Why carbon rims?

[MikeD]

It seems now that the De Gendt crash was not caused by the hookless nature of the rims, but by fracture of the rim itself after hitting something (a rock). I was on a long ride, 40 miles in, out in the middle of nowhere and hit a pothole with my aluminum rim and the tire instantly pinch flatted and the rim got all bent up but didn't break. The tire did not come off the rim. I was able to straighten the rim up enough to complete the ride and I did not crash. Carbon fiber is not a ductile material. If you exceed its yield strength, it does not bend, it fractures.

What's so great about carbon rims over aluminum? Maybe a little weight savings? They don't work all that well with rim brakes either, and can deform from braking heat. They suck in wet weather too.

[prototoast]

Generally speaking, they are lighter, stiffer, and can be molded into more aerodynamic shapes. On the road side of things, they are often made to be as light as possible, which does increase the risk of failure, but a heavier carbon rim can be both lighter and stronger than an aluminum rim. While aluminum rims tend to bend not crack, forces that will bend an aluminum rim can leave a carbon rim unaffected.

[EB]

On mountain bikes, I am only on carbon hoops. They are superior for that application in every way, though as such they are often as heavy or heavier than alloy hoops. The primary advantages are tunable stiffness, moderate weight even at modern internal widths, and very high strength. Aggressive riding will inevitably damage alloy rims and frequent truing is inevitable - most carbon wheels mountain bike wheels I’ve owned never needed truing once and shrugged off hits that would have dented or tacoed alloy rims. There is definitely a point at which they will fail and shatter - but that point is well past where an alloy rim would also catastrophically fail.

For road rim brake wheels, on the other hand, I stay away from carbon - just can’t stand the braking issues, especially long descents in the wet which are common here. For road disc or gravel, it’s a toss up - the advantages I described for mountain biking aren’t as evident because you’re not throwing the bike down crazy stupid rock gardens.

[benb]

The lighter claim does not hold up all that well with a lot of these deep carbon rims.

In general it seems most people are using heavier wheelsets than 10-15 years ago but are generally riding much deeper sidewalls. It also sounds like even at the Pro Tour level the weight of the bikes has actually gone up.

It is really a tradeoff of light vs aerodynamic where they've decided the aero benefits are more important.

Surely there are some benefits there but it really feels like the industry is chasing it's own tail and making change after change just to facilitate more people being on deeper more aero rims more of the time. At one point it seemed like you only saw these deep rims coming out on elite racers in certain circumstances where they knew the aero benefit could have a payoff, now we're down to Cat 6 riders using them even though they're wearing a jacket that's luffing in the wind and riding an upright position and the weather is bad. Say in the last week of riding I'd say 90% of the road bikes I saw while out on the road had deep carbon rims.

I guess I would need to try some, but just say the last week it has been incredibly obnoxiously windy and if those deep rims have any additional annoyance factor in crosswinds it would really harsh my ride.

I really think disc brakes would not have moved anywhere near as fast without the push to get more and more people on deep carbon rims and solve the carbon + rim brake issues. If you absolutely must be on carbon rims disc brakes make total sense, but if you were ambivalent on carbon rims than disc brakes seem much less necessary.

[Likes2ridefar]

I use carbon with disc brakes because it performs better in every way and is one of the few changes on a bike I can immediately notice a difference.

I agree they aren’t as great with rim brakes in wet conditions.

[mstateglfr]

Originally Posted by benb

The lighter claim does not hold up all that well with a lot of these deep carbon rims.

In general it seems most people are using heavier wheelsets than 10-15 years ago but are generally riding much deeper sidewalls.

If you get a carbon rim with a similar depth as an aluminum rim, the carbon rim will likely be lighter.
So you can then get a carbon wheelset that is more aero than an aluminum rim(deeper section) wheelset and it can weigh the same as or even lighter than the aluminum wheelset.
It doesnt inherently have to be heavier.

I recently switched wheelsets on my gravel bike. Yes, more aero wheels with tires that measure out to 43mm may be a waste, but this same thing can apply to a road bike so the point still stands.
- Old wheels were HplusSon Archetype rims, bitex hubs, 28f/32r butted spokes, brass nipples. 23mm deep and 25mm wide. 1817g
- New wheels are BTLOS rims, bitex hubs, 24f/28r butted spokes, brass nipples. 35mm deep and 29mm wide. 1473g

So my new wheels are 344g lighter(12.1oz), slightly wider so tires dont lightbulb quite as much, deeper for some sort of aero gain, and I can confidently reduce spoke count without being concerned with flex.
Even if I got the 45mm deep rims(asymetric too, for spoke tension) on the same build, my wheels would weigh 1520g with the same 24f/28r spoke count.
So they would still be 300g lighter than my alloy wheelset while being more aero and not compromising on component quality.

Yes I am aware that alloy disc wheelsets can weigh less than the wheelset I own and cited for these examples. With that said, I have found that it isnt common to see alloy disc wheelsets weigh much less than the 1473g BTLOS wheels I purchased. So even if the wheelsets weigh the same, there is some level of aero benefit for a road tire, between the carbon rim being deeper and wider.
My carbon wheels were handbuilt and properly tensioned and cost $650 shipped to me. I really didnt see anything in alloy that was a better mix of weight, rim measurements, and cost.



ETA- even the Hunt 34 Aero Disc alloy wheelset, which is about as deep as my carbon wheels, is slightly narrower with fewer spokes while weighing almost 100g more and costing $50 more. Do those small differences really matter? Maybe not, but at the same time, they certainly dont make the alloy wheelset more appealing.

[deluz]

I have noticed pros riding all kinds of different rim depths.
Here is Evenepoels winning bike at the World championships:



He is using 33mm deep rims and he won on a solo breakaway.
Assuming those were chosen due to the amount of climbing in the race. For myself I went with BTLOS 30mm rims because I don't care about aero, I just wanted the lightest possible rims. They are stiffer than alloy and probably still more aero than most any alloy rim. I feel the rims are robust and I do not do rides with potholes and I am very cautious when I ride, braking is sufficient but much louder than alloy. I have no regrets using these rims.

[bfd]

I recently bought a set of BTLOS carbon rim brake wheels and love them! They hold up to my 200lb weight, are aero (45mm deep rims), and super light (the wheelset came with a listed weight of 1305g (729g rear and 576g front)! That's tubular wheel weight!

The weight was a surprise as the estimate they gave when I finished selecting the parts was 1325 +/- 25g, so I was expecting 1350g! Still the wheels have been fantastic and with Reynolds blue pads, I find the braking to be excellent, although I haven't ridden them in the wet. There's little to no flex and they seem to hold up to everything I put them through as I do occasional rides on gravely roads.

I'm now thinking maybe I should get a set for my Della Santa, which has standard 32h Mavic Open Pro rims and Campy Record hubs...lol

Of course, YMMV!

Good Luck!

[Dude]

I'm at the point where i'm like "why aluminum rims?"

There's the cost of alum rims being cheaper but seriously that's it. Most impacts that dent alum rims won't effect carbon rims.

Braking performance is moot on disc brake bikes. I'm not here to debate that (but rim brake folks are wrong).

[HowardCosellsPR]

I find that carbon withstands way more abuse before failing. Period. That said, I don't ride ultra-weight weenie wheels and... im little (135-140lbs). I might still ride aluminum on road (though I don't), but the value proposition for me especially gravel and dirt favors mid-range carbon. Simply less maintenance and durable as it gets (for me). As for braking, I also don't understand why anyone who lives in places with hills and/or rain doesn't ride discs... but... I suppose burying one's head in the sand can be relaxing at times.

I cracked my first carbon wheel while 'road' biking two weeks ago. Hit a baby-head at 30mph while descending a very rocky jeep track in Arizona . The sidewall was crushed/cracked, but the wheel was totally solid/true otherwise. I rode out after installing a tube. Oops. Had that wheel been aluminum, I likely would have taco'd the wheel and gone over the bars. That said, the same wheel had taken so many hits, over the last 6yrs I was kind of shocked that it hadn't happened sooner.

Perhaps apples to oranges but.... I raced mtbs fairly seriously between 1989-1999. In that time, I tacod, cracked, bent, and dented a countless aluminum rims. Some of these wheel incidents resulted in injury, some did not. I've never broken a carbon rim while mtb'ing and, now, only one while gravel-riding. So... my score is 1 carbon fail than required putting in a tube vs like 100 alu failures that resulted in anything from hospital visits to long walks home.

Hell, I can count on my hand the number of times ive even had true my gravel or mtb carbon rims.

[benb]

Denting rims is so far off my radar it's not even funny. I've never managed to do that in 25 years of riding. I have cracked rims between the spoke holes more than once but that was usually after like 20k miles. There have been certain types of wheels/rims that have been resistant to that though, so it's not like it's universal I'm going to do that on all alloy rims. I have broken frames too, I'm not real gentle and I'm bigger than some of you.

I am real careful with tire pressures though FWIW and am not a "heavy" rider that manages to bash into everything.

I've never dented/bent a rim on MTB either, including racing back in the day.

BTLOS certainly has nice prices.. they are in the same price range as the nicer alloy wheelsets I've had. How is their customer support, etc.. if you need it?

However specing out 35mm wheels with DT swiss hubs on BTLOS, they are within 50g of my alloy rims anyway. The 55mm rims are slightly heavier than my alloy setup. Probably more aero, but would I notice it and would they be more annoying in crosswinds? Running tubeless would swing it one way or the other.

Realistically this is a strictly "buy a new bike" thing. If I buy a new bike and a complete package works price wise and includes discs + carbon wheels that's how I'd end up with a carbon wheelset.

[prototoast]

Other than all the benefits of carbon rims, which I don't care about, why should I buy carbon rims?

[StressStrain]

Carbon rims have been great for me: durable, lightweight, aero shapes, etc.

[Likes2ridefar]

Originally Posted by prototoast

Other than all the benefits of carbon rims, which I don't care about, why should I buy carbon rims?

Ride quality is enough for me. The rest the stuff I agree, I could mostly care less about weight and aerodynamics. I ride 1600 gram carbon gravel wheels because they ride nicer than other wheels I’ve used of equivalent or less weight or that are more aerodynamic. My mtb wheels are 1500 grams and 3mm wider and maybe 10mm deeper than the gravel wheels. They are upgrades from aluminum OEM wheels that came with the mtb. They have improved the ride quality and traction with +5mm increased internal width - 30mm - and are shaped nicely which seems to have resulted in less pinch flats/ruined tires. It doesn’t hurt they weigh over one pound less than the dt Swiss wheels they replaced.

[flying]

Originally Posted by MikeD

What's so great about carbon rims over aluminum? Maybe a little weight savings? They don't work all that well with rim brakes either, and can deform from braking heat. They suck in wet weather too.

TO be honest I always thought this way & well before any hookless problems.
I always thought it was basically a marketing push. Put all the pro's on it & well basically same as always after that.

But they pretty much stopped development of alloy rims after that except a few like Campy Shamals or HED RC series etc. Which is a pity because they could make alloy deep aero rims too but instead it started the tail wagging the dog & we know what followed