In praise of titanium - and Spa Cycles

[threebikesmcginty]

Here you go. http://www.zambikeszambia.com/

I'll list the benefits.
Organic
Biodegradeable.
Low carbon footprint to the point of being a carbon sink.
Talking point.
Rust proof.
Can be planted and will grow a bike tree.

Con: Can be eaten by pandas.

 

[John the Monkey]

Con: Can be eaten by pandas.

Totes adorbz though.

 

[jayonabike]

Well I can tell a difference between the carbon, steel and titanium bikes I ride. I can even tell a difference between the 2 carbon bikes I ride. I guess I must be special.

 

[John the Monkey]

Well I can tell a difference between the carbon, steel and titanium bikes I ride. I can even tell a difference between the 2 carbon bikes I ride. I guess I must be special.

Is that an inherent quality of the frame material though? I can tell the difference between my Steel tourer and Aluminium roadie, but would hesitate to argue that it's entirely because of the materials they're made of.

 

[jayonabike]

Same saddle, same wheels, seat post, bars and stem. The only difference is frame material. I am the special one.

 

[PhilDawson8270]

Frame has the exact same geometry too?

 

[Yellow Saddle]

My local bike shop acquired a bamboo frame for a reason I cannot recall.

Dreadful thing which weighed a ton because of all the lumps of metal used to hold it together.

Every bike shop on the block acquired one of those. I had to assemble one for a customer. Now there was a frame making me with for titanium. The bloody thing was skew and I could not get the front derailer to work, the chainline was way off. It could accommodate a front brake (on the metal suspension fork) only since the rear brake mounts had some issue - I can't remember what. I doubt it ever went round the block. It did get lots of comments whilst it was standing in the workshop though.

 

[John the Monkey]

Same saddle, same wheels, seat post, bars and stem. The only difference is frame material. I am the special one.

Then revel in it, old thing, revel in it.

 

[Milkfloat]

YS - a a serious question. Surely the damping properties (is this density or how close the fibres are?) of the material itself play a part as well? Let me try and give an example as I am struggling here - I am thinking hammers (my second favourite tool). Hammers come in many different shapes and sizes and many different materials. If I were to get my steel headed hammer out and my rubber headed mallet and hit a massive steel block, I know it is going to hurt a lot more using the steel headed hammer.

I hate to quote Wikipedia, but here it is stated "Modifications have also been made with respect to the effect of the hammer on the user. A titanium head has about 3% recoil and can result in greater efficiency and less fatigue when compared to a steel head with up to 30% recoil.[10] Handles made of shock-absorbing materials or varying angles attempt to make it easier for the user to continue to wield this age-old device, even as nail guns and other powered drivers encroach on its traditional field of use."

I know a hammer is very different to a bicycle, but it was the best theoretical example I could come up with. Is it the fact that the bike is a pseudo triangle that makes all the difference?

 

[Venod]

Don't know how the hammer story relates to bike frames but a very interesting analogy, I have used all sorts of hammers extensively, I will have to read the Wikipedia entry.

What is your favourite tool.

 

[Yellow Saddle]

Not quite, any maneuver exceeding 1G is an aerobatic maneuver. For regular civilian flight, forces won't exceed 1G.

@Yellow Saddle iirc, on average Titanium is the equivalent strength of steel but at half the weight (comparing to low-grade steel alloys)

To compare specifics, a commonly used 531 tubing for bicycles is around 800MPa (UTS) at around 8g/cm^3 compared to 3AL titanium used on many cycles at around 900MPa but only around 4.5g/cm^3

So it's clear to see that Titanium is almost half the weight for the same strength as steel used in bicycles.

HOWEVER, comparing this to something common like 6061 Aluminium 325MPa at 2.7g/cm^3 you can get a material as strong as steel at 3/4 of the weight.

If you pay a bit more for 7005 aluminium, then you can get around 400MPa at pretty much the same density. You get the same strength of Titanium with around 20% more weight, on a 1.5kg titanium frame, you'll only be looking to save 250g by choosing Titanium.

Raw titanium is heavier than raw aluminium, but 3AL titanium alloy is lighter than both 531 steel tube, and 6061/7005 aluminium, and stronger at the same time.

The most common Ti alloy used in bicycles is 6%AL 4% V and as I warned early on in the post "strength" is a vague definition. However, if I look at all the bicycle failures I've examined, it has always been through cracking. Therefore I choose to compare strengths in fracture toughness. I could use fatigue limits, but a frame builder can easily compensate for that and alu builders of course do. This particular Ti alloy has a fracture toughness roughly correspondent to it's density, if you compare aluminium, titatnium and steel.
However, even if we were to use Young's modulus, where it more or less matches that of steel, it doesn't mean that a Ti frame can be made to the same dimensions as a steel one and therefore be lighter (because it is less dense) but still as strong as the steel one. The tubing can simply not be drawn to those dimensions and still have a reliable end product.
Ti is for instance, eminently unsuitable for sprockets. It just doesn't wear nearly as slowly as steel, yet, it is placed in cassettes for a)bragging point reasons and b) weight reasons. That still doesn't mean it is an appropriate material for the job.
My very premise to the debate is that Ti is an inappropriate material for the job.

 

[stoatsngroats]

Interesting thread, can have a second to comment?

The phrase horses for courses really is part of the whole metallurgist conundrum, and surely the single most important thing is robust suitability for the task. Whilst any BSO allows some people to enjoy their cycling, and a 1kg carbon frame is necessary for others to derive their enjoyment, whether Ti/carbon/Steel/Alu or wood is used, isn't about the individuals enjoyment that which matters?

would I ride a wooden bike? Maybe, If it rode well, (wow, think about the kudos of sustainable commuting!)

I'm less worried about the strength v weight v compliabiity than I am about how my bike reliably rides wherever I choose to take it?
Aren't you?

 

[Arrowfoot]

Enjoyed the debate and learnt a lot. Thanks PR, YS and many others.

 

[Yellow Saddle]

YS - a a serious question. Surely the damping properties (is this density or how close the fibres are?) of the material itself play a part as well? Let me try and give an example as I am struggling here - I am thinking hammers (my second favourite tool). Hammers come in many different shapes and sizes and many different materials. If I were to get my steel headed hammer out and my rubber headed mallet and hit a massive steel block, I know it is going to hurt a lot more using the steel headed hammer.

I hate to quote Wikipedia, but here it is stated "Modifications have also been made with respect to the effect of the hammer on the user. A titanium head has about 3% recoil and can result in greater efficiency and less fatigue when compared to a steel head with up to 30% recoil.[10] Handles made of shock-absorbing materials or varying angles attempt to make it easier for the user to continue to wield this age-old device, even as nail guns and other powered drivers encroach on its traditional field of use."

I know a hammer is very different to a bicycle, but it was the best theoretical example I could come up with. Is it the fact that the bike is a pseudo triangle that makes all the difference?

Nothing wrong with Wikipedia. It cuts to the chase and greatly helps understanding. It is always a good starting point. I don't quite understand why the Wikipedia hammer head has so much less recoil than a steel hammer. with he article doesn't say. However, I agree and understand that different materials behave differently when used as a chisel. I specifically used the chisel analogy to demonstrate impact transmitted through a long rigid cylinder. And to stretch the analogy a bit further, lets picture the two chisels which transmit the vibration/shock from the road to the rider being the fork and the seat stays.
In order for those to dampen the shocks reaching your sit bones and hands, there has to be significant compliance (give) in those two members. The "give" has to be the range of the impact and impact is easy to measure. Simply look at the road and decide how big the gravel is.
To get back to the recoil example for titanium as mentioned in the Wikipedia entry. I am not sure, and will think about this a bit, why this is so. But I don't think it is relevant since we are concerned with primary force, not a secondary one.
Now if we consider that the "chisels" in question, no matter which of the materials we use, are essentially rigid in the plane we're concerned about. You just cannot concede that they would give as much as the size of a piece of gravel - say 3mm. And if your imagination doesn't allow that picture, materials data sheets will convince you. And remember that a 27% improvement on a 3mm movement (shock amplitude) is hardly perceptible when you already have the tyres and saddle doing most of the work.
We could argue that a fork, being curved (sometimes) would bend and thus give. It doesn't. It is still too rigid over that small curve. As I said, once you've hammered a headset race onto a fork supported at the bottom by a wooden block, you will instinctively know what it is essentially solid even with the huge forces of the hammer. As an expert hammer user you would have developed a feeling for when the workpiece support absorbs too much energy for the hammer to be efficient. Hammer users will instinctively choose to work directly above the leg of a workbench rather than in the sprung centre.
Further, let's use the ruler-on-a-desk analogy. Wood resonates nicely and admittedly you don't feel the vibration on the clamping hand. Translate that to how a frame absorbs shock and you will see that you have an unworkable frame. It is essentially a boiled noodle with no rigidity at all. It won't steer and it won't allow standing pedaling.

 

[Yellow Saddle]

If you pay a bit more for 7005 aluminium, then you can get around 400MPa at pretty much the same density. You get the same strength of Titanium with around 20% more weight, on a 1.5kg titanium frame, you'll only be looking to save 250g by choosing Titanium.

.

7000-series alu has problems with extrusion and welding and most frame manufacturers will avoid it.