Having just been reading yet another thread about a broken carbon MTB frame I was wondering if they really are as fragile as they seem to be?

I’m lucky enough to never have had a bike go pop and never had to get warranty work done on a frame. Never had carbon, just aluminium and steel. I had thought my next new purchase (Not any time soon!) would probably be carbon as at the top end of my expect budget seems to be filling up with lower down the range carbon. There seems to be loads of problems with dodgy manufacturing and build quality though and I’m not keen to join the list of woe.

So, the question is how many people that have trashed a carbon MTB frame or bought one that needed warranty work/replacement have also had the same problem with any aluminium or steel frames they’ve had in the past?

Most carbon damage can be fixed, even upto tube replacement. Repair vs replacement cost is often a lot better for carbon even compared to premium steel frames.

yet another thread about a broken carbon MTB frame

Good point. It’s great that no one ever posts threads about failed aluminium/steel/ti/etc frames…

The simple answer is no.

The slightly longer one is that like anything, some are well made, some less so. Some of them fail. Choose a brand that has a good reputation and it’ll probably be fine. Just like a alu/steel/ti/etc frame.

FWIW, I’ve broken loads of frames made of steel and alumnium. I’ve broken one made of carbon and that may have been user error with hindsight.

Thanks for the replies. Interesting you say to choose a reliable manufacturer as names I’d expect to be in that list crop up often in the broken category.

Anyway, that misses what I was getting at as I know all frames can fail and can then be fixed. What I was wondering was have those that have had problems with carbon also had problems with other materials.

There’s a good chance that the reason I don’t burst frames is that I don’t ride the often or hard enough. I’m interested to know if the failure rate is rider led or bean counter led.

Back when I got my first MTB in the early 90’s everyone was going lighter and lighter and the dream bikes were made of wafer thin aluminium. It went so far the frames started to fail (Manitou fs, Alpinestars Al-Mega I’m looking at you!) so they stopped trying to make the bikes light at all costs and started adding some strength. I wonder if the same is/will happen with carbon?

Mainstream manufacturers will already tell you that they are designing and building carbon frames designed for strength and not weight-saving.

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

If you can’t be arsed watching the whole video, just skip ahead to 5:00

Yup, I’d tend to agree with the above, I’ve no experience with frames, but carbon fibre, like for like in size and thickness and quality of layering is not much lighter than ally alloy .. It is however a shed load stronger and stiffer.

The issues seem to arise when the weight aspect is pushed.. Like with wheels, which I have a small amount of experience with, plus some engineering knowledge.. people going for low spoke counts and thinly layered XC rims when they should be going normal spokes with AM wheels, then wondering why thier indestructible carbon wwheel collapse beneath them.

Like for like it’s stronger, stiffer, and a better material, but it’s not indestructible.

If you buy a bike suited to what you are doing with it, from a manufacturer who actually does proper testing, you are extremely unlikely to come a cropper.

Buying a sub kilo XC frame and building it up as a hardcore hooligan bike is going to end in tears. And splinters of carbon.

In almost exactly the same way as if you try to use a light weight metal race frame as a hooligan bike. Except no carbon splinters.

FWIW one of the great disappointments in life is that my 10 year old, horrendously outdated carbon FS won’t break. I’ve even started doing stupid stuff on it in an attempt to get it to snap, crack or crunch.

No joy yet. No new carbon either.

I basically ride the same circuit almost every time I go out and over the last seven years I’ve used 5 bikes – 4 aluminium (2 f/s) and one carbon – and only the carbon has failed with a cracked seat tube after very little use. All 5 are xc bikes used on an xc course.
If you look at the inside of the seat tube you can see a depression were the crack is so I guess it’s a manufacturing defect, the replacement has no such mark.
It’s certainly made me think twice about carbon and I don’t think I would go that route again.

However one of the alloy frames has severe corrosion so that material also has issues…..and steel isn’t an option for me.

I am a carbon convert, while I don’t necessarily subscribe to the idea that it’s ideal for all applications, the simple repairability of a composite frame vs a metallic one has real appeal to someone like me.

I won’t kid myself that I am in anyway handy with a torch, but any bugger with basic equipment and a bit of space can mix some epoxy and repair a composite frame…

But it isn’t just a case of mixing some epoxy and glueing it together as the structure of the fibre weave will have been compromised, you will need to replace that lost strength/rigidity and glue doesn’t do that. There will almost certainly be stress in that area and the crack will flex which causes it to open up again.
The only repair I would consider is one that involves inserting a support inside the damaged area.
In my example I was considering inserting/glueing a cutdown seat post as a repair but the warranty process was painless so why bother.

My main sport is hockey. What’s funny is that the view of carbon vs metal is completely reversed.

Hockey sticks are given some real abuse with constant impacts and wear.

Aluminium sticks were banned due to them shearing dangerously and suddenly. The metal fatigued and cracks would propagate badly.

Carbon (and aramid, fibreglass, etc) sticks are exactly the opposite. Fantastic impact resistance. Also due to the woven construction it would stop cracks going through the material, and the lightness of it all meant that there was simply more volume (far thicker walls) of material to protect from impacts and catastrophic fails. Carbon is softer and so you can easily get surface damage and cracks (see 1000+ posts on “is my frame cracked”), but this is the surface cosmetic layer. Even if it was crumbling from abuse, you could play on and on with a failing carbon stick and it would just get softer and softer. Metal? No chance. Jagged shard in someone’s leg.

It’s always funny to often see exactly the opposite views in biking. Having smashed things for years with sticks made out of carbon and aluminium, I’d have carbon everytime for a bike frame given the choice.

@patagonian

And if a frame is out of warranty or you aren’t the original owner? Just bin it?

It’s actually quite a cost effective solution…

In theory no repair is perfect in practice most will be fine, adds a few grams and perhaps not be totally aesthetic but then you’ll save hundreds of quid…

If you still have your broken frame, whatever state it’s in, and “carbon fear” prevents you getting it fixed, I recommend shoving it on eBay and recouping some money, just be clear about the damage and that it’s for someone else to repair…

There’s much less focus on the quality of carbon in MTBs than road, where most riders know that T800 or high-modulus carbon tends to be lighter for the same stiffness and often gives a better ride.

MTBers seem prepared to pay MORE to little companies like Evil with a poor reputation for carbon than to companies like Giant who can claim to have real expertise in-house.

I got shafted by Trek over a problem with a carbon frame so it’s not always a question of going with the big boys – but if it came to it I’d be more optimistic about a carbon repair than an aluminium one TBH.

I have snapped 3 alloy bikes and to date the carbon bike is still intact despite a couple of biggish offs , the alloy bikes were all from big companies. As already said, carbon is stronger if made well. The problem with all bikes is we think they are well made, until they break.

I’ve snapped/cracked 1 steel, 2 aluminium and 2 carbon frames in general XC use. So far my main conclusion is that Giant anthems are reliable either in Al or carbon.

Material choice is probably the least important factor in how long a frame lasts.

@Cookeaa
No I never said bin it, I did consider repairing it (and one day I still might) but not without supporting the fix internally – glue alone won’t hold it.
So a seat tube with a cut down post glued in – yes. Any shaped part of the frame – no that’s not a diy fix.

And it’s worth mentioning that a professional repair was quoted at about 250 with an additional 80 if I wanted the fixed section painted which is getting close to the price of a new frame.

Personally I’d prep the outside and lay up some fibres across the crack on the outside. It won’t look beautiful of like a pro repair, but should fix it. Similarly you can DIY fix on shaped parts as long as you’re not bothered about aesthetics (I reckon I could actually make a decent looking job of a lot of fixes, but wouldn’t necessarily be that bothered).

Hmmm, Seat tube is an interesting one, as the ideal fix should leave you with a usable seat tube without the need for an internal shim or chopped off post left in there…

Have you considered coating a post in Mould release/wax to use as a temporary support so you can run a thinner resin in and fix the de-laminated fibres? Then you can remove the post and apply an external ‘splint’ ~3″ either side of the original damage, to reinforce the whole area…

The other option might be to create an inflatable silicone bladder for temporary support, again something which can support the initial repair from inside and then be removed, leaving you with a usable ID…

You won’t be the first one to repair a composite seat tube, I would search YouTube, something is bound to turn up…

any shaped part of the frame – no that’s not a diy fix.

Triangular section seatstay, DIY repair on my road bike, ~1300 miles and no issues yet (touch wood) if it was going to fail I’d have expected it in the first few hundred miles…

Any tube profile can be repaired, you just need to be creative…

If you look on youtube, I guess you want to look for damaging carbon frame. There is a vid of some kid who has a broken frame, it was replaced, and he takes a hammer to the old frame to see how strong it is. I was quite surprised what it put up with, I used to make carbon parts for motorbikes and they were never that durable.

The crack is well down the seat tube so if I was to repair it then an insert wouldn’t interfere with the normal seat post.
Diy Seat and chain stay repairs on a hard tail mtb I’ll pass on – I wouldn’t ever trust them and it would spoil the enjoyment of riding but hey that’s just me!

The crack is well down the seat tube so if I was to repair it then an insert wouldn’t interfere with the normal seat post.
Diy Seat and chain stay repairs on a hard tail mtb I’ll pass on – I wouldn’t ever trust them and it would spoil the enjoyment of riding but hey that’s just me!

If you’re not happy doing a DIY repair yourself and its not worth paying for a pro one, then just sell it on to somebody who is.

Diy Seat and chain stay repairs on a hard tail mtb I’ll pass on – I wouldn’t ever trust them and it would spoil the enjoyment of riding but hey that’s just me!

So what you are really saying is that you don’t really know enough about composites to say whether they are repairable or not, so you’re just going to assume they can’t?

Fair enough.

I’ll give you £50 for it…

Make/model/size?

I dont believe chain stays or seat stays are a DIY repair – nothing to do with knowledge of composites – I just wouldn’t go down that path as I’m not going to ride something I don’t totally trust. Unless I could get to both sides of the damage its a non starter as a home repair. Yes they can be repaired professionally but that is a different matter.

They’re pretty much the easiest bits to repair – straightforward tubes. You just wrap them in cf with epoxy and compress. I’ve seen several examples. A couple still going strong over 10 years later…

Another good example

http://singletrackworld.com/forum/topic/my-diy-carbon-frame-repair