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I havent had the best of experiences with carbon wheels, and feel like I've probably reached a point now where I'm done with them, for a number of reasons.
Firstly, reliability. I've now cracked 2 x Enve rims, 3 x Derby rims & 1 x LB. I noticed earlier this week I had cracked the Derby rim on the rear, which prompted me to check the front LB rim which is also cracked, good job I checked it closely as it looks like it's cracked around a number of the nipple holes.
Prior to this, I've never considered myself a rim wrecker. Yes, the odd ding in rims was normal, and a bit of truing, but that's really been my lot. For me at least, I think it's fairly conclusive that carbon rims don't work for riding & racing with a gravity bias, unless you like replacing rims, a lot.
The next bit, having gone back to some Flows on the same hubs, having ridden carbon wheels for quite some time, I'm amazed how much more compliant the wheel feels.
Carbon has always felt harsh to me on choppy terrain, off camber stuff and flat corners can become a bit of a liability as the wheel was so stiff, it would just deflect. High lines became a bit of challenge, and it always felt like I was running too much compression on my suspension due to the harsh feedback.
One ride back on aluminium rims and I'm sold, even excluding the reliability issues I've had, the ride is so much nicer. The harshness has gone, the bike doesn't seem to get unsettled mid corner by chop and as a result, I can corner harder. A bit of Google tells me I'm not alone in my thoughts of the 'feel' they create, and there has been talk of considerably faster WC racers than me trying to make their carbon wheels more compliant, as they felt too stiff.
I think they have their place still, but for me, it's not on a 150+ travel bike that gets raced, used & abused.
I wonder if anyone else here feels the same.
WIth carbon it's all about the build. How did you build the enves/Derbys?
One set was built up with Supercomps & the other with Revolutions, can't remember which was which though..
[quote=Hob Nob ]there has been talk of considerably faster WC racers than me trying to make their carbon wheels more compliant, as they felt too stiff.
I'm sure with 2.5" tyres and 8" of suspension travel the lack of 1 or 2mm of flex in the rims makes for a very harsh ride.
I expect there is a little more than a couple of MM lateral flex difference between a carbon & aluminium rim. Let alone at the sort of speeds they ride at.
Which is probably why they are experimenting with ways to introduce more flex into a wheel.
Different experience here bud. I find I can run lower pressures on wide carbon rims whilst still maintaining tyre carcass stability. The leads to softer more compliant running and as a result more grip.
The difference in stiffness between the rim material is in my opinion negligible compared to the sqidge the tyre provides.
I've had zero reliability issues with LB rims too.
Have you seen the promo video for the new stans carbon rimmed wheelset? Looks like they've engineered some flex into those.
Cracked the rear light bicycle rim after 2 peaks rides. Still pretty miffed about that.
They do "Crash replacement" for postage cost iirc
Have spoken with a few riders who've had similar thoughts about carbon rims.
Personally, as a 29er fan, I'm loving the extra stiffness they bring. Those I've spoken to that have been less than happy with carbon rims have all been on 26" or 650b.
Mboy do you think on a 29er carbon brings rim stiffness up to 26er standard.
Different experience here bud. I find I can run lower pressures on wide carbon rims whilst still maintaining tyre carcass stability. The leads to softer more compliant running and as a result more grip.
It's interesting to hear other people's opinions, as we're all different. I can't get on with the low pressure feeling, constantly feels like the tyre squirms in corners. Plus I got a shed load of pinch flats running tubeless with lower pressures.
Personally, as a 29er fan, I'm loving the extra stiffness they bring. Those I've spoken to that have been less than happy with carbon rims have all been on 26" or 650b.
I think on a 29" they make more sense, more so for trail riding, rather than flat out riding & racing.
Maybe I have cloth hands or something but I can't tell any difference between my old flows and my 33mm LB rims. Well, other than the weight and width at least. Harsh? Not for me. But with fat tyres and a bucket of travel maybe that's not too surprising. It's only really once I get down to flimsy wheels- my traversees frinstance with less, lighter spokes etc- that I start to notice real differences. And tbh I'm usually pretty aware of differences in frame, fork, pressures etc.
As far as unreliable- I've killed a Flow Ex on the second ride, cracked 719s and 721s and a Flow to death... Even my old (weaker design) LB rim performed up to or past the standard set by all that lot.
(ps- not to say there is no difference, just that there's none I can feel. I switch back and forth between wheels reasonably often)
It makes sense that DH hard chargers who can't run low tyre pressures because of pinch flats and tyre squirm in high G situations wouldn't feel the benefit of a carbon rim.
Ime, those benefits mostly come from a light stiff and wide foundation for a soft and pliable tyre, and that doesn't serve DHers in the ways I described above.
As hob nob says, it's pretty clear this works for trail riding, but less so in a race environment.
A tyre and rim make a wheel system together, I don't think you can draw conclusions on one component without due consideration of the other.
Rim flex is considered very important by pro DHers for maximising grip in corners - wheels are often built with particularly low tension compared to production wheels.
Just because you have inches of suspension (which is working in the wrong direction in corners anyway!), and fat tyres and a frame which flexes, doesn't mean that wheel flex isn't important - it's essentially a complex group of springs acting in series.
Those same DH racers are usually running low pressure anyway, in the 25-30psi region much of the time. There's plenty of info online to confirm all this stuff if you do some reading.
Furthering what scienceofficer and chiefgrooveguru said, I remember many years ago, almost 20 in fact, when Carl Fogarty was riding the Ducati 996 in the WSB series. The ever dominant Ducati was cited as having a weak link with its traditional single sided swingarm, so Ducati Corse built some prototype dual sided swingarms that increased stifness greatly and at the same time reduced unsprung mass...
Foggy was over a second per lap slower during testing on the new swingarm, and quickly went back to the old, heavy, flexy single sided swingarm for the season (winning it in style)... His view was that feel was far more important than stifness, something which Valentino Rossi has also been highly critical of (especially whilst with Ducati) of the bikes he's ridden in his MotoGP career...
Stifness isn't necessarily better! Though the bigger the hoop, the more flexible it will be naturally, so sometimes making it out of a stiffer material makes sense anyway.
No right or wrong answer here I feel, just like tyres this is going to be a hugely subjective topic...
Mboy do you think on a 29er carbon brings rim stiffness up to 26er standard.
Hard to say.
You're more than welcome to try mine out if you pop in to see us to tell for yourself...
but they're really expensive and all the top bike builds use them! them must be at least 15 times better!
waa!
chiefgrooveguru - MemberRim flex is considered very important by pro DHers for maximising grip in corners - [b]wheels are often built with particularly low tension compared to production wheels[/b].
That there.
I popped a shiny new set of Roval Fattie Sl carbon on my Bronson, first impressions wow I could really feel the weight loss & increase in rolling momentum, carrying more cornering speed but after a while the harshness became evident, I was continually messing with fork shock & tyre pressure, in the end I just adapted to them stopped messing ran the pressures as normal & now enjoy them, that said over a long day (5hrs)I can honestly say I'd prefer alloy & a mates Bronson with WTB KOM rims feels superb, be it flex what ever it feels great so the carbon wheel debate will continue.
[quote=chiefgrooveguru ]Rim flex is considered very important by pro DHers [s]for maximising grip in corners[/s] because they buy into cycling BS - wheels are often built with particularly low tension compared to production wheels.
Spoke tension makes ZERO difference to wheel stiffness unless it is so low that spokes are completely detensioning under load - which not only results in very non-linear wheel stiffness, but also makes the wheels a huge amount weaker, neither of which I'd have thought ideal for pro DH racers. If they think that's a good idea then I'll take their thoughts on the disadvantages of wheel stiffness with Lot's wife.
actually thats not true... sort of. Spoke tension does effect the ability of a wheel to absorb impacts, although its not necessarily [i]felt[/i] as a variation in stiffness. the effect is caused by the decreasing rate of elastacity in spokes as tension increases. As an example a typical spoke might elongate by a full mm if you increase the tension (through load) from 50 KGF to 100, but going from 100 to 200 only gives an elongation of 0.6mm on the same spoke. As I said this doesn't effect stiffness to a notable degree in terms of the deflection of the overall wheel (especially in context of a tyre as well), but it does enable the wheel to to flex a tiny amount more for the same load, giving a less 'buzzy' ride maybe (?) but more importantly that stretch is enough to begin distributing the rolling loads more evenly over more spokes, leading to increased durability of the wheels under impact. The same effect is felt from plain guage to Double/triple/quad butted spokes.Spoke tension makes ZERO difference to wheel stiffness
So maybe the DHers bought into the hype, or maybe they are looking for marginal gains, since lower tension spokes will be less likely to break, and more likely to survive an impact (whether or not its actually a notable difference its still a 'true' effect), and they'll take it since it might help.
Rumour has it the SP Syndicate team have brand new Enve rims every run !
According to Enve the Syndicate team only broke 10 runs all last season. If you speak to Jason Marsh and Greg Minnaar about spoke tension (as I have) it's quite interesting. Nothing really to do with pure grip in corners, more to do with allowing the wheel to track better and not be deflected.
The analogy to motorbike chassis/wheel stiffness is a bit moot. There is all about numb absorption when the bike is leant so far over the suspension is ineffective. That's quite unlikely on a push bike off road!
Spoke tension makes ZERO difference to wheel stiffness
"Hello over-simplified world of physics, it's much nicer over here in the real world of engineering where we know that blanket statements like that are just silly!"
Interesting thread. Im planning a new bike and new wheels. So Hobnob / anyone - which wheels would you recommend for an Enduro style bike then ?
Rumour has it the SP Syndicate team have brand new Enve rims every run !
Enve site -"In addition to Greg’s historic win, Syndicate’s mechanics didn’t need to rebuild a single M90 carbon downhill wheel during the race weekend which is a first at Fort Bill."
Surely no one is surprised by FUD on an Internet forum?
Interesting thread. Im planning a new bike and new wheels. So Hobnob / anyone - which wheels would you recommend for an Enduro style bike then ?
Depends on your budget really.
When I get home, I'll rebuild my wheels onto some DT EX471 rims, probably with Supercomps. I already have the DT 240 hubs, so should be a reasonably light & strong wheelset that will last a bit longer.
Currently waiting to hear if the respected brands will 'warranty' this latest round of broken rims (thought I may as well ask at least). If they will, then great, I'll build them up and probably put them on my planned little ~120mm trail bike build. Hopefully they will find their happy place there 🙂
When I was speccing up a 29er Ti HT to replace my 26er Ti HT the only way I could get anywhere near on weight was to look at carbon rims - especially as there was no way that Crests would survive in 29er flavour (based on the constant rebuilding for my 26er).
So I kept the 26er 🙂
reedspeed - MemberRumour has it the SP Syndicate team have brand new Enve rims every run !
That's the nice thing about rumours- you can just make one up and straight away, "rumour has it!" 😆
[quote=benpinnick ]the effect is caused by the decreasing rate of elastacity in spokes as tension increases. As an example a typical spoke might elongate by a full mm if you increase the tension (through load) from 50 KGF to 100, but going from 100 to 200 only gives an elongation of 0.6mm on the same spoke.
That is a complete load of rubbish. If the spoke elongates by 1mm when you increase the tension from 50 to 100kgF then it will elongate by 2mm when going from 100 to 200kgF. Because they obey the laws of physics just like everything else. Feel free to do some testing, or present the results of some testing which shows them breaking the laws of physics...
[quote=chiefgrooveguru ]
Spoke tension makes ZERO difference to wheel stiffness
"Hello over-simplified world of physics, it's much nicer over here in the real world of engineering where we know that blanket statements like that are just silly!"
Well wheel stiffness testing has shown that the physics is accurate. Physics still works the same in the real world. Engineering is after all just applied physics, and in my structures labs we were expected to be able to calculate the expected deflection under loading - in the real world structural engineers (proper ones building bridges etc.) rely on physics based calculations.
That is a complete load of rubbish. If the spoke elongates by 1mm when you increase the tension from 50 to 100kgF then it will elongate by 2mm when going from 100 to 200kgF. Because they obey the laws of physics just like everything else. Feel free to do some testing, or present the results of some testing which shows them breaking the laws of physics...
Luckily I don't need to do testing as the spoke manufacturers publish the data themselves. Why don't you check it out yourself? You might find it interesting.
I work in the Oil & Gas industry & I know it's a million miles away from Bikes but the same principles apply relating to steel & it's properties, every single thing we touch has to be torqued up to prove traceability if we have a leak or something fails in any way, we must comply strictly to Bolt tension be it by hand or hydraulically stretched & everything has a yield point where by it's elasticity fails & it lets go & surely if a wheel were to deflect so much the spokes become over tensioned then they would let go i.e weaken to a point where they effectively fail to hold the wheel in shape & it collapses under impact???
What increasing spoke tension does in a wheel is reduces the rate of spoke fatigue (a good thing) and increase the load required to make groups of spoke go slack. Once some spokes go slack the amount of flex experienced suddenly goes up. I cannot see how any of this is of benefit. Better tune a wheel reaction to loads by altering spoke count, spoke gauge, bracing angle and rim stiffness than by reducing spoke tension.
What do hill riders are probably describing is they want a wheel with lateral stiffness that is not too high so it does not snap back when heavily loaded then unloaded. It may also be the contact patch remain larger when a wheel is able to flex with the tyre over very uneven off camber rocky surfaces.
This is why I ride rigid and like it. I use stiff carbon tubular wheels in one 29er and wide stiff alloy rims in another rigid 29er and I am happy as every component seems to compliment each other. I ride xc though I don't downhill so I hope I am not talking out of my arse.
Also when did 25 to 30 pis count as low pressure. I run 20 psi in my 2.2" race king tyres. There is no squirm and higher pressure make the bike hard to control. 23 psi in the geax saguro tubs seems perfect. Any lower the tub squirms any higher and ride is too harsh.
Just realized that I may have confused the physics graduates with the use of the word elastic... Which of course would be inappropriate for what I was describing. Spokes pretty much never operate within their elastic zone so it's not elastic it's just deformation. But I guess the physicists knew that already so maybe it wouldn't be so confusing?
If spokes did not deform elastically in a wheel then they would loose tension over time which does not happen so they deform elastically when under tension in a wheel. Your entire post is confusing to me.
[quote=benpinnick ]Just realized that I may have confused the physics graduates with the use of the word elastic... Which of course would be inappropriate for what I was describing. Spokes pretty much never operate within their elastic zone
I think it's you who is confused if you reckon spokes aren't in their elastic zone in normal use.
Though I think I understand what you were going on about in your previous two posts now though - you were talking about the elongation of spokes being non linear when they are being plastically deformed past the yield point?
If as you claim the spoke manufacturers provide data which supports your claims, why don't you just give me a link rather than me going off on a wild goose chase. They're not going to provide data showing non-linear elastic deformation because it doesn't happen, so I'm not exactly sure what I'm supposed to be looking for, and I can't see anything at all relevant with a quick check (not surprising - no point in them providing data on elasticity of spokes when anybody who knows anything about materials can work it out from the x-section).
oh and thanks bm... your post is pretty much spot on. The correct way to make flexier wheels (if that is really an advantage) is either with thinner spokes or less spokes. Of course either of those will make for a weaker wheel, but not as much as low spoke tension, and unlike low spoke tension they will make a useful difference to stiffness.
From an interview with Olivier Bossard earlier this year:
"I don't know if riders are still playing with the spoke tensions now on their bikes, but we discovered during the years [at Sunn & VProcess] that the spoke tension has a big effect on the balance of the bike..."
Which simply proves to me that riders haven't got a clue what they're feeling. Though I'm somewhat surprised at Olivier not applying a little bit of his knowledge to the subject and believing the BS.
It is also quite important to get rim stiffness and the stiffness of the spokes and the effect of bracing angle to be complimentary.
What I mean is if you have a very stiff rim that is under supported by the spokes can lead to groups of spokes going slack but if a less stiff shallower rim is used with more thicker spokes then that horrible situation can be avoided as the shallower rim actually deflects less opposite the point of load than the deeper stiffer rim if the lateral stiff for both wheels is the same. Odd huh but true. This is more clearly seen in some road wheels. Deep stiff carbon rims with a very low spoke count can deflect enough at the brake track to cause the nds rear spoke to go completely slack. In that case up the spoke count. This is why more mtb rims should have off set drilling as that problem is entirely avoided.
How many people belive centrifugal force is real rather than an apparent force caused by newtons first law of motion. I think the same applies to that interview.
Which simply proves to me that riders haven't got a clue what they're feeling. Though I'm somewhat surprised at Olivier not applying a little bit of his knowledge to the subject and believing the BS.
Or anyone with a more open mind would see that there is a lot going on with a bike being ridden hard and that their oversimplification is causing them to miss the point...
You do realise that it's lateral, not radial, wheel stiffness that is the bigger issue?
The trouble with having an open mind is that people will insist on coming along and trying to put things in it. Lateral stiffness is just as unaffected by spoke tension as radial stiffness - because the spoke doesn't care which direction the wheel is being loaded and still obeys Hooke's Law even when the bike is being ridden hard and there is a lot going on.
bm0p700f
Centrifugal force you say... isn't that the same as what goes around comes around ??? sorry boys but this has got far too out of hand come on lighten up.
aracer, the biggest professional teams who use every advantage they can get and test back to back are saying spoke tension has an affect on ride quality. Rather than try and shout them down with science, use the scientific approach, i.e. try and work out why people are experiencing a phenomenon which (appears) to contradict the basic facts.
Of course the answer that will come out is that a wheel is a complex system when you look at the aspects of force application from a point on a rim and transfer through the system to the centre of the hub. Yes spokes act in a linear manner (generally, dont forget they properties change as they are stretched due to the change of cross sectional area) but more so you also need to consider the spoke connection to the hub, nipple and the material and design of the rim, all of which will be affected by an increase/decrease in spoke tension.
Which simply proves to me that riders haven't got a clue what they're feeling. Though I'm somewhat surprised at Olivier not applying a little bit of his knowledge to the subject and believing the BS.
I know what I've felt. The only thing I've changed is the rims. The bike is noticeably less skittish on high speed, rough, flat corners, it feels more in control because it's not what feels like the limits of the tyre grip, due to deflection from stiffness. I can hit, and hold high lines without feeling like the bike is going to wash out, so all in its a positive change.
I've also noticed I've buzzed the seat stays with the tyre, so all of a sudden 'something' is flexing more than an extra 1-2mm as you put it.
It seems to me a carbon rim can be too stiff, to the detriment of the ride.
Using science involves as a first principle applying Occam's Razor. It is far, far more likely that there is a problem with the measuring device than that physics doesn't apply. I'm sure the placebo effect is just as great when riding bikes.
To a normal person a wheel might seem like a complex structure, but actually in structural terms it's quite simple. The change of the x-sectional area of the spoke under tension is miniscule. All the other bits you mention are also normal structural parts which all also obey Hooke's Law.
p.s. Hob Nob, I'm not disputing what you're feeling (not here, not now 😉 ) simply commenting on people using low spoke tension to get a more flexible wheel.
well I cracked an LB rim this weekend
punctured on the qualifiying stage at UKGE and thinking I was aaron gwinn !?! tried to ride down, till a loud bang in a rock garden.... crack half way thruogh the rim
anyway , bit of tape over the hookless bead and they resealed, slight wobble to the wheel, but still pretty true
so rode it all day Sunday, took a the first stage easy but in the end I hit everything as normal and it was a rough, rocky, rooty course with a fair few drops and jumps thrown in
I was a bit sad to see the end of the rim but ive had it for 16 months, and its done 2 ews, a year of ukges, dhh races, bikeparks, uplifts and stuff and I can now add it to my list of broken wheels from mavic, shimano, alex etc
and just checked the LB website and they offer an 18 month crash replacement policy for a small fee + postage, which im very happy with!
fwiw, i think they are a bit stiffer, I run my suspension slightly softer, but i also feel they accelerate quicker than my ally rims
It does seem odd to me that for MTB people use their carbon rims for everyday use.
For TT and Tri you have race wheels and training wheels and your race wheels only come out for races and cost about 4 times the price of your training wheels.
but maybe i am missing something?
I find it very easy to ignore the possibility of buying something so amazingly expensive. So the news that they are also a PITA is very welcome.
🙂
If spokes did not deform elastically in a wheel then they would loose tension over time which does not happen so they deform elastically when under tension in a wheel. Your entire post is confusing to me.
I think its a little more complex than that. The spoke as a component is outside of its elastic range, but we have to remember that a spoke is not a uniform material made up of a number of parts from a mechanical perspective (several thicknesses, a bent bit etc) , some of which will still be elastic at certain loads, some not. The point I was trying to get across (albeit badly) was:
At low tensions, the spoke is more 'stretchy' (not elastic - the SPOKE is not elastic at this point as that would mean it needs to obey Hooke's law as someone was kind enough to point out) therefore less likely to suffer a permanent damage from an impact. Pillar spoke publishes the data for each spoke if you want to check it out. You'll notice that the uniform elasticity ends around 80KGF for pretty much most butted spokes, after this it begins to detoriate.
You'll also notice that the plain gauge spokes exhibit the kind of more distinctive kink you would expect from a uniform material's stress-strain curve where the elastic phase ends and they begin to deform, whereas the more butting etc you have on the spoke the more smoothed out the curve becomes as the spoke continues to be elastic beyond the limit of some of its elements.
However, I think its safe to assume that some of the spoke is still in its elastic phase at this point (as you point out bm) but not all. hence why wheels just don't fall apart. The amount of stretch of the spoke begins to be a falling rate therefore.
I'm not actually saying it works as a useful thing (running loose spokes), you might have noticed that I caveated the possible reasons with maybes and question marks. I kind of thought it might be useful to consider why a downhiller might want looser spokes, although I could have just written 'You're wrong' and got the same level of angst in the responses I think.
What I am saying is that its not as simple as spokes under different tensions yield the same results, thats not going to be true as the spokes will be behaving differently under different tensions. What Im not saying too is that stiffer spokes make stiffer wheels. Oddly all the testing I have seen done on this subject (which normally conclude with the statement 'tension doesn't effect stiffness' actually show a marginal, but consistent gain in stiffness as tension is relieved... I have no opinion on this but it seems odd no-ones looking at it. I guess the change is too small to care about.)
Hob nob I don't disagree with you for the riding you do a less stiff rim might actually allow your tyres at the pressure you use to maintain a better contact patch. Do you buzz the stays with the stiffer rim or the more flexible one. How deep is your flexible rim and how deep is your carbin rim. I have tried to put an explanation of what you feel in my earlier post.
For me however I have a set of velocity blunt sl rims 28h laced to novatec hubs with sapim grace spokes. These wheels flex, it don't like them much my rather stiff bike feels like it wollows with them on. Put in a set of stiff wheels and my ability to ride at a higher pace improves probably because I find the bike more control able at speed. My riding is probably very different to yours it just the tracks of East anglia for me.
The trouble with having an open mind is that people will insist on coming along and trying to put things in it. Lateral stiffness is just as unaffected by spoke tension as radial stiffness - because the spoke doesn't care which direction the wheel is being loaded and still obeys Hooke's Law even when the bike is being ridden hard and there is a lot going on.
Have you got a reference to show that a bicycle spoke at normal operating tension obeys Hokke's law? I have no idea whether they are tensioned beyond their elastic limit or not, but the laws of physics can cope even if they are 🙂
A real wheel isn't simple. The interfaces between spoke and rim at one end and spoke and hub at the other end add a lot of complexity that the oversimplified physics model isn't considering.
[i]It does seem odd to me that for MTB people use their carbon rims for everyday use.[/i]
We use all our good gear every ride :-), no point having it otherwise IMO.
have you got a reference to show that a bicycle spoke at normal operating tension obeys Hokke's law? I have no idea whether they are tensioned beyond their elastic limit or not, but the laws of physics can cope even if they are
Check out these two spokes' breaking strength graphs:
the first - A plain gauge spoke is pretty conventional hookes law stuff. Its a fairly uniform spoke and so its behaviour is uniform. The elastic phase is the straight bit at the start, the deformation phase the curved second part. spoke tensions are viable between 50-200 as a rule, but normally in the range of 80-150 so you will see that unless you run a pretty slack wheel (50) you've exceeded the elastic limit of the thicker spoke (P13) with pretty much any hit.
[img] 
[/img]
the second - a bladed, triple butted spoke. This has a very different curve. You will notice its not got a distinct kink, this is because the individual parts that make up the spoke are behaving differently and the combined effect is much smoother. At higher tensions some of the parts of the spoke are still elastic, some not. This spoke will be far better able to absorb impacts without permanent alteration to the spoke meaning it will stay truer longer, although its not necessarily 'stronger'.
[img] 
[/img]
In relation to this whole discussion on Hookes law, what this means is that if you want a stiffer wheel (discounting for a moment the lateral/radial and torsional stiffnesses and going with lateral as thats what most people think of), as we know you need thicker spokes (no debate there), plain gauge offering the stiffest build as its the most consistently thick. However, in order to compensate for this a lower tension will allow the spoke to remain inside its elastic limits more easily, which clearly is a benefit in terms of the longevity of any wheel.
The problem with any such debate is the basis 'Pro downhillers use looser spokes to get a better wheel' is the sort of quote that appears on Pinkbike or similar that doesn't take into account any of the other variables in play. It may well be true, but they probably didn't just loosen off the same spokes they might ordinarily use. That technique will be in combination with other factors not mentioned (if indeed at all).
Thanks. That makes sense.
Some of the boffins on here need to have a word with my mate, a shiny new capra with mavic wheels, every ride & I mean every ride it snaps front spokes & they go with a right bang, two in one day recently on the Ard Rock.
Yorky, if his wheels are under warranty send them back rather than dicking with them. They shouldn't be doing that, they're mis-built and may fail dangerously.
I was a bit sad to see the end of the rim but ive had it for 16 months, and its done 2 ews, a year of ukges, dhh races, bikeparks, uplifts and stuff and I can now add it to my list of broken wheels from mavic, shimano, alex etc
And therein lies the great carbon dilemma. I have a warehouse littered with dead wheels of all types. Alu ones (fairly chunky at that) that have lasted a single UKGE, carbons that lasted a year or more and still going strong, and everything in between. The question isn't whether your carbon wheel would have survived better or worse than an alu rimmed one, more whether you're happy that you paid probably 3 x the price than an alu one for the time you got out of it.
I see a few carbon rims advertised as being indestructible and laugh my ass off. There's no such thing as an indestructible rim, its a lot of emperors new clothes going on! Carbon rims have their good and bad points. The issue for most people is the cost of getting the good points is higher than they are willing to pay given the bad points still exist (at any price point). It all comes down to how much you want those good things, and how much you're willing to trade to get them.
theglover - MemberFor TT and Tri you have race wheels and training wheels and your race wheels only come out for races and cost about 4 times the price of your training wheels.
but maybe i am missing something?
A big part is, my carbon wheels cost me way less than many people spend on alu ones- they're not that much more expensive than frinstance a Pro 2 on Enduros hope hoop, despite also having far better hubs, and way cheaper than a Crossmax. That's a wee bit of an unfair comparison since I build them on used hubs but that's how it shakes out.
I've actually gone the other way round and fitted cheaper, more disposable wheels for racing- there's been a couple of times when I've ridden out a stage on a flat, I don't mind doing that on my hammered old traversees but I wouldn't want to do them on my nice wheels 😆
Stan's new carbon jobbies seem pretty tough going by the footage at 0:55 in this video. Would like to see the same for normal rims and LB jobbies. Makes me think thread lock is a good idea when building.
Check out these two spokes' breaking strength graphs:
Hmmm, except they show the deflection rate [i]increasing[/i] as you apply additional force (as you'd expect from stainless steel or aluminium).
Which is the opposite of what they were posted to illustrate.
I suspect increasing the tension will give a stiffer wheel (beyond a given load anyway) because spokes start to go into compression, therefore don't contribute to the stiffness of the wheel. This is why up to a point increasing the tension is good.
Unfortunately, beyond that point, you get into the shallower slope part of the stainless steel (or in some cases alu) stress/strain curve, and the strain in each spoke increases more for a given load. This will also cause fatigue as fatigue is controlled by the change in strain.
Other things may come into it, like the resonant frequency of a spoke changing as you change the tension (this may make for a more harsh feel under some spoke tensions) - and I'm sure feel is massively important especially to people at the top level.
Anyway, OP, are you sure your spokes aren't over-tensioned if they are causing cracking around the nipples?
You're correct philjunior, those numbers I quoted earlier I pulled off the wrong graph. They would be more like the other way round in fact. In terms of whether or not a spoke is more likely to be elastic at a lower tension or not though that's not particularly important. I think the first of the two graphs pretty much highlights the point that rocketdog asked which is whether spoke tension alone would be enough to mean a spoke was deforming rather than elastic at a normal tension.
Its interesting to look at how the different spokes behave on the pillar site if you care about that sort of thing... double butted are fairly 'normal' but with a much bigger elastic section than pg, triple butted and quad butted you then start to see some weirder results where you get the opposite effect and the spokes reduce in elongation with the increase in force for a while. Anyone who cares to explain that I would be interested to hear your thoughts. [skulks off into a dark corner anyway]
Can I just congratulate those of you who've spent your bank holiday monday arguing on the internet about physics.
Well done.
I'm at work 😉
I'm at work
Same here.
🙁
Me too.
OK so heres one for the physics bods to ponder....
Jobst Brandt, in the Bicycle wheel, claims that wheels stand on their spokes, as opposed to hang. Given the stans video earlier that made me think of something I never quite got... how that works. Given a spoke is essentially free floating in its spoke hole, how does the spoke support any weight? Whacking a rim from above is surely the same as applying a force through the rim at the base in a general kind of way? Force is force no matter what direction its applied. Add to this the fact that I once read a (very detailed and techy) study that looked at spoke patterns and stiffness. In that study, it showed that under normal load, the spoke tension is increased relatively (in the grand scheme of things) evenly across all the spokes other than the couple at the bottom, which experienced a massive loss in tension. How would this be the case if the bottom spokes are under compression (hence the loss of tension)? That compression needs to be transmitted to the hub... that force would be applied most directly into the spokes vertically above the hub I guess? If they are also experiencing some compressive forces from the push from below, surely they would also show a loss of tension not an increase? Hmm. Thinking about it though I guess the force goes into the axle not the spokes above... that still doesnt answer the question as to how a free floating spoke would carry any load at all. And more over why is everything else under increased tension if the axle is carrying the load transmitted by the 'pillar' spokes?
Surely it makes more sense that whats actually going on here is that the spokes now under increased tension (all the other spokes other than the ones at the bottom) are in essence resisting the desire of the rim to become oval under load, which is what prevents the wheel from collapsing?
Am I missing something really obvious?
EDIT: To highlight my confusion imagine you removed a quarter section of the spokes of a wheel. Now sit on your bike with the 25% at the bottom, then with the 25% at the top... which way round does the wheel collapse?
More nerd reading [url= http://sheldonbrown.com/rinard/wheel/index.htm ]here[/url]
... so I thought that sounds like a fun experiment. So I took an old wheel and cut 7 spokes out (in a row). No issues with it missing spokes down, missing spokes up - notable vertical flex in the wheel! I chopped a couple more out just for the craic. missing spokes down the wheel felt ok, missing spokes up and the wheel was all over the shop (as you might expect) but I could feel the spokes in the base bouncing in their holes. They certainly weren't supporting any weight.
I'll come back to the issue about the spoke stiffness under varying tension, as I need to do a bit more research - clearly I was wrong about the linearity, though even with those curves it's not far off and as pointed out actually working in the opposite way to suggested - stiffness decreases with increasing tension (which might explain the very small variation seen in Rinard's testing). Something seems wrong though, because given a Yield strength of 520MPa for stainless steel, a PG spoke would yield at 166kgF, rather higher than shown. Some other issues I'll come back to...
Though I thought I'd try and help with the Brandt standing on spokes thing. He's not suggesting there that the spokes have an absolute compressive force in them - as you've recognised they can't do that. However they can provide a relative compressive force through the principle of superposition of forces within a pre-stressed structure by a decrease in the tension force.
Essentially the thought process is that with your static pre-stressed structure you consider that the force on each element is zero. Now when the tension on the bottom spokes decreases under loading, within that model that is a compression force. Because the effect is exactly the same as if you had thick spokes capable of transmitting a compression force with zero pre-tension - as you've recognised the only significant change in tension is for the bottom spokes and the effect on the hub of them decreasing in tension within that pre-stressed structure is exactly the same as if they were solid spokes with zero pre-tension transmitting a compressive force.
So no, he's not suggesting they transmit a real compressive force, but superposition of forces is an important concept in structural engineering (lots of pre-stressed structures around - pretty much any bridge built of concrete is). What he's pointing out here is that the popular idea that when you load the axle the load is taken by an increase in tension in the top spokes is incorrect.
Unfortunately your experiments with cutting spokes don't prove anything useful, because as soon as you cut spokes you no longer have the same pre-stressed structure which this concept relies on. Though I think you've already understood the most important point without realising it.
OK, I get it - so the important factor here is the change in forces not the 'direction'. Still confuses me more though having tested the two ways up. Without the bottom spokes the wheel is pretty much unchanged, other way up and its useless... which leads me to believe the model is oversimplified as the wheel is capable of surviving without the spokes with Brandt claims are the ones doing all the work, and I don't believe (for no good reason than I don't) that there presence in the wheel suddenly makes the other spokes fairly irrelevant, which is what he would lead you to believe was the case when you read the book Which in my head is where I was going.
Thinking more about the concept that extra tension != stiffer wheels, it occurs to me that the testing is fatally flawed surely? if in real life the wheel at the point of lateral deflection (assuming that generally occurs at the contact point) is also experiencing a massive loss of tension as would be implied by the graph I read about, then surely that would effect the stiffness of the wheel? More specifically, if the spokes at the point of deflection are affforded little or no tension due to the compressive load already on them (i.e. they might as well not be there) then at that point does the rim not become the most important factor, followed by the surrounding spokes? And would therefore greater tension within a wheel not lead to a 'stiffer wheel' even if the deflection test in lab conditions showed otherwise. Is it possible that all the lab tests are basically bunk because they ignore this important variable?
Just thinking out loud as to why anecdotal evidence might conflict with the lab evidence.... I question everything!
The greater the tension (within reason) the more the supplementary spokes will be involved in supporting the system under dynamic loading.
Spoke stiffness is only dependent on its length, shape, cross sectional area and young modulus. Tension plays no part but in a wheel tension plays a part of sorts. If the deflection at the rim is large enough and typically groups of the nds spokes go slack or for a front wheel the right side then wheel stiffness will drop.
So a wheel needs to be stiff and spoke tension high enough laterally and radially to avoid this under normal conditions. Notice how a separate stiffness and spoke tension they are not the same but both play there part in preventing slack spokes. Slack spokes fatigue quickly and fail and it also how a wheel goes out of true. If the wheel is built properly and tension is high enough and the wheel is stiff enough then thread lock is not needed. Thread lock in my opinion is there to mask an underlying problem of a bad build or inappropriate components.
Creating a stiff wheel is also why I prefer hubs that give the best bracing possible. Every little helps. A lot of this is over thinking what makes a good wheel. Speaking as a wheel builder it is pretty simple. A good wheel is one you enjoy and one that is reliable for the use intended. For it to be reliable the spokes must not go slack or at least it should happen infrequently. This is one reason why 29er rims are wider than smaller rim sizes it not just to change the tyre profile it to increase stiffness of the wheel so it survives use.
A bank holiday taking wheels is time never wasted however the only way to answer all the questions you have is fine to element analysis but I am not sure what benefit the answers will bring.
[quote=benpinnick ]the wheel is capable of surviving without the spokes with Brandt claims are the ones doing all the work, and I don't believe (for no good reason than I don't) that there presence in the wheel suddenly makes the other spokes fairly irrelevant, which is what he would lead you to believe was the case when you read the book
That's certainly not what he's suggesting. They're only doing the work (by changing in tension) because it is a pre-stressed structure - the other spokes are very important to that pre-stressed structure. Hence as I mentioned above if you cut any of the spokes out it is no longer the same pre-stressed structure so any results are irrelevant.
Though I've just checked what Jobst says in his book (you won't be surprised I have a copy!) and he comes out with the analogy with a wooden wheel which I thought about mentioning, and TBH does a much better job of explaining the concept than I could - I'd suggest just re-reading that section a few times!
Regarding loss of tension at the bottom of the wheel, even if all the load is taken by 2 spokes (checking Jobst's FEA analysis, he has 3 spokes taking most of the load because the load is at a spoke, but the outer 2 only take half the load of the middle one) , then assuming pre-tension of 125kgF that's only a loss of ~1/3 of the tension. So the spokes still shouldn't completely detension under a side-load - if they do you would get a huge decrease in stiffness, but that would also be a non-linear change and something you'd know about. Also a really bad thing in terms of wheel strength if that happens, which is one reason you don't want low spoke tension.
[quote=chiefgrooveguru ]The greater the tension (within reason) the more the supplementary spokes will be involved in supporting the system under dynamic loading.
<sigh> that is also a load of rubbish for all the same reasons that spoke tension doesn't have a significant effect on stiffness. Unless of course spokes are going completely slack, but I think everybody agrees that shouldn't be happening.