Why carbon frame damage needn’t mean the scrapheap for your bike

Inside Australian composites repair facility Paint My Bike

Carbon fibre is a bit of a wonder material in the cycling world. It’s lightweight, and depending on the layup can be tuned to be stiff on one axis, and noodly on another. It can also be moulded into radical shapes to cheat the wind.


Unfortunately for such a cycling industry mainstay, the high-modulus carbon used in bike frames and components is quite brittle, despite its high tensile strength. Designed to handle forces on a certain axis, a sharp impact from a different direction, say from a crash, has the potential to cause serious damage.

Take a look through any secondhand bike site and you’ll find pages of late model carbon frames with cracks, broken seatstays, and crushed carbon parts. Fortunately though, if you’ve got a broken bike all may not be lost – because quite a lot of damaged carbon fibre can be repaired.

Here you can see the repair in progress from the inside, but also the joint when the frame sections were bonded together during manufacturing:

You can see the spot where this frame was bonded together at the factory. You can also see the extra filler material used in the joint

Keen to find out more, we were pleased when Australian repair shop Paint My Bike invited BikeRadar behind the scenes to see how its team breath life back into beaten and battered rides.

“When you think about it, most frames are moulded in pieces and then bonded together. We do essentially the same thing when we’re repairing a frame,” explains Gary McDonald from Australian repair shop Paint My Bike.

“You’d be surprised how many integrated seatposts cut too short we get from bike shops. We’ve even had quite a few frames come in for repair, and as we sand the paint off we find repairs that look like they’ve been done before the bike ever left the factory.”

Fixing a carbon frame is, in fact, considerably easier and more effective than trying to mend a broken alloy one, and the repair will be as strong or stronger than the surrounding material. Yes, there is a slight weight gain, but we’re talking less than the difference between an aluminium and titanium bottle cage bolt.

Even better, composite repair specialists that fix up your injured steed can also seamlessly match paintwork and decals, leaving even the most scrutinising eyes none the wiser.

Seamless repairs

Housed in a rather industrial looking area, and hidden inside an unassuming blue building, Paint My Bike has a fully outfitted composite repair facility as well as – likeits name suggests – a high-end spray booth.

“Every repair we do, we want to be seamless both in paint but also in tube shape and thickness,” McDonald tells BikeRadar. “Not only do we want to avoid that big black ball of carbon at the repair site because it’s ugly, but the mass of material creates a weak point on either side of the repair.”

There isn’t a whole lot on a bike that cannot be repaired, and a quick look around the workshop reveals everything from classic frames from the early days of carbon fibre, to bikes that couldn’t be more than a week old. Damage ranges from crushed steerer tubes to broken forks and sheared seatstays. Plenty of bikes have sustained damage from roof racks.

With the paint removed we can see the size of the crack:

Your broken frame can probably be fixed

For each repair as the paint is sanded back to determine the extent of the damage, the layup is also visually assessed and will be matched where possible. That said, concessions in creating an identical layup will be made to ensure a strong repair, and McDonald explained that cross woven twill carbon is sometimes used in place of unidirectional, “so there are fibres in more directions with less layers”

As the layup plays a major factor in the ride quality of a carbon frame, you’d think removing or replacing a piece would make a noticeable difference. Paint My Bike worked extensively with now defunct Aussie pro team Budget Forklifts, fixing all manner of damage on team bikes, and McDonald and crew would quiz the riders to see if they could pick up any difference.

“Not a single rider could feel a difference in ride quality, even after sizable repairs,” McDonald says.

Your bike isn’t a plane

When you research carbon repair, often you’ll find outfits using ultrasound machines for ‘ultimate accuracy’ in diagnosing the extent of the damage to your frame. This method is used in the aerospace industry, when the failure of a few fibres could mean the deaths of hundreds of people. There’s a few repairers use this method, and even Canyon says it puts bikes through a scanner when they come back for warranties, but according to McDonald that’s not necessarily the best method for determining the damage to carbon bikes.

“With ultrasound it’s very difficult to pick up cracks – it mostly finds voids and delamination. From our experience it also can’t tell the difference between filler and a void,” he says. “Almost every bike manufacturer uses filler between joins and over imperfections in the frame, and these show up as voids on ultrasound. Many brand new frames will fail an ultrasound test, a bike is not a plane and they are not manufactured to the same standards.”

The aerospace approved tool for determining if the carbon components a plane is damaged. they work pretty well on bikes too:

This is the aerospace approved tool for finding damage to carbon fibre

“The aerospace approved method for finding damage to carbon fibre is an acoustic tap hammer. If you go down to the airport right now you’ll find engineers tapping around looking for damage.” McDonald says.

If we learned one thing from the day, it’s that there’s no sense crying over frayed fibres and cracked tubing – find out how to get them fixed. Check out the mega gallery above to find out more about carbon repair.


*This is not a ‘How to’ article, nor is it comprehensive in the techniques used as each repairer has their own method, and there were a few things that the staff at Paint My Bike wanted to keep under wraps.