[Closed] what does "STIFF" mean?

so can anyone tell what a stiff stem feels like ?

just ask the ladies ?

or gayers, obviously...

In terms of fork's lateral stiffness, it means more accurate tracking and less sideways deflection. Stiff stems twist less, so again, more accurate feeling. Same goes for cranks.

But I think I know where you're going with this - what's the point of having stiff 'everything' and then spending 1.5 grand on a sus frame. I concur entirely.

[url= http://www.stif.co.uk/ ]STIF[/url]

😉

"what's the point of having stiff 'everything' and then spending 1.5 grand on a sus frame"

Because the stiff sus frame will have been designed to allow only movement in the suspension direction, not laterally (Well thats the idea)

Stiff is good, dead is not. Aluminum is described as a dead material as when made into a frame produces something that dosent absorb shocks, it reverberates them. This is why Aluminum fatigues alot quicker than Steel.

Titanium absorbs vibration very well, lending itself to a comfortable ride. It dosent have much flex though, so it can be classed as being laterally stiff. Generally, stiff frames and components are good. Flexible components, are not.

Happily, as with many such things, while the differences involved are noticeable and measurable, they affect the enjoyment of the amateur sportsman very little.

😉

stiff cranks feel stiff (hard to notice unless you back to back test some cheep truvative ones on a square taper BB against some newer HT11 ones)

ditto frames, full sussers tend to wag their swing arm's from side to side, so a stiff one generaly* inproves things.

a ti/steel frame will be less stiff than a alu one, but the idea is to shape the tubes so that its flexy verticaly (giving a few mm of suspension) and not horisontaly or in torsion.

Theres a video somewhere of a frame being tested on a machine, a big rigid pole thriough the headtube and a ram bending it back as if the forks were slaming into rocks repeatedly. You'd be supprised how much frames flex!

How much felx is a personal thing, some people like easton RAD cove stiffee's, other like Ti jones'.

*some felx is needed, if it were entirely rigid then it would snap, flex allows forces to be distibuted through the structure, hence why headtubes are gussetted, as the frame flex's the gusset helps transfer that load to the down/top tube. Ditto the cannondale propet, in its first MBR review it was slated for beign "flexy" in a recent one they couldt praise it enough!

Oh I do love to see the amateur material scientists come out and get it totally wrong. 😆 at dooge - where did you get that lot from?

but the idea is to shape the tubes so that its flexy verticaly (giving a few mm of suspension) and not horisontaly or in torsion.

Theres a video somewhere of a frame being tested on a machine, a big rigid pole thriough the headtube and a ram bending it back as if the forks were slaming into rocks repeatedly. You'd be supprised how much frames flex!

Well all thats showing is how much the frame flexes on that test rig. Not on a ride.

a ti/steel frame will be less stiff than a alu one,

why?

but the idea is to shape the tubes so that its flexy verticaly (giving a few mm of suspension) and not horisontaly or in torsion.

Really?

I'm no metallurgist but what doodge said sounds like rubbish 🙁

I doubt its possible to feel the differnce in flex between one 4 bolt stem and another... maybe a real long, cheap 2 bolt stem you might.

Think cooked and dry spaghetti.

tinsy -
I doubt its possible to feel the differnce in flex between one 4 bolt stem and another... maybe a real long, cheap 2 bolt stem you might.

The difference is quite alarming actually. Once you fit a "stiff" stem to your bike and go ride you'll wonder how you managed without it.

You'd be supprised how much frames flex!

No I wouldn't. I've been watching aerial shots of sprint finishes in the TDF for many years.

I could make you a VERY stiff steel frame, just give me a welding rig and some scaffold bar.

I could also make you a very flexible ally one. Where did I put my bacofoil?

"Well all thats showing is how much the frame flexes on that test rig. Not on a ride."
presumably the test rig is designed to replicate a reality? otherwise its a pointless test?

"why"
higher tensile/compressive strength, so less material used, so mroe flexible (modulous tends to vary less than absolute strength). Yes could could make the alu more compliant with thinner tubing and spending more moeny, but equaly you could spend more money on the steel one as well.

"Really? "
well a steel frame flex's more, torsional and lateral flex are generaly bad things (ever ridden a shopper bike, they hate corners as the frames cant keep the wheels lined up!) that leaves a bit of vertical compliance to remove some fo the vibraion formt he rear wheel.

Ol' Sheldon says:

"Much of the commonplace B.S. that is talked about different frame materials relates to imagined differences in vertical stiffness. ... Virtually all of these "differences" are either the imaginary result of the placebo effect, or are caused by something other than the frame material choice.

rigid metal is rubbish at absorbing shock and vibration. Lead might work.

gnar, I must be shite then, have ridden 4 different 4 bolt stems, a Specialized, Hope, Thompson Elite and Thompson x4 not noticed any stem flex on any of them.. Like I said maybe if I had a 1ft long quill stem I would have noticed, but between 4 different 4 bolts I cant tell..

thisisnotaspoon, I believe the test rig was to test frames to destruction, to show up any weaknesses in the design or manufacture.

Stiffness is good when it is in the place you need it and bad when it is in the place you don't.

Forks, cranks, rear triangle, do you want them all to be the same level of stiffness? I don't think you'd get me on that bike!!!

Modern racing motorcycles are built with "controlled flex" as with no flex the suspension does not work went leant right over - sus forces work vertically but the sus movement is at 60 degrees from the vertical. without some flex they get chatter.

On the tandem when braking hard you can see the front fork flex back towards the frame by an inch or two. One day the headtube will snap off

tinsy

gnar, I must be shite then, have ridden 4 different 4 bolt stems, a Specialized, Hope, Thompson Elite and Thompson x4 not noticed any stem flex on any of them.. Like I said maybe if I had a 1ft long quill stem I would have noticed, but between 4 different 4 bolts I cant tell..

I'm sure it's not because you're shite.

Maybe you're just a buttery smooth rider, or maybe you are very light, or perhaps you have arms like a six year old girl, or perhaps your frame and fork have a relatively large amount of flex meaning you cannot appreciate the relative stiffness of a given stem, maybe you dont stray off of fire roads. Or perhaps all the stems you tried were similarly stiff.

Anyway I went from an FSA dh 4 bolt stem to a Diabolous. The difference was immense, despite the FSA being 30mm and the diabolous being 65, the diabolous was much much stiffer. Just sitting on the bike without moving you could appreciate the difference.

On the tandem when braking hard you can see the front fork flex back towards the frame by an inch or two.

well a steel frame flex's more, torsional and lateral flex are generaly bad things (ever ridden a shopper bike, they hate corners as the frames cant keep the wheels lined up!) that leaves a bit of vertical compliance to remove some fo the vibraion formt he rear wheel.

TJ, excactly my point, some felx good, some flex bad.

I had some manitou minutes, they flexed so bad that the steerer rubbed on the inside fo the headset cup's! Thats bad flex 🙂

imagined or not, my current DMR feels much less harsh than my old carrerra aka merrida aka specialized hardtail.

It's the amount something deforms due to given loading.

http://en.wikipedia.org/wiki/Stiffness

Can o' worms.

As regards stem - I have a 120mm bonty stem (light two bolt) and a 75mm thomson - with them installed on the bike there was zero flex - the frame was held rigid - I leaned my full weight on one end of the bar and the other end of the bar did not move at all - so under my full weight on a long lever no flex.

You do notice stiffer components, if you are paying attention.

On my Pace bought in 2001, I initially had XTR cranks on it (from 2000 I suppose) but I went to a Middleburn XC duo when it arrived. The difference was quite surprising as up til that point I didn't believe crank flex would make any difference.

As for stem and bar flex - if you sprint hard heaving on the bars, you'll notice it flex. You can clearly tell on my XC race bike.

Fork flex affects how stable your bike feels on big rocky bits - not visually noticeable but you can really feel it when you move to something stiffer.

Wheels can flex too - I've got Mavic 317s on Sapim super thin spokes on my 5 and they are too flexy - the spokes are too thin I think. You can really tell when hitting the rocks as the frame and forks are stiff but you get pinged off line very easily.

Frame flex - well, tricky one this. As I understand it (and I know there are framebuilders on here of which I am not one) some materials absorb vibration at different frequencies due to their density and young's modulus etc etc, and how much of the energy going into the deformation of the material is stored as potential energy and how much is released as heat through friction.... or something.. anyway materials differ in how they transmit vibrations I think. There's also other considerations for instance alu is not as strong as steel but lighter, so you can make frames with larger diameter tubes which will flex less. I'm guessing the fabled 'spring' of ti frames comes from the fact that the tubes are thinner, like a steel frame, so that they flex - but the thing is lighter which makes the whole bike feel more sprightly...

Although some ti bikes are quite stiff and dead, and some alu bikes are springy and lithe. My old Pace for instance was very flexy (so much so in the BB area that I couldnt' honk out of the saddle cos I'd lose the chain off the big ring). The rear triangle on the other hand was reasonably stiff so it rode nicely.

This is all armchair theorising tho, but it IS certainly the case that stiffness in certain areas of the frame changes the way it rides. For other components, stiffness is pretty much universally good. Apart from bars and seatposts maybe 🙂

Hmm I sound slightly drunk in that last post, don't I?

As regards stem - I have a 120mm bonty stem (light two bolt) and a 75mm thomson - with them installed on the bike there was zero flex - the frame was held rigid - I leaned my full weight on one end of the bar and the other end of the bar did not move at all - so under my full weight on a long lever no flex.

This is impossible.

You mean "I could not detect or see any flex".

If you loaded the front of the bike, the front tyre wold compress. So the bar appearing to "not move at all" would suggest the other end has rotated slightly to counteract the compression on the front tyre.

Stems twist. They just do.

some materials absorb vibration at different frequencies due to their density and young's modulus etc etc, and how much of the energy going into the deformation of the material is stored as potential energy and how much is released as heat through friction.

nah.

Also beware of using words like thinner. A tube is a structure with an outside diameter and a wall thickness. How you play with those makes frame rides how they do.

Also beware of using words like thinner

I meant smaller external diameter when I said thinner...

Also with regards vibration absorbtion, I reckon it does happen but I don't know if it makes a difference with metals etc. Certainly happens with rubber 🙂

some materials absorb vibration at different frequencies due to their density and young's modulus etc etc, and how much of the energy going into the deformation of the material is stored as potential energy and how much is released as heat through friction.

no, the word is 'hysteresis', which is low in many metals and high in rubber, explaining their mutually exclusive use for frames and tyres, for instance.

Hysteresis? With respect to materials and loading isn't that just another name for plastic deformation?

With respect to materials and loading isn't that just another name for plastic deformation?

no - even in nonplastic deformation some work is done

Stiff: 75-150 CuKN/m^2, an approximate N value of 16-33

or for field observations "cannot be moulded by fingers, can be indented by thumb"

and that, is a Geotechnical Fact.

no, the word is 'hysteresis', which is low in many metals and high in rubber, explaining their mutually exclusive use for frames and tyres, for instance.

I was going to type hysteresis, but then I read the wikipedia entry and realised it wasn't quite what I meant.

How does Carbon fibre compare to metals on that score tho? Everyone in the road community knows the value of carbon for reducing 'buzz'.

Hysteresis? With respect to materials and loading isn't that just another name for plastic deformation?

As sfb says, but to elaborate, all common engineering metals used in bicycles have such a low hysteresis that they absorb vanishingly small amounts of energy compared to the amount absorbed by the tyres/saddle/your bum. The springiness of a ti frame is all in the BB deflection, not in the vertical direction, hence what people think of as a comfortable frame is just noodly and not actually any more comfortable at all.

splay too

Everyone in the road community knows the value of carbon for reducing 'buzz'.

splay too

Interesting. In the context of frame vibration I would have referred to that as damping, but you live and learn.

OK brant - no detectable flex. I was putting a large torsional load on the stem and I could detect no flex. The unloaded side of the bar had no visible movement in relation to the bike frame The bars were flexing nicely - about 10mm on the loaded side but the unloaded side did not move in any detectable way relative to the bike frame.

Define "knows".

It's widely accepted that carbon frames absorb a lot of road buzz. My own experience backs this up to an extent. Are you going to tell me (and the roadie community) that this is all nonsense and we're being duped by carbon frame marketing?

quite easy to engineer soemthing to bend in one or mroe directions only.

take a sheet of paper, its quite easy to bend to make a tube,

now try this
bending it in one of the other two dimensions to make a circle? its impossible.

This engineering stiffness in one dimension is quite straightforeward.

so apply this to a bikes chainstays, you want them as stif as possible horisontaly, so make them as square as possible (BB shell, stays, hub axel is your square) now brace it (only possible arround the BB).

You could ride a bike like this, but it would probably be too flexy (probably wouldnt work at all in fact).

So now you add some seat stays, make them as long as possible to make them springy (GT tripple triangle, dropped top tubes, jones, retrotec etc), and make them just stiff enough to keep everything working.

Torsional stiffness is usualy dealt with by the dropouts, a 12mm axel clamped tightly will hold the axel and dropouts in a fixed allignment, stoping one moving independantly of the other, thus keeping everything stiff.

The trouble with that analogy, tinas, is that a bicycle frame is rather more like a vertical piece of paper than a horizontal one. Any conventional frame design is far, far more stiff in a vertical direction than laterally, since for the rear triangle to flex vertically you have to compress the stays along their length ( 😆 at the idea that GT stays make the bike more flexible as they're longer, given they're welded onto the seat tube).

molgrips - yes you are all being duped! Deflections are so small that even though the hysteresis is a lot higher the carbon frame can't possibly be having the magic effect which is attributed to it.

Booger, didnt realise I was a complete numpty! Surely the thing about Aluminum being a dead material is right? Or does it feel dead in relation to steel because of the diameter of tubing and wall thickness?

Certainly ally has a different 'feel' to steel or Ti, regardless of whatever metallurgy and engineering, (and Brant ;0)), might say. Some years back I had a little hardtail, a Cannondale M800 Beast Of The East, with XT, '97 orange Bombers, and a pretty stiff wheelset consisting of Mavic D321 rims on Hope XC hubs. Fun little bike, 14" BB height, rode it around Chamonix. Then got a Handjob frame and transferred everything but the vee-brakes to it and rode a 17 mile loop on the Marlborough Downs I'd ridden the week before. The difference was startling. Previously I'd got to the end feeling absolutely hammered, but with the steel frame I felt much less tired, like I could do the same loop all over again. This isn't some abstract but actual on the trail observation. There is a reason springs are made from steel or titanium, and not aluminium. Lateral flex could certainly be noticed on hardtails with vee's or canti's, when honking out of the saddle you could hear the brakes rubbing on the rims.

I can remember years ago trying a trek carbon road frame which felt like it had been made from a piece of wood compared to the 853 frame which was my normal ride.

the late Sheldon Brown does (as usual) an excellent explanation - but it really pre-dates the success of carbon fibre (US fiber) technology

http://www.sheldonbrown.com/frame-materials.html#stiffness

is'nt stiffness the opposite to sloppy design?

There is a reason springs are made from steel or titanium, and not aluminium.

You don't think there's some chance the rather different geometry of the M800 and Handjob might have had something to do with the perceived difference in comfort? Not that I trust actual on the trail observations, given how inaccurate and variable from day to day the human body is as a measuring instrument, and how susceptible it is to the placebo effect.

By that I presume you mean the fork flex TJ mentioned earlier?

Nope. Top tube/seat tube deflection too.

There is a reason springs are made from steel or titanium, and not aluminium.

Fatigue limit is not the same as modulus of elasticity.

Pretty much everyone on this thread would do well to read [url= http://www.ibiscycles.com/tech/materials_101/ ]these articles[/url] by Scot Nicol. Written nearly 15 years ago but more than relevant to the above discussion.

I've got three Whyte 19's, (an original AN6 alloy, a race with carbon seat stays and a Ti) they all have the same forks stem bars and to be totally honest I'm not sure if I can tell if one is stiffer than the other, but I love riding all three of them so what does it matter?

Nope. Top tube/seat tube deflection too.

The magnitude of which is what though? Sure it has more effect than rear triangle flex, but we're still talking tiny deflections compared to the other flex in the whole system (like fork flex!)

Dibbs - you heathen unbeliever!

since for the rear triangle to flex vertically you have to compress the stays along their length

No, not really - they can bow outwards or inwards. If you have S shaped ones as many bikes do, they can compress like springs. Only a tiny bit, obviously.

If you have S shaped ones as many bikes do, they can compress like springs. Only a tiny bit, obviously.

Except that springs don't compress like that. Coil springs are compact torsion bars.

Top/down tube, shirley?

No - the loads encountered by the front "triangle" deflect it in the manner on a cantilevered beam. Triangles are good at supporting point load (like in a rear triangle), but a front triangle doesn't have loads applied like that.

I am enjoying this thread.

There aint half some pish being spouted on it though.

Cracking troll BTW.

I am looking forwards to warming my hands on my ti frame at the bottom of the next downhill, with the heat that built up in it due to hysterical forum postings.

Anyone mentioned resonance yet?

Or the adverse effects of a misplaced gusset?

No - the loads encountered by the front "triangle" deflect it in the manner on a cantilevered beam. Triangles are good at supporting point load (like in a rear triangle), but a front triangle doesn't have loads applied like that.

No, not really - they can bow outwards or inwards. If you have S shaped ones as many bikes do, they can compress like springs. Only a tiny bit, obviously.

My mate used to have a very cheap racer (back in the day before we started calling them road bikes) that was so flexy you could very easily make the back tire rub on the chain stays when riding it.

Dunno what it was made of though, tin maybe.

Ah, the misplaced gusset;

'tis a terrible affliction that manifests itself in spurious ramblings and verbal excreta. Commonly known as "getting your knickers in a twist", about nothing of import.

Stiffness can be both good and bad, dependant upon what component we are talking, and in what context.

An example is in motor sport; a few years ago it was accepted by the "experts" that a stiff motorcycle frame was the answer to all handling problems; checkout the Sheene and Roberts era GP bikes and you'll see they had massive power through flexy frames. However, as suggested above, a certain amount of flex, in the right direction, actually helps the handling. Quite a long time ago I used to be involved in Karting. A friend of mine entered the schoolboy championships with a chassis made of wood and won nearly every race. The other entrants had much stiffer steel frames, which meant on the corners they were lifting wheels and losing grip, whereas my mate's Kart, because of the flex in the wood, easily kept all it's wheels in contact with the ground. He could literally drive around the outside of people on certain corners.

I had a Cotic Soda, that when I was sat on it stationary, I could bend and flex and twist the whole front triangle. However, when riding i couldn't detect any of that - I was focusing more on the ride than the frame flex.

Except that springs don't compress like that.

Coil springs aren't, no. There's more than one kind of spring tho.

Except that the seatstay load path on most bikes is within the tube (which is pretty much a given for a straight tube with normal end loading), hence they won't be bowing at all.

Hmm, not sure about that. If you build a bike with massive chunky seat stays, you'd look at it and think 'that looks harsh riding' and you'd probably be right.

Old Pace square tube frames had plain square tubes as seat and chain stays. Later models had the same tubes and material, but the faces of the tubes were milled out. Result - a much more comfortable frame. Why? something's flexing somewhere. My money's on the chain and seat stays 🙂

My money's on placebo effect. Nice to see you're using "it looks uncomfortable so it must be" now.

My money's on placebo effect.

🙄

Nice to see you're using "it looks uncomfortable so it must be" now.

Cept that's not remotely what I said. I was drawing a link between engineering and people's experiences. If you see something thick and heavy looking chances are it won't be supple and light. Your own experience of the world tells you that.

Is this attack Molgrips day or what? Why all the aggro?

If you see something thick and heavy looking chances are it won't be supple and light. Your own experience of the world tells you that.

There's so much of this that isn't "common sense", that appealing to that is ludicrous.

The whole point is that it doesn't make any significant difference how chunky you make the stays since the flex there is already negligible.

I just disagree! Large diameter tubes = stiff tubes, that's surely clear?

Can someone do FEA on some models of frames so we can see the various modes of vibration caused by different types of trail noise?

but the faces of the tubes were milled out. Result - a much more comfortable frame.

I see 2 factors:
1) we are all highly suggestible and willing to feel/see/hear things which are not really there
2) it doesn't matter how flexy the frame is, it will still not absorb any of the vibration - the best example being a spring, which undergoes massive flexion, yet they are never used without damping because they just store and release the energy

F*ck off barnes - you didn't ride the bike, you have no idea. Don't tell me I'm a highly suggestible imbecile that can't tell sh*t from shinola without the attached marketing material.

Springs are a shite example because they're nothing like bike frames. If trail vibrations set up say a transverse oscillation mode in your seat stay, where's all the kinetic energy of the trail impacts going? left and right, that's where, not up and down into the seatpost and your arse. Why don't you try this experiement: get a nice green flexy stick and fix it to the front of your car. Then push the stick repeatedly. Does the car move? No. Does the stick flex? Yes. So the vibrations of your hand moving are being absorbed by the stick, cos the stick is flexy.

Why do you think some frames are harsher than others then? Or are we all imagining that too?

Don't tell me I'm a highly suggestible imbecile

being clever may actually make one [b]more[/b] susceptible to suggestion, and I said "we are all"

get a nice green flexy stick and fix it to the front of your car.

car, wot car ?

So the vibrations of your hand moving are being absorbed by the stick, cos the stick is flexy.

I this has to count as one of the worst experiments not involving death [b]ever[/b] and for the life of me I cannot understand what it's supposed to demonstrate 😐

Why do you think some frames are harsher than others then?

I don't know that I [b]do[/b] think that - there are so many different factors it's hard to pin down a single effect, particularly if you're measuring with a flexible and possibly delusional doofus made of meat :o)

So, the stick is absorbing energy of you pushing it?

We have finally debunked Newton's 3rd law.

I think you're ignoring the fact that the force exerted is simply not enought to overcome the reciprocal force of the car, and that the stick then returns to it's original state when you release your force.

PS. I'm really enjoying this troll.

Calm down dear, it's only the internet! You really should try reading the posts you're replying to - Simon's not being personal, just pointing out that everybody is susceptible to suggestion. Meanwhile if you read mine properly, you'd notice that I point out it really doesn't make any difference if you make the tubes stiffer, since they are already stiff enough that any flex is totally overwhelmed by flex elsewhere. That and the diameter is irrelevant to the stiffness of a tube in compression - the only important quantity is the total amount of metal used.

You don't need to do FEA - basic structural analysis is enough to show that any deflections in the frame are tiny.

Why do you think some frames are harsher than others then? Or are we all imagining that too?

I'm really enjoying this troll.

Oh, but 😆 at the stick experiment, now I've worked out what he's on about. Try attaching your stick to a balloon, molgrips, and see how much energy it absorbs then!

Later models had the same tubes and material, but the faces of the tubes were milled out.

It was actually a constant section extrusion in the rear stays. It wasn't milled out.

Hey brant - any comments on my serious question about why you're considering the main triangle front end as a cantilevered beam, and why the seat tube stiffness is important?

Try attaching your stick to a balloon

if you haven't got a balloon will a condom do instead ?

PS my reference to 'doofus' with not intended as in insult, except to myself 🙂
PPS I'm still working through the [url= http://www.ibiscycles.com/tech/materials_101/1/ ]article[/url] posted above, which is quite informative.