Is steel the holy grail of frame materials?

greg66_tri_v2.0

rjsterry wrote:

JonGinge wrote:

rjsterry wrote:

Flippin' Nora, the perils of a throwaway comment. Having been well and truly shot down I would say that the current trend for massive BB junctions on CF frames for stiffness where you really need it, is something that looks difficult to replicate in steel (what with steel coming in tube form. and carbon in 'sheet' form), and I would admit that a real out-of-the-saddle stamp can really flex my frame. But it does spring back, so that energy isn't all wasted, it's just a slower transfer from pedal to wheel.

If money is no object, then I'm sure you can get a better (however you want to measure that) frame from CF or Ti than from steel, but on a more limited budget (I just can't afford Ti) and where durability and longevity are primary concerns, I'd say steel is at least competitive with Al and cheaper CF.

As for the corrosion argument, components still seize into Ti and CF frames every bit as much as steel, and unless you really neglect your bike, frame corrosion isn't really a problem as evidenced by the large number of old steel frames currently being reused as SS and FG.

The economies of scale have obviously changed, since all the major manufacturers went over to Al as their entry level material. My steel frame came as part of a £400 bike, but now steel has become an expensive niche material.

Bzzzt. Fizzics fail.

I'll admit to being a little rusty, but do explain. As far as I remember, if you flex a spring, then you are storing energy in it, e.g.old fashioned alarm clock. Admittedly less efficient than having a more rigid BB, but still, what am I missing.

Ok - Correct that you compress a spring and you store energy in it. Spring expands and you get that energy back.

But on a bike it doesn't work like that. Your leg drives the pedal. Some of your energy goes to deforming the frame. That's stored in the frame for a short period. Now, that energy hasn't gone to the pedal stroke, which is what you want it to do. When the frame "un-deforms", that energy still doesn't go into your pedal stroke - he frame pushes back laterally. So the energy *is* stored, but when it is released, you don't get it back.

Think of trying to hammer a nail in to a warped piece of wood. Every time you hammer, the force of the blow gets diverted into flexing the wood. The wood unflexes between each blow, but you don't get that stored energy back, and it doesn't release in a form that drives the nail. Basically, you get knackered and the wood does a shimmy-shimmy dance for you. Much like a flexy frame.

wgwarburton

rjsterry wrote:

...If money is no object, then I'm sure you can get a better (however you want to measure that) frame from CF or Ti than from steel, ....

No, I don't think you can. You can get a "better" frame if you measure it in a particular way (Light? Stiff?) but for non-competitive cycling there isn't anything that's "better" overall than steel.

This is, of course, just my opinion (and it's worth what you paid for it).... anyone who knows me will confirm that I'm a clueless, gibbering idiot that can't be trusted....

Cheers,
W.

greg66_tri_v2.0

JonGinge wrote:

The recoil is lateral which your legs have to absorb. No additional forward momentum but slighty more tired legs.

Err, yeah. That too. If you like the pithy, short version.

rjsterry

Ta for that. Slightly ashamed at how rusty my physics has got.

solsurf

And there was I thinking I had a great reason to buy another bike, shame as I really fancied a steel road bike.
Although I would have to keep the Felt, for testing purposes as well.

As it goes I am currently trying to demonstrate my need to buy a genesis crois de fer (steel). My wife says no, but there is still room in the garage for the N+1 rule to work.

Wooliferkins

symo wrote:

Of course the ultimate material is currently being developed in a lab somewhere

http://www.yehudamoon.com/index.php?date=2009-07-30

wgwarburton

Greg66 wrote:

.... When the frame "un-deforms", that energy still doesn't go into your pedal stroke - he frame pushes back laterally. So the energy *is* stored, but when it is released, you don't get it back. ....

I don't think it's that simple. The frame flexes at the top of the pedal stroke but it doesn't stay flexed for long. As soon as you start to ease the pressure off the pedal, the frame will bend right back and the energy you put in there is released as you finish the stroke, driving the bike forwards. There's obviously some energy loss in the bend/unbend of the frame but it's small. It may even be more efficient overall, if this process is a better match biomechanically than a rigid frame... that's pure speculation, though.

Cheers,
W.

edit- stray comma, back where it belongs.

rjsterry

Solsurf - you can still buy a steel bike as an elaborate experiment to compare the two materials. For some proper (?) pseudoscience, you could get one custom made to mimic the geometry of your Felt as closely as possible.

WGW - I think Jon & Greg (are they also doing Masterchef at the moment?) are right. When the frame flexes, the BB is rotating roughly on an axis running horizontally front to back. When this returns to its unflexed position, the released energy doesn't go back into turning the BB axle, but probably mainly goes back into your legs, to be absorbed by your knees. The springiness is only useful (as a shock absorber) if it is limited to the vertical plane.

don_don

I read somewhere years ago, that a certain amount of flex at the bottom bracket was a good idea when riding hard out of the saddle. The flex would allow the cranks to stay closer to the vertical whilst the bike was tilted over, therefore making pedalling more efficient. This may be tosh though...

solsurf wrote:

And there was I thinking I had a great reason to buy another bike, shame as I really fancied a steel road bike.
Although I would have to keep the Felt, for testing purposes as well.

As it goes I am currently trying to demonstrate my need to buy a genesis crois de fer (steel). My wife says no, but there is still room in the garage for the N+1 rule to work.

Now we see the real reason for the question and I feel we should support solsurf in his endeavours. So, yes mate, steel is the ultimate and you have to have it!

Can any of you maths bods amend the N+1 rule to account for frame materials one doesn't already have?? :idea:

itboffin

Il Principe wrote:

Rich158 wrote:

Oh and at the risk of starting another debate, my first Campy groupset feels fantastic and just keeps working without any fettling needed. I don't think I'll be going back to the big S on road bikes

Well at least part of your post makes sense...

So what's the frame on your SS made from?

Rich158

The ss is steel, but definately on the large side for my diminutive frame. It wasn't until I got the Condor that I realised just how good steel can be

Pound for pound I feel a decent steel frame represents the best value for a do it all bike, it's not as costly as CF or Ti, has a good fatigue life and is reasonably light. I'm seriously considering sticking to the Acciaio, upgrading the groupsetand wheels, and not bothering replacing the Madone if the insurance ever pays out.

+1 IP, I'm a definate Campy convert now, I've seen the light

Jay dubbleU

I have the best of both - steel frame with carbon forks - unfotunately this years model is all steel

wgwarburton

rjsterry wrote:

...WGW - I think Jon & Greg (are they also doing Masterchef at the moment?) are right. When the frame flexes, the BB is rotating roughly on an axis running horizontally front to back. When this returns to its unflexed position, the released energy doesn't go back into turning the BB axle, but probably mainly goes back into your legs, to be absorbed by your knees. The springiness is only useful (as a shock absorber) if it is limited to the vertical plane.

I disagree- the frame flexes laterally when you push down on the pedal, as it un-flexes, it pushes back up. If you stopped mid stroke, the unflexing would try to push you upwards, be defeated by gravity and end up driving the bike (and you) forwards instead. It's my belief that this is what happens as you pedal.
Cheers,
W.

daviesee

Jay dubbleU wrote:

I have the best of both - steel frame with carbon forks - unfotunately this years model is all steel

Each to their own.

I deliberately avoided the carbon forks option for my bike :P

rjsterry

And still no-one has explained why you don't get Ti forks. Paging Roastie!

prawny

rjsterry wrote:

And still no-one has explained why you don't get Ti forks. Paging Roastie!

I'm sure I read somewhere that it was because it's awkward to work around the crown area, could be wrong thoug, I so often am.

symo

prawny wrote:

rjsterry wrote:

And still no-one has explained why you don't get Ti forks. Paging Roastie!

I'm sure I read somewhere that it was because it's awkward to work around the crown area, could be wrong thoug, I so often am.

You are probably right as Ti welding is a sciencei n its own right.

greg66_tri_v2.0

WGWarburton wrote:

I disagree- the frame flexes laterally when you push down on the pedal, as it un-flexes, it pushes back up. If you stopped mid stroke, the unflexing would try to push you upwards, be defeated by gravity and end up driving the bike (and you) forwards instead. It's my belief that this is what happens as you pedal.
Cheers,
W.

?

The frame flexes laterally. When it unflexes, it moves laterally, back in the direction it came. If you stop mid stroke, the unflexing would push your feet sideways, not upwards. You need vertical unflexing to get an upward force.

(By lateral frame flex, I'm referring to the left/right displacement of the BB area of the frame during each pedal stroke. Although the force applied to the pedal is vertical (or at least at right angles to the lateral movement of the BB), there is enough distance between the foot and the BB shell to generate a moment, such as to displace the BB shell laterally.

The leftward lateral movement of the BB shell takes place when the right foot foot is applying pressure - 1 o'clock to 4/5 o'clock. As the cranks pass through the dead point (somewhere close to 6 o'clock on the right, 12 o'clock on the left) there's no pressure on the BB shell and it returns to neutral. The rightward lateral movement then follows on as the left foot applies power.

The unflexing phase takes place during the part of the pedal stroke when power isn't being applied, hence why you get no return from it, and why the energy used to flex the frame is wasted. )

Radioactiveman

I ride a bike made from spaghetti its extremely stiff but does flex a hell of a lot when it rains

redddraggon

symo wrote:

solsurf wrote:

rjsterry "Carbon is very good at what it does, but does seem to always be destined for Sunday Best bikes due to its brittleness."

now I'm worried! are you sure about this? Is my carbon Felt going to fall apart? As well as the zipp wheels and handlebars :shock:

Well tbh the majority of carbon frames are not being put to the demands of your pro peloton rider. As for the harshness, carbon can be laid up in a variety of ways so that it can be stiff around the BB and flexible where needed at the seat stays. Again look at the Cervelo R3 and RS, both bike designed to be stiff for sprinting and compliant enough for cobbles.

Titanium in its common bike form 6Al-4V has some great elongation (compliance) properties according to the Newnes pocket book of materials (1994; other engineering source books are available from your nearest engineering bookseller.). The seat stays on my planet X road pro take advantage of this, they are thin and curved so that the high tensile strength is used effectively.

If we look at the nearest equivalent steel to reynolds 531, AISI4130 we can see that it offers elongation of 10% in its common form. Whereas for Ti 6Al-4V then it is 14%, so I don't buy steel being more compliant than Ti argument either. (PS the elongation figures are not a fantastic guide to material compliance in a bike frame but give a 'feel' for it, the real test for this would be to look at the creep and S-N curves for both materials).

So it is MHO that Ti is the ultimate "natural material" and Carbon being the ultimate "performance material" if correctly built. Steel sorry nah it goes a funny brown colour if you can't keep it immaculate.

Most Ti frame are made from 3/2.5. The PX Road pro definitely is.

The 3/2.5 also have better elongation properties than 6/4 but 6/4 is stiffer.

Ti forks do exist.

Is it amateur materials science day on the commuting forum today?

John Stevenson

rjsterry wrote:

And still no-one has explained why you don't get Ti forks. Paging Roastie!

Because their steerers are dimensionally constrained by the common standards for headsets and stems.

Compared to steel, titanium frames have bigger tubes with thinner walls, which takes advantage of the material's lower density to produce a lighter frame. But you can't go bigger in a fork without redesigning the headset and stem, and if you don't you end up with a steerer that's too flexible or no lighter.

It has been tried. Gary Fisher messed about with rigid titanium mountain bike forks back in the 80s or 90s, and had 1.25in headsets and stems made to accommodate them. He ended up deciding it was all a bit pointless and went back to steel. Shortly afterwards suspension forks took over and rendered it all moot anyway.

For road bikes, it's hard to see how titanium could better the lightest carbon forks. However you engineer it, there's just not going to be much metal in a 300g titanium fork.

Morati of Hungary did make titanium road bike forks, but they weren't exactly light:

http://morati.extra.hu/brochures/morati ... g_2-01.pdf

And I think that's the answer: it can be done, but you don't end up ahead in the handling or weight departments compared to carbon.

wgwarburton

Greg66 wrote:

....The unflexing phase takes place during the part of the pedal stroke when power isn't being applied, hence why you get no return from it, and why the energy used to flex the frame is wasted. )

This is where we disagree- I don't think the frame hangs around until you get round to pushing it back the other way. I reckon that as soon as the pedal pressure begins to come off, the frame will begin to unflex.

At TDC (12 o' clock) you are pushing forwards on the pedal, between 1 and 4 o' clock you are pushing down hard. Roundabout 4 to 5ish you are easing off, ready to bring the pedal back up and start on the other side. At this point I reckon the frame straightens itself out and the energy is released between you and the wheel- ie it drives the bike forward. Effectively, your power stroke is extended because some of the energy that you put in at the top of the stroke is stored in the frame and released towards the bottom.

Cheers,
W.

rjsterry

Just had a look at those Morati forks - a little chubby, no? Can see why that didn't go anywhere. I'll leave Greg66 and WGW to slug it out except to say that when I have felt my frame flex, I would have said that the movement was twisting or lateral, and not vertical (based on the fell through my legs, but also the fact that as Greg pointed out, you are applying the force eccentrically (think that's the right word). Also if there were any vertical rebound back through the pedal, your knee would flex and absorb the energy, as by definition, this spring back would happen when you released the pressure on the pedal and your legs not being rigid. Gravity doesn't really enter into it, especially if you are seated.

Roastie

rjsterry wrote:

And still no-one has explained why you don't get Ti forks. Paging Roastie!

My 2c on forks:
I've been looking into either sourcing or designing Ti forks for our bike, and was actually chatting to my partner about it just this morning!

Ti forks are available from boutique builders, usually MTBs. Given that forks can be fiddly and that it is often easier just to use something off the shelf, most bike brands will just opt for a proven carbon product in the case of high end bikes. Also, to get a Ti fork that would be stiff enough in the right directions to handle properly but remain light weight might be a fairly tricky engineering exercise, but not impossible. The fork in particular is one of those areas that plays to the strengths of carbon fibre, and I doubt you could make a similarly performing Ti fork as light as a carbon fibre equivalent. And the cost would likely be crazy.

I'm sure it is possible to do, just depends on the will & resources to do it. Given that carbon fibre does the job so well, and is so fashionable, I'm not sure when/if this will happen. I also greatly doubt you could make a Ti fork as light as one made from carbon fibre (Edit: as John Stevenson very rightly pointed out).

Nothing to do with steerer dimensions. 1 1/8" is plenty to make a stiff enough steerer out of Ti. The more critical area is the fork crown, and how the fork blades attach at the crown.

Roastie

Throwing a few more cents in, my opinion on best frame material:

I would hazard to say that there is no such thing (as the best frame material). It really is a case of horses for courses. Far more important than the material is the design of the frame. A good design will play to the strengths of a material, and as much as possible negate the negatives. But, of course, there are some material properties that simply can't be designed out.

My personal favourite is a high quality, double butted steel - my dream Sunday best would be built from a Columbus XCr tubeset. Or, at the other end of the scale, for a proper "do-it-all" application, I would hazard to say that double butted 4130 chromoly is unbeatable (of course, specified with suitable tube wall thicknesses).

As for material strengths/shortcomings:
1) steel: To lump all steel tubesets in one basket would be a grave error. Common negative? Steel rusts - but then again, new stainless tubesets don't.
- cheap "high-tensile" steel: BSO territory. In one word, rubbish
- 4130 chromoly: in here I put workaday tubesets like 520/525/etc. Highly versatile, ride well, cost effective, tends to be a little heavy. But yeah, it rusts.
- High end steel: the sky is the limit. 853, Zero, XCr, Deda Niobium, … In a word, lovely. Very light, and properly stiff frames are possible. But expensive, can be dent prone due to thin tube walls (depending on the tubeset). Some require specialised fabrication methods. Rust.
- Stainless steel: 953 et al. Yum.

2) Alu: As per steel, lumping it all into one category (as marketers like us to do) is highly misleading. The only commonality is that alu has a limited fatigue life that can't practically be designed out. All Alu is prone to salt corrosion too.
- cheap alu alloys: BSO or one step up. Weak, so you need a lot of material to make it strong enough, so heavy.
- 6000 series: Not great, usually need a lot of material to make it strong/stiff enough, so tend to be heavy. Also, big wall thicknesses mean harsh ride. Ok for a utility.
- 7000 series: Getting better. A well designed 7005 frame can be delightful. High strength & thinner walls mean proper light weight. Can make a beautifully stiff frame. Great for shorter distance racing like crits, often hell on longer distances.
- Exotic alu alloys: Scandium alloys, proprietary alloys like "Kinesium", whatever Cannondale use on their CAAD9 frames, Dedacciai EM2, etc. Depending on design, can be totally sensational. Some ride with the smoothness of steel, most have the drive efficiency of carbon. My favourite for racing (on a reasonable budget), mostly because a minor off doesn't necessarily mean a wrecked frame and the end of your season.

3) carbon fibre: Ditto, you get the cheap stuff, the super stiff high-mod material, and the hybrids like woven-in flax or bamboo fibres. But arguably a narrower range than the metals. Common shortcoming is lack of impact resilience, limited life. I am no carbon expert, but here it really is about the frame design and lay ups. Great for pro race bikes because you can build a very efficient, stiff platform. Great for sportive bikes/Sunday best because they can be designed with good power transfer, smooth ride but crucially the look of a pro bike. Carbon fibre gives the designer a great deal more freedom so compromise is less of a limiting factor. Negatives? Not very resilient - doesn't like being bumped in directions it isn't meant to be bumped in. Not great for something that needs to take life's knocks. In a sense, a bit "throwaway". But yeah, you can make sensational riding bikes from the stuff, and it can look great. Probably the least versatile of all the materials because, bar the demands of pro or ultimate race bikes (and this is debatable), all the other materials can do the job just as well, if not usually better, for the given application.

4) Ti: As per the others. The only disadvantage is that is is more prone to fatigue fracturing than steel, but good design can negate this, so a bit of a non-issue. Highly corrosion resistant, very resilient.
- plain Ti tubesets: Not really all that light, I'd say on a par with better 4130 tubesets to get the same riding characteristics - but with the advantage of corrosion resistance and far greater resilience. Some design compromises are required.
- Double butted tubesets: Overcome many of the compromises of plain guage Ti, but at a price. Can make properly light frames. Very design dependent, and can ride however you want it to. Moots Vamoots is a great example: Brilliant race bike not made of plastic.
- Exotic Ti: With Ti, the alloying is less of an issue, so the difference in actual material is far smaller - 99% of tubesets are 3Al-2.5V (not 6/4 which is great for machining of small parts like dropouts, but not so great for making thin wall seamless tube). Exoticisms are things like hydroforming, complex butting (Van Nic and Lynskey are doing cool stuff), lugged Ti/carbon combinations. It is probably more challenging to design a Ti frame that ticks all the boxes, but one that does is lush.

All in all, it is all about compromises. I like good steel a lot. I also like Ti. Alu I only like in very specific situations. And I don't care much for carbon, but it does have its place. But like I said at the beginning - more important than the material is the design, how it rides and how suited it is to the intended purpose.

symo

redddraggon wrote:

symo wrote:

solsurf wrote:

rjsterry "Carbon is very good at what it does, but does seem to always be destined for Sunday Best bikes due to its brittleness."

now I'm worried! are you sure about this? Is my carbon Felt going to fall apart? As well as the zipp wheels and handlebars :shock:

Well tbh the majority of carbon frames are not being put to the demands of your pro peloton rider. As for the harshness, carbon can be laid up in a variety of ways so that it can be stiff around the BB and flexible where needed at the seat stays. Again look at the Cervelo R3 and RS, both bike designed to be stiff for sprinting and compliant enough for cobbles.

Titanium in its common bike form 6Al-4V has some great elongation (compliance) properties according to the Newnes pocket book of materials (1994; other engineering source books are available from your nearest engineering bookseller.). The seat stays on my planet X road pro take advantage of this, they are thin and curved so that the high tensile strength is used effectively.

If we look at the nearest equivalent steel to reynolds 531, AISI4130 we can see that it offers elongation of 10% in its common form. Whereas for Ti 6Al-4V then it is 14%, so I don't buy steel being more compliant than Ti argument either. (PS the elongation figures are not a fantastic guide to material compliance in a bike frame but give a 'feel' for it, the real test for this would be to look at the creep and S-N curves for both materials).

So it is MHO that Ti is the ultimate "natural material" and Carbon being the ultimate "performance material" if correctly built. Steel sorry nah it goes a funny brown colour if you can't keep it immaculate.

Most Ti frame are made from 3/2.5. The PX Road pro definitely is.

The 3/2.5 also have better elongation properties than 6/4 but 6/4 is stiffer.

Ti forks do exist.

Is it amateur materials science day on the commuting forum today?

Sorry Newnes don't quote 3/2.5 in my edition so I went with the most common material for frames. Ditto for the nearest equivalent for steel. Amateur is not in my lexicon when it comes to Mechanical Engineering but I am not a materials scientist granted.

For me High End Carbon and Ti bikes are the ultimate. I would even love an Aluminium S1 as a training platform.

For me steel as Roastie points out has to be expensive to be truly good which for me limits as a n 'ultimate' material.

Now what I could tell you about the materials in aero turbine blades..........

rjsterry

So we seem to have concluded that high end steel, high end carbon, Ti (by definition High end) or even some high end aluminium, make great frames. Hmmm.

No, I'm just being contrary.

I still think only Roastie has properly looked at the longevity/durability question (not of much interest to the pros, but v. important to cash-strapped commuters), where steel scores quite highly. Depends what you are looking for.

redddraggon

symo

The amateur materials jibe wasn't aimed at you Twas aimed at the whole forum what with this thread and DDDs bamboo thread.

John Stevenson

rjsterry wrote:

So we seem to have concluded that high end steel, high end carbon, Ti (by definition High end) or even some high end aluminium, make great frames. Hmmm.

Which rather suggests, as I've always believed, that it's not the material, but what you do with it that matters, provided you start with a material that's sufficiently strong you can make a reasonably light frame out of it.

supersonic

Far more important than the material is the design of the frame. A good design will play to the strengths of a material, and as much as possible negate the negatives. But, of course, there are some material properties that simply can't be designed out.

Absolutely.

It is simply wrong to say steel frames flex more than alu, alu is more uncomfortable - it depends on the design.