Robert A

I have a CAAD12 with rim brakes. I am thinking of upgrading the wheel set from aluminum to carbon I'm concerned about braking issues and heat buildup with rim brakes. I do ride in the Santa Monica mountains, and long, step descents are not uncommon. Am I making a mistake to think about carbon rims, or is it do-able?

Second, would it make much of the difference if the rims took tubular tires?

Miles2go

The gear on my bike is/was found on world tour racing bikes. Pros have to brake hard going really fast and not long ago many were on carbon wheels with rim brakes. Mine is a Cervelo R5 (last year of rim brake) running Campy Bora WTO 45s and I descend Mount Lemmon many times a year. I wouldn't trust every wheel, just like I don't trust every carbon wheel, period. I have friends that have had wheels collapse underneath them, and those are wheels I would never have bought myself. Stick with quality and you shouldn't have any problem.

Seattle Forrest

There are carbon hoops with alloy brake tracks.

​​​​​​I've always wanted an R5.

smashndash

I don't like that the bar for carbon rim brakes is just "do they assplode". Most carbon rim brakes won't assplode. They'll probably stop you too. But good brakes are powerful, predictable, hard wearing, and resistant to fade. My carbon rim brakes are none of those things. Swisstop black prince pads are $50 for a set of 4 and disintegrate like cheese under hard braking.

I don't care how well made a brake track is - you can't beat physics. Carbon rims are all made of the same resins and fibers. You can significantly overheat a rim in just one corner going ~50mph. It won't be enough to melt the rim, or even totally destroy your braking capacity. But you'll significantly increase the wear rate of your pads and you'll have much less bite.

You can experiment with harder pads, but you're just going to be picking a different poison (like rim wear or wet weather performance).

EDIT: A well-made brake track texture and additives in the rim to increase thermal conductivity/capacity can significantly change your experience. It might be the difference between experiencing a heart-stopper moment and not. But barring any objective data on this, I'm going to say that any increase in resistance to fade is going to be marginal compared to going with alloy.

I'd say that an alloy rim with fairings like the HEDs would be much better. I imagine they'd be more popular among pro ranks if they were UCI legal. Especially on wet stages.

I believe the poor performance of carbon rim brakes is the reason why we've seen such enthusiastic adoption of disc brakes among amateurs. Amateurs aren't racing for their livelihood, but still want the woosh woosh of carbon rims. Disc brakes are the solution.

SoSmellyAir

Sigh. And I just finished installing carbon fiber wheels under rim brakes earlier today for my first ride on them tomorrow.

Miles2go

I've never had fade, or want...much less need for more braking power than found with the Campy Bora WTO brake track and their pads...and I love riding mountains. After two full seasons on them, they still look (and sound) brand new.

smashndash

don't worry too much about it. I still send it on my carbon rims. I just don't brake as late as I used to, and I avoid absurdly steep (like -10-13%) technical descents. Those aren't fun anyway. You spend more time braking than coasting.

Fair enough. What pads do you use?

Miles2go

Campagnolo.

SoSmellyAir

I have installed the set of SwissStop Black Prince which came with my new wheels, and an extra set of SwissStop Yellow King which I had ordered at the same time as my wheels because I heard that carbon rim brake blocks wear out much faster than their alloy counterparts. Is Campagnolo better than these brake blocks on other brand wheels or just the default that comes with its wheels?

SoSmellyAir

The area of the OC where I live and bike is relatively flat compared to where all you hardcore BF roadies ride.

AlgarveCycling

I have Zipp 303's, SRAM Red callipers and Corima brake pads on my Wilier. It stops very well in the dry, although still not as good as my disc-braked Trek.

In the wet, zero contest, the disc-braked bike is far better. Doesn't stop me riding my Wilier, I just take into account the different braking characteristics and I've never had a braking incident where I could not stop when I needed to. In fact, I choose my Wilier for racing - albeit due to weight over all else.

I'm still very much a fan of rim brakes and carbon hoops still work with the right pads. However, there is no denying that disc's are, ultimately, better.

seypat

Which side of the equation is most important to you? Lighter wheels so you can climb faster? Peace of mind so you can bomb the descents like Thor Hushovd? That's what it boils down to. The way you worded your question and the mention of tubulars makes me think a new bike with disc brakes is your best option.
Myself, I don't like climbing, but love to descend. Climbing is slow, tedious and boring. Getting to go down the other side is what makes it worth it.

Greatestalltime

Yep. WTO and some Bora 50’s with Campy pads and both have better braking than my c24’s with shimano pads.

Miles2go

When a rider buddy makes this point (which I do agree with as far as ultimate braking performance), I often ask, "Tell me about all the times rim brakes let you down, or failed you." Crickets, and sometimes even an amazed realization in response.

Miles2go

I've only used the Campagnolo pads with these wheels, so I can't offer a comparison, sorry.

AlgarveCycling

Rim brakes have worked very well for decades. They get the job done, no doubt and I'm not about to ditch my Wilier because it doesn't brake quite as well as my Trek.

For me personally and why I do see a place for discs as an option, I wouldn't ask "how many times have they let me down" though - albeit I have had some late stops in the wet before but nothing to phase me and deter me. The real advantage of discs for me personally is on fast descents. An example would be a local 6km 7-10% descent I often do where speeds are high and it is twisty. My PR on that descent is on my disc-braked bike and for good reason: I can brake later, more confidently. My rim-braked bike has me wondering at 80km/h if it is going to make the corners; I am braking earlier to make sure.

There is absolutely no doubt that in high speed descents, discs make you faster. I ride with plenty of Pro's who agree. It is less about being let down by failing to brake and more about speed gains from braking later, faster for many of us. The "let me down" issue only comes into play in the wet and where pads meet carbon. Alu rims not so much an issue in the wet. Discs are better for speed - sorta like aero is better for speed. A non-aero bike will work just fine, not let you down, but aero will save watts, make you faster. I see discs in a similar light.

woodcraft

"My carbon rim brakes are none of those things. Swisstop black prince pads are $50 for a set of 4 and disintegrate like cheese under hard braking.
I don't care how well made a brake track is - you can't beat physics."

[QUOTE=smashndash;22489839]don't worry too much about it. I still send it on my carbon rims. I just don't brake as late as I used to, and I avoid absurdly steep (like -10-13%) technical descents. Those aren't fun anyway. You spend more time braking than coasting.



Muddy the waters much?



To the OP- tubular carbon rims pretty much avoid the heat build up issues, and in my experience braking performance is fine rain or shine in my quite hilly area, that shouldn't be the reason to switch to tubular tires.

smashndash

not really. The point is that (my) carbon brakes are no better than adequate. The fact that I have to change my braking style and choose my routes to accommodate my brakes is pretty damning. But that's a tradeoff I'm willing to make for the woosh woosh.

Miles2go

The original poster didn't sound like they were considering changing bikes to adopt disc brake use, and asked about failure, issues, etc. Not the advantages of discs vs rim brakes.

Miles, smiles, & tailwinds!

SoSmellyAir

I am happy to report that I survived my first ride on my new carbon fiber wheels today, and even managed to brake hard when someone swerved left as I was overtaking them. But the initial braking does have a pulsing sensation, similar to ABS (Anti-lock Braking System). Heard the whoosh all too briefly before it was drowned out by the angry swarm of high pitched bees freehub.

GhostRider62

Not all carbon rims are the same. Higher temperature resins cost a lot. There are some data out there. I was recently in the market for new carbon rim braked wheels and it came down to Zipp 404, Bora 50, and Farsport Ventoux. Zipp was out because of hub and body problems. Campy did not do as well as the Farsport in the braking destruction test and loose balls are slower than high quality cartridge bearings. I've taken my 200+ lbs 50 mph down 15% gradients and braking the whole way as in the wrong way in order to test heat build up. For me, I don't consider delamination an issue. YMMV.

Robert A

Correct.

Robert A

I'd appreciate comments on my second question relating to carbon tubular rims. Are the heat issues less of a concern due to the different rim construction?

soonerrebel

The heat generated and possible delamination is less with tubular carbon rims. There is more material to dissipate the heat in how tubular rims are constructed.

woodcraft

I ride tubulars almost entirely, & have checked heat build up, particularly at one extreme location: ~800' twisty drop, much over 10%. One must brake much of the time to stay on the road, alternating front and rear brakes. Putting hand to rim at the bottom, the CF is quite warm but manageable. Excessive heat buildup can soften the CF composite, but can also overheat the air in the tire, causing a blowout. Tubulars are better in this respect as well since the tube is insulated from the rim by the tire casing and and the tires can handle higher pressures. Rider weight, riding style (cautious descending can be a problem), and location are factors. A lightweight rider won't have issues but a clyde has a narrower safety margin. In general, CF clincher rims are a fundamentally poor design, IMO.