titanium frame strength

I was always a believer that titanium was uber strong. After doing a seach on Titanium frames, one of the posters mentioned that heavy guys flex titanium frames too much. I weigh 220 and was thinking of titanium after all the good things that I'ver heard. Was that poster wrong?

 

Like all bike frames, depends on the frame. If made with smallish tubes, it may 'flex' 'too much' but decent titanium frame builders recognize titanium tube characteristics and build accordingly. Moots, Lynskey, Habanero makes some really nice ti frames, even for big, strong riders. As materials go, I think titanium, if designed and built well, is pretty much the ideal material.

 

You are confusing strength and stiffness. Titanium is strong, but the stiffness has much more to do with tube diameter than the build material. The best metal for stiffness is Aluminium, as it is the least dense and consequently can be made into wider tubes for any given tube weight. Clearly, stiffness also depends on welds/joins/lugs, and I imagine that the effects of material on stiffness at these sites are more complex. Aluminium,as with other materials, can be made stiffer than you need or want, and this is why we don't see too many superfat tubes on road bikes.
It seems to me that many Ti consumers actually buy the bikes for the supple, springy ride that they are perceived as having, and consequently the manufacturers possibly choose not to make the tubes too wide for fear of disappointing the market.
Bikes don't actually need to be all that strong, as peak loads are small.

 

Titanium is stronger than steel for the same weight, so they make the tubes with a thinner wall. This makes em flexier and a bit lighter for approximately the same strength. Bike builders are sort of stuck with what the titanium tubing manufacturers produce, so asking for a stiffer frame may not be practical, but wouldnt hurt to ask. A designer like Thylacine could give you the run down.

 

As I have read it, minimal tube wall thickness is limited to about 1/50th of tube diameter regardless of metal; lower wall thickness and you get "beer-can" folding of the tube. So for a given tube diameter, a Ti wall thickness is not necessarily able to be lower than steel wall thickness.
But, I think that you are right about the frame makers not having much choice about Ti tubing dimensions.

 

Having never used a titanium frame, I only go on what I read in mags- articles by experts in the field. They reckon Ti has unlimited fatigue cycles or something like that... they say that it can flex for ever. without microscopic cracks forming. Aluminium is not good because it cant flex, it needs to be super stiff, because any flex will weaken it. One of my riding partners cracked his Al frame in less than 10,000kms... behind the bridge that sits behind the BB.

 

Take some time and research carefully what you're looking for. Ti or steel is wonderful for your size. Carbon also works as well. It is a question of the engineering behind it. Ti, although extremely strong, is prone to flexing, there is no question about it, it is one of the inherent strengths of the material but that's a long drawn out discussion. A lot of what can give you a pleasurable/efficent ride is going to be how the tubes are cut and shaped. That is where the science of bike building comes into effect. What you ought to do is research the frame designs carefully when looking for a bike moreso then what the Ti type is if you're defiantely wanting to go with Ti. Now, be forementioned, you pay for what you get with Titanium. If you go bargin basement, you'll get a bargin basement frame that is straight gauge tubing not reinforced (butted, etc). Other then round tubes are more costly. Sybex does them at a bargin price however, you're getting Russian built frames that leave a little to be desired but are good riding.

Consider some of the steel options out there if you're really worried about durability. Although not as sexy, Serotta still produces a ton of wonderful ones as does Pegoretti.

Most of all, talk with a shop or company that knows how to deal with your weight range. Good luck!

 

I thought magnesium was even better than Aluminium in this regards?

Though does suffer from that pesky oxidization issue.

 

I have a Titanium road bike and when I was over 220lb flex was never an issue. I'm now down to 190 and I don't notice any flex. Titanuim used to have a name as being flexy when builders were using CP titanium. With 3/2.5 this isn't a problem.
I'd certainly buy titanium again if I ever needed to.........

 

I guess so, but do Mg frames exist?

 

yes they do and they make tandems too!

http://www.paketa.com/

They make the lightest tandem available that weighs only 10.5kg complete

 

Interestingly, the frame weights for the road bike and MTB are not listed on the site. Perhaps the weight advantage is less than stellar?

 

Oh yes, I am the proud owner of an 04 model Pinarello Dogma. Blurb from the Pinarello site...

"MAGNESIUM
Magnesium, most commonly used in the aerospace and automotive industries is hard to work with and extremely hard to weld.
However, magnesium has always been a material that frame builders have longed to use as its characteristics are ideally suited for the construction of competition bicycle frames.
Magnesium is, in fact, 35 percent lighter by volume than aluminum with an ultimate strength in the range of carbon fiber.
DOGMA® FPX is an explosive bike, the response of every pedal is felt immediately."

 

My experience with titanium stiffness:

I'm 27 - now amateur racer in Italy - sprinter - 57 kg per 163 cm, so I'm quite light.

I thought I would never be "sensible" to materials, I'm so short, a small frame is compact, isn't it? So I thought that I would never had felt any difference between my old Giant TCR Hybrid (alu / carbon) and my new Rewel titanium... (search rewel with google, they're italian craftsmen, a small company of 3 people). I bought the titanium on 2007/12 for the new season. Weight: 1326 grams in size small.

Results: a disaster. the frame is *really* flexy if compared to my old alu (ok: I was using a monster of rigidity). So I just sold it on ebay and I bought another hybrid alu / carbon frame (I also saved some money...this new frame is 1141 grams in size small). I *need* a stiff frame, I don't want to lose any watt on the asphalt.

Interesting: maybe the problem was the quality of the titanium. The frame was in titanium 6 - 4 entirely... though this alloy (6 Al 4 V) is commonly used only for bottom bracket or junctions... that's why the frame was *that* heavy, I suppose...

 

I am 210# and ride a spectrum super ti, Tom Kellogg and Jeff Duser design incredible bikes in both steel and Ti. As much or as little flex as you want and custom made for YOU for about what you would pay for a stock bike from the big manufacturers. I dont own either but I understand Serotta and Seven make great custom Ti bikes. You would be surprised how little it costs to have a bike made for you by real craftsmen.



http://www.spectrum-cycles.com/index.htm

http://www.serotta.com/

http://www.sevencycles.com/