Forum Replies Created
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fukawitribe writes a lot of
fukawitribe writes a lot of crap which I’ve snipped.
..I see you’ve reached the dismissive stage and moved onto insults, earlier than I thought too, ah well..
For the record i’m not entirely ignorant of the physics behind the materials and structures, although CF composites are very far from being a subject I claim to have in depth knowledge of, and spent a fair chunk of my PhD work researching work on non-linear materials behaviour (mainly biological) and was lucky enough to be working with some very nice and bright theoretical and experimental guys who knew quite a lot on the subject. If that makes any difference to you, probably not, as i’m probably too ‘retarded’ or ‘dense’. The links I followed in your generous bread-crumb of knowledge for the terminally dense had some useful, if well known, bits of information – most of which you seemed to misconstrue in the broader discussion of composite frame. You keep missing the point that ultimate tensile strength and Youngs modulus are not the be all and end all of the physical properties of a structure.
So i’m no CF expert, but I think I know enough to point out some holes in your arguments however – although I would be grateful for real composite experts (of which there are some on here I believe) to correct me and point out where i’m talking shite – it’s called ‘learning’ and I love it, even when I have to give up some of preconceptions and prejudices, which is not always easy.
If you really can’t see anything in the list of points I made that isn’t ‘crap’ and doesn’t impact on your reasoning then would be little point in continuing anyway I guess – as you’ve shut up shop on that it is thankfully irrelevant.
FWIW, the engineers who read this site are yet to respond to my posts and
point out any area were I’m factually wrong.Your post about athletic prostheses was factually wrong, which I pointed out to you – no reply on that yet. Why don’t you start there ? You don’t have to explain to me, as you’re not responding to me anymore (huzzah !), but why not do so to your potential audience of admirers in search of education ?
The carbon fibres in the
The carbon fibres in the composite are serving no useful purpose and they
could be built entirely of the matrix material ie. polymer or whatever it is.
But plastic blades doesn’t sound quite as “cool” as carbon fibre.I guess when reality doesn’t agree with your outlook you can always go invent a new one. Go look at how these things are made and how many layers of fibre are used in the construction of these types of athletic prostheses and then come back and tell everyone how irrelevant they are, please.
..or just redefine what a composite material is I guess, that seems to work for you.
I said that carbon fibre
I said that carbon fibre composite materials can withstand relatively large deflections without suffering failure or permanent deformation – that first one was one example. The Santa Cruz ones show dynamic and quasi-static deflections with appreciable strain. All marketing fluff apparently… There were also further suggestions for examination, it would appear you haven’t bothered – or chosen not to mention it.You said
People who say
that carbon fibre composite frame x is less stiff than frame y made out of the
same material are fantasists. The material just doesn’t flex to any degree
before failing.There are various grades of carbon fibre composite. I suspect (although I
don’t know) is that the only important property that differs is that some
grades are stronger (ie. have higher UTS and E) than others and they use the
stronger (and probably) more expensive grades for more expensive frames.
You’d be able to use thinner/narrower/lighter tubes for a frame of a similar
strength to one built of an inferior grade...so it doesn’t flex to any degree before failing, clearly rubbish. You talk about the lay-up influencing behaviour then decide the only important property is ‘strength’ – re-examine your logic there please.
You ignore resin properties despite being instrumental to much of the behaviour of the material, e.g. vibration absorption – quite useful in a frame. It might be worth your time looking more at that.
There is little discussion of strength versus brittleness in CF.
You seem to ignore structural forms and there’s a cursory and simplistic mention of lay-up – that’s fairly fundamental to any meaningful discussion. There’s more to composite physical properties than uniform, circular tubes in tension.
You seem obsessed with UTS and Youngs modulus as though it defines a composite structures behaviour – and extension as a proxy for strength.
I am utterly uninterested in the irrelevant coda about composites being using for decorative uses – every material in vogue will be used like that at some point and has no bearing on it’s suitability for a particular engineering use.
ianrobo wrote:I have 25mm and
I have 25mm and my pressure is at 125 normally, 90kg in weight but seems way higher than what is said hereWellllll, it does seem pretty high even given the weight, but if you’re OK with it then it’s clearly not an ‘issue’. That said, you could always try dropping 10-20-30psi and see if you like it, nothing much to lose.
barrydocks wrote:fukawitribe
Hi Barry, just a quick question – if you’re more a low torque/high cadence sort of person wouldn’t you be better off with a shorter crank, especially as you are quite a ‘small chap’ ? I’d have thought a shorter crank would help with leg angle at the top of the stroke as well but if you’re happy with your setup then it’s moot – not meaning to question what you like but I thought i’d say something. Hope you find the chainrings you like. Cheers
No, for any given gearing, the shorter the crank the lower your cadence is and the more torque you need to produce to turn the pedals.I suspect 175mm cranks are too long for me but I used these in the past without a problem and don’t get any knee pain if I get the seat height right
Aye, indeed true at the same gearing and power you’ll need more torque however the ‘spinning’ aspect was something that came up as I was chatting to a fitter a couple of weeks back. My interior knee angle is quite acute at the top with 170mm, and my thigh quite flat, and discussing moving to 165mm. I think what he was getting at was the consequence of the shortening is that you gear down because you’re effectively self-selecting for torque anyway, hence the rise in cadence for a given effort. Lower gear to keep the torque similar, higher cadence to maintain a given level.
That said, if 175mms don’t cause any discomfort then no need to consider smaller – it was just a thought – and you get the advantage of a slightly better lever out of the saddle on the climbs. @crikey – yep, 2.5mm apparently isn’t really that noticeable, maybe unless you’re really on the edge of the long end and going longer (that bit my guess, might be bollocks) and it wouldn’t have been recommended to try and chance for such a small amount if it had been possible.
Hi Barry, just a quick
Hi Barry, just a quick question – if you’re more a low torque/high cadence sort of person wouldn’t you be better off with a shorter crank, especially as you are quite a ‘small chap’ ? I’d have thought a shorter crank would help with leg angle at the top of the stroke as well but if you’re happy with your setup then it’s moot – not meaning to question what you like but I thought i’d say something. Hope you find the chainrings you like. Cheers
freebsd_frank
Fukawitribe writes:
Carbon fibre composite structures can support relatively high degrees of
deflection without failing or inducing permanent deformation.What structures though? I used the example of a simple tube, assuming the lay
up of the fibres would be in-line with maximal stress.How about a link to the description of such a structure and it’s mechanical
properties? I know it’s such a hassle to back up baldly stated facts, I seem
to be the only one on here who does.For tubes try here
and other fun from Fabio Gigli or Google Santa Cruz carbon crush test or similar. Or perhaps, as mentioned by others, look at running prosthetics – hey, look in the sky at planes, at old carbon frame soft tails, at aero blades, carbon spokes, boats, leaf springs, at all sorts of shit.
From what I read on that site, carbon fibre’s mechanical properties are
directional. Whilst you could in theory make a bendy carbon fibre composite by
not using the directional properties of the fibre and instead rely on the
properties of the matrix instead, to quote from the article I gave you a
link to, that wouldn’t make sense (why use a strong material and then not make
use of that property?) and in practice:Because of the way the crystals of carbon fibre orient in long flat ribbon or narrow sheets of honeycomb crystals, the strength is higher running lengthwise than across the fibre. That is why designers of carbon fibre objects specify the direction the fibre should be laid to maximize strength and rigidity in a specific direction. The fibre being aligned with the direction of greatest stress.
And later under the heading: Carbon Fibers are brittle:
When the fibers bend they fails at very low strain. In other words carbon
fibre does not bend much before failing.You suspect wrongly.
This is getting tiresome: to the next muppet who doesn’t supply any links,
from now on I wont bother replying.You know one thing, amongst many, I can’t recall you mention this whole time is resin… you might want to consider that next time you’re educating the world with your knowledge of composite materials.
No more on this thread now Frank, you want to have more discussion -we’ll take it to another. Create it and publish the link – let the OP get on with what they want to talk about.
freebsd_frank wrote:Carbon
Carbon fibre composite whilst strong, with the caveats above, is brittle.
It will fail before it has deflected to any extent, like glass.Those are some of the properties of carbon fibre composites.
Carbon fibre composite structures can support relatively high degrees of deflection without failing or inducing permanent deformation.
There are various grades of carbon fibre composite. I suspect (although I
don’t know) is that the only important property that differs is that some
grades are stronger (ie. have higher UTS and E) than others and they use the
stronger (and probably) more expensive grades for more expensive frames.You suspect wrongly.
Batchy wrote:fukawitribe
OP, what track pump did you go for?Looking to get one with a gauge on myself.
I’ve just lashed out all of £5.99 for an Aldi track pump. To be honest I doubt whether there is anything out there that comes close to this item for value. It is a super pump with gauge and it is very solidly built considering the price. Check one out you will be amazed.Hope it lasts longer than the ones they’ve had before..
Yes! This latest version is a completely different beast comparerd to Aldi ‘s previous pumps. It has a metal barrel and foot plate and the pump action is as smooth as silk ! You really need to check this out seriously !If I didn’t have a decent one already, i’d be interested in at least seeing what it was like. However I do, and the one thing that drives me mad with most pumps is the valve head – nothing comes close to the Birzman snap-it head IMO – so that’s where my money will probably be going next time. Twenty-odd quid would be a bloody good deal for the ease and precision every time I pump up tyres but my Blackburn works so well apart from that wee irritation it seems a bit silly to go there now. Good luck with it, be curious to hear how it goes as a recommendation for others.
freebsd_frank wrote:Why are
Why are the wider rims better than Open Pros? I’ve told you above that rims have little to do structurally with a wheel but anchor spokes and tyres. Your opinion is entirely bogus; you cant tell the difference between wheels with rims of similar section and weight. Mechanically and aerodynamically any
difference is going to be so vanishingly small as to be not measurable let
alone to be noticed by the rider.The reasons why wider road rims might be advantageous have been talked about ad naseum in the cycling press over the last couple of years, it has little to do with structural issues, e.g. the effect on tyre volume are very, very, very far from vanishingly small so it would be odd if nothing could be noticed at all, wouldn’t you say ?
freebsd_frank wrote: Those
Those who think brand x
feels more comfortable than brand y? Fantasists.
..
Yes, some tyres use grippier rubber compounds than others so you
wont get so many miles out of pair. Some are more puncture resistant than
others dependent on how they’re carcassed and with what material. But more
“comfortable”? Fantasy.Frank, when you think about the logical consequences of what you’ve just written I think, I hope, you’ll realise that it’s clearly nonsense and reconsider… perhaps you’ve been listening to Beastie too much 😉
Batchy wrote:ibr17xvii
OP, what track pump did you go for?Looking to get one with a gauge on myself.
I’ve just lashed out all of £5.99 for an Aldi track pump. To be honest I doubt whether there is anything out there that comes close to this item for value. It is a super pump with gauge and it is very solidly built considering the price. Check one out you will be amazed.Hope it lasts longer than the ones they’ve had before..
ibr17xvii wrote:OP, what
OP, what track pump did you go for?Looking to get one with a gauge on myself.
Sorry to butt in, but Evans have the Birzman Maha really rather cheap, e.g. the IV is about 24 quid
http://www.evanscycles.com/products/birzman/zacoo-maha-iv-track-pump-ec050466
They seem to get universally excellent reviews
http://road.cc/content/review/84544-birzman-zacoo-maha-iii
http://www.cyclingweekly.co.uk/reviews/pumps-puncture-repair/birzman-zacoo-maha-iii-track-pump-49-99
http://www.bikeradar.com/road/gear/article/best-floor-pumps-for-road-cyclists-33412/Even tempted to replace my Blackburn for the head alone…
Batchy wrote:Surely the
Surely the optimum pressure of any tyre is somewhere between those that the manufacturers state on the side wall.Well the obvious question is optimum for what under what conditions. I’ve yet to find a tyre whose quote minimum figures were not very heavily on the high side for my weight (~74kg) and the type of riding I do in the UK, YMMV clearly. I can’t imagine ever going even remotely as high as the maximum for anywhere outside of a track in this country.
freebsd_frank wrote:
Martyn_K writes:
They even climb very well in comparison to a set of lighter, low profile rims i also own.
Do you mean they climb better than the lighter, low profile rims?
OTIO