Now there doesn’t seem a great deal of difference in weight with the latest aluminium rims, I am wondering if it is the slightly lower weight or stiffness that make carbon wheels better/easier to pick up and keep speed?
Are there any interesting non roadie based articles to read on this?

What leads you to the conclusion that carbon wheels are “better” ?

They sound more awesome for starters.

Wider and stiffer, you can get 35mm wide rims at a weight that works on an XC bike, in aluminium they’d be 600g, in carbon 400g.

Rims have been getting wider for years but there was a limit to how wide they could go before they got flimsy (mavic rims used to be bombproof, then DT were wider but more fragile, then Stans were wider but no worse but no lighter than DT). Carbon’s just the next logical step.

So you can have a 35mm wide XC rim, or a 400g DH rim depending on your perspective.

I wish I had gone for a narrower rim for my 29er as it’s more of an XC bike but I went for 30mm inner width carbon rims and now my 2.25″ tyres almost rub the stays (Solaris) and I didn’t take advantage of the lower weight that I could have done.

Aluminium rims are catching up but I can’t see any way an aluminium rim can compete on weight once you get over 25mm internal width.

If constructed well and for hard use a carbon rim should also be a lot tougher but in a very bad impact you may find they break rather than yield.

For me, weight and durability. I know not everyone agrees but on my 26er I had a sub-1600g wheelset that proved tougher than the 1900g wheelset (Stans Flow Ex) it replaced. I had a look and after some big hits, a load of enduro races and uplifts, and a decent number of miles, they have some scratches and a single little chip in one rim. I tried to use a 1600g metal wheelset in the same bike for the same riding and it was a total failure.

(I broke an original Lightbicycle rim, the really lightweight one… It weighed as much as a Stans Olympic but took as much punishment as a downhill rim before it died. I can’t ask for more)

Personally unfussed about wheel stiffness, I can feel it but I don’t really care. But I love the feeling of a lighter wheel. (I wouldn’t say weight alone adds up to much of a measurable performance difference; but it does add up to an attitude difference, the bike feels keener and more responsive. And that makes me ride faster and more on it.

aracer beat me to it.

The funny thing is I like carbon bike bits and own lots of them – I’m just realistic about the real benefits 😀

The funny thing is I like carbon bike bits and own lots of them – I’m just realistic about the real benefits

I am entirely unconvinced as to the real world benefits of any of my carbon components compared to their decent quality alu brethren. And all the metal stuff cost a fraction. And I’m a cheapskate. I’d not pay £700 for a wheel set, let alone a rim.

I like my 27mm INt width LBicycle carbon rims, not sure they are more than 50 grams lighter than alloy ones could be but they feel pretty damn stiff compared to the MAvic Crossmax SX they replaced. No complaints here for the money, but they’re certainly not earth shatteringly different

Not convinced by them. Didn’t like the stiffness. Looked at them again recently for weight savings, figured I’d save 150g tops per rim. In reality that’s naff all in comparison to my 1kg tyres and 85kg frame.

You don’t save that much weight really and they feel meh if I’m honest.

I’m 100% convinced by carbon wheels.

For something a small fraction lighter than my previous alu rimed wheelsets I’ve got something stronger, wider and stiffer.

The last point might not be high on many people’s lists, but the other points are certainly going to be of interest!

My LB wheels may have cost twice as much as my previous wheelsets… but they’re already on track to lasting longer. I’d have defiantly had the adjustable spanner out by now with my old rims to take some dents out after the life they’ve had so far!

85kg frame

Were on On One selling them off cheap? 😉

My logic follows north winds thought entirely.

mtbfix – Member

I am entirely unconvinced as to the real world benefits of any of my carbon components compared to their decent quality alu brethren. And all the metal stuff cost a fraction. And I’m a cheapskate. I’d not pay £700 for a wheel set, let alone a rim.

neither did I… I probably put about £400, maybe £450 into my 29er Lightbicycle carbons. Which is pretty much exactly what I paid for my alu rimmed fatbike wheels now I think of it. Still expensive, obviously, but not so far off what you’d spend for an equivalent quality alu wheelset, and they have top quality hubs etc too.

For something a small fraction lighter than my previous alu rimed wheelsets I’ve got something stronger, wider and stiffer.

The last point might not be high on many people’s lists, but the other points are certainly going to be of interest!

Stronger – nope. My wall of shame prove otherwise. I’m not the only one in my regular riding group with this experience either. Wider yes. but the reality of difference between a my 25mm aluminium rims & my old 30mm carbon rims is bugger all. They don’t magically make you faster, run lower pressure, stop tyres rolling off the rims etc. In fact, I would struggle to tell any noticeable difference. Stiffer – yes. Not a good thing over a decent aluminium wheelset IMO.

I think the main ‘they must be better because’ – people can look at their bike & say LOOK, TEH CARBONZ!

Best way to think about carbon is it’s different and flexible (usage) in what ou do with it. You can build in the charactaristics you want. Shapes that are not possible in metal can be in CF.

Carbon still conforms to the laws of physics so you’re still trading weight for strength/stiffness. A light carbon wheel won’t be as strong as a heavy carbon wheel. You’re saving a couple of hundred grams over metal wheels maybe – that will either be important to you or not and depends on how much 200g is worth to you bearing in mind the majority of the weight in a wheel is the tyres, hubs, cassette, spokes etc. Lighter wheels accelerate quicker, heavier wheels act like a flywheel and maintain speed better – what do you prefer? Some people like stiff wheels and is their holy grail, and others like a bit of compliance. Again, what’s your preference.

I don’t reckon I could tell the difference in 200g of weight in a wheelset. Maybe if I rode two bikes back to back I might detect a difference. I’m sure i’m carrying over 200g more mud and dust at the end of a ride than at the beginning and know I can’t tell any difference in the bike at the end of the ride compared to the beginning.

But they do look bling and for that probably worth it alone. Aesthetics is a perfectly good reason to choose kit as anything in the real world just like with every other product we buy.

My int30 LB rim wheels feel easier to accelerate than my int25
LB noticeably stiffer, which takes a bit of getting used to but I prefer it

Would l love to get some for my 29er as it feels so much slower to get moving

That snake oil is MTB Viagra for me

Weight for the corresponding strength. While you can get light ali rims they may not be that strong. A tough carbon AM use rim is likely a lot lighter than the ali equivalent for the same strength.

Acceleration? I guess could be a factor. My current carbon everything bike certainly does shift. Quite surprised really as went from 26 to 650b and was expecting to be more difficult to accelerate, but this thing just goes. Perhaps it’s just general low weight of the bike. On the other hand it could be fitness as been riding a lot recently.

Wheel stiffness in terms of how much it moves around under cornering and acceleration is mostly determined by number of spokes, spoke tension and bracing angles rather than stiffness of the rim.

But carbon, or rather right type of carbon appropriately manufactured, allows a rim of sufficient stiffness/strength to achieve those spoke tensions to be made at a lighter weight than a rim made from aluminium. There are added benefits beyond the material properties, e.g. relatively easy to vary thickness of carbon to reinforce spoke holes, to do that with aluminium requires machining the aluminium away between the spoke holes which is expensive.

The thing that scares me about carbon is the failure mode, tends to go bang rather than bend like aluminium.

Stiffness, every time.

My son and my cycling buddy ride identical Tarmacs with the same groupsets and the same Veloflex Corsa tyres. The only difference is the wheels; my son has entry-level Ksyriums and my buddy SLS Ksyriums. The difference in the feel and ride of the two bikes is remarkable; the bike with the much stiffer SLS wheels handles better and just feels more “controlled”. There doesn’t seem to be any difference in the ride quality, which is more down to frame and tyres.

To me, it seems like if it’s even a bit lighter that has to be a good thing. Will that one component alone make a huge difference to performance? Probably not. If you make that %age weight saving across the bike will it? Again, not really, but it’ll make a bit of difference and it’ll feel nicer.

(I don’t have any carbon rims, mostly due to price)

determined by number of spokes, spoke tension and bracing angles rather than stiffness of the rim.

[video]https://www.youtube.com/watch?v=_n5E7feJHw0[/video]

If spokes are within a normal range, tension doesn’t make a blind bit of difference. Spoke tension isn’t why carbon rims are stiffer. They are laterally and vertically stiffer because of the material and the fact the rims are usually wider and deeper for a given weight. Where they fall down, is when the spokes are too few in number or too lightweight – which causes the wheel to flex in a twisting/torsional manner.

Wheel stiffness in terms of how much it moves around under cornering and acceleration is mostly determined by number of spokes, spoke tension and bracing angles rather than stiffness of the rim.

No it’s not.

The bit you’re worried about is the bit of the wheel nearest the ground. Most of the work is being done by the spokes in the top half of the wheel. How stiff the rims is will determine how much movement there is between the relatively fixed top half and the free to move bottom half.

What work is being done by the spokes in the bottom half is only possible for as long as the rim is pulling out on them, overcome that (i.e. if the rim isn’t stiff enough to resist whatever vertical force you apply) and there’s nothing.

Which is why my road bike, my XC bike and my ‘enduro’ bikes have all had 32spoke wheels on more or less the same hubs, I suspect the mountainbikes actually have narrower flange spacing to allow for the disk mounts too.

The thing that scares me about carbon is the failure mode, tends to go bang rather than bend like aluminium.

IIRC Northwind rode a completely split carbon rim for a few hours/days afterwards, apart for no longer being tubeless it was fine.

Whether it dents or cracks (or either can fail completely catastrophically in a crash) isn’t really an issue, either way your tyre will probably go flat and your rides over unless it’s bodgeable.

er, no. Most of the work is being done by the 2-4 spokes at the bottom of the wheel in the flex zone. There is very little tension change in the spokes at the top of the wheel under loading. That’s because a wheel is a pre-stressed structure which enables the spokes to effectively support a superposed compression load (all provided none of the spokes go slack, but in a properly built wheel in normal use they won’t). Yes a stiffer rim makes a difference to wheel stiffness, but not really on transfer of the load to the spokes – hence the spoke thickness, number of spokes and bracing angle does have a significant effect on the stiffness.

What work is being done by the spokes in the bottom half is only possible for as long as the rim is pulling out on them, overcome that (i.e. if the rim isn’t stiff enough to resist whatever vertical force you apply) and there’s nothing.

A rim on its own certainly isn’t stiff enough to resist the vertical forces applied – it only does so because it is built into a prestressed structure.

A rim on its own certainly isn’t stiff enough to resist the vertical forces applied – it only does so because it is built into a prestressed structure.

A carbon rims is, spokes almost just hold it in place around the hub.

For me, staying true is a big advantage of carbon.

Under the load of a rider? 😯

A carbon rim might be stiffer than an alu one, but wheels built with them still rely on the strength of the tensioned structure – a carbon rim is nowhere near stiff and strong enough on its own to support the load.

Feel free to do an experiment to check, but it would be an expensive experiment.

Money init?! Why is a Santa Cruz better than a YT, why is a Audi better than a Skoda, why is Superdry better than George at ASDA?

It’s because the owner can sit atop them and smile knowing that’s he’s better than his Alu rim riding mate because he spent more, therefore he has more, therefore he’s worth more therefore he’s better.

It’s a cornerstone of a consumer society – it’s better because it cost more, therefore it must be better. See the hatred and anger people show when someone sticks ENVY looking stickers on a ‘cheap’ carbon rim – no one likes a cheater!

thisisnotaspoon – Member

IIRC Northwind rode a completely split carbon rim for a few hours/days afterwards, apart for no longer being tubeless it was fine.

3 or 4 days around south wales on the hardtail, aye, including riding down BPW on the flat first… I pretty much forgot about it. It’s hard to really compare but it was exactly the same sort of hamfisted blow and similiar impact that killed my flow ex, and that one definitely wasn’t doing any more riding…

Hah. I just started using flickr again, it turns out the last 2 pics I uploaded were that cracked wheel, and the 2 pics I just uploaded are ChrisL’s broken Ibis Mojo. Flickr: Destroyer of Carbon. I should get some pics of my ****ed Next cranks.

[url=https://flic.kr/p/wEHiMp]IMG_3970[/url] by Northwindlowlander, on Flickr

Take a unbuilt alloy rim and twist it in your hands – it’s quite easy to distort whereas a carbon rim is far, far stiffer. I’ve got carbon road and MTB rims – there’s not really a comparison between the two as they’re really designed to do two different jobs. My carbon MTB rims allow me to run a wider, stiffer rim for a significant weight reduction- an equivalent alloy rim would be 30-40% heavier. The wider the rim, the greater the benefits too, plus the benefits of wider tyres – but that’s another debate.

Carbon can just be fixed with a bit of epoxy and/or gaffa tape 😀

(I don’t really claim this, but sounds like it could)

Interesting opinions on wheel stiffness. I notice many top Enduro racers plump for alloy over carbon and interestingly didn’t Jared Graves get his mechanic to wind the spoke tension off as the wheels feel too stiff or harsh otherwise?

Perhaps too stiff. But not really tested back to back. Wheels do need a bit of flex.

But mostly for me its about when you get a puncture – with Carbon you have to stop and fix it there and then. And not ride to the bottom because the rims cost £1k! Not much good in a race run which is why I suspect many racers dont use them.

my roval wheels are pretty wide and stiff enough without much weigh penalty. There are plenty of alloy options.

If spokes are within a normal range, tension doesn’t make a blind bit of difference.

and if spoke tension is below the normal range then the wheel will be a floppy mess, hence spoke tension is a factor in determining wheel stiffness, even if you consider it to be just a step function.

The bit you’re worried about is the bit of the wheel nearest the ground. Most of the work is being done by the spokes in the top half of the wheel. How stiff the rims is will determine how much movement there is between the relatively fixed top half and the free to move bottom half.

What work is being done by the spokes in the bottom half is only possible for as long as the rim is pulling out on them, overcome that (i.e. if the rim isn’t stiff enough to resist whatever vertical force you apply) and there’s nothing.

Wha the… If for example you apply load to the bottom of the wheel, that subtracts tension from the spokes at the bottom of the wheel, this adds tension to all the other spokes on the wheel. The forces are distributed around the whole wheel, because all the spokes are connected via the hub and rim.

Which is why my road bike, my XC bike and my ‘enduro’ bikes have all had 32spoke wheels on more or less the same hubs,

Because the formula that makes a stiff wheel, makes a stiff wheel.

I suspect the mountainbikes actually have narrower flange spacing to allow for the disk mounts too.

Front wheel most likely, rear wheel probably not.

Whether it dents or cracks (or either can fail completely catastrophically in a crash) isn’t really an issue,

I’m just a bit paranoid about things exploding on me. I have flat spotted aluminium rims when landing large drops and I wonder if a carbon rim would shatter in that kind of situation rather than deforming like aluminium. I suspect carbon materials and manufacturing is improving all the time and stuff being made now is failing less/safer than older stuff. Surely aluminium rims have not shattered since the days of yore, they bend (absorbing energy in the process).

either way your tyre will probably go flat and your rides over unless it’s bodgeable.

This is why I carry a spare tube 🙂

Carbon can just be fixed with a bit of epoxy and/or gaffa tape

Erm… Well I would have thrown some epoxy on that cracked rim that northwind pictured before riding on it for a few more days. 😀

It will, but then any wheel built with spoke tension that low is a badly built wheel which you will notice instantly. For any properly built wheel spoke tension has no effect on stiffness (well actually counter intuitively, the data I’ve seen suggests that higher tension makes the wheel very slightly less stiff). Yes it is a step function – and the impression given by suggesting that spoke tension affects stiffness is the one that many people believe, that even in a well built wheel increasing spoke tension increases stiffness. Hence it is at best a misleading statement.

Though I’m willing to give you a bit of slack, as it’s clear you understand how wheels work better than most on here 😉

I suspect the mountainbikes actually have narrower flange spacing to allow for the disk mounts too.

Front wheel most likely, rear wheel probably not.[/quote]

Though to be fair it’s front wheels where this is more of an issue, as they do get lateral loading in normal use – if your rear wheel is getting significant lateral loading that implies something is going badly wrong already.