Carbon Fibre frames - What's the big deal ?

Fresh Air Rider

I thought that the big advantages with carbon fibre were reduced weight and improved ride quality.

The Time VXS carbon fibre road bike on the following page weighs in at 8kg

http://www.fatbirds.co.uk/TimeVXSCarbon ... 199.99.htm

The Van Nicholas Chinook Ti bike on the following page weighs in at 8.2 kg

http://www.fatbirds.co.uk/VanNicholasChinook56cm..htm

Not really much of a weight saving and Titanium road bikes are also praised for having an excellent ride quality.

I'm often reading of carbon fibre frames spectactularly cracking and very recently on these forums there was an account of this happening after the wind blew the bike over after it had been left standing in the back garden.

With the above in mind, I can't really see the big attraction with carbon fibre. Maybe it is just a fashion thing.

I like to hear other folks opinions.

alfablue

I think Carbon frames are now getting to be cheaper than Ti as they become a mass market product, just like how Alu frames started out way more expensive than steel, and are now the norm right from budget levels. I have not ridden carbon, but have a Ti mtb, and the ride and weight are good, as you say, and should have more crash resistance. I think I would like a carbon road bike, but I would keep it for "best" not commuting or the like, because of nervousness about crash damage.

Felix-da-house-mouse

i have a carbon framed cannondale (see my link) and its gr8,i've fell of it in the wet and its fine as far as i can see, plus if you buy it new you should get a garuntee that specifies if the frame cracks etc then it will be replaced within so many years of purchase. overall its a good ride handles really well and is pretty quick too.

Eurostar

I've been agonising over a new frame for a year, and I'm certain that carbon frames are mostly a fashion thing - that's if you define fashion as being about looks as well as trends.

The frame is only a small proportion of the total weight. The lightest carbon frames are just under a kilo, the lightest steel ones are just under 2 kgs. So a carbon frame allows you to save about a kilo, maybe more. There are plenty of 'heavy' carbon frames which weigh 1.5 or 1.7 kg. You can build a bike of around 7.3 kg with a steel frame if you go for light tubing e.g. Reynolds 953. If you want to get the weight down to the 'ultralight' level, something close to the UCI limit of 6.8 kg, you have to have a carbon frame plus a whole load of ultralight carbon or titanium components. Component weights and examples of ultralight bikes are over at the weightweenies site http://tinyurl.com/2we2mu. It all boils down to money. Most people seem to spend £3.5k+ to get down to that sort of weight.

Ride quality can be stiff or springy with any frame material. Comfort is more about frame design. There is a myth that all carbon frames are good at absorbing road shocks - it's not true. Some carbon frames are painfully stiff. And a steel frame can be as comfy as you like if you design it that way.

Carbon frames can't be mended, so they're best regarded as consumable items. Steel frames can and do go on for 25 years. If you whack them, they dent. Not the end of the world. If you need a new tube the old one can be cut out and a new one put in at a reasonable cost. I was quoted £150 for a new top tube for my Condor 753.

Don't know all that much about titanium frames, but I've never heard of one being repaired.

Carbon can be made into beautiful swooping shapes, with flared aero seat tubes and very deep aero fork blades. So they're good for time triallists, and you get some nice broad surfaces on which to put a stunning paint job. There's not much as much scope for exciting paint jobs with thin steel cylindrical tubes.

If you want a custom frame you won't find an affordable one in carbon. I know of 3 custom carbon framebuilders, Serotta, Parlee and a French one I've forgotten. They are all VERY expensive.

For touring in third world countries steel frames are thought best because if you snap your forks on a taxi in Calcutta you can get them bodged together by the nearest bloke with a welding torch. That's the theory. Never heard of anyone actually doing it! What's more likely is that you'll make several nasty dents in your steel frame and it won't matter. I've got some murderous-looking dents in the top tube of my 23 year old 753, but it rides fine. If it was carbon it would have been wrecked two or three times over.

Fresh Air Rider

Thanks to all three of you for your views.

I think I fancy titanium of all frame materials because of its logevity and comfortable ride.

Having said that, I love the look of your Cannondale Felix.

EuroStar - You have obviously been researching the pros and cons of different frame materials in great depth and thank you for such a detailed reply.

I have also read that the perfomance of aluminium frames deteriorates with use. Presumably this is due to the flexiby of general use that causes the frame to lose stiffness.

rohloff-rich

I don't ride hard and I've broken a Ti mtb - the stuff is not indestructable by any stretch of the imagination, although it should be, IF built right. :roll:

I ride a carbon road bike and would do so happily all day everyday without fear of breaking it

Eurostar

Compared to steel, ti is brittle - it can snap or crack, and you can't get it mended. So if longevity is your priority, steel is the obvious choice.

But because steel is regarded as traditional rather than innovative a lot of innovative designs are just not available in steel - although it's an excellent material. Steel has an image problem, so if anyone manufactures an innovative steel frame it's tough to sell. All the customers who are bold enough to buy something innovative think that steel is very old school, and they want the latest thing, i.e. carbon. So almost all the steel frames you can buy are very traditional designs...and the crusty image goes on and on. Here is one of the few funky steel frames on the market, the Kirk Terraplane. The seat stays are heat treated and bent to suit the weight of the rider so the rear triangle absorbs just the right amount of road shocks to give a very comfy ride. I want one!



And i have to repeat that any material - including ti - can be built into a stiff frame which gives a harsh ride. So really you have to choose each frame on its merits.

The interesting thing about ti - or one of the interesting things about it - is that you can get a really cheap, top quality custom frame! Several members of the old C+ forum did this by sending the exact frame dimensions they wanted to a chinese manufacturer called XACD, which builds frames for lots of posh brands. As far as I can remember they were very pleased with the results and the efficiency of the guy they dealt with. If you do enough searching I'm sure you can track them down for advice. I just had a quick google and found this guy http://ronniethescot.blogspot.com/feeds/posts/default His frame was such a bargain that if he wrecks it he can afford to just buy another. If you don't want to design your own frame I'm sure you can find someone else to do it if you ask around.

Ti also looks great polished, which saves on the cost of a paint job.

Dorian Gray

Fresh Air Rider wrote:

I thought that the big advantages with carbon fibre were reduced weight and improved ride quality.

Stiffness complicates things though.

Steel is a pretty good material for bicycle frames because of the reasons Eurostar mentioned. The raw material is dirt cheap, it's easy to work with, frames made from it are durable and repairable, and they absorb road buzz nicely. The disadvantages of steel are that it rusts and it is very dense. The high density of steel limits the diameter of the tubes used, and this is a problem because fat tubes are the easiest way to make a bike stiff.

Why are fat tubes stiff? Because when a tube bends, one side (the outside of the bend) is stretched while the other side is compressed. By increasing the distance between the two sides, i.e. making the tube fatter, the material is given more mechanical leverage to resist bending. Doing the calculations reveals an interesting fact: increasing the tube thickness increases its strength even if the tube walls are thinned so that the fat tube in total uses the same amount of material as the thin tube. So by making the tube thicker, we increase its strength without increasing the weight. A win-win.

Why not make the tubes truly obese then, with paper-thin walls? Because as we fatten the tube and shave the walls to increase strength, we reach a point where the walls are so very thin that they become a liability. Coke cans are extremely strong despite their very thin walls: you can sometimes stand on an empty one if you add your weight slowly. But the slightest disturbance to the walls (a very light tap with a stick, for example) causes the wall to buckle and the can to collapse catastrophically. This is the risk we run when making a bicycle tube very fat with very thin walls: a slight ding, never mind a crash, could cause the whole thing to collapse like that coke can.

Back to steel. Steel is about two or three times stronger than aluminium, but three times heavier too. Due to this high density, if we try to make a fat bicycle tube from it, the walls become excessively thin, and therefore prone to buckling from daily knocks and accidents. Aluminium is much less dense, so we can form it into enormously fat tubes which still have walls of sufficient thickness to avoid catastrophic buckling. In fact, due to the strength advantages of fat tubes, aluminium frames are normally vastly stiffer than steel ones despite weighing less.

But steel has another property: it is quite elastic, that is, it can be deformed quite substantially and still return to its original shape. In fact, it can suffer significant strains indefinitely without any reduction in strength. Aluminium on the other hand is much less elastic: when deformed it soon reaches a point where it won't return to its original shape, i.e. the frame is bent. Additionally, even very small strains, if repeated enough times, will cause aluminium to fail due to metal fatigue. This property means that aluminium frame makers have no choice but to make an extremely stiff frame: if it flexes much, the frame will very soon crack in use due to fatigue. Steel frame makers on the other hand can reduce material until the frame bends a little under pedalling strains, confident that these strains will not cause long-term harm to the frame. This flexibility gives steel frames the comfortable ride for which they are famous.

Titanium is quite like steel in that it is very elastic, does not suffer fatigue as long as it is designed so that normal strains fall within the "fatigue limit", and is dense enough that tube fatness is limited compared to aluminium. But titanium is very corrosion-resistant and has a significant strength-to-weight advantage over steel, so titanium frames are usually a lot lighter than steel frames. The great thing about titanium is that it can withstand enormous deformations without fatigue: it simply springs back to its original shape, unharmed. This property tempts bicycle designers to remove so much material that the frame becomes very flexible indeed (and extremely light), because they know even large strains won't cause failure.

Into this mix comes carbon fibre reinforced plastic. This material is made with a lot of very thin carbon fibres, combined into a "weave" that is then bonded in epoxy. Carbon fibre is certainly fashionable at the moment, but it also has undeniable advantages for bicycle frames. It has a low density and enormous strength-to-weight ratio, which can be heightened yet further for specific applications by customising the weave so that more carbon fibres lie in one orientation than the other.

The result is frames that are as light or lighter than titanium, but much stiffer in the directions that matter for transferring power from the pedals to the wheel. And despite the high stiffness in this orientation, the frame can be designed to absorb vertical shocks from bumps on the road, in effect giving the best of all worlds: the stiffness of aluminium with the comfort of steel and the lightness of titanium. And on top of that, a carbon frame can be easily made into an aerodynamic shape, which is very difficult to do with metal tubes. Carbon fibre is also corrosion resistant. Can you see why frame designers might be tempted by the stuff?

The catch is that it takes great engineering knowledge and manufacturing know-how to take advantage of these properties of carbon fibre without compromising the safety and lifespan of the frame. If I designed a carbon fibre bike I'd probably make a dud that weighs 2 kg, flexes like a bodybuilder, transmits every bump to the rider and cracks in six months. Whereas I could probably design a reasonably light, reasonably good, steel frame.

The scary thing is that we still haven't reached the full potential of carbon fibre. Nanotechnology is pushing the boundaries forward all the time. And Boeing's large-scale use of carbon fibre in the new 787 has prevented the price of carbon fibre falling as quickly as it otherwise would have in the last couple of years. As worldwide production ramps up, we can look forward to ever-cheaper carbon bikes that continue to improve in ride qualities.

For this reason, I suggest you get used to the idea now rather than in ten years when £300 carbon bikes will no doubt be sold in Halfords and Decathlon. Meanwhile however, enjoy your metal bike. I know I'd certainly prefer a well-designed titanium steed with an indefinite lifespan over a flashy carbon bike designed with unknown engineering competence. Just don't go for the lightest titanium frame you can find, because it will flex like crazy and may even break if the designer pushed beyond the limits.

Sorry for going on and on and on here, by the way! To paraphrase Mark Twain, I didn't have time to write a short post so I wrote a long one instead.

Eurostar

Good stuff DG! Some questions for you:

- what affects the speed that rust attacks a steel frame? Can rustproofing methods help? Or do all steel frames rust badly if used in the rain and kept in a damp garage? I'm waiting for my 753 to turn to dust but it's showing no signs of it. Some people seem to think that 20 year old 753s are inevitably very rare because they all died years ago.

- why isn't ti more widely used by custom framebuilders? And what makes it so hard to repair?

peejay78

i have a steel framed condor accaiao, it's a light weight racer and thus far, over the two years i have had it, has gleaned countless admiring glances from peers riding less 'trad' steeds. it has the same tubing used by pinarello and pegoretti - the dedecciai 16.5 - and the frame weighs about 1.6kg. some of the tube walls are very thin (0.4mm on the top tube) - which sort of contradicts the previous post.

best of both worlds, light steel frame, carbon fork and oversized carbon seatpost.

amazing bike.

Eurostar

I think DG was implying even thinner walls than that. 0.4 mm sounds very thin but it's not unusual nowadays. Even my 23 year old 753 has 0.5 mm. 953 goes down to 0.3 mm. Scary when you think about going downhill at 50 mph - the paint is probably thicker than the tubing.

Here is some interesting blurb from Reynolds:

The question that Reynolds personnel are often asked is 'What is the best material for a bike frame?'. As you can see, there are several things to consider, depending on your priorities and riding style. The surprising finding from a technical angle for most people is how close the specific stiffnesses are (stiffness-to-weight ratio). The frame design and manufacture has to optimise the advantages of each material and Reynolds now provide customised butted tubing in aluminium,magnesium, steel and titanium.

It comes down to personal choice, how you intend to use your bike and your riding style.

'The Steel is Real' lobby does have its backers, especially for comfort on long rides, and where the high material stiffness and durability is important. We also see a number of riders switching back to steel in the last couple of years, now the weight gap between steel frames and other durable frame materials has closed sigificantly. A frame that has been protected against corrosion will last a lifetime of hard riding, so our 953 steel could offer a great combination of features to a rider. 853 and 631 steels remain a core product for Reynolds with continuing specification on high-end steel frames.

Aluminium - Our X-100 material aims to bridge the gap between the high strength of steel and low density of aluminium, whilst allowing a lively but durable ride. Current alloys based on 6061 and 7005 alloys normally require larger diameters to maintain frame stiffness but also offer shaped tubes and low weight at a reasonable cost . Reynolds will have a limted amount of X-100 due to supply constraints for this aerospace alloy.

Magnesium's major advantage for frames is vibration damping, due to its' low stiffness. Welding Mg frames is a challenge for most builders, so we expect to see this material used in bonded frames.

Titanium offers a great combination of ride, strength, corrosion resistance and durability. It lends itself to cold working production methods that can significantly improve the tensile strength of a bicycle tube. A great frame material choice, but the price of titanium tubing is continuing to rise at present. Our seamless butted 6-4 titanium (the only one in the bike industry) remains our of favourite materials but worldwide production of seamless 6-4 will always be limited, making this a premium cost tube-set.

proto

Dorian Grey, excellent post, thankyou.

peejay78

agreed....

ricadus

Perhaps the (mass market) industry doesn't like steel either, precisely because it is repairable and longer lasting. There's been a lot of consolidation in the bicycle manufacturing industry over the years, so that now these bigger companies have to either hope for perpetual growth in the popularity of cycling or that existing customers replace their bike more regularly than once every 25 years!

eh

Eurostar: To stop it from rusting keep it dry and keep it away from things like salt which hugely increase the corrosion rate. Cetainly don't leave it wet, in a damp garage, especially after rides in the winter. Some folks do use corrosion inhibitors (framesaver?) on the inside, to stop corrosion from inside out, but I've seen no real evidence to suggest they improve the lifespan of the frame, although you would hope it does. Also keeping the paint on the outside in good nick will make a big difference. Steel is a top material though and if looked after correctly should last years and years.

Ti is interesting I've lost count how many times people say it is THE material for lifelong lasting frames and if it was simply the material in question that would be correct. However, it is so difficult to join together correctly that stacks of Ti frames fail at the joints, be that welds on modern ti frames or the glued bonds on older Dyna-tech style frames. Good example being the fairly recent pics of the cracked Litespeed on this forum.

Personally I think carbon is the frame material of choice for road race frames, but aluminium certainly has its place. Oh and aluminium frames despite all this talk about fatigue last well, I've got one that has over 10,000 miles on the clock, plus has seen heavy use on the turbo and it is still a top ride.

Essentially all the 4 materials can be used to make good frames, with carbon edging the lightweight battle, but with strong pros and cons for all.

acorn_user

One of the main problems with Ti is finding welders that can work with it. It is very difficult to weld, and most guys who can do it are working in the aerospace industry and making lots of money... making lots of money is something most small frame builders do not do...

Fresh Air Rider

I suppose that's why companies like Van Nicholas, Enigma and Sunday Bicycles get their ti frames manufactured in the far east.

Dorian Gray

Eurostar, rust obviously requires water and oxygen, but the latter is a bit hard to control! So try to store it in a dry location (low relative humidity). If your garage is damp then take your baby into the bedroom. Rust increases in an acidic environment (low pH), so acid rain will cause more problems than tap water. But again, you can't do much about that. What you can do is make sure any holes in the frame are blocked to prevent water getting into the frame during a wet ride. The area around the seat post clamp and the top of the seat post itself are areas you should look into if you're worried, because these areas are soaked with water from the back wheel. Standing water causes much more damage than humidity in the air.

As eh mentioned, the most important thing you can do is make sure the paint coat is in good condition so that rust doesn't start forming. Rust is permeable to moisture, so a layer of rust will transmit moisture into the good steel below, spreading the rust. So it's best to avoid any rust starting at all.

Steel frames can last for decades without rust problems if the paint is kept good and they're not left with standing water in the tubes.

Regarding titanium and its high price, titanium is the 9th most common element in the earth's crust, so it's not rare. What makes it expensive is that it's difficult to extract metallic titanium from the common titanium dioxide. The Kroll process that is used is extremely time-consuming (nearly a week for a small batch) and consumes expensive magnesium and a lot of electricity, which drives up the price of the metal.

Working with titanium is also difficult. Unless all welding is done in an inert atmosphere, contamination with air will make the material brittle and lead to failure around the weld. So all areas of the frame that are above 400 degrees C during welding must be completely protected from contact with air, including the root side of the weld (inside the frame). In practice this requires the use of water-cooled welding torches with large ceramic cups and gas lenses, plus customised trailing shields and water-cooled heat sinks for each weld, not to mention expert welding skills to use all of this effectively. It's not easy to repair a titanium bicycle because all this would need to be set up, which isn't practical for just one weld.

So basically, I think the reason it isn't used more by custom builders is that they just don't have the stomach for all that. Especially as they would have to charge much more for a titanium frame, and price matters in the real world, regardless of how fantastic a material might be in an ideal world.

peejay78: very nice bike, but how much did that set you back?

paul_smith_srcc

Indeed Van Nicholas and Sunday are from China, Enigma Tawain; wouldn't let the location put you off as the workmaship is first class. Derosa are built by them in Italy and Merlin, Litespeed in the USA, expect to pay more for those; as to if they are better built as a result is of course a matter of opinion.

As for published weights many simply add up the sum of components to list a weight so be careful, always recommend that if you are chosing a bike with data based on that to get an actual bike weighed, rim tapes, tubes, bar tape, cables, stem spacers, bottle cage bolts may all be light yet together they all add to the total weight

Paul_Smith
www.bikeplus.co.uk

Fresh Air Rider wrote:

I suppose that's why companies like Van Nicholas, Enigma and Sunday Bicycles get their ti frames manufactured in the far east.

TheNomad

Eurostar wrote:

Compared to steel, ti is brittle - it can snap or crack, and you can't get it mended. So if longevity is your priority, steel is the obvious choice..

Going to disagree with the cannot be mended quote.

I have a friend in Leicester that can repair ANY carbon fibre product as long as it hasn't shattered. If it is cracked, split, snapped, etc, it can be repaired & will be stronger than what it was originally. All of his carbon fibre used is formula one grade or higher, and he uses a variety of resins depending on the modulus of carbon used for the repair. All his repairs are also auto-claved (as long as the item can fit into the auto clave)to remove any microscopic air bubbles that may be trapped in the carbon. I don't know if he has done any cycle frames yet, but for the price of the frames, most of them have a low carbon content in them as proper high modulus carbon is very expensive indeed (far more pricey than the cost of most carbon frames).

leonlikestrees

slightly off on a tangent now, but does anyone know of a Ti custom frame builder in the UK?

I don;'t want a frame, just some modifications to the braze-ons on my Ti cross frame. It's the sort of thing I'd just get Argos to do on a steel bike, but I don't know anyone who works with Ti.

Eurostar

TheNomad wrote:

Eurostar wrote:

I have a friend in Leicester that can repair ANY carbon fibre product as long as it hasn't shattered. If it is cracked, split, snapped, etc, it can be repaired & will be stronger than what it was originally.

That's iintriguing. I wonder if the bike industry wants us to believe that carbon frames can't be mended? If your friend wants some more business perhaps he could repair some bust handlebars or forks or something for a magazine. I think it would make for interesting reading. On the other hand perhaps his service is so unusual that he's kept busy by rich customers, e.g. F1 teams?

Maybe it would be profitable to set up a franchise for mending carbon fibre bike components?

Monty Dog

The trouble with carrying out repairs to carbon is to be able to certify that the frame is safe thereafter - by carrying out the repair and charging someone for the priveledge, they are going to assume that is is safe and carries some form of 'warranty' . In doing that repair, you may also be taking responsibility for the integrity of the 'whole' frame. ATB Sales have just lost a court case for a pair of aluminium bars failing on a Marin which seriously injured the rider, despite him having crashed them previously. Problem would be trying to get insurance to cover 'personal liability' i.e. you repair a frame, which subsequently fails - how do you prevent losing everything during potentially expensive litigation? You could use ultrasound or similar, but it just adds to the cost - applying the epoxy bandage is easy - proving the effectiveness of the repair is far more difficult.