Johan Bornman Posted November 11, 2009 Posted November 11, 2009 I'll have a bash at explaining this...Basically when you pedal away on your bike' date=' a number of forces act on the frame. The two biggest are on the power stroke, the first being the physical push of the pedal, and the second being the act of pulling on the handlebar. Now we know from Newtons laws that there must always be equal and opposite reactions taking place, so if you work out how hard you pedal (lets say a value of 10) and how hard you pull (lets say a value of 5) then you need to find a value of 5 elsewhere... and that's the flex in your frame. Flex is also known as deflection, and is basically the measurement of how much out of true you bike moves whilst under stress. [/quote']Not really relevant, but the difference between the '5' force and the '10' force in your example makes the bike sway from one side to the other..... or fall over... no ways that the frame is flexing because of this, in fact I'm pretty sure that the forces are almost identical - but somebody more technical can explain.On the original topic, have never ridden a Ti frame You are of course right. The arithmetic in the example is not quite right. The force in the handlebar is the result of the downward force on the pedal minus that that ends up going directly to the road. If the bike is leant over whilst pedaling from a vertical direction, that force is larger. The force on the handlebars will be zero only if the pedal is exactly in plane with the frame, which is impossible with our bicycle designs.
Johan Bornman Posted November 11, 2009 Posted November 11, 2009 Had the opportunity of getting off my Yeti asr straight onto a Yeti asr carbon. The sensation was one of a much stiffer ride. The bike felt extremely responsive and very different to mine which has similar if not exact geometry.Was this purely a placebo of getting on a bike that is pure bling or attributable to frame material/geometry. The carbon also has an integrated seat post. Could this make a difference? I can't vouch for the relative stiffness of the two bikes but that is very, very easy to measure if you have two identical bikes. If you have access to both, we can quickly do it. As for the "Responsiveness". That was the double-dose placebo kicking in. It is directly related to the bike's looks and price tag.
Hermanus Cycles Posted November 11, 2009 Posted November 11, 2009 I agree with JB,ti is not ideal for bike frames,unless you are small and light,the stuff flexes like bamboo.And yes ally can be made much lighter for much less. I have also heard Ti owners mutter"this frame will last forever" so who wants a frame that will survive a nuclear war?
Ox_Wagon Posted November 11, 2009 Posted November 11, 2009 Would love to be able to find the picture of the Ti bike a spotted a while back on mtbr.com... Some niche mtb manufacturer in the States... the name of the company starts with a "C" - they've designed a hardtail Ti frame' date=' with the seat tube and seat stay area designed in such a way that they 'meet/join' very close above the bb - the saddle was planted on a ridiculously long titanium seatpost - stretching all the way down to the post, and in this way introducing "flex" into the ride, and (allegedly) offering the qualities of a soft-tail... Will do some googling.... [/quote'] Your not thinking of the Idis Bowtie? I wonder if there is anybody making steel full sussers?Ox_Wagon2009-11-11 06:39:05
Bos Posted November 11, 2009 Posted November 11, 2009 Would love to be able to find the picture of the Ti bike a spotted a while back on mtbr.com... Some niche mtb manufacturer in the States... the name of the company starts with a "C" - they've designed a hardtail Ti frame' date=' with the seat tube and seat stay area designed in such a way that they 'meet/join' very close above the bb - the saddle was planted on a ridiculously long titanium seatpost - stretching all the way down to the post, and in this way introducing "flex" into the ride, and (allegedly) offering the qualities of a soft-tail... Will do some googling.... [/quote'] Your not thinking of the Idis Bowtie? I wonder if there is anybody making steel full sussers? there is no way you are telling me that thing is as stiff as say my blur...
RodTi Posted November 11, 2009 Author Posted November 11, 2009 Would love to be able to find the picture of the Ti bike a spotted a while back on mtbr.com... Some niche mtb manufacturer in the States... the name of the company starts with a "C" - they've designed a hardtail Ti frame' date=' with the seat tube and seat stay area designed in such a way that they 'meet/join' very close above the bb - the saddle was planted on a ridiculously long titanium seatpost - stretching all the way down to the post, and in this way introducing "flex" into the ride, and (allegedly) offering the qualities of a soft-tail... Will do some googling.... [/quote'] Your not thinking of the Idis Bowtie? I wonder if there is anybody making steel full sussers? MADNESS ! Would love to be able to see one of these bikes in the flesh...Nope - not the one I'm thinking of. I might have saved a pic of the bike at home - will have a look tonight, and pop in on here if I find it!
EigerSA Posted November 11, 2009 Posted November 11, 2009 I'll have a bash at explaining this... Basically when you pedal away on your bike' date=' a number of forces act on the frame. The two biggest are on the power stroke, the first being the physical push of the pedal, and the second being the act of pulling on the handlebar. Now we know from Newtons laws that there must always be equal and opposite reactions taking place, so if you work out how hard you pedal (lets say a value of 10) and how hard you pull (lets say a value of 5) then you need to find a value of 5 elsewhere... and that's the flex in your frame. Flex is also known as deflection, and is basically the measurement of how much out of true you bike moves whilst under stress. [/quote'] Not really relevant, but the difference between the '5' force and the '10' force in your example makes the bike sway from one side to the other..... or fall over... no ways that the frame is flexing because of this, in fact I'm pretty sure that the forces are almost identical - but somebody more technical can explain. On the original topic, have never ridden a Ti frame You are of course right. The arithmetic in the example is not quite right. The force in the handlebar is the result of the downward force on the pedal minus that that ends up going directly to the road. If the bike is leant over whilst pedaling from a vertical direction, that force is larger. The force on the handlebars will be zero only if the pedal is exactly in plane with the frame, which is impossible with our bicycle designs. ok guys... I was just trying to explain as simply as I knew how the reason why there was flex in laymans terms for slowbee, and what the flex was a result of... sheesh!
RodTi Posted November 11, 2009 Author Posted November 11, 2009 I'll have a bash at explaining this...Basically when you pedal away on your bike' date=' a number of forces act on the frame. The two biggest are on the power stroke, the first being the physical push of the pedal, and the second being the act of pulling on the handlebar. Now we know from Newtons laws that there must always be equal and opposite reactions taking place, so if you work out how hard you pedal (lets say a value of 10) and how hard you pull (lets say a value of 5) then you need to find a value of 5 elsewhere... and that's the flex in your frame. Flex is also known as deflection, and is basically the measurement of how much out of true you bike moves whilst under stress. [/quote']Not really relevant, but the difference between the '5' force and the '10' force in your example makes the bike sway from one side to the other..... or fall over... no ways that the frame is flexing because of this, in fact I'm pretty sure that the forces are almost identical - but somebody more technical can explain.On the original topic, have never ridden a Ti frame You are of course right. The arithmetic in the example is not quite right. The force in the handlebar is the result of the downward force on the pedal minus that that ends up going directly to the road. If the bike is leant over whilst pedaling from a vertical direction, that force is larger. The force on the handlebars will be zero only if the pedal is exactly in plane with the frame, which is impossible with our bicycle designs. ok guys... I was just trying to explain as simply as I knew how the reason why there was flex in laymans terms for slowbee, and what the flex was a result of... sheesh! EigerSA - you sometimes got to have thick skin to post on the Hub... But don't let any of this stop ya! Or - you can simply do what I do - which is post a hell of a lot of drivel, without actually saying anything - and then sit back and watch the pro's fight it out... Find it much easier to learn something that way... BTW people - did some googling of the Ibis Bow-Ti - insane bike! Check out mtbr.com - they have pictures up of a re-build done earlier this year - seriaaas bike-porn imo! Ps - You can still have them custom made today, by the gentleman that did the initial design for Ibis... Will only put you back about $4,000.00 - for the frame...
Capricorn Posted November 11, 2009 Posted November 11, 2009 Most of the properties given to Titanium by the marketing department is nonsense. ?Firstly' date=' titanium has half the atomic weight of steel and double the atomic weight of aluminium. In other words, it is not as light as they will have you believe.?Secondly, it has half the tensile strength of steel and double that of aluminium, which puts it sort of halfway between steel and alu. However, an alu frame can be made stronger and lighter because the alu tubes can be drawn thinner than Ti ones. Ti doesn't like to be "worked". It gets hard as it is machined/bent/welded and also cracks easily if the heat treatment after welding isn't perfect.[/quote']Atomic mass:Since the majority component of steel is iron (Fe), let's go with the atomic mass of iron (exact atomic mass of steel ?is function of the other elements added ?to make steel, ie it's not an fundamental element like Fe): 55.84Titanium: 47.87 or about 86% of that of iron. definitely not half.Aluminium: 26.98 or 48% of that of Fe.Tensile Strengths:Aluminium:Commercially pure aluminium has a tensile strength of approximately 90MPa and can be improved to around 180MPa by cold working. The heat treatable grades can develop a tensile strength of around 570 MPa and even higher in some alloys (7001). This figure compares favourably with mild steel which has a tensile strength of approximately 260 MPa.Iron (again note the exact tensile strength of a steel depends on it's other components):iron type | Tensile strengthIron whiskers 11000 Ausformed (hardened) steel 2930?Martensitic steel 2070?Bainitic steel 1380?Pearlitic steel 1200?Cold-worked iron 690?Small-grain iron 340?Iron containing dissolved carbon 140Single crystal of pure iron 10Titanium:Aerospace Grade 5 is the most common grade. It is the workhorse of the titanium industry. Grade 5 titanium is an alloy (90% titanium, 6% aluminum, 4% vanadium) and is harder than CP grade, with a tensile strength of over 896 MPa. Grade 5 is tougher because of its greater hardness and alloy composition. When anodized, aerospace grade titanium colors are slightly more vibrant than CP grade titanium colors.?CP Grade 2 is 98.99% pure, unalloyed titanium. This grade is softer than the Aerospace Grade 5, (but still harder than gold) and has a tensile strength of over 275 MPaNot sure where u get your numbers from JB. Reverse marketeering gone awry? jj..
NinjaManiak Posted November 11, 2009 Posted November 11, 2009 Most of the properties given to Titanium by the marketing department is nonsense. Firstly' date=' titanium has half the atomic weight of steel and double the atomic weight of aluminium. In other words, it is not as light as they will have you believe. Secondly, it has half the tensile strength of steel and double that of aluminium, which puts it sort of halfway between steel and alu. However, an alu frame can be made stronger and lighter because the alu tubes can be drawn thinner than Ti ones. Ti doesn't like to be "worked". It gets hard as it is machined/bent/welded and also cracks easily if the heat treatment after welding isn't perfect.[/quote']Atomic mass:Since the majority component of steel is iron (Fe), let's go with the atomic mass of iron (exact atomic mass of steel is function of the other elements added to make steel, ie it's not an fundamental element like Fe): 55.84Titanium: 47.87 or about 86% of that of iron. definitely not half.Aluminium: 26.98 or 48% of that of Fe.Tensile Strengths:Aluminium:Commercially pure aluminium has a tensile strength of approximately 90MPa and can be improved to around 180MPa by cold working. The heat treatable grades can develop a tensile strength of around 570 MPa and even higher in some alloys (7001). This figure compares favourably with mild steel which has a tensile strength of approximately 260 MPa.Iron (again note the exact tensile strength of a steel depends on it's other components):iron type | Tensile strengthIron whiskers 11000 Ausformed (hardened) steel 2930 Martensitic steel 2070 Bainitic steel 1380 Pearlitic steel 1200 Cold-worked iron 690 Small-grain iron 340 Iron containing dissolved carbon 140Single crystal of pure iron 10Titanium:Aerospace Grade 5 is the most common grade. It is the workhorse of the titanium industry. Grade 5 titanium is an alloy (90% titanium, 6% aluminum, 4% vanadium) and is harder than CP grade, with a tensile strength of over 896 MPa. Grade 5 is tougher because of its greater hardness and alloy composition. When anodized, aerospace grade titanium colors are slightly more vibrant than CP grade titanium colors. CP Grade 2 is 98.99% pure, unalloyed titanium. This grade is softer than the Aerospace Grade 5, (but still harder than gold) and has a tensile strength of over 275 MPaNot sure where u get your numbers from JB. Reverse marketeering gone awry? jj.. Those numbers may have come from that old marketeering nemesis, the science textbook. If you were to build a frame from 1 mol of each, maybe what you said was true, but to misquote people misquoting Thomas J, "Not All Mol's are born Equal" http://www.sheldonbrown.com/frame-materials.html
Johan Bornman Posted November 11, 2009 Posted November 11, 2009 I'll have a bash at explaining this...Basically when you pedal away on your bike' date=' a number of forces act on the frame. The two biggest are on the power stroke, the first being the physical push of the pedal, and the second being the act of pulling on the handlebar. Now we cut cut cut cut cut cut [/quote']ok guys... I was just trying to explain as simply as I knew how the reason why there was flex in laymans terms for slowbee, and what the flex was a result of... sheesh! Aag Eiger, relax my friend. Nobody is kakking you out. We're just nit-picking. Pretend we're just a bunch of okes around a fire, drinking beer and laughing at the drunk one that can't subtract 5 from 10. You see how someone whipped out a periodic table and corrected my vague memories of the atomic weights of steel, vs Ti vs alu. Stick around this is fun, or better than TV in anyway.
Capricorn Posted November 11, 2009 Posted November 11, 2009 Ninja: to pass it out of hand and attempt to belittle the facts contained in textbooks is more than misleading: its disingenous. Whole industries were built on those very textbooks. Maybe they all got it wrong?Besides, it was very clearly noted that physical charactistics of alloys will differ from the elemental ones. ?
Johan Bornman Posted November 11, 2009 Posted November 11, 2009 Capricorn, you are right. I had my ratios wrong. I'm shocked all over again to see just how heavy Ti really is. Which reinforces the point of it being an innapropriate material for the job.As a rule of thumb, the weight of an alloy is very similar to the base material, since the alloying additives are present in such small proportions. For these discussions, the atomic mass of the steel used in bicycles is basically that of iron, etc. We see that a lot in rim brochures - "Lightweight aluminium alloy" - no matter which alloy, it will still weigh what aluminium weights, give or take a gram on the overall weight of the rim. But I digress. For those of you interested in the science that supports bicycling physics, read the best layman's book on structures, materials and general common sense ever writted: Structures or Why things don't fall down, by JE Gordon. Published by Penguin and available from Exclusive Crooks from time to time. It is brilliant. What I really like about Gordon is that he makes the only reference that I can find, to the inventor of the wire-spoked wheel and, he analyses the way it supports the hub perfectly.
Kiwi Posted November 11, 2009 Posted November 11, 2009 One of the great properties of Ti is that it can bend repeatedly without the metals properties changing and eventually cracking. The higher the grade of Ti the better. That's why Litespeed and Lynskey frames cost so much, they are using aircraft grade ti. The frame should keep its original properties indefinitely. When F1 cars were allowed to run any ride height they wanted Ferrari went as far as removing the front shocks completely and building the a- arms out of titanium and tuned the flex to create suspension. Naturally the FIA banned the idea pretty quickly. Here's the Womans Xtera World Champs 2008 winning Ti bike: no pivots needed - short travel though.
BogusOne Posted November 11, 2009 Posted November 11, 2009 One of the great properties of Ti is that it can bend repeatedly without the metals properties changing and eventually cracking. The higher the grade of Ti the better. That's why Litespeed and Lynskey frames cost so much' date=' they are using aircraft grade ti. The frame should keep its original properties indefinitely. When F1 cars were allowed to run any ride height they wanted Ferrari went as far as removing the front shocks completely and building the a- arms out of titanium and tuned the flex to create suspension. Naturally the FIA banned the idea pretty quickly. Here's the Womans Xtera World Champs 2008 winning Ti bike: no pivots needed - short travel though. [/quote'] The bike in the pic above is a Soft Tail and NOT a full susser
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