Carbon rims; harsh, stiff & unreliable…

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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..

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 – Member

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.

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.

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.

Spoke tension makes ZERO difference to wheel stiffness

actually thats not true… sort of. Spoke tension does effect the ability of a wheel to absorb impacts, although its not necessarily felt 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.

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 – Member

Rumour 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!” 😆

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…

“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!”
[/quote]

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.

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…”