Repair quotes from photos
We get lots of inquiries where people send a photo of the damage found on their bike and ask us for a repair quote.
Mostly it isn't possible to do this because the majority of structural damage is often not visible on the surface, but within the carbon "laminate". As discussed in previous articles, carbon composite is made up of many thin layers and the common failure mode is for these layers to separate, we call this delamination.
This is why we use Ultrasound scans to determine the extent of the structural damage that requires repair, in the same way the aerospace industry does.
Ultrasound is the method of choice for finding delamination in carbon composite due to it's sensitivity and accuracy. With our methods we can find critical damage which could cause a catastrophic failure that would otherwise be unseen until it's too late.
There have been many cases where a frame comes in with what looks like a small mark on the top tube or even no visible mark at all. When the Ultrasound scan is done however we find large areas of tube to be delaminated, sometimes this renders the frame beyond the point of a safe repair and it is recommended to replace the frame.
Photos can still be useful for quoting on the paint repair of the item and based on experience if the part should be even considered for an assessment, however photos do not tell much of a story on what the significance of the structural damage may be.
Ride safe.
Crazy Advertising Claims
I often see and hear advertisements from repairers saying that after their repair the bike is "as good as new" or "even better than new". This may be the case for the paint, however the structure is a bit different.
These sort of comments just highlight a lack of understanding on composite materials. The fundamental principal of advanced composites is having a strong well aligned fibre carrying the load. Once this fibre is broken or cut, it will never be the same.
The way loads flow through the structure will be different and with an optimised laminate there is not much room for error as the margin of safety is quite low. This is evident in the way frame weights have been getting lower and lower. As the design loads are better understood the factor of safety tends to go down.
So what does all this mean for a repair?
A well executed repair should meet the original parts properties allowable specification. That is the part should be able to meet acceptable load criteria.
It is also very important to match the stiffness of the original part to avoid stress concentrations adjacent to the repair, thus it is important to match the materials as close as possible and infact not be "much stronger" than original.
Because there is an area of discontinuous fibre it will never be exactly the same because the repair is dependant on a good bond interface to the existing material. This is why resin selection for repair is critical as it needs to be an adhesive as well as a resin.
So theoretically a repair will never be as good as new, however it should be within the acceptable design limits of the structure allowing further use of the part.
How does this relate to bike frames?
The good news is that typical bike frames are made up of sections joined together, often in a similar way a proper repair is done. The frames are made of many smaller pieces of fibre joined together so the discontinuous fibre theory is less relevant, depending on the location within the frame. Frames are nowhere near the fully optimised continuous fibre theoretical ideal due to production limitations.
In almost all cases with a well executed repair on a bicycle frame you will not be able to notice any of these small changes in the way the load flows through the part. The bike will ride the same as before and the final weight after repair should also be close to the original.
The other popular myth is "undetectable repairs", well, they are detectable to us as we have specialist Non Destructive Inspection methods such as Ultrasound and our other techniques. With these methods we can find defects that the manufacturer doesn't know exist. These methods are required for composites used in aerospace, particularly repair so as to provide quality assurance that the repair is within the specification. These methods provide safety for flying in an aircraft and with our process when"low flying" on your bike!
For further information read the article below:
Black Art or Engineering article here.
Why Use Ultrasound article here
Internal Electronic Shifting Conversions
We often get asked about doing internal Di2/EPS conversions to frames that were not originally designed with this in mind.
Can I just drill a few holes where I want the cables to come out?
Drilling holes in a frame is NOT recommended, be it carbon, aluminium, steel or titanium.
Performance bicycle frames have been engineered in the factory to have minimum weight for the loads placed upon them. Drilling a hole removes material needed to carry the loads and also acts a stress concentration.
A factory ready electronic shifting frame has had analysis done on the structural implications of the holes and extra material placed around the area to distribute the loads. The location of each hole and the structural design is carefully considered to ensure it is safe.
Without this analysis the frame is NOT safe to ride.
The image above is an extract from the Kenworth truck manual. As you can see they have very clear guidelines for drilling holes in the chassis. They are rightly concerned about the structural implications of drilling holes in 10mm thick steel beams.
Drilling holes in the frame will also void your factory warranty and also may have legal implications if it fails and people get hurt. Yes we are conservative, all those years working with aircraft we used to say “nobody wants a plane to fall out of the sky”. The same way I don’t want to see people get hurt while out enjoying riding their bikes.
The battery also needs to be considered, Lithium batteries without the correct protection circuit are prone to fire if incorrectly handled, you definitely do not want an internal fire in the seat tube of your carbon frame. This issue actually recently grounded the Boeing 787 fleet
We always recommend using a frame and parts designed and tested for the purpose intended.
Safe riding.
Repair article in MTBA Magazine
Here is an article that was published by MTBA Magazine about carbon repair on mountain bikes.
John Hardwick (the Editor at MTBA) came to our workshop and documented a typical repair, on his own Scott Spark which suffered top tube damage.
The article in pdf format can be found here (1.1Mb)
A close up look at carbon.
Here is a video showing a close up view of what carbon really is.