Flex, titanium versus steel!

[Carsten G]

The only thing you test on that way is how stiff or soft your wheels are, sorry to say it but you have a lot to learn about frames and how to compare them.

Its very common that people test that way but that don't make it right, when talking stiffens in a frame its not sideways you are loosing energy its on the long side of the bike.

I have even seen that some takes the rear wheel off and presses the rear stay together to see how stiff the stay is and say that a frame is soft, maybe they should focus on the hub/wheel and skewers instead cos that's the real problem, some want light parts but don't want to pay premium price so buy crappy but light and they have the problem.

Best way to compare is on the track where you take a run on 20km and gives it all on all frames and the compare average speed then you have a picture you can use to something and also have an idea what makes your pedaling round also when tiered, the longer your pedaling keeps round and speed are good the more power you get in the gravel so hit the gravel and have fun the same time

 

[Blackstar]

Bit of nerdy trivia:

If the frames were made so the strength was the same - by changing the thickness or bore of the tubes, the stiffness would be like the chart below.

6061 Aluminium would give the harshest ride;
853 steel in the middle;
and 3Al-2.5V Titanium would be the 'flexiest'.

So yeah, Ti frames tend to be flexier than steel.

Could be a good thing in a hardtail.

 

[RobMac]

Your test doesnt look very scientific or under controlled conditions you'd really have to take the wheels off and sit both frames in a jig :?
With respect I wouldn't come to any conclusions from your test.

 

[Blackstar]

Your test doesnt look very scientific or under controlled conditions you'd really have to take the wheels off and sit both frames in a jig :?
With respect I wouldn't come to any conclusions from your test.

Yeah. That would be the best way.

The figures came from the properties of the materials, and then multiplied to give a stiffness when the strengths were the same.

Might be the wrong way to go about it, but seemed to agree with experience.

Any engineers around?

 

[Exeter Man]

Any engineers around?

Erm, yes

Stiffness is a function of Young's Modulus (relating to the material itself), moment of inertia (relating to tube diameter and thickness), and length (this can probably be ignored assuming consistent frame geometry).

As was mentioned earlier in the thread, titanium has a lower Young's Modulus than steel, and will therefore deflect (or spring) more if the tube diameter and thickness are the same. Variations in geometry, tubes dimensions and jointing methods could yield different results of course

Regards

 

[Blackstar]

Would like to ride a Ti hard tail some day.

Another thing for the bucket list

Nice bikes BTW.

 

[Anthony]

Stiffness is a function of Young's Modulus (relating to the material itself), moment of inertia (relating to tube diameter and thickness), and length (this can probably be ignored assuming consistent frame geometry).

As was mentioned earlier in the thread, titanium has a lower Young's Modulus than steel, and will therefore deflect (or spring) more if the tube diameter and thickness are the same. Variations in geometry, tubes dimensions and jointing methods could yield different results of course

Yes, but the tube diameter and thickness are not the same.

Titanium is far less dense than steel, so even though the Young's Modulus of steel is more than 1.5 times that of titanium, that's measuring stiffness in relation to volume. If the volume of material in a titanium tube is more than 1.5 times that of a steel tube (as it might well be in a bike frame), their stiffness will be about the same.

 

[Exeter Man]

Yes, but the tube diameter and thickness are not the same.

Titanium is far less dense than steel, so even though the Young's Modulus of steel is more than 1.5 times that of titanium, that's measuring stiffness in relation to volume. If the volume of material in a titanium tube is more than 1.5 times that of a steel tube (as it might well be in a bike frame), their stiffness will be about the same.

I agree - tube size is a very significant factor. It's not the volume per se though. For example, a large diameter thin tube may contain less material than a small thick one, but will be stiffer due to the greater moment of inertia.

Actually, this is all starting to sound a bit boring . Riding bikes is much better than discussing the theory

Regards

 

[TheGreenRabbit]

Is this turning in to mine stiffer than yours contest ?

 

[Exeter Man]

Is this turning in to mine stiffer than yours contest ?

Glad that my missus doesn't read this forum, or she would take this opportunity to publicly air her disappointment

Regards