Ti v. Carbon

redddraggon

I didn't say them all

rake

your genaralising to try and give that impression. false.

neeb

balthazar wrote:

Still, CFRP and aluminium outlasting steel and titanium frames, in a well conducted fatigue test, is somewhat upsetting to purveyors of received wisdom.

True.

I heard that carbon effectively doesn't fatigue in the way that metal does as long as it isn't damaged, it just breaks if you bend it far enough...

With Alu, might it be the case that the metal could gradually fatigue in a way that changes the properties of the frame even if it isn't actually broken, whereas Ti for all practical purposes only fatigues at particular points where it has been weakened, e.g. by welding?

blorg wrote:

I have two Ti bikes including my best bike (a Litespeed Archon) and currently three carbon ones... have had two additional carbon bikes in the past. And lots of aluminium.

Wow, that's a pretty good stable from which to make comparisons... What carbon frames do you have, and how does the Archon compare? And as the Archon and the Amazon are two very different Ti bikes, do they ride as differently as you would expect, or is there a common "Ti feel"?

Scrumple

This is getting dull....

And down to opinion.

Both have distinct advantages. The rest you sometimes need to discover for yourself!

This argument is in danger of being done again!

blorg

neeb wrote:

Wow, that's a pretty good stable from which to make comparisons... What carbon frames do you have, and how does the Archon compare? And as the Archon and the Amazon are two very different Ti bikes, do they ride as differently as you would expect, or is there a common "Ti feel"?

The current carbon bikes are a Planet X road, Planet X track and Focus MTB (so not much comparison with that one.) Also have a Kinesis alu/carbon hybrid cross bike. Previous carbon frames were a Focus Cayo and a Trek 5000. Previous aluminium bikes included a Trek road bike which in the same geometry and same everything else was substantially harsher than the 5000, very stiff and fast though.

The Archon is a very nice bike and seems to me very stiff in terms of power transfer while still being a comfortable ride. I've done long stuff on this one like the Tour of Ireland and Raid Pyrénéen and had no troubles at all with comfort. I also race it. To be perfectly honest though I think the Planet X (my winter bike) rides and handles very similarly. I have the contact points set up exactly the same.

The Trek 5000 was probably the outright most comfortable I ever had but it has been a while.

I don't think there is really a common Ti "feel" between the two bikes, I would probably be in the camp of believing tyre width/pressure to be more significant. The Archon is a road bike and handles like one, lighter and more nimble. The VN is nice for touring and not too heavy unloaded but it does feel more sluggish than the road bikes. As I say the Planet X feels closer to the Archon in terms of ride than the Van Nicholas does. Indeed my cross bike probably feels closer to the road bikes than the VN does.

To be honest though I don't know that I am overly sensitive to minute details, I have a lot of bikes and get on well with all of them. Maybe there are some princess and the pea types for whom the differences would be more important

I do suspect that a lot of what is said about bikes and materials is baloney... I like my Ti bikes but you would have to ask why every single pro is on a carbon one.

balthazar

neeb wrote:

With Alu, might it be the case that the metal could gradually fatigue in a way that changes the properties of the frame even if it isn't actually broken, whereas Ti for all practical purposes only fatigues at particular points where it has been weakened, e.g. by welding?

I have no idea. That's a question for metallurgists, or at least, materials experts. Perhaps Redddragon could help you.

Apart from any revelations on that subject, I think the message from that EFBe report is that frame design, and manufacturing care, are more important for fatigue life than the frame material. I prefer steel bikes for other reasons, and trust that a well-made one is adequately durable.

Evil Laugh

glenncampbell wrote:

'Tis not I - they're just great prices! I know what you mean though :-)

Thanks for making one of my all-time favourite tunes btw!!

ugo.santalucia

balthazar wrote:

neeb wrote:

With Alu, might it be the case that the metal could gradually fatigue in a way that changes the properties of the frame even if it isn't actually broken, whereas Ti for all practical purposes only fatigues at particular points where it has been weakened, e.g. by welding?

I have no idea. That's a question for metallurgists, or at least, materials experts. Perhaps Redddragon could help you.

Apart from any revelations on that subject, I think the message from that EFBe report is that frame design, and manufacturing care, are more important for fatigue life than the frame material. I prefer steel bikes for other reasons, and trust that a well-made one is adequately durable.

Aluminium alloys don't have a fatigue limit, in simple words they suffer fatigue even at very low stresses.

Steel and titanium alloys do have a fatigue limit and tipically this is higher (about 100-200 MPa) ,than the common cycles of stress in road cycling... if you don't do too much pave', that is...

There is a good description here http://en.wikipedia.org/wiki/Fatigue_limit

Scrumple

I'd rather eat nails than read that.

balthazar

ugo.santalucia wrote:

Aluminium alloys don't have a fatigue limit, in simple words they suffer fatigue even at very low stresses.

Steel and titanium alloys do have a fatigue limit and tipically this is higher (about 100-200 MPa) ,than the common cycles of stress in road cycling... if you don't do too much pave', that is...

There is a good description here http://en.wikipedia.org/wiki/Fatigue_limit

Thanks for that. I understood that there is a threshold, I just didn't know how mutable it is. That ordinary steel spokes remain below that threshold is the source of the advocation that old–proven– spokes are preferred. However, it seems from those test results that the material fatigue limit is not a major player in bike frame failure.

neeb

blorg - thanks for the reply, very interesting.

So for a fast road bike, maybe you can get much the same performance from Ti as from carbon, but you pay more for it. In return you get the timeless, rugged practicality of a frame made out of bare metal that will always look new given a quick polish with a scouring pad.

I do suspect that a lot of what is said about bikes and materials is baloney... I like my Ti bikes but you would have to ask why every single pro is on a carbon one.

I guess the really top-end carbon frames are always going to have an edge in terms of weight and/or performance, but I wonder if it's enough to make any practical difference. It would be fascinating to see if a pro team could compete at the highest level nowadays on something like an Archon. A top Ti bike could get under the UCI weight limit without too much bother (and without being a noodle like the Litespeed Ghisallo), so the small edge that carbon has might not count for much in practice. It may just be that the small, Ti only companies don't have the clout to sponsor pro teams, and the big companies that produce both carbon and Ti know that it's carbon that sells... (and is replaced more frequently)

ugo.santalucia wrote:

Aluminium alloys don't have a fatigue limit, in simple words they suffer fatigue even at very low stresses.

Steel and titanium alloys do have a fatigue limit and tipically this is higher (about 100-200 MPa) ,than the common cycles of stress in road cycling... if you don't do too much pave', that is... Very Happy

There is a good description here http://en.wikipedia.org/wiki/Fatigue_limit

Thanks, yes, that's what I was thinking of (but remembering rather vaguely)

blorg

neeb wrote:

So for a fast road bike, maybe you can get much the same performance from Ti as from carbon, but you pay more for it. In return you get the timeless, rugged practicality of a frame made out of bare metal that will always look new given a quick polish with a scouring pad.

Yes, that is pretty much it. Once you go above a certain level with bikes anyway I think you are paying more for it because you want it than for any practical performance benefit it is going to give you; most of us here I presume are amateurs. The main differences are in the engine not the bike.

I think many pros would generally win on just about anything and they ride what they are told to an extent. The last protour appearance I can recall was Litespeed sponsoring Lotto in 2002. I'm sure an Archon could be "competitive," you could certainly get it to 6.8kg without too much effort (I think mine was 7kg stock.) For non climbing stages many pro bikes seem to be a fair bit above the limit anyway, if you believe the pro bike reviews on this site. (The few I've seen in the flesh have been 6.8 spot on though.)

Armstrong was a big fan of Litespeed; he won his world championships in 1993 on one and rode a Blade TT bike rebadged as Trek in his 1999 tour.



But I think carbon has evolved now to the point where it is the optimal material for race bikes. This doesn't mean however that I can't still want one in titanium, I just don't feel I have to justify it in terms of how it is in some way "better" than carbon because frankly it is not. It is not significantly disadvantaged as to performance and may have advantages in other areas, mainly in subjective ones. I like my bike and that is good enough for me.

ugo.santalucia

balthazar wrote:

ugo.santalucia wrote:

Aluminium alloys don't have a fatigue limit, in simple words they suffer fatigue even at very low stresses.

Steel and titanium alloys do have a fatigue limit and tipically this is higher (about 100-200 MPa) ,than the common cycles of stress in road cycling... if you don't do too much pave', that is...

There is a good description here http://en.wikipedia.org/wiki/Fatigue_limit

Thanks for that. I understood that there is a threshold, I just didn't know how mutable it is. That ordinary steel spokes remain below that threshold is the source of the advocation that old–proven– spokes are preferred. However, it seems from those test results that the material fatigue limit is not a major player in bike frame failure.

Well the slow development of cracks in aluminium alloys is a common problem. That is due to fatigue, I'm afraid.
I know more than one person who had his alu frame replaced after 2-3 years of intense use. Luckily the warranty covered for it and luckily they spotted the crack before it led to total failure

balthazar

ugo.santalucia wrote:

balthazar wrote:

ugo.santalucia wrote:

Aluminium alloys don't have a fatigue limit, in simple words they suffer fatigue even at very low stresses.

Steel and titanium alloys do have a fatigue limit and tipically this is higher (about 100-200 MPa) ,than the common cycles of stress in road cycling... if you don't do too much pave', that is...

There is a good description here http://en.wikipedia.org/wiki/Fatigue_limit

Thanks for that. I understood that there is a threshold, I just didn't know how mutable it is. That ordinary steel spokes remain below that threshold is the source of the advocation that old–proven– spokes are preferred. However, it seems from those test results that the material fatigue limit is not a major player in bike frame failure.

Well the slow development of cracks in aluminium alloys is a common problem. That is due to fatigue, I'm afraid.
I know more than one person who had his alu frame replaced after 2-3 years of intense use. Luckily the warranty covered for it and luckily they spotted the crack before it led to total failure

I don't think anybody is disputing that fatigue is the usual failure mode for bike components, regardless of material. My point was that steel and titanium frames, which may be expected to survive indefinitely if they are stressed only below their material fatigue limit, still –in practice– tend to fail from fatigue, the cracks probably initiated by other causes, such as poor design or manufacturing control. This is illustrated in the test report I cited, in which an aluminium alloy frame was left standing on the battlefield, so to speak. Hence, the material fatigue limit (which you explained) is not practically decisive for bicycle frames.

neeb

Hence, the material fatigue limit (which you explained) is not practically decisive for bicycle frames.

I suppose this depends on whether in practice steel and Ti frames are likely to be subjected to the type and number of repetitive stresses used in the test (they admitted that it is not feasible to relate this to mileage), whether the ones that failed in the test were representative (they may have been bad samples, and welding technology, particularly for Ti, may have improved since the test was done), and whether the inevitable fatigue that Alu must suffer through not having a fatigue limit perhaps causes other problems before it leads to complete failure (and how predictably complete failure results from such inevitable fatigue - again, the sample size is not large enough...)

I'm just being a devil's advocate - it's an interesting article and the answers are not obvious.

balthazar

neeb wrote:

it's an interesting article and the answers are not obvious.

I agree: this stuff shouldn't be taken as read – that's how myths start! Unfortunately, I don't know of any other publicly available data like this, for comparision. EFBe continue these tests, but they charge for it, and the results aren't public.

However, though the sample size of this test is too small to generalise, it's results are de facto revealing, in showing that the majority of failures were not as expected. If you had presented the bikes beforehand to a general interested audience, such as those on this forum, and asked them to predict which would fail earliest and how – I guess most people would have predicted a roughly opposite outcome. Even if the causes were unexpected (material inclusions, poor welding, and so on), those are realities that real bikes and buyers face.

rake

if im honest i think they are cutting it a bit too close to the wire on all materials for my liking.
i wait for a touring bike to be suggested.

glenncampbell

Evil Laugh wrote:

glenncampbell wrote:

'Tis not I - they're just great prices! I know what you mean though :-)

Thanks for making one of my all-time favourite tunes btw!!

Good man! It's not easy being a rhinestone lineman etc. . . .

To be very honest on the forum here I built up a carbon road bike and then a carbon MTB hardtail because it was a lot, lot cheaper - the tarmac cost £1,500 less than the litespeed build I was drooling over and I bought an XTC carbon frame 2nd hand for £275 and swapped some parts over, then went mad on the forums buying xtr stuff but that's another story ;-( . I've had good performance from both, and if the carbon frame breaks which is likely with my rubbish riding, I'm going to get a Ti replacement - which was the plan all along - get a new BB & Headset, then swap the groupset over. Yummy.


Also - consider this because I certainly did - hardly the gordian knot solution - buy a Ti AND a carbon bike - enjoy both!!

gupta-patel

What about a brass frame?

Pross

But I think carbon has evolved now to the point where it is the optimal material for race bikes. This doesn't mean however that I can't still want one in titanium, I just don't feel I have to justify it in terms of how it is in some way "better" than carbon because frankly it is not. It is not significantly disadvantaged as to performance and may have advantages in other areas, mainly in subjective ones. I like my bike and that is good enough for me.

Well said! Too many people spend too much time justifying their choice of bike / frame material when the key point is 'is it right for you?'.

neeb

What about a brass frame?

Not being an engineer it was quite fun for me to try to use what I have learned on this thread and others to work out why this might not be a good idea...

I think you could make a workable bike frame out of brass, it would just be unnecessarily heavy, although (perhaps surprisingly) not unusably so. The tensile strength is comparable to Alu but it's about 3 times as dense.. so your frame might weigh about 3kg, It would also suffer from comparable fatigue issues to Alu due to having a low/non-existent fatigue limit. It has a similar Young's modulus to Ti but the thickness of the tubes would need to be much greater, so I imagine it would be uncomfortably stiff.

Did I get it right? (question for the engineers...)

It would look very cool though...

ugo.santalucia

gupta-patel wrote:

What about a brass frame?

You can't play many new tricks with an old dog and this one is an old one indeed.

I think the future of metals is in these intermetallic compounds, things like the titanium aluminates used in aerospace. Not sure they can be drawn into tubes though, I suspect not.

If one looks for lightness at all costs, then why not give a chance to aerogels? At the moment they don't meet the criteria, but there could be significant improvements... and boy, those are light... pretty much the same density as air! Infact they even scatter light as air does, appearing blue as the sky!

I am also rather intrigued by those bamboo frames I have seen somewhere...

blorg

Calfee do high-end bamboo bikes. Bamboo Bike Studio in New York run a class where over a weekend you build up your own bamboo frame. (NPR article here.) Ride quality of bamboo is reputedly very comfortable and it is a practical material for making bikes in the third world.