"stiffness"
phoebian
Posts: 497
I see it mentioned all the time for different bike parts and such, but what is it referring to?
How rigid something is?
How rigid something is?
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amount of or lack of flex."Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
yes. how little it flexes
most people who claim to feel stiffness in their components are regurgitating manufacturers claims.0 -
Stiffness usually means stronger, as in you get no flex...however if you compare stiffness in frames (alloy to steel say) many prefer the slight flex in an alloy frame as the ride is more forgiving..though the steel framed purists may disagree...0
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A 'stronger' material can allow thinner tubing, and it is this smaller diameter tubing that flexes more, thus 'stronger' materials like steel can be used to make more resilient and flexy frames.
This is my understanding of it all anyway
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I disagree ...Pudseyp wrote:..though the steel framed purists may disagree...Canyon XC 8.0 '11
Whyte 19 steel '100 -
So, putting strength to one side. Is flex good or not?0
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ride_whenever wrote:steel is less stiff.
Eh ??? I am not a metallurgist but do work in Aerospace and disagree..alloy is generally softer then steel so therefore less stiff..obviously temper has it's play...take two 10mm bars one in aluminium and one in steel and see which one is easier to bend !0 -
Depends how far you want to go into metallurgy - if you look at the Young's Modulus of a typical steel versus a typical aluminium, you will find the steel can bend quite a bit further than the aluminium and still return to it's original position. This is the "flex" people are talking about here.
Steel can deform more for a brief period, and return. Aluminium can only take a smaller amout of force and deform and then still return to it's original shape.
Look it up in Wikipedia
Young's Modulus of Aluminium ~69 GPa (giga Pascales)
Young's Modulus of Steel ~200 GPa (giga Pascales)
The confusion arises in that, according to Metallurgy (i.e. Science), Steel is stiffer than Aluminium.
But according to commong usage, most people would describe an aluminium frame as giving a stiffer ride than a steel one - it's more to do with the earlier point made, that because steel is stiffer, you can get the same strength from thinner tubes, which are in turn more flexible, so give a softer ride. Most aluminium frames have to be built up thicker to give the required strength, so with simply more material in the frame, they aren't as flexible.
(I hope my old physics teacher doesn't read this for fear of having got completely the wrong end of the stick!)Cannondale Synapse 105, Giant Defy 3, Giant Omnium, Giant Trance X2, EMC R1.0, Ridgeback Platinum, On One Il Pompino...0 -
true but larger diameter tubes provide greater stiffness over smaller steel tubing. you also assume in your analogy the same amount of material is used. more aluminium is used in the bikes than steel.
you are correct in steel is less flexible as a material but not in the contexts and structure of a frame0 -
99.9% of riders will agree that steel is flexier. Yes it is denser for the same mass, but you will use less material making a steel frame compared to an alloy frame, therefore the steel frame is flexier.Pudseyp wrote:ride_whenever wrote:steel is less stiff.
Eh ??? I am not a metallurgist but do work in Aerospace and disagree..alloy is generally softer then steel so therefore less stiff..obviously temper has it's play...take two 10mm bars one in aluminium and one in steel and see which one is easier to bend !0 -
Thank you all for the detailed answers. I think I understand it a little better now.
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Steel is THREE time stiffer than aluminium. It is also three time denser than aluminium.
Tube diameters and thickness have a huge impact on overall stiffness of a tube or frame. I have ridden flexy alu frames, and very, very stiff steel ones. Generally steel frame are a little flexier. But you can't pigeon hole them any more.
One mans comfort is another mans flex. One mans stiffness is anothers harsh ride.0 -
you will find the steel can bend quite a bit further than the aluminium and still return to it's original position. This is the "flex" people are talking about here
That is elongation, rather than stiffness.0 -
I've ridden Glentress red route a billion times on both my Morewood Shova and my Orange Patriot, and the difference in flex is really noticable.
The Shova is a relatively delicate frame, certainly compared to the RSJ that is my Patriot, and it definitely flexes more, particularly the swingarm. This isn't a bad thing, as it gives a slightly more forgiving ride and seems to find more grip than the Patriot.
The Patriot itself is a monster frame, stiff as a 17yr old at a lapdancing bar. There's very little flex in it and this means that its a bit more of a harsher ride in my opinion, and it slides far more abruptly, having said that it does feel like it can survive anything short of a nuclear assault. They both run the same tires and wheels, although different suspension is of course a factor.0 -
As far as I know Stiffness, Strength, Hardness and Toughness are different parameters for a material.0
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and remember that flex is designed in at certain points...I think the new trek xc carbon frame flexes about an inch at the back...
this gives a carbon hardtail, with a squishy back end....not like suspension....but enough to take out tail chatter etc...Whenever I see an adult on a bicycle, I believe in the future of the human race.
H.G. Wells.0
