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Technical FAQ: Resurfacing carbon brake tracks, disc/caliper combos, and more

In this week's Technical FAQ, Lennard Zinn answers questions about resurfacing brake tracks, disc/caliper combos, and more

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Re-surfacing brake tracks

Dear Lennard,
I have a set of Easton EC 90 carbon tubular rims that I use for ’cross. They are awesome despite being a little more than four years old and showing wear on the braking surface (they are not disc brakes). Can the braking surface be resurfaced? If so, how? Do you have any experience with this?

They’re great wheels that I am not able to replace at the moment and upgrading to discs is totally out of the question right now. It seems like ’cross can wear the surface down more than road use, so I would like to think there is a solution out there besides buying new wheels. But I am not aware of how it is all done. I would love any advice you could give!
— Dan

Dear Dan,
It had never occurred to me before to even think of doing such a thing. I am very interested to know as well and did some research on it. Unfortunately, the brake track cannot be resurfaced, if you mean by adding material, by any of the manufacturers I’ve contacted. Their responses are below. I also asked carbon-fiber repair firms, and only one of them would do it, and the others offered reasons for not doing so. See those responses below as well. If you were to somehow resurface it, I’m certain that it would void any manufacturer warranty you might have on the wheel.
― Lennard

From Reynolds:

Inherent in high-performance rims is the design concept for minimum wall thickness that will provide a “reasonable” life span. Unfortunately, this means that there is no additional sacrificial material that could be machined off in a resurfacing operation. In theory, ceramic could be deposited on the worn surface, and then ground smooth. As you may recall, I laminated a ceramic layer onto the surface of the carbon during the molding process (it was a production product for Lew rims), and also experimented with ceramic that was deposited after molding, and then ground smooth (never a Lew production process). For reasons not pertinent to this topic, neither is ideal as a current state-of-the-art solution for a new/production rim, however with significant resources (more cost than the cost of a new rim), a ceramic compound could be deposited to the braking surface of a worn rim and then ground smooth. This would be a solution/process for resurfacing a worn braking surface on a carbon rim.

Reynolds manufactures a ceramic brake track rim that is sold under the brand Pacific Rims, and it is sold as an OEM product to certain customers who request this brake track. The reason we do this is to avoid the hassle of needing to use a special brake pad. The ceramic makes the braking surface super durable and although it’s not marketed as a CX product, it would work well for that application. The down side of this rim is that the braking is not optimized for stopping power or heat-resistance, and it does not perform as well as our CTg laminate with the Cryo-Blue pad. It would, however, solve the problem Dan has experienced associated with CX use.
— Paul Lew
Director of Technology and Innovation Reynolds Cycling, LLC

From Zipp:

I can only speak for ours, officially. But they cannot. Most brake track surfaces, ours included, are integrally constructed and are not capable of being deconstructed to resurface them.
— David Ripley
Technical PR Manager
Zipp Speed Weaponry

From DT Swiss:

On the record, we do not recommend “resurfacing” of our carbon braking surfaces due to all of the variables involved. Especially given the brake track is both a structural and functional part of the rim. This is because we simply cannot vouch for the quality, materials used or the experience possessed by the facility or technician on a repair in the field.
— Matthew McClendon
Marketing/Account Executive
DT Swiss, Inc.

From ENVE:

No, there is not a process that can add material to a brake track after it has worn away. I mean, you could do it, but the structure just wouldn’t be there.

Riders would do best to just ensure they keep their pads fresh and clean/clear of debris.
— Jake Pantone
Marketing and Sponsorship Manager
ENVE Composites

From Easton:

During normal use, the carbon on the brake surface will wear. This typically takes longer than with aluminum if the correct pads are used, however weather has a big effect on the duration. There is no process for resurfacing the braking area of a carbon tubular or clincher rim.
— Adam Marriott
Product Manager, Easton Cycling

From Mad Fiber:

No one has commercialized brake surface renewal on carbon rims. Partly it’s the obvious trend we haven’t yet outgrown, that carbon rims should be extra light. So damage befalls them usually before brake track failure. Also, many carbon rims outlast the equivalent aluminum for braking, so the incentive is weaker. But probably the strongest trend is obsolescence. We’re learning so much, several year old carbon rims are relics. This won’t always be as the technology matures.

Today, there’s no agreement on resin systems for carbon bike equipment and that chemistry is key. Various systems are not compatible for a dozen reasons. You’d have to know everything proprietary about the original system to succeed. The very fact of widespread, successful carbon frame repair shows how much less is expected of them (gram for gram) compared to wheels and rims. You can often just layer it on thoughtfully and without regard for any thermal events. And the resulting weight increase is acceptable.

But I still dream of some sort of plasma/ceramic paint that fixes the worn brake track. We’ll probably all be switched to disks before that comes around.
— Ric Hjertberg
Founder, Mad Fiber

From Velomax:

I am assuming by “resurface” he means sanding down or otherwise abrading the existing surface to make it smooth again, since laminating a composite to an existing structure is beyond the experience of the average person.

The brake surfaces are intended to accommodate wear due to the natural abrasion of the brake shoes. For the most part, this wear is imprecise, so the laminate of the brake track is constructed with the knowledge that wear will occur. So it stands to reason that controlled wear, in this case intentionally resurfacing the brake tracks (by sanding them down), shouldn’t be any worse than brake shoe wear. But there are limitations.

Carbon fiber does not have good abrasion resistance, so the brake track area typically has a non-carbon fiber scrim (typically fiberglass) as its top surface. When you wear through this layer, your rim’s days are numbered. Also, any layup requires overlap of the plies, so in some areas of the brake track the abrasion layer scrim will be twice as thick where layers overlap. When you start to wear through the scrim, there will be areas of the brake track that are worn down to the carbon fiber, and other areas that are still scrim. The friction of the different materials will also be different, which could be one of the reasons that the user is experiencing uneven braking. So in this case, refinishing means removing all the remaining scrim so that the only thing that remains is the carbon.

At some point, the brake track is simply worn too thin, and the wheel is done. This situation is no different for an alloy rim. Also, at some point the rim is simply worn out, and needs to be replaced.
— Brad Hunter
Founder, Velomax

Answers from carbon fiber repair professionals
From Calfee Design:

Generally, no. Rims have the potential to become heated beyond the glass transition temperature of the epoxies we can use for repairs. This would cause the material to become soft and gum up the brake pads, potentially locking up the wheel, causing an accident. Having said that, a person could resurface it with epoxy but make sure to never let the rims get too heated while braking. Best to transfer the fancy rims to a disc compatible hub and never use rim brakes on them again. One should not use rim brakes on carbon rims unless you are prepared to replace them when worn out.
— Craig Calfee
Founder, Calfee Design

From Broken Carbon:

Unfortunately I can’t. I don’t know anyone that can, as a matter of fact. It’s just too hard to get the width uniformity required for consistent braking.
— Brady Kappius
Founder, Broken Carbon

From Spyder Composites:

Yes we do/have, but only if we can’t talk the customer into a new set of hoops through their LBS. The way I see it, if the owner is experiencing brake wear problems he is using the wrong pads, the wrong rims, or the equipment is past its useful life and he/she needs to treat themselves to a new set of wheels.

We do have a device similar to a truing stand we use to machine the brake surface before and after we coat the rim.
— Frank Moir, Owner
Spyder Composites

From Ruckus Components:

We used to offer this as a service but don’t anymore. It just turned out to be too much work on our end.
— Shawn Small
Chief Engineer
Ruckus Components

Disc/caliper brake combo

Dear Lennard,
With the trend toward disc brakes on road bikes, why bother with a disc on the rear? It would make carbon rims without special braking surfaces possible, but isn’t the vast majority of stopping power in the front? With front disc and rear caliper, people could retrofit existing bikes just by replacing the fork.
— Russ

Dear Russ,
You could run a standard rim brake on the rear and a disc on the front. That’s how mountain bikes used to be when disc brakes first came out — a V-brake on the rear and a disc brake on the front. Then you only buy one wheel, one brake, and the fork.
― Lennard

Feedback: Avoiding derailleur hanger damage when shipping a bike

Dear Lennard,
After having a handful of occasions where my hanger has been bent despite removing the derailleur, I leave the derailleur on the hanger but remove the hanger/derailleur combination from the frame. This eliminates the need to carry a DAG in your box.
— Darius

Feedback: Anti-seize lube

Dear Lennard,
I read about your pet peeve regarding copper-based anti-seize. I’ve been using moly-based engine assembly lube where anti-seize lube is needed. It works great and doesn’t have issues with copper flakes like other anti-seize compounds. You can pick some up fairly cheap at most auto parts stores.
— Kevin

An American in France

What’s it like to be an American cyclist living in France? Watch to get professional road cyclist Joe Dombrowski’s view.