Hole in Carbon RimI discovered a gaping hole about 1" x 3/8" in my carbon fiber rear rim, at a spoke. The rim is a Fulcrum S-19 Racing (22.5x622x28), that I ride on about 100 miles a week, so I imagine this rim is kaput.

The rims are about 4 years old and came on the Specialized Tarmac 2017 when I bought the bike. Right now I am using the bike for just regular road cycling, no racing, so I don't need the bike to be light and have carbon fiber.

#1 Are there any issues with switching both front and rear rims out for less expensive alloy rims?

#2 Can you just switch out one rim, the rear, and it change to alloy, and leave the other, the front rim, carbon fiber?

#3 Just to verify- the damaged rim is unfit for further use?

#4 Any point in installing the used rear cassette on a new alloy rim?

Thanks for any feedback - Street Roller

  • 1
    A clarification: are you sure these are carbon rims? I think this is an OEM wheelset that may have been similar to the Racing 4, and I know the Racing 4 is aluminum rims. Generally, higher-end bikes would come stock with carbon wheels. If that were carbon, I'd expect to see torn fibers at the part where the hole is.
    – Weiwen Ng
    Commented Jan 5, 2021 at 23:26
  • 2
    If the brake track is silver, it's definitely aluminum. Otherwise, you could Google the wheelset - the problem with this one is that the S19 may be an OEM-only wheelset, so I didn't find anything informative. Last, you could try tapping the rim with your fingernails. Carbon rims will sound more hollow than aluminum rims. Unfortunately, this is hard to describe in writing, and the difference is less than the difference between tapping frames with your fingernail. I just tried it, as I have one carbon and one aluminum wheelset in my house.
    – Weiwen Ng
    Commented Jan 5, 2021 at 23:34
  • 1
    That is an oddly-square hole.
    – Criggie
    Commented Jan 6, 2021 at 6:14
  • 1
    Worst comes to worst, carefully scratch the paint. If it’s shiny underneath, then it’s aluminum. If it’s dull and soft, then it’s carbon. The rim is probably beyond repair anyways so you won’t harm anything.
    – MaplePanda
    Commented Jan 6, 2021 at 7:59
  • 1
    This is a typical three letters agency assassination attempt. I would go off grid if I were you.
    – user54543
    Commented Jan 6, 2021 at 15:53

3 Answers 3


Consider yourself lucky that the wheel did not fail on you.

Are there any issues with switching both front and rear rims out for less expensive alloy rims?

No issues just tradeoffs based on what you have now (e.g. aero, weight, looks, etc.). Some brands I would look at are

  • Mercury Wheels - You could score some carbon aero wheels pretty cheap there. I am eyeing those potentially down the road

  • DT Swiss - I think their 1400 series alloy wheels are good, but pricy for an alloy wheel

  • Bontrager Paradigm Elite - Effectively I think Bontrager used a DT Swiss hub and possibly other parts to make their version of a super light alloy wheel

  • Mavic is another one that people have had good luck with too

Can you just switch out one rim, the rear, and it change to alloy, and leave the other, the front rim, carbon fiber?

No issues in doing that, but honestly if one wheel gave out like that, you may what to do both sooner than later.

Just to verify- the damaged rim is unfit for further use?

I am all for duct tape and super glue, but that wheel is done.

Any point in installing the used rear cassette on a new alloy rim?

Yea to save money. I mean an Ultegra Cassette is about $80-90 and if the one you have now is still good why not use it. If you have been on top of changing your chain when it stretches, it is possible that the cassette is still good.

  • 2
    Agreed - one spoke hole has failed completely, so its load has been spread to the adjacent spokes, each is now doing ~50% more work and in the other direction so could suffer the same tear-out. That rim is toast though the spokes and hub are probably reusable.
    – Criggie
    Commented Jan 6, 2021 at 6:12
  • 1
    Please read the rules about product recommendations
    – ojs
    Commented Jan 6, 2021 at 7:10
  • 1
    @ojs I am merely suggesting where to begin doing research to find a good value wheel, which is nontrivial. Those are places I would look and are not endorsements. I do not see anything against code of conduct trying to help an OP in this manner. If I said you should buy X wheel by X brand and was affiliated with it, that would be different. Commented Jan 6, 2021 at 11:16
  • 1
    No issues in doing that, but honestly if one wheel gave out like that, you may what to do both sooner than later. From the look of it, that's a low-spoke-count rear wheel. 100 miles a week for four years is about 20,000 miles. That's actually a pretty good lifetime for a low-spoke-count rear wheel of any type. The front wheel is probably fine. Commented Jan 6, 2021 at 16:05

Whatever material that rim is, it's completely unfit for further use. The area around the spoke has completely pulled out from the rest of the rim. The rim's structural integrity is in doubt, plus it is also out of true.

In principle, there shouldn't be any objective issue running one alloy and one carbon rim, provided you changed the brake pads for the new alloy rim. The brake pads for carbon and aluminum rims are made of different materials. You may not see effective braking using a carbon pad on an aluminum rim. Otherwise, it's mainly an aesthetic drawback to have mismatched rims.

For your stated use case, alloy rims will provide better braking, especially in the wet, than carbon. Carbon rim brake rims are expensive and slightly higher-maintenance toys. There is nothing objectively and intrinsically wrong with liking expensive toys, however. Also, I don't believe this failure mode is common on quality aluminum or carbon rims. For carbon rim brake rims, the higher-maintenance bit mainly amounts to using different brake pads, plus you should probably be more conscientious about cleaning the rim surface after wet rides (remove grit, reduce wear), plus your braking in wet rides will be poorer, plus on extended descents (which not all of us do) you need to be conscientious about braking in pulses (don't drag the brakes, this can melt the resin in the rims after too long).

For the cassette, if you consistently changed your chain before it got too worn, the cassette is likely to still be quite usable. If it is worn, then you should recycle it, as it is likely to cause wear to a new chain. Generally, chain checkers are pretty cheap, and I do recommend that most cyclists get one. However, your local bike shop will generally check for you. The issue with cassette wear is that it is hard to assess visually unless the cassette is very obviously worn (and if it's that worn, it's too much too late, and a new chain would skip on the cassette anyway). Basically, if a new chain skips on the cassette, replace the cassette.

In general, it's often possible to acquire a new rim and rebuild the wheel. In addition, some wheel companies may offer a crash/damage discount on parts, even if the wheel is out of its warranty period or if the damage was clearly the user's fault. It doesn't hurt to ask Fulcrum, although they may not do this. (NB: this does look like a warranty case if you're still in warranty, and I'd suggest asking the store that sold you the bike about this if you think you might be in the warranty period.) Outside of replacing with OEM parts, you or your local bike shop could usually lace an aftermarket rims and spokes to the hub if you were not able or willing to source a replacement rim from Fulcrum (which might be relatively costly). However, some Fulcrum wheels use an unusual spoke arrangement where there are two drive-side spokes for every one on the non-drive. If there are 21 spokes on the rear hub, then standard aftermarket rims are not made in this drilling and you would need a Fulcrum replacement. For at least some Fulcrum wheels, there are no spoke holes in the rim bed, and a wheel builder may need to use special tools to insert the nipples. It's possible that your local bike store may be unable to handle this on their own. If either of those are the case, that might push you in favor of trying to source a replacement wheel or set of wheels, especially considering the rim brake market is probably relatively weak.


You’ll need a replacement rim with the same ERD (effective rim diameter) and hole count. There are no “dependencies” between rear- and front wheels, they can be completely different.

Keep in mind that you’ll have to true and dish the wheel when you replace the rim. At the very least you’ll need a spoke wrench but a truing stand, spoke tensiometer and experience would help a lot. If you have it done at a bike shop it can easily cost as much as a cheap-ish replacement wheel.

I’d only replace the cassette if it’s already very worn. The only “work” you safe by doing it together is taking out the wheel.

From your photo and other photos I’ve found on the internet (as well as somebody stating 1700g weight for the wheelset) I doubt this rim is actually carbon. Do you see any fibers sticking out of the hole? Any delamination? The braking surface definitely looks like aluminium. If it – despite how it looks – has a carbon braking surface you hopefully have brake pads for carbon which you’d have to replace with “normal” brake pads.

  • It does not seem to be a carbon wheel. Commented Jan 6, 2021 at 17:08
  • For the OP's reference, check the Wikipedia article for a photo of what a delamination is. Basically, carbon fiber is a laminate (i.e. multiple layers) composite (i.e. carbon fiber + resin) material. Delamination is a fancy but more exact term for breaking. en.wikipedia.org/wiki/Delamination
    – Weiwen Ng
    Commented Jan 6, 2021 at 19:20

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