Re: {BL} Digest for bicyclelifestyle@googlegroups.com - 3 updates in 1 topic

[David Duncan]



I don’t notice any difference between aluminum and titanium and I have both.  Sheldon Brown’s article on frame material choices compares those two materials and steel and how material stiffness affects design:

https://www.sheldonbrown.com/frame-materials.html

 

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On Aug 13, 2022, at 8:48 PM, bicyclel...@googlegroups.com wrote:



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• Seatpost - 3 Updates

Seatpost

Lee Legrand <krm...@gmail.com>: Aug 13 01:29PM -0400 Hi All, hope everyone is well.   Is there a difference between an aluminum and titanium seatpost in terms of stiffness? As an engineer, I would think titanium seat post is stiffer because of its tensile strength, assuming the same moment of inertia but from reading online, it seems that the titanium gives more and not as stiff as aluminum which tells me sectional area is greater in aluminum than titanium.   Your thoughts?   Thanks

Ken Freeman <kenfre...@gmail.com>: Aug 13 04:37PM -0400 I think it's based on the modulus of elasticity ("modulus" for short). The ability of a spring to deflect when pushed versus to resist deflecting is based on the geometry of th part and it's material springiness. All steels have dang close to the same modulus. Other metallic elements and metallic compounds or alloys will have different values for modulus. I don't have the moduli of a range of elements or other structural materials ready to hand, much less in my head. The parameter essentially represents how much a cube of steel (or of marshmallow) will deform if it is under pressure. Stiffer materials deform less.   If you can maybe look up "engineer's bible" there should be a table of moduli, or just google something like "table of elasticity."   I'm an EE, not an ME or a materials scientist but I do a lot of systems analysis, so I've learned that following the right basic question will get you farther.   Ken Freeman, Ann Arbor, MI USA         -- Ken Freeman Ann Arbor, MI USA

Lee Legrand <krm...@gmail.com>: Aug 13 07:29PM -0400 The stiffness of a material is based on the material properties and sectional area. Yes modulus of elasticity mattress but again, Titanium appears to be stronger than aluminium and E is higher for Titanium. I am concerned that because it is stronger, is it built thinner to be equal or less in sectional area to have the same stiffness as an aluminum post or less. Does you feel more bounce in rides with Ti than Al.

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