I totally get that you can create magical shapes in carbon that are harder to do in allu . But why would you choose a carbon frame full suspension over an alloy one?

The weight savings dont seem to be that much for a lot of extra cash

Direct power transfer mainly and I found it to be confidence boosting.
The handling characteristics seem to be quicker and feel generally nicer.

Apart from the rear qr end I had on my xc frame.

I now don’t have a carbon full suss and had it briefly although I would recommend trying one.

Stiffer frame means the suspension follows the designed path, not flexing all over the shop, have a look at the Liteville in the classifieds, seen a few of them for sale with dents. Far more likely to end up with dents than a failed frame it seems.

I’m not sure if your saying dents are a good thing?

What frame are you looking at getting andybrad?

I think it comes down to stiffness and weight. ie for a given stiffness a carbon frame can weigh less than aluminium, but as you mentioned you do have to pay extra for it.

I had a carbon full suss(ibis mojo HD), now have an aluminium full suss (orbea Rallon), I dont think the price premium is worth it for the weight saving.

Not always lighter than there Ali cousins but supposedly ‘tougher for the same frame weight’.. The classic example (few years old now) is the Scott Ransom, were there was Ali frame failures reported (bb area)but no or very few carbon ones (annotatal internet reports, so how true..)

Bling innit.

More seriously, as mentioned above, can be made stiffer where it matters, without much extra weight, meaning the suspension acts in an up and down axis, rather than side to side through flex with less weight penalty than alu. Still not convinced? I refer you back to my first point.

Lighter (and you can convince yourself of direct power transfer,confidence boosting (in the car park)and feel generally nicer superior).

Depends on what the manufacturer offers , doesn’t it ? And what you want in a bike. I like the ride of carbon FS more than anything else I’ve owned.

That said it’s difficult to compare unless you can get the same bike like an ally and carbon tallboy together. We did, and no question the ally was a flexy bugger around the crank and a fair bit heavier. But the price difference is plenty.

The flex thing is interesting. We seem to have convinced ourselves (with some help from ‘the industry’) that flex is a bad thing.

In MotoGP around the early noughties they pursued chassis stiffness above all else and thought the top notch Ohlins, Showa etc suspension would take care of the rest….what they found in reality was that when a bike is leaned over the sliders for the shock and forks don’t work nearly as well as when in the vertical plane….

….as advanced (and eye wateringly expensive) as MotoGP suspension was it couldn’t change the fact that a fork doesn’t work as well at 45 degrees as it does when stood upright, they found ‘chatter’ from the surface was travelling up the forks and into the ultra stiff chassis and unsettling the riders who found it hard to gauge grip levels etc.

They got round it by engineering flex into the chassis and it’s now accepted that a certain amount of chassis flex is desirable as they still haven’t found a way to eliminate ‘stiction’ from forks when asked to work at an angle other than vertical….now I know the speeds are somewhat slower in MTB than MotoGP but it does make me smile that MTBers seem to be going through the same process of wanting ever stiffer chassis….and then resorting to plus sized/large volume tyres to get the grip back and improve comfort levels….which just wouldn’t be necessary with a chassis that had a proper engineered level of flex built into it.

Always amusing when someone talks about putting Pikes (or similar) on the front of their hardtail to stiffen things up!….really?!….go with slimmer stanchions like on a Revelation and enjoy a far nicer ride.
Anyway rant over, give me a ‘flexy’ rear end of an Orange-5 over something so stiff it can’t track properly and skips around all over the place.

Deviant – not sure I agree that the bike industry is pursuing stiffness over all things. Road bikes have been going on about being ‘verticaly compliant and laterally stiff’ for years. My understanding (admittedly mostly marketing-led) is that the directional nature of carbon allows you to get it to flex where it needs to and be stiff elsewhere.

MotoGP as a relevant comparison?

Really?

What stiff or fs frames are getting plus tyres on?

While I agree with the MotoGP thoughts, for a F/S MTB you need it stiff so you can then make the suspension work properly.

I’ve a carbon F/S and it’s light and stiff, whereas my Ti HT is light 🙂

Yup. Go stiff with carbon and then get a lefty on there to overcome the failings of conventional forks when side loaded.

Not just moto gp, that applied across the whole motorbike industry- there was a long time when basically all motorbikes were too flexy so they just added more stiffness at every opportunity, without really thinking about it much. Eventually honda made the rc51, discovered it was too stiff, so there was a big change of direction. Now, it’s just not really a thing that’s talked about much, they still change designs but it’s stopped being part of the marketing. Not like mountainbiking where you can still sell things with “3% extra stiffs”

Stevious, the carbon thing and engineered flex is a genuine property of the material and if done well can be great….my concern is that Ducati spent several seasons and millions of pounds and still couldn’t get their carbon chassis to work properly or flex in a way the riders understood, in the end they reverted to Alu.

I’m skeptical that a bike manufacturer has cracked it where MotoGP failed….it just seems to be bike manufacturers claiming additional stiffness every year and no comments about flex like its a taboo subject or something.

Frame stiffness in MTBs… I can actually speak first hand, rather than some theoretical argument from Moto GP.

I’ve tested quite a few different rear ends on the same bike, going from pretty flexy to stiffest in class, and I haven’t found a disadvantage to the very stiffest rear end at all, other than a tiny bit more weight. Suspension works better and I can make it do exactly what I want easier, be that drift or grip. It also gives you more of a sense of what the rear tyre is doing.

I think everyone here can speak first hand, unless there’s anyone that’s only ridden one bike? 😕 The reference to other industries just broadens the discussion

I agree with deviant the assumption that your shock will do all the work has to be fallacious, you’re never going to get the sensitivity out of a bicycle shock that a degree of flex will lend to a frame, I”m not talking wibbly wobbly bendy just a bit of tuned flex to help take care of general trail buzz and angled lumps…

Composites lend themselves to engineering that balance of strength and elastic compliance, along with weight savings all better than any other material IMO…
The only real downside is price…

I’m just looking at the spectral. The carbon one is more expensive and I’m struggling to see a benefit. Same with the stumpjumper

Yes I get the bling but unless its going to last a few years longer I don’t get the minimal weight savings

I see carbon and latter the next wonder mix/blend material marketed to cash (or credit)-flush men as the next ‘thing to be seen with’ on the trails.

Alu can be used for years. As can carbon but a alu frame can be blasted, raw’d, refreshed etc whereas carbon?

For the weight saving is carbon really worth it? My Commencal has a slight rear flex- I like that. Its the front that should be stiff. True?

Plus 650b- Wow its faster in a straight line but we arent roadies

Flex isn’t good if you can make your bottom bracket area move.

I recently bought a Trek Fuel 9.8 27.5 bike.

The deciding factor was the carbon front triangle with an alloy swing arm design.

The combination of carbon triangle and the more highly stressed alloy rear triangle won me over.

I have seen a few reports of the swing arm (carbon) failing. To be frank though, all mountain bike frames have been reported as failing regardless of the material.

Steel is probably the most resilient, and can be repaired etc.

I like all the materials and tend to be guided by the bike design and intent really.

I have the carbon Fuel, alloy Stache 9 and a steel Jones.
Regards

Denis

Rone that’ll be the old 456 ti..

hora – Member

Alu can be used for years. As can carbon but a alu frame can be blasted, raw’d, refreshed etc whereas carbon?

Carbon can be painted, of course

I remember an interview www Max Commencal (Dirt I think), and they were discussing the the Sunn golden era and the steel a Radical race bikes. He said they experimented with super stiff bikes and found that they didn’t ride as well and were slower. They actually built flex into their bikes (and Olivier Bossard’s suspension) as stiff bikes were either slower or they broke.

The main thing was to have the bike flex in the right place and direction (rather than being generally noodle) and that’s where carbon frames come in. It’s why decent steel hard tails feel ‘nice’.

Had a couple of alloy FS bikes and one carbon, but ridden a lot more. IME carbon seems to provide a more ‘neutral’ medium for suspension. It seems to me (IMHO of course) that it flexes less and let’s the suspension do what it needs to do more. Tests of some frames seem to suggest it is more robust and resist breakage – see Santa Cruz tests for an example.

Personally, there is another dimension as despite my skill level, I like riding high-end kit and justify it by the length of time I retain it and also my length of time at the coal face! Both justifications are somewhat questionable… 😉

I understand that carbon can be slightly more damping than alloy. But is this necessary on a full suspension?

Stiffness for me. I HATE rear end flex. My old LTC seemed to corner by telepathy. Until it cracked. Carbon frames just feel more accurate. Is it worth it? It depends on the price difference really and not all carbon is created equal. The frame will still need to be well designed and constructed which not all are IMHO.
Wouldn’t touch one with less than a 5 year warranty with a stunt c0ck.

The ride quality with carbon is – at its very simplest – subtly different. Carbon is to ali – what plastic is to, erm.. ali. This ‘plasticyness’ provides a level of vibration damping, that simply feels right to my carbon-o-phile hands..

The other thing carbon gives is astonishingly precise stiffness for power transfer and steering input.. Combined with frame compliance where needed to take the sting out of big hits… I own 4 carbon MTBs and 4 ali, so have a fair comparison to base this on.. 🙂

Vibration damping.

This damping gets through the suspension?

It’s worth remembering that EVRERYTHING is a spring. Nothing is perfectly stiff.

But, when people say “the frame was to stiff” what they actually mean to say is “the frame was too stiff for the current suspension kinematics” ie, if you have a limp frame, you can have stiffer suspension elements (generally crappy dampers with loads of stiction (zero speed friction) and it still works. But hang those crappy suspension elements on a stiff frame and suddenly you’ll notice their shortfall…….

Secondarily, carbon fibre has a high {b]specific[/b] stiffness and tensile strength. As such that tells you nothing about the actual stiffness of any given frame, made out of any material, as that is all about how the material is shaped and used. You can easily make a carbon frame less stiff than an ali one, and conversly you can easily make an ali frame stiffer than a carbon one!!

I’ve read plenty of stuff where bike designers talk about the importance of flex in full suspension bikes. It’s actually harder to get the right amount of flex in a carbon frame because you can’t go through multiple iterations of prototypes easily as with an alloy frame. FEA will get you so far but it’s too complex an issue to merely simulate, you have to build and test.

Regarding where the stiffness should be, the last place you want flex is fork stanchions. They cause judder and thus reduced grip under hard braking whilst if they’re bending when the fork is trying to compress or extend the bushings will bind and inconsistently stiffen the suspension. The flex which allows the tyre to track the ground when leant over should come from the tyre, rim and spokes and head tube to down+top tube junctions. There should be minimal fore-aft flex.

Likewise at the back, you don’t want any flex to happen around the bearings or bushings or they will bind and stiffen the suspension. Flex should come from the tyres, rim and spokes and along the long sections of the swing arm / triangle so it doesn’t affect the kinematics.

This is one of the risks with the new trend towards wide carbon rims – great for pummelling through rock gardens in a straight line but how much grip in the turns are they costing? What will we see the pro DHers and Enduro racers using when their sponsors have super wide rims available?

Skimmed the above, but one thing worth noting is that most manufacturers alloy bikes top out at a certain price point. If you’re buying a complete full suss off the peg and want decent to high end parts it’ll most likely be carbon.

I’ve had the experience of demoing multiple identical bikes in alloy and carbon as well as owning an alloy and carbon version of the same bike built with identical parts. Carbon is much nicer to ride, and the weight is noticeable, especially when you get up to 160mm bikes. However I currently ride alloy having snapped a couple of carbon bikes 😉

Also, just as opinions on tyres vary hugely with riding style and rider size/weight, so will opinions on the stiffness/flex of a frame. The variation in rider weight between amateurs is huge compared to the variation in the pro field. Plus smaller pros will often have a higher strength:weight ratio so will load their bike like a bigger rider.

maxtorque – Member

But, when people say “the frame was to stiff” what they actually mean to say is “the frame was too stiff for the current suspension kinematics”

Not really- frame stiffness isn’t just in the direction of the suspension after all. Frame flex can provide movement in other directions (which can be good or bad- frinstance I liked the smear and twist in my 224’s swingarm, it gave the wheel a bit of additional independent movement and a bit more traction. My Herb was a much stiffer design and while it had better suspension it lost out a bit on that.

Ben Cruz (Cannondale enduro racer) races on a carbon frame but does all his practising and personal riding on an alloy frame because they crash better!

because the one I wanted (mid travel trail 29er) happened to be carbon

it’s certainly stiffer faster and lighter than my 2004 Blur!