It does not take into account susceptibility to fatigue, for example.
That said, Ti has >30% higher strength-to-weight than aluminum, and about 10% higher than steel.
There's a reason you don't see 3.5-lb. steel frames.
Originally Posted by pvd
Time to stop believing the hype and start doing some science.
I know for a fact that is not true. I'd love to see what you got, though.
Strength-to-weight (or specific strength) as it is defined does not give a complete picture of a material's performance. It does not take into account susceptibility to fatigue, for example.
That said, Ti has >30% higher strength-to-weight than aluminum, and about 10% higher than steel.
There's a reason you don't see 3.5-lb. steel frames.
True that, to add to it this doesn't take into account the treatment of the metal.
Annealing, case hardening, tempering, quenching, and other processes modify the lattice structure of the crystalline material. These processes can take the EXACT SAME base material and completely change strength/stiffness/fatigue properties.
I've got a book on material strengths (at work), and it states that all metals, with the exception of a few exotic things like gold/platinum, have the same strength to weigh ratio give or take 2%
I didn't believe it when I first read it, and had to create a speadsheet to prove it to myself.
If you don't have a size limitation, there is no real advantage to titanium, that can't be overcome with a proper redesign.
Originally Posted by meltingfeather
I know for a fact that is not true. I'd love to see what you got, though.
Strength-to-weight (or specific strength) as it is defined does not give a complete picture of a material's performance. It does not take into account susceptibility to fatigue, for example.
That said, Ti has >30% higher strength-to-weight than aluminum, and about 10% higher than steel.
There's a reason you don't see 3.5-lb. steel frames.
It's not Strength-to-weight, it's stiffness to weight ratio what's almost the same.
My old Ti bike - Kona King Kahuna '98 - was plenty stiff. I chose that frame specifically because the larger diameter shaped tubing in the front end would make it stiffer and I knew that XL frames especially require that due to the longer tubes.
Ti frames can be built up relatively solid, if the builder is experienced, aware of your size, weight and riding style and isn't restricted by a requested frame weight limit.
I know for a fact that is not true. I'd love to see what you got, though.
Strength-to-weight (or specific strength) as it is defined does not give a complete picture of a material's performance. It does not take into account susceptibility to fatigue, for example.
That said, Ti has >30% higher strength-to-weight than aluminum, and about 10% higher than steel.
There's a reason you don't see 3.5-lb. steel frames.
Perhaps you're misunderstanding what I wrote from that book.
Strength is a statement of resistance to 5 physical forces that exist.
They are tension, compression, torsion, bending, and shear.
And you are 100% correct about fatigue ... Titanium does not do as well in this category as steel.
With that said, all designs are a compromise, and material choice, size, and geometry, are all compromises.
The example I worked on, dealt primarily with a bending force, and when comparing steel to aluminum, to obtain an equal resistance to that force, the aluminum diameter was increased until the resistance was equal to steel, at which point the weight was basicaly the same.
As was stated earlier in the thread ... A design change can eliminate the flex being discussed, and the best method to acheive this IMO would be triangulation.
I will also admit that my book reference is dated, and titanium might have been in that exotic category, as it was probably written prior to Russia flooding the market with titanium.
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Originally Posted by pvd
Originally Posted by Nevada 29er
