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Hardtails and theoretical flex

StoneboyStoneboy Posts: 20
edited May 2010 in MTB general
Having had a few hardtails over the years I have to wonder if there is any truth in steel ones flexing more than aluminium ones etc. Now; I work in the metal industry so have some knowledge about steels, aluminiums and titaniums (amongst others) and agree that they do behave differently; but when welded into a fairly small triangle I wonder if there really is any meaningful flex. Think a comfortable seat will make more difference.

One of the mags should do a controlled test using controlled loads and measuring machinery, unless perhaps they are concerned about the power of the advertising dollar if they dispell an industry myth :wink:


  • supersonicsupersonic Posts: 82,708 Lives Here
    It depends on the frame tube profiles. As you know, steel is stiffer than aluminiumn, but as alu has no fatigue limit and a lot less tensile strength, the tubes are oversized which massively increases stiffness.

    Generally. Some alu frames flex more than steel ones. So it does really depend on the final structure. I would say most flex is not in the vertical plane though, and agree that a saddle, and big tyres may have more effect for comfort.
  • NorthwindNorthwind Posts: 14,675
    edited May 2010
    Triangles are very strong but the edges of the triangle can still compress... I did a ride on my Soul where the rear mech broke and I converted to singlespeed. Every so often it'd manage to shift down, and compress the seatstays- the wheel'd almost jam solid from the huge chain tension, then when I took the QR off the stays would spring back to straight and fire the wheel up in the air :lol: So definately there's room to flex there!

    But, as SS says it's not about the material, my old Scandal felt more like a "typical comfy steel bike" than a "harsh alloy bike" but my brother's old Rufftrak steel frame is about as stiff as a Chameleon. Construction is just as important.
    Uncompromising extremist
  • captainflycaptainfly Posts: 1,001
    I think the point is you can design in some flex with smaller steel tubing that has no detriment to the logevity of the frame wheras doing this will aluminium this would soon cause fatigue and failure.
    Mongoose Teocali
    Giant STP0

    Why are MTB economics; spend twice as much as you intended, but only half as much as you wish you could afford? :roll:
  • neninjaneninja Posts: 424
    The rear triangle on my XTC Composite was supposedly designed to flex by something like 1.5 inches to give an almost suspension like feel over the rough stuff.
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