Are carbon frames strong enough?

[billium]

I am looking to upgrade my 3 yr old Cube Acid hybrid to full suspension so I can keep up with the rest of the crew on rides around the South Downs but am concerned about the use of Carbon frames/parts in new bikes.
In the past I considered Carbon expensive and fragile, but lighter - thus suitable for exotic road bikes.

Now many EMTB companies are using Carbon frame parts, but as I scan forums like this one I am seeing lots of stories of cracked pivots or heads with long warranty fights resulting in eventual replacement of the Carbon piece.

This does not bode well for bike repair AFTER the warranty has expired and several companies warranty frames for only 3- 5 years!

A 3 year warranty did not worry me when buying my last Cube because I knew it could be repaired by any good welding shop. When looking at a new Cube Stereo or Haibike Allmtn I wonder if the bike will be junk in 5 years!

• Given that Carbon EMTB frames have not been around that long, how risky is it to buy a bike on a budget with Carbon frame without a lifetime warranty?
• Will bad frames fail quickly within the warranty period - so low risk to owner?
• Or, can Carbon frames deteriorate slowly over many years of punishment?
• Can they be repaired at all?

 

[Stihldog]

I don’t think manufacturers wouldnwant a reputation of frames breaking or cracking. That info would travel pretty fast nowadays.
After the 2020 Rail 9.7 triangle cracked, trek replaced it right away. (Under warranty). Neighbour broke the frame on his Rail 9.7. Trek replaced that and all the labour involved (under warranty). I don’t know what could happen once I’m outside the warranty period but I do smash it around quite a bit and haven’t had an issue since. I don’t think I would want it repaired but rather replaced.

Edit; *wouldn’t

 

[billium]

You would think so but in todays 'seller's market' perhaps some just don't care. Take a look at the Haibike forum for numerous people with cracked carbon frames at bushings.

AllMtn 6&7 - Warning - Check your rear triangle bearing locations for cracked paint!

Evening all, Next issue on these bikes! - If you're on the Haibike UK owners group on facebook then you will already be aware of this. Check all your linkage bearing areas for cracked paint approx 3-4 mm's around the outside of the bearings (2 by the rear wheel axle and the 2 just behind/below...

www.emtbforums.com

Thanks for bringing up Trek - I just assumed they were expensive but they have competitive Rail 5 AND I see they have a lifetime frame warranty so they are now high on my list.

 

[2WheelsNot4]

Kona do a lifetime warranty on their frames. After purchase you register them like with many things.
In that it has a disclaimer saying that all alloy and steel frames are covered by this warranty, but NOT their carbon frames.

So from that we can deduce that Kona dont see carbon frames as being something thats going to be around and certainly not robust enough to be covered in a long term guarantee.

 

[Dax]

Buy an alloy frame

 

[ebikerider]

Carbon is an easy repair. Lots of manufacturers have lifetime warranties on their frames so if it is a big thing for you choose one of them.

Or buy alloy and keep rewelding it if/when it cracks.

There's risk in everything, just don't overthink it or you'll miss riding.

 

[urastus]

Alloy is just easier. CF frame quality is largely dependent on the person who laid the frame. CF needs alloy inserts for threads etc. which creates more areas of potential failure. Quality isn't necessarily improving; it seems the opposite since covid and supply train issues. I'd avoid any alloy frames with blind welds - essentially the welds are mostly ground away leaving the weld area weaker. Function over form if you want to enjoy your ride.

 

[ilostmypassword]

Alloy. Peace of mind.

 

[Another One]

I am looking to upgrade my 3 yr old Cube Acid hybrid to full suspension so I can keep up with the rest of the crew on rides around the South Downs but am concerned about the use of Carbon frames/parts in new bikes.
In the past I considered Carbon expensive and fragile, but lighter - thus suitable for exotic road bikes.

Now many EMTB companies are using Carbon frame parts, but as I scan forums like this one I am seeing lots of stories of cracked pivots or heads with long warranty fights resulting in eventual replacement of the Carbon piece.

This does not bode well for bike repair AFTER the warranty has expired and several companies warranty frames for only 3- 5 years!

A 3 year warranty did not worry me when buying my last Cube because I knew it could be repaired by any good welding shop. When looking at a new Cube Stereo or Haibike Allmtn I wonder if the bike will be junk in 5 years!

• Given that Carbon EMTB frames have not been around that long, how risky is it to buy a bike on a budget with Carbon frame without a lifetime warranty?
• Will bad frames fail quickly within the warranty period - so low risk to owner?
• Or, can Carbon frames deteriorate slowly over many years of punishment?
• Can they be repaired at all?

Why don't you try and find what bikes are suitable for your needs then look at warranties etc after, I find this question unusual sorry. So just for an example would you buy a bike that does not suit your needs with longer warranty than a bike with short warranty but suits your needs, both priced the same.

 

[BeBiker]

Can they be repaired at all?

 

[emtbPhil]

Cube Stereo Hybrid 140 HPC here - carbon main frame and alloy rear triangle.
I believe I'm a little bit over the weight limit when geared up, have thrown it through everything, including doing some very silly jumps at Leeds Bike Park and Dalby Forest, not a single issue and it's done 1500miles now

I think most of the carbon cracks on emtb's I've seen on here have been a manufacturing problem, if it concerns you just grab a 2nd hand bike, if it's not cracked in the first 6 months at least you know it's not a design issue or manufacturing fault.

 

[billium]

Why don't you try and find what bikes are suitable for your needs then look at warranties etc after, I find this question unusual sorry. So just for an example would you buy a bike that does not suit your needs with longer warranty than a bike with short warranty but suits your needs, both priced the same.

Because one of my 'needs' is that I expect and require an expensive bicycle to last many many years!
I still have a 22 yr old Giant that works just fine. How many 10 yr old Carbon EMTB frames are out there - any?

So, longevity is part of my checklist as I search for a new 5-6K bike.
If pricing for a bike was the same for their Alloy version and Carbon version and the weight difference was only 1Kg I think I would choose Alloy unless they offered lifetime warranty or at least reasonable repair cost.

 

[emtbPhil]

Because one of my 'needs' is that I expect and require an expensive bicycle to last many many years!
I still have a 22 yr old Giant that works just fine. How many 10 yr old Carbon EMTB frames are out there - any?

How many electric mountain bikes with carbon frames were for sale 10 years ago?

If it bothers you that much just get an alloy one

 

[RustyIron]

Now many EMTB companies are using Carbon frame parts, but as I scan forums like this one I am seeing lots of stories of cracked

Hold your horses, Hoss.
I thought this "debate" was settled twenty years ago. Nowadays all the top-tier bikes are carbon, and aluminum is used only to meet a lower price point. Aluminum certainly doesn't have the longevity against fatigue, as carbon does. So if you want to keep your frame for a long time, carbon is the only way to go. I'll admit I've broken carbon parts, but I've broken FAR more aluminum parts. And the only broken frames I've had to deal with have been aluminum.

A topic of conversation right now on this very forum is regarding "2022 Giant Reign Frame Cracking." It'a a brand new aluminum frame, an many of them are exhibiting cracks. The Fanboys tell us it's not a crack. Other folks don't care what they call it, we just won't ride frames that even "look" like they're cracked. This is only one example, so it's hardly relevant to our discussion, but I mention it because it cracks me up. Get it? "Cracks" me up!

Here's a short video from Pinkbike, that does some failure testing on both aluminum and carbon.

 

[emtbPhil]

^^

All of the haibaike and trek cracks from what I've seen are more of a design issue. Which is likely caused by not being far into the emtb offering and huge demand meaning some testing is skipped.

Definitely don't see it as a carbon cracks and aluminium doesn't

People think carbon is just for lightness, but it's actually (when done right) a lot lot stronger too

 

[steve_sordy]

Watch that Santa Cruz vid to the end.

 

[billium]

Thanks for the link - video is 17 min long but the short version is that these guys can fix most problems - for under £200 ( but you have to get them a stripped frame) .
So it appears that a broken Carbon EMTB could be repaired at a reasonable price once out of warranty.

Based on this I will consider Carbon framed bikes too.

 

[R120]

All frames can break, and most of the well documented cases of frames that have an issue are dow to inherent design faults in the first place rather than material.

In the MTB world a frame being alloy, steel or carbon doesn't make one more premium than the other. Look at the bikes dominating the DH WX Podiums, mostly alloy, or at least an even mix of carbon and alloy.

As in many industries material choice is as much about perceived customer appeal as intended use - much easier to flog an EMTB for 10k if its carbon, and the general bike buying public still perceive it as the super bike material, whereas nowadays its pretty much just another bog standard way of making a bike.

If looking for a bike that will last a long time, its as much about looking at how the bike is put together as what its made of. I would be far more concerned about not being able to get hold of some part that was all the rage for a couple of years and then went out of manufacture being used on a build than what the bike was made of.

 

[BeBiker]

A false assumption would be that an alu bike frame crack is easy to repair.
I have a Alu AC Tig welder at home, I"m a more than decent welder.
Filling up such crack by welding is easy, but aspects like the preparation, cleaning, grinding, inspection, weakening by over-rigidizing, QC, tests, finishing,... are exactly the same as what the carbon guy says in the video.

 

[stygz1]

This sounds like a discussion from 10 years ago on a regular MTB forum.

Carbon is stronger. Carbon costs more. How much are you willing to spend......

 

[Planemo]

Watch that Santa Cruz vid to the end.

I have been very much educated on just how much stronger carbon frames are! Amazing.

And I think that if that testing had been done in the UK, they would have broken 4568 health and safety rules. Especially the last 'test'

 

[Streddaz]

I am looking to upgrade my 3 yr old Cube Acid hybrid to full suspension so I can keep up with the rest of the crew on rides around the South Downs but am concerned about the use of Carbon frames/parts in new bikes.
In the past I considered Carbon expensive and fragile, but lighter - thus suitable for exotic road bikes.

Now many EMTB companies are using Carbon frame parts, but as I scan forums like this one I am seeing lots of stories of cracked pivots or heads with long warranty fights resulting in eventual replacement of the Carbon piece.

This does not bode well for bike repair AFTER the warranty has expired and several companies warranty frames for only 3- 5 years!

A 3 year warranty did not worry me when buying my last Cube because I knew it could be repaired by any good welding shop. When looking at a new Cube Stereo or Haibike Allmtn I wonder if the bike will be junk in 5 years!

• Given that Carbon EMTB frames have not been around that long, how risky is it to buy a bike on a budget with Carbon frame without a lifetime warranty?
• Will bad frames fail quickly within the warranty period - so low risk to owner?
• Or, can Carbon frames deteriorate slowly over many years of punishment?
• Can they be repaired at all?

It’s not as easy as just welding a cracked alloy frame. The frame will need to be heat treated as they are made from 6061 T6 aluminium. Once you weld it you affect the strength of the frame around the weld. The only way to fix this is to heat the whole frame to 530 degrees C and without jigging the frame it will distort all over the place.
Without the heat treatment the frame with be significantly weaker around the welded section and most likely fail again.
Aluminium, unlike steel has a finite fatigue life, meaning eventually, it will fail. This may take many years of abuse but eventually it will crack.
Carbon fibre on the other hand can quite successfully be repaired as long as the repairer knows what they are doing.
The downside of carbon is that damage can sometimes be difficult to see compared to a metal frame.
I think overall most manufacturers have their designs pretty sorted these days and most frame failures, whether carbon or alloy come from crash damage that’s well beyond the design intent.

 

[Mikerb]

Throughout this thread folk refer to "Carbon"...as if that actually tells you anything!! It doesn't. "Carbon composite" is a little more accurate but still merely tells you it is a composite construction involving ....at least in part.....one of several categories of carbon, and potentially other materials (e.g glass/kevlar/australian pine etc) in mat format bonded together with one of several different categories of epoxy.........using a variety of different contruction methods ( pre preg/wet etc).
A composite consisting 100% carbon fibre matting where the selected mats consist high modulus carbon, and using a mix of UD and different matrix mats consistent with the compression, stretch and flex requirement at each part of the frame can be light and very strong but absolutely no 100% carbon composite construction is impact resistant in the way in which is claimed in that SC video.....and neither does the a bsenc of an obvious breakage of the tube guaranteed that it is not delaminated and will subsequently fail when a compression or stretch force is later applied.

 

[JP-NZ]

Nowadays all the top-tier bikes are carbon, and aluminum is used only to meet a lower price point. Aluminum certainly doesn't have the longevity against fatigue, as carbon does. So if you want to keep your frame for a long time, carbon is the only way to go.

This is 100% correct.

 

[ilostmypassword]

This is 100% correct.

This is based on the life of the frame being without impacts to sharp edged terrains such as rock gardens. I've personally crashed alloy bikes onto rocks with minimal damage that would have splintered plastic frames.

 

[urastus]

This is based on the life of the frame being without impacts to sharp edged terrains such as rock gardens. I've personally crashed alloy bikes onto rocks with minimal damage that would have splintered plastic frames.

that's the thing really - despite all the figures, alloy is just more robust and tolerant to some damage. Damage to a carbon frame is much more of a weakness - it's like opening the flood gates.

I know of folk who have tried to get minor damage to their cf frames fixed. I say minor but it's enough to know that is going to cause a break there at some point. Tassie has some high end boat builders (lots of yachts). When they see what seems a basic repair, apparently it isn't. New frame. A specialist shop like that one in the UK would be awesome if they were all over the place - but just two shops?

 

[Varaxis]

Carbon's very risky in resale, because it can be hiding damage that's not visible to the naked eye.

Carbon products tend to cost 50% more than their aluminum alternative (e.g. $2k alloy frame, $3k carbon frame).

Carbon tends to only be strong in one direction, and relatively susceptible to impact damage.

Designing frames to do well in those lab tests is akin to teaching kids to just pass tests in school. The real world effectiveness is quite questionable. Some might be doing just fine out there, but the people who pick these half-baked things up might end up frustrated that they're being burdened with the prototype nature of these experiments or whatever.

I'd rather stick to the mainstream-enthusiast level, rather than throw money at some "heirloom" quality thing that promises that its quality is so good that it will last through multiple builds or whatever. Stuff gets outdated in the ebike world faster than the rest of the mtb industry, and the mtb industry sure does a good job of making people want to refresh their bike every 2-4 years.

 

[Streddaz]

that's the thing really - despite all the figures, alloy is just more robust and tolerant to some damage. Damage to a carbon frame is much more of a weakness - it's like opening the flood gates.

I know of folk who have tried to get minor damage to their cf frames fixed. I say minor but it's enough to know that is going to cause a break there at some point. Tassie has some high end boat builders (lots of yachts). When they see what seems a basic repair, apparently it isn't. New frame. A specialist shop like that one in the UK would be awesome if they were all over the place - but just two shops?

There's a guy in Deloraine that does carbon frame repairs. I've seen one frame that he's done and it looked pretty good but can't comment on the structural integrity.

 

[irie]

...
Carbon tends to only be strong in one direction, and relatively susceptible to impact damage.
...

In principle carbon fibre is strong in tension and weak in compression but there are myriad different ways of laying it up.

Basically, impacts cause compression. In general, under severe compression alloys will dent whereas carbon fibre will fracture.

 

[Mteam]

if you're looking for value for money then go aluminium, if you want your bike as light as possible then go carbon fibre (but you will pay more for it) . Strength doesnt come into it at all with mtb frames.

Either type of frame can crack/fail, but neither should, and one type shouldnt be more likely to crack than the other.

For what its worth, the only frames that have cracked on me have been aluminium, all the carbon fibre bikes I have owned have never cracked.