What happens on the trails is perhaps best described using the jagged speech bubbles from a comic strip: There's a nasty "Krack" when a branch rips the derailleur hanger off the frame. Something like a "Prock!" sounds when a boulder that is too high crushes the down tube in front of the bottom bracket, and a shouted "Sh...!!!" with three exclamation marks indicates that the bike leaning against the hut has tipped over and is lying in the scree with a broken top tube.
While a commonplace crash rarely leaves more than paint damage and an ugly dent on a metal frame, with carbon it's quickly game over. The leading material in lightweight construction copes well with all forces that attack from the right direction. However, undosed force turns a high-end carbon frame into a kilo of hazardous waste in no time at all - in view of frame prices of up to over 4000 euros, this is not only an ecological disaster.
Repairing carbon is almost always possible - it's more a question of price
Even before the current carbon wave on mountain bikes, Dr Stefan Frank-Richter could not accept that such high-tech treasures could be ruined after a minor mishap. His gateway drug to lightweight cycling was the lightweight wheels developed over 25 years ago for racing bikes - one kilo per wheelset, a kind of secret weapon in professional sport, but unaffordable for him as an amateur. As a precision mechanic and physicist, however, he then delved so deeply into the subject of carbon repair that he was able to repair these parts - initially as a personal challenge, then increasingly professionally, as the racing teams also had to buy such wheels at a high price.
Today, Dr Frank-Richter runs one of the few established carbon repair businesses with his company Phönix Carbon and has long since outgrown the tinkering niche. Since almost everything on mountain bikes is made of carbon, he and his competitors have so much to do that some companies have to ask their customers to be patient and wait up to five months. Turnover at Phönix Carbon is said to have increased by around 500 per cent within three years. For urgent cases, such as before
races, some companies offer an express service at a high price. "You can do almost anything," says Dr Stefan Frank-Richter, "the question is rather who wants to pay for the effort."
The question of what is worthwhile is not always a simple maths problem. Eberhard Schirmer from CarboRep has found an almost universal formula for this: "We come into play when the manufacturer cannot offer an acceptable solution," says Schirmer. "This can also be a crash replacement, where the replacement frame would cost two thirds of a new one, but the repair would only cost 20 per cent. Or the manufacturer simply can no longer supply a replacement, as is usually the case with 26-inch bikes." But there are also bikes with emotional added value: some designer pieces or vehicles of great successes and experiences are nursed like a sick pet - in this case, repairing the broken carbon helps.
Even minor repairs beyond cosmetics cost over 300 euros, because handling with sophisticated lightweight construction involves a lot of experience - and not least the responsibility for the life and health of the customer. Artful paintwork to conceal the damage is on top of that. The profession of carbon repairer is not officially regulated and therefore not officially recognised, but according to our research, there are probably no more than ten small and micro businesses in German-speaking countries that carry out complex wheel repairs professionally. The majority are technically adept tinkerers who have acquired expert knowledge and a feel for the material through experimentation and training, who build their own devices and who repair the delicate carbon with a sure instinct.
As far as their technical requirements are concerned, the high-end craftsmen are initially at a disadvantage compared to industrial frame production. Current carbon frames are produced in large moulds, which are covered on the inside with larger or smaller carbon blanks. Practically everywhere on the frame there are several different layers, which are finally baked together in the mould using internal pressure and heat. A carbon doctor must now try to reproduce this material structure and this process - without a mould, without a layout plan, with lower pressure than in the industry and with a ready-painted frame, which for this reason alone cannot withstand the heat used in the manufacturers' huge ovens.
The Stone Age way of repairing the carbon would be to wrap resin-soaked fibre bundles or strips of carbon matting around this area. So thick that it is guaranteed to hold, regardless of how it looks. The current methods are much more subtle, both visually and technically. To preserve the look and riding characteristics, the repairer reproduces the original tube. To do this, he grinds the material thinner by tenths of a millimetre, starting a few centimetres away from the damage. There is then only enough material left near the crack to serve as a base for the new layers. During the sanding process, the repairer can also see the structure of the original carbon fibre mats at this point and can then reproduce it with new material.
Repair companies replace the high pressure that compactly bonds the layers together inside a manufacturer's mould with pressure from the outside. Shrink films or vacuum sleeves compress the material while it hardens. It is then ground down to such an extent that the pipe diameter is approximately restored. However, the more delicate the area and the thinner the walls of the frame, the more likely it is that the repair will bulge outwards, even with careful work. A little more material than in frame production is unavoidable: if a thin to medium frame tube breaks, the repair adds around 50 grams of extra weight, as we found out during test repairs. An alternative method attacks invisibly from the inside of the tube: If the opening in the bottom bracket shell or head tube allows it, a kind of balloon is covered with the laminate, pushed through to the damaged area, inflated and thus presses the repair material into place from the inside - with counter-pressure from the outside if necessary. Such a repair is invisible on the outside, but because it cannot be sanded down, it makes the frame a few grams heavier.
You have to be able to afford to be bothered by it: There's a lot of carbon out there, and it's getting more every day. The former miracle material has decided the material issue in its favour from the middle class upwards. It's not just environmentalists who are worried about this. But as the number of problems has grown, so has the quality of the solutions: repairing kinked, crushed and perforated pipes is filling the order books of specialists. And this option is a real comfort to anyone who suffers a 3000-euro driving error.
Carbon repair: How it works with a professional
Carbon repair companies - a selection
- Carbon Bike Service Amtzell (Lake Constance) Tel. 07520/9139999
- Carbon Clinic Riederau a. Ammersee
- CarboRep Erlangen, Tel. 09131/9725848
- Phoenix Carbon Bad Honnef
- PolyTube Cycles Hückelhoven, Tel. 02433/4 58 45 70
- Triple M Kallwang (AT), Tel. 0043/ 676/ 3601242
Carbon repairs: What works, what doesn't?
Not every repairer deals with every conceivable type of damage. However, the professionals we interviewed were fairly unanimous as to which standard damage can be repaired in a technically sensible way.
Rims
Carbon rims that have buckled due to massive rock contact can hardly be repaired satisfactorily. There is a risk of imbalance and the cost of an exact rim profile is immense. A new rim is usually cheaper. Individual spokes torn out of the rim base, on the other hand, are worth enquiring about.
Bearing seats
Corrosion between aluminium inserts and carbon frame on the rear triangle, worn press-fit bearing seats - these can be saved in case of doubt. If necessary, a suitable aluminium sleeve can be re-turned and laminated in.
Handlebars, seat post
A broken handlebar or cracked seat post can often be repaired in theory. However, even if safety is guaranteed, this is usually not technically or economically viable. An exception could be seat posts with a very special cross-section, which are no longer available as spare parts.
Frame tubes
Repairs to the tube run are the classic problem among the experts we interviewed. Almost everything, from a forced break to a chain suck to a longitudinal crush, can be repaired. Prices start at two to three hundred euros without painting. That can easily be worth it.
Dropout
Right-hand dropouts and derailleur hanger are frequent victims of chain salad and rocks on the side of the road. Such a crash can even completely tear away the thread of the thru axle. In the vast majority of cases, the damage can be repaired.
Pedal cranks
The laminated pedal threads are exposed to extreme loads and can come loose in the long term or if the pedal is hit hard. What a pity! Damage to carbon cranks requires such extensive restoration work that a replacement is almost always cheaper. In some cases, however, re-gluing is possible.
No safety concerns with repaired carbon - Interview with Dirk Zedler
Dirk Zedler, bicycle and e-bike expert, knows from his own investigations: Carbon frames and parts that have been professionally repaired also hold up reliably in off-road use.
BIKE: What typical frame damage can be repaired without hesitation?
DIRK ZEDLER: A top tube destroyed by falling over or handlebar impact and a torn dropout are the frontrunners in terms of damage. Then there are down tubes that have been crushed when riding over obstacles. All of these repairs are actually manageable in the course of the tube. I have no safety concerns if an experienced specialist repairs them. Some time ago, we analysed overhauled frames in breakage tests: none of them broke at the repaired point.
And where are the limits?
I would not recommend repairing handlebars or seat posts. These parts are most likely to have safety problems anyway. It is also difficult if you want a repair to be completely invisible. This is only possible with a lot of effort and a good painter. But then the paintwork may be more expensive than the repair. The price often marks the limit of what makes sense.
To what extent and for how long is the repair company liable for its work?
If the company doesn't give a more extensive warranty, it's a two-year warranty. But we've never had a lawsuit on the table involving such things. Professional repairs last!
How does carbon compare with metals in terms of repairability?
Even if carbon certainly doesn't have a great environmental footprint: It is easier and more reliable to repair than aluminium. And fatigue fractures are practically non-existent.
Gradual healing of carbon damage to the bike
1. take a photo
Regardless of whether it was an open break in the frame tube or an unclear "crack" in the assembly stand: The repair companies appreciate clear photos and a precise, written description of the damage before sending it to them. They tend to have little time for detailed phone calls.
2. check damage
Does the crack in the paintwork indicate damage to the carbon fibre? Experienced repairers can often find this out on test benches without having to completely remove the paint: damage in the tube reduces the frame stiffness.
3. lamination
The actual job of the repairer. Cracks and holes disappear with fibre material and resin, sandpaper and shrink film.
4. varnishing
Some repairers also paint, including restoring logos. Others have tried and tested partner companies. The finish can be expensive: Always take this into account!
