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Dear Lennard,
An x-ray technician recently told me that fluorescent penetrant inspection could work to inspect carbon fiber parts for defects. Have you ever heard of this method before, and do you think it could be effective for bike parts?
—Chris
- Breaking or cracking your carbon fibre bike is every cyclist's worst nightmare! Ollie took a visit to Carbon Bike Repair to find out if carbon is repairable.
- Carbon fiber is so densely compacted, and the fibers are layered in such precise orientations, that a small crunch tends to stay small, unlike fiberglass that once it shatters or delaminates, there's no telling how far it's split.
- If the seat tube is cracked, it'll keep cracking no matter what you do as a workaround, short of welding it up to stop the crack from growing. Then you might need the shim. And who knows what else, which is probably why Calfee said they couldn't fix it.
Dear Chris,
Good question! Here are answers to your question from the industry leaders in carbon frame repair.
― Lennard
From Calfee Design:
“It can help to see the very fine cracks on damaged frames. But we use a 10X loupe for that.”
Craig Calfee
Calfee Design, Inc.
Carbon frames can break certainly, and we’ve seen more than a few torn, crushed or punctured tubes come through our office, but the method of failure is different. I spent a good afternoon surfing the internet trying to find examples of carbon frames or forks which had snapped suddenly while being ridden due to an unnoticed fault or previous.
From Ruckus Composites:
“We have been using fluorescent penetrant dye for about 8 years out here. Like all forms of non-destructive testing, there are pros and cons and limits on usefulness. Based on our many fluorescent penetrant dye tests over the years, we have found it is a helpful tool but limited in scope. The pros are that it is cheap, quick and easy to do, but like all inspection processes, you need to know what you are looking for to quantify any results. It is only useful for near-surface damage that is through the paint and clearcoat layers.
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There are also many types of dyes out there. Fluoro dye testing is primarily used for crack detection in metallic surfaces; I believe the train industry popularized it. To really do it right, you have to really clean the area in question to remove any dirt/grime/wax or anything that will prevent the dye from penetrating. Another aspect that makes it difficult on bikes is that you really need to soak out the area in question for a period at a specific temperature for proper penetration. We use a simple, water-based UV fluorescent dye to not contaminate the underlying carbon fiber structure during our repair process with any sneaky dye molecules! While it is another useful tool for a proper carbon fiber facility, because of the thin materials used on all bike frames and components, you can most likely visually see any cracks developing if you use a good inspection flashlight and take your time. But UV dyes make for some very compelling images!
Shawn Small
Owner/Engineer, Ruckus Composites
Dear Lennard,
For a long time, I have been whining about the lousy skewers that Rocky Mounts are using on their roof racks. How after a month they no longer lock, and, unless if they’re lubed regularly, they get really stiff and don’t clamp properly. Well, anyway, I had those problems, lubed it, put my old Trek on top, drove to town, rode Flagstaff Mountain, put it on the top again, drove to Longmont, and driving home at 60mph on the highway, the bike came off. Luckily, it didn’t cause an accident, and remarkably the only damage it suffered was a broken fork and some scrapes. There is no other visible structural damage.
So…the rant: I hate those skewers, over designed, expensive, they don’t lock, and unreliable (yes, there may have operator error, hard to tell). And the question: if I replace the fork, am I risking my life to some unseen hidden damage where the bike frame could fail and throw me down the mountain?
—Derek
Dear Derek,
Bummer! Glad you asked. Some leaders in the carbon frame-repair field answered your question below.
― Lennard
From Broken Carbon:
“Any time we come across a situation like this, we automatically recommend a replacement frame. Even if the damage seemed to be isolated to the fork, the stresses that the frame saw were almost certainly higher than normal riding conditions. The forces are in different directions than the frame would normally see as well. It’s just not worth the risk of something happening down the line.”
Brady Kappius
Founder, Broken Carbon
From Calfee Design:
“We do this kind of inspection quite a bit. We clean the frame and look closely for cracks. A coin tap test is very effective. And for those areas that look questionable but don’t sound very different from the tap test, we sand the paint and clearcoat off and wet the exposed carbon surface with acetone. You can quickly see where acetone stays wet in a crack as it evaporates. Similar to the flouro-dye test but without the flashy colors. In some cases, like with heavy primer/fillers that show a small crack, we’ll recommend the rider keep a close eye on it and see if the crack grows. A tiny mark is placed at the end of the crack with a razor blade. 90% of the time, it’s a paint crack that doesn’t grow. 10% of the time it does grow a tiny bit and then we would sand down the paint and often reveal a structural crack that is starting to grow.
Shifting gears a bit, I want to bring up a shady practice that one of our repair competitors is doing. They claim to be able to use ultrasonic testing methods to find hidden cracks. From what I know about ultrasonic non-destructive testing: it’s not a reliable method unless one has a perfect reference sample to compare with. And that’s only with sophisticated (expensive) equipment.
Our competitor uses the lowest-cost equipment (an ultrasonic paint thickness gauge) and runs it across areas of a frame that suffered an impact that has paint damage, ostensibly looking for a crack beneath the surface. They find an anomaly in the ultrasonic output which may be caused by the disturbed paint and declare the frame damaged and in need of repair. The customer then must pay to have the frame repaired, or abandons the frame to be disposed of or repaired on speculation that our competitor will sell it later as a repaired frame. Furthermore, competitor claims to be certified by the ASNT Level II. A quick check on ASNT.org and you can see they are not listed. Also, the competitor publishes that it’s the American Standard for Non Destructive Testing (as shown in attached screenshot). But ASNT is actually the American Society of Non Destructive Testing. A convenient mistake?
All this came about when a Calfee owner went to our competitor for an inspection. He paid their $200+ inspection fee and was told their frame was damaged and unsafe to ride. Not feeling confident of that evaluation, he sent us the frame. We inspected it and found no damage beyond some chipped paint. I’ve got photos proving all of this if you are interested. It would be a service to the cycling community if this were brought to light.”
Craig Calfee
Founder, Calfee Design, Inc.
From Ruckus Composites:
“Great question and a surprisingly common scenario. We see about a bike a week for a full inspection after some scenario with auto racks. I usually look at it from a projectile motion viewpoint. Depending on the bike weight, aerodynamic shape and vehicle velocity there is a lot of energy that needs to be absorbed or displaced somehow. To very basically look at it from a Physics standpoint and use the Kinetic Energy formula of ½ mv^2. (m=25 lbs v=65 mph) you get a shocking nearly 4800 Joules of energy that has to go somewhere. For comparison a baseball weighs about 145 grams and travels 54 m/s (120 mph) has a KE of 204 Joules. A 0.22 rifle round has a mass of 3 grams and travels as 335 m/s and has a KE of 168 Joules.
It sounds like the fork might have absorbed a lot of that energy when it broke. From my experience, the frame is likely damaged as well. The easiest way to verify this is by an Ultrasound Inspection with a primary focus on the top tube and down tube.”
Shawn Small
Owner/Engineer, Ruckus Composites
Dear Lennard,
I have an e-bike, and it has to be leaning on a wall perfectly still when I turn it on, or I get an error code. Holding it up isn’t good enough. Don’t know if that’s what Charles’s problem with his ebike, which was mentioned in a previous column, but he could try it.
—Tamar
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is a custom frame builder and purveyor of non-custom huge bikes, a former U.S. national team rider, co-author ofThe Haywire Heart, and author of many bicycle books including (DVD), as well as Zinn and the Art of Triathlon Bikesand Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a bachelor’s in physics from Colorado College.
Follow @lennardzinn
Carbon bike builders want you to buy new frames when you break one. We’re here to say you don’t have to.
Carbon Frame Seat Tube Crack Kit
Mountain bikers fully adopted the use of carbon as a frame material over the past decade, but not without hesitation. The lightweight and desirable ride characteristics outweigh the material’s impact fragility and premium price in the mind of most riders I know.
But stories of small cracks leading to unrideable frames also abound.
I personally had three frames already in my stable of “retired” broken carbon frames before an experience in New Zealand led me down the path toward repair.
“Just send it to the shop and they’ll fix it right up,” the nonchalant Kiwi told me. And the journey began.
‘Sketchy’ World Of Carbon Bike Repair
And so I learned about the seemingly sketchy world of repairing a carbon fiber mountain bike. Universally, every single bike brand I talked to told me this was NOT A GOOD IDEA. They spouted all sorts of reasons from liability concerns, to the difficulty of the procedure, to the danger of a repair failing during extreme riding.
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The brands all suggested repair was not worth the risk and buying a discounted replacement was the safest option. Most brands warranty frames against manufacturing defects. In all but one of the frames, brands declared damage unequivocally my fault (or the airlines’, shippers’, etc).
DIY Carbon Repair?
I bought a $99 DIY carbon repair kit from Amazon and tried my hand at a repair. In the end, it was more than I felt comfortable with, and the voices of the bike manufacturer’s warning echoed in my head: “What if it breaks when you are riding?”
My repair was ugly and rough. I was too timid to do anything but ride lightly on pavement.
Professional Carbon Bike Repair
But then I found Appleman Cycles based out of Minneapolis.
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From the website:
“Appleman Bicycles can repair your damaged, broken, busted, or cracked carbon fiber frame! Nearly every carbon fiber frame can be repaired no matter how severe the damage. I use my vast knowledge and experience in advanced carbon fiber structure repair to bring your bike back to it’s original strength, safely. With a turnaround time of 3 days, you’ll have your bike back quickly.
It’s a myth that carbon can’t be repaired. In fact, carbon fiber is one of the most repairable materials and each Appleman repair is covered by a 10 year warranty! Repairs add no measurable weight and don’t alter the ride of the bike.
–
Don’t worry… get it repaired!”
Oh snap! Carbon frame before repair
Interview: Carbon Frame Repair Expert
Matt Appleman has fixed carbon frames since 2011. He also repairs wind turbine blades in his role as a composite engineer.
I sent him two frames and a host of questions. I wanted to know if his repairs would last.
Most bike manufacturers recommend against this practice – but your website (and others) claim it is very safe. Why do you think there is a disconnect?
Most people don’t know that carbon fiber is the most repairable material. As they say in The Princess Bride, “Anyone who says differently is selling something.” Repair is bad business for big manufacturers. Legally speaking, they want to limit their liability. Financially, they want to sell you a new frame.
How many carbon repairs (frames) have you done?
I’ve done 350 frame repairs (1,000+ counting wind turbine repair). I’m a one-man shop and split my time between building custom carbon fiber frames and repair work.
Are there certain breaks that you would not repair? What and Why?
I don’t repair carbon fiber components: handlebars, forks, seat posts and the like. It’s cheaper to get a new part.
Rims: you have so much heat, friction, and extremely high forces on very small areas that repair isn’t practical. On the other hand, disc wheels (as in TT disc wheels) are repairable, except along the brake track. It’s pretty common for them to get pierced by a pedal during transportation.
I tend not to repair damaged or loose metal bottom bracket sleeves. These sleeves often loosen up because of poor frame design, and I can’t fix poor design. Sure, I could re-glue it and it might last you a season, but I don’t perform a repair if it’s not going to last for the long haul.
Have you ever had a repair fail?
Nope. I don’t repair a frame unless I know it’s going to be durable and outlast the rest of the bike! Strength and durability are my primary concerns. Sometimes someone brings me a frame that can’t be repaired safely and I hate to be the bearer of bad news, but a repair doesn’t make sense in some situations.
Are there different concerns/steps in repairing a damaged road bike vs. mountain bike?
Every frame is unique whether it’s a road or mountain frame, so it gets a unique repair. I dig into the frame and see what is damaged, how deep, and to what extent. Repair is part art and part science. I combine these two to evaluate, design, and perform the repair.
So yes, a mountain bike repair will be different than a road bike repair because the bike was (hopefully) designed to be stronger. That being said, even repairing the seat stays of two road bikes will be slightly different as they’re different bikes. I can read carbon fiber damage like a book.
What is the average price range of a carbon repair from your shop?
The vast majority of repairs are $300 for your typical seat stay, chain stay, and top tube damages. Other repairs range from $250-$400.
Turnaround time?
Standard turnaround time is one to two weeks. I offer expedited repair of about 24 hours for an additional $50. I also have the ability to do same day turnarounds for emergencies.
Being that I don’t do any paint work, I am able to turn repairs around quickly. Paint adds a lot of time and cost to the repair. I’m very practical and structurally-minded when doing repairs so I choose to show raw repair.
It’s also a myth that carbon fiber needs to be “protected” or “covered” so that the elements don’t damage it. This is false. In fact, carbon fiber/epoxy is chemically inert and doesn’t react to the elements.
What is the most technical/difficult part of the repair process?
I think carbon repair as a whole is all technical and each step has its own technical aspects. I’ve been doing repairs long enough it has become second nature, but I really enjoy the breadth of knowledge required of the repair process. Diagnosing damage, paint removal, layup design, applying the layup to the frame — it’s all technical, and requires a lot of practice and skill to perform efficiently.
What are the most common things you repair?
Seat stays and chainstays are by far the most damaged tubes. The stays are wider on the frame and less protected by the rider in the event of a crash. Seat stays are especially prone to damage as they are the least structural tube of the frame and the most exposed.
Do you make custom frames?
Yup. I build full carbon fiber frames for road, CX, mountain, and gravel riding. I customize every tube to the rider’s height, weight, and riding style. This deep level of customization through varying carbon materials, layup schedules, and diameter helps create the wonderful, lively ride Appleman is known for. Doing repair certainly upped my custom frame builds as well. When doing repairs I get great insight on what breaks, why, and where. I take these cues and design my frames to be tougher, stronger, and more durable than mass produced bikes.
Repaired Carbon-Fiber Frames Tested
I’ve repaired four frames total now (both at Appleman and a shop in New Zealand), and spent the last season training and racing on these repaired frames. The first few rides always spooked me going hard into any rough section or fast corner. But I soon forgot, so much so I’ve loaned the bikes out to other traveling racers with full confidence.
The only downside I can think of is that now I am even rougher on my bikes, taking less care in packing my bike for long flights and bumpy truck rides.
But as they say, “diamonds last forever.” And diamonds indeed are made of carbon.