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The spring of steel?

carbonfibrecarbonfibre Posts: 72
edited May 2009 in MTB general
My step-dad, who's like well clever, reckons that steel shouldn't feel any spingier than alu'. So what's the deal: are makers of steel frames chuckling at the gullible punters spending more on frames that weigh more?

Oh yeah, hello, by the way.

Posts

  • WhytepeakWhytepeak Posts: 2,616
    Generally steel frames do have a springy feel to them, even though steel is a harder material to aluminium. Steel has a greater strength to weight ratio to aluminium, so can be built with thin tubes. The thin tubes flex, so the ride of a steel frame is more forgiving, akin to using lower tyre pressures.
    Now that we are strong ought to bear the infirmities of the weak and not to please ourselves. ROMANS 15:1
  • carbonfibrecarbonfibre Posts: 72
    Steel has a greater strength to weight ratio than aluminium?

    Is that actually true?

    Why aren't aeroplanes made out of steel then? See the flex on those wings?
    Pretty damn springy!
  • supersonicsupersonic Posts: 82,708 Lives Here
    It is how the material is fabricated that gives the frame its ride qualities. Steel is three times stiffer than aluminium (youngs modulus). But double a tubes diameter and its stiffness increases by a factor of eight. Steel is three times denser than alu. Alu will fatigue under repeated flexing.

    So alu can be made into stiff, large diameter tubes, while steel, which doesn't fatigue in the same way, usually has narrower flexier tubes.

    But you can have stiff or flexy frames of either.

    S
  • WhytepeakWhytepeak Posts: 2,616
    Steel has a greater strength to weight ratio than aluminium?

    Is that actually true?

    Why aren't aeroplanes made out of steel then? See the flex on those wings?
    Pretty damn springy!

    Steel is a strong material that flexes.
    Chromoly Steel, (steel alloyed with chrome and molybdenum) is even tougher and is used on bikes that take some stick.
    Aluminium can be built lighter due to advancing technology in tube formation.

    The needs of an aeroplane are miles away from a humble bike, (quite literally :lol: ) so steel is not used - can't be bothered / don't know enough to give a full explanation. :roll:
    Now that we are strong ought to bear the infirmities of the weak and not to please ourselves. ROMANS 15:1
  • supersonicsupersonic Posts: 82,708 Lives Here
    Steel isn't an inherently flexy material - it is stiffer than aluminium and titanium.
  • WhytepeakWhytepeak Posts: 2,616
    And titanium is stiffer than aluminium?
    Now that we are strong ought to bear the infirmities of the weak and not to please ourselves. ROMANS 15:1
  • supersonicsupersonic Posts: 82,708 Lives Here
    Yep - typically twice as stiff.
  • RaymondavalonRaymondavalon Posts: 5,346
    edited May 2009
    Talking of Ti.. saw one of these with my own eyes in Swinley today..

    Jones_Bicycles_3D_Spaceframe_frame-850-65.jpg

    Now that front fork just fascinates me beyond belief.. being Ti and rigid.. how does that fair up against an all rigid steel or aluminium bike?
  • NorthwindNorthwind Posts: 14,675
    edited May 2009
    My step-dad, who's like well clever, reckons that steel shouldn't feel any spingier than alu'. So what's the deal: are makers of steel frames chuckling at the gullible punters spending more on frames that weigh more?

    It depends on the frame construction too... My brother has an early-00s Saracen steel hardtail which is as rigid as you can imagine, horrendous piece of rubbish it is. My Soul is known for its flexiness, and I love it dearly for it, add a fat rear tyre and it's like having a very very very short travel full suss :) The BFe, on the other hand, has the exact same geomery but it's much stiffer. But my Scandal, which was scandium, was barely any less flexy than the soul, and a lot more so than the BFe. But then my mate's Chameleon is probably stiffer than all of the above.

    TBH if I could have got an ally frame with the exact same geometry as the Soul, and maybe a wee bit of boing in the rear triangle like my Scandal, and a bit lighter, I'd have one. But such a bike does not exist. People who get too hung up on material shouldn't be taken very seriously IMO.
    Uncompromising extremist
  • supersonicsupersonic Posts: 82,708 Lives Here
    Try some titanium or carbon frames NW ;-).

    If built right of course lol.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Talking of Ti.. saw one of these with my own eyes in Swinley today..

    Jones_Bicycles_3D_Spaceframe_frame-850-65.jpg

    Now that front fork just fascinates me beyond belief.. being Ti and rigid.. how does that fair up against an all rigid steel or aluminium bike?

    It is built to flex. Mostly in the vertical plane - could be done with steel too.
  • phzphz Posts: 478
    only got personal observations to offer here but i recently (2 or 3 weeks ago) switched from a thin steel frame (DMR trailstar) to a fat alu one (identiti mr hyde) with pretty much the same build spec-wise

    for pretty much the same sized frame the identiti is noticably stiffer and less flexy in the rear triangle than the trailstar (fat box section alu versus thin steel tubes) - the alu frame seems to transmit acceleration forces better but is skippier / more skittish on 'power' climbs and harsher feeling on the bumpy downhill bits

    slainte :arrow: rob
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