Black Art or Engineering
There is a perception that working with carbon is some kind of "Black art", that it is done by people who have some kind of magic touch to get things looking right again.
Let's dispel that myth right now, it is NOT a black art, it is Engineering pure and simple.
Repairing a carbon bike is engineering because it is a loaded structure. Riding a bicycle particularly at speed such as descending or sprinting places large loads on the individual parts and these parts need to be engineered to deal with those loads. A repair is no different, the repair needs to be engineered and designed just as the frame is engineered and designed or it will fail just like a poorly designed frame fails.
When repairing a carbon bike the first most obvious step is to know what damage exists, how does one repair something without knowing the full extent of the damage. As in aerospace the best method for this on bikes is an Ultrasound scan.
Once the damage has been assessed the repair needs to be designed so that the part will perform in a similar way under load as it did pre-repair. The number of plies, the ply angles, the grade of carbon, resin and the compaction level, all need to be considered. Substituting these factors will have an effect on the bikes ability to perform under load.
If these factors are not fully considered, for example by simply wrapping extra layers of carbon around the damage, the load paths will be significantly different. The repair may not fail itself, as it is probably significantly stronger and stiffer than the originally designed frame however the frame will fail next to the repair. This is obviously not a well engineered approach.
As discussed in previous technical articles, the resins ability to perform at different temperatures is also critical. Use the wrong resin and the repair may not perform on a hot day, causing a failure. The weight of the repair should also not be significantly different to the original. For many common repairs the frame should be within 10 grams of the original weight.
Of particular concern is the idea that as long as the repair looks good visually, everything is ok. When people pick up their bike from us they say "it looks good", because this is what they see. However the underlying structure is what really matters. A poor structural repair can be painted to look nice, but will it have the right structural properties to perform as required? When descending a mountain at 90 kph, do you think of the bling paint job or if the bike will hold together?
The thing about failures is that they typically occur when the loads are the highest and thus the consequences of the failure are also the highest. Sprinting at full power or high speed descents down mountains can cause serious injury or even death if the frame fails. This is serious, repairs just like bikes needs to be engineered to perform.
In summary a good repair is engineered to perform just as the frame is engineered to perform, consider this when choosing a repair service.