Why carbon rims?

[Bob Ross]

Originally Posted by deluz

I do not do rides with potholes

I need to move to wherever you live.

[kppolich]

Generally lighter, stiffer, more options for depth or rim profile too. Plus they can bend without breaking rather than bent/ding in alloy.Really shines for disc brake vs rim brake where the braking surface (carbon) could wear down or struggle in the wet.

Again, generally speaking and by no means the gospel.

[benb]

Originally Posted by flying

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

Eh.. pretty sure as soon as you make deep rims the carbon does really win handily.

There were deeper alloy rims but they were pigs IIRC.

[flying]

Originally Posted by benb

Eh.. pretty sure as soon as you make deep rims the carbon does really win handily.

There were deeper alloy rims but they were pigs IIRC.

If I recall correctly the HED's are not heavy for a 40mm at under 1600gr

But that aside the weight penalty for carbon is also that the bike industry next claimed due to carbon wheels it was necessary to move to disc brake as carbon not stopping well in the wet with rim brakes.... so I guess we could say ultimately carbon wheels added a bit of weight there of the "total" package

But mainly as I said development stopped so we will never know how far it could have gone.

[ridethecliche]

The specialized roval alpinist slx wheels are al and light if you're interested in that sorta thing.

Originally Posted by 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!

Woah. That's awesome!

[benb]

Originally Posted by flying

If I recall correctly the HED's are not heavy for a 40mm at under 1600gr

But that aside the weight penalty for carbon is also that the bike industry next claimed due to carbon wheels it was necessary to move to disc brake as carbon not stopping well in the wet with rim brakes.... so I guess we could say ultimately carbon wheels added a bit of weight there of the "total" package

But mainly as I said development stopped so we will never know how far it could have gone.

Yep, that's what I keep going on about. Carbon wheels were a good portion of the technical reason they could push disc brakes so hard.

It is not hard to remember the discussions of people who were early carbon rim adopters before disc brakes where people were trying lots and lots of different brake pads to try and get good performance.

And personally I saw a whole lot of carbon rim + rim brake pack riding incidents where those riders had horrific stopping distances compared to those of us on alloy rim + rim brake. Sure some riders got it right, but others had trouble with some wheels on some days in some weather and it was scary. Disc definitely solves that.

It's easy to forget carbon rims have been around a long time already.. first time I saw one was about 20 years ago, but I'm sure they were around before that. Once they became fashionable and affordable they got a lot of people to buy an entire new bike which was obviously great for the industry.

[flying]

Originally Posted by benb

Yep, that's what I keep going on about. Carbon wheels were a good portion of the technical reason they could push disc brakes so hard......................

It's easy to forget carbon rims have been around a long time already..

True kind of a tail wagging the dog progression

Yes they have been around a long while I had the Campy low profile Hyperon Tubulars back in 2004.....But decided pretty quick the juice was not worth the squeeze for myself as the
Hyperons tubs were 1289gr & my Mike Garcia clinchers were 1412gr stopped way better & were my first foray into clinchers

[Mark McM]

A few comparisons between aluminum and carbon rims:

Forming the sidewalls of a clincher rim, which have sharp bends and has to withstand the tire's pneumatic pressure, is much easier with an aluminum extrusion than with a carbon composite. Additionally, carbon fiber matrixes may lose more strength under braking heat, so rim brake carbon sidewalls often have to be further reinforced. This means that for shallow rim brake rims, carbon fiber rims typically aren't much lighter than aluminum rims.

As far as forming aerodynamic shapes: There is a lot of freedom in creating shapes for both aluminum rims (whose shapes are created with extrusion dies) and carbon fiber (which are formed in 3 dimensional molds). So for any given rim depth and width, an aluminum rim can often be just as aerodynamic as a carbon. The big caveat here is that aerodynamic drag tends to decrease as rims get deeper, and there is a limit to how deep you can make an aluminum rim. So for shallower rims (less than 30mm), there is little aerodynamic advantage to carbon over aluminum, while for deeper rims carbon is more aerodynamic simply because it is so difficult to make a deep aluminum rim.

The limit on aluminum rim depth is due to the way rims are made: First, a straight extrusion is made by forcing an aluminum billet through a die to form the cross-sectional shape. Then the straight extrusion is rolled (curled and bent) into a spiral of the appropriate diameter for the rim, and the spiral is cut and the ends joined to form a hoop. The deeper the cross-sectional shape of the extrusion, the more difficult it is to bend without distorting and crushing the cross-section, so the practical limit to aluminum rim depth is about 40mm, with most aluminum rims being shallower than this. Also, deep aluminum extrusion wall thickness can't be too thin, or else the walls may buckle during the rolling process, which tends to result in deep aluminum rims being heavier than similar depth carbon fiber rims.

At a given weight and depth, carbon rims tend to be a bit stronger and stiffer than aluminum. On the other hand, carbon fiber is more brittle, so when it's yield strength is exceeded, it is more prone to fracture, whereas aluminum may be bent or deformed. So while an aluminum rim may get bent under some given impact that a carbon rim may escape unscathed, at a higher impact force the aluminum might just bend a little more while the carbon rim may fracture. Both carbon and aluminum rims increase strength and stiffness as their depth increases, and deep rims in either material can be quite robust.

As far as cost, carbon rims tend to require more labor to produce, so they tend to be more expensive.

So why the popularity of carbon fiber rims? Despite costing more, people appear to have been sold on the aero benefits of deeper rims, as well as their lighter weight. Or maybe they just like the looks better.

It is also interesting to note that the popularity of carbon fiber rims has been a strong driver of some other technology trends, some of them quite divisive. For example, it is more difficult and more expensive to make good performing and reliable rim brake carbon rims, and this has been a large part of the move towards disc brakes on road bikes. This is a bit of an irony, as carbon rims are often preferred due to their lighter weight, but at the same time a bike with carbon fiber rims and disc brake is often heavier than a similar bike with aluminum rims and rim brakes. More recently, the difficulty and cost associated with manufacturing carbon rims with hooked sidewalls has led to a move toward hookless rims by some manufacturers. Due to the need to use wider, lower pressure tires, this may cancel out some of the aerodynamic benefit of carbon fiber rims. (Hooks add very little cost to aluminum rims, so hooks are not likely to be disappear from aluminum rims anytime soon.)

[Mark McM]

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. It also sounds like even at the Pro Tour level the weight of the bikes has actually gone up.

Another large change over the last 10-20 years is that for the first many years of carbon fiber rims, they were only made for tubular tires. It took the carbon fiber rim makers quite a few years to figure out how to make clincher versions. The clincher versions were quite a bit heavier than the tubular versions (typically 100+ grams per rim).

[Mark McM]

Originally Posted by flying

If I recall correctly the HED's are not heavy for a 40mm at under 1600gr

HED made full carbon fiber tubular rims for many years, but for clincher rims they took took a hybrid approach, using a shallow aluminum extrusion and bonded on a thin walled carbon fiber "fairing". This resulted in a rim that was just as aero as a full carbon rim of a similar depth while only being a little bit heavier - but having much better braking than a full carbon rim.

HED is interesting in that they have been at the forefront of technology when it came to performance, while at the same time being conservative when it came to safety and reliability. On the one hand, they patented the first toroidal rims shapes (which the rest of the industry went on to copy) and were among the first to drive toward wider rims; while on the other hand they never produced a full rim brake clincher rim because they weren't satisfied with the ability of carbon clincher sidewalls to take rim brake heat, and they have not made any hookless rims.

[flying]

Originally Posted by Mark McM

HED made full carbon fiber tubular rims for many years, but for clincher rims they took took a hybrid approach, using a shallow aluminum extrusion and bonded on a thin walled carbon fiber "fairing". This resulted in a rim that was just as aero as a full carbon rim of a similar depth while only being a little bit heavier - but having much better braking than a full carbon rim.

HED is interesting in that they have been at the forefront of technology when it came to performance, while at the same time being conservative when it came to safety and reliability. On the one hand, they patented the first toroidal rims shapes (which the rest of the industry went on to copy) and were among the first to drive toward wider rims; while on the other hand they never produced a full rim brake clincher rim because they weren't satisfied with the ability of carbon clincher sidewalls to take rim brake heat, and they have not made any hookless rims.

Thanks that is right & I had actually forgotten how long it took for carbon clinchers to surface & how we wondered how a carbon clincher could be strong enough.

Also interesting about HED & technology
Thanks

[jdp211]

Originally Posted by Mark McM

HED made full carbon fiber tubular rims for many years, but for clincher rims they took took a hybrid approach, using a shallow aluminum extrusion and bonded on a thin walled carbon fiber "fairing". This resulted in a rim that was just as aero as a full carbon rim of a similar depth while only being a little bit heavier - but having much better braking than a full carbon rim.

HED is interesting in that they have been at the forefront of technology when it came to performance, while at the same time being conservative when it came to safety and reliability. On the one hand, they patented the first toroidal rims shapes (which the rest of the industry went on to copy) and were among the first to drive toward wider rims; while on the other hand they never produced a full rim brake clincher rim because they weren't satisfied with the ability of carbon clincher sidewalls to take rim brake heat, and they have not made any hookless rims.

The post script to this/also worth noting, those hybrid wheels (the Jet series) were incredibly heavy for a performance wheel (current series 46mm versions are quoted at 1600g, 1800g for the 60mm).

[benb]

Originally Posted by jdp211

The post script to this/also worth noting, those hybrid wheels (the Jet series) were incredibly heavy for a performance wheel (current series 46mm versions are quoted at 1600g, 1800g for the 60mm).

There are still modern all carbon wheels in similar depths that are near those weights.. those aren't that heavy.

And the aero stuff says 100-200g makes absolutely zero difference unless you're strictly doing a hillclimb that stays above what 7-8% for the entire race.

It doesn't even matter if there is an HC climb in a ride/race. Unless that climb is basically the entire duration of the ride/race the more aero wheel apparently wins over the duration of the ride.

Now whether I need to care about this for going out and riding for fun.. I want to know which of these wheelsets is least annoying in high winds.

[weisan]

1996





2023

[Mark McM]

Originally Posted by jdp211

The post script to this/also worth noting, those hybrid wheels (the Jet series) were incredibly heavy for a performance wheel (current series 46mm versions are quoted at 1600g, 1800g for the 60mm).

As benb says above, the Jet wheels aren't exceptionally heavier than many all carbon wheels (and lighter than some).

For example:

HED Jet4: carbon/aluminum, 46mm deep, 1600 grams
Enve 45: all carbon, 45mm deep, 1561 grams
Zipp 303 S: all carbon, 45mm deep, 1530 grams

Also remember that disc brake rims (like the Enve 45 and Zipp 303 S) are supposed to be lighter than rim brake rims (like the HED Jets). Were the Enve 45 and Zipp 303 S made in a rim brake version, the weights might be closer still.

There is a perception by many that anything made out of carbon must by definition be much lighter than the same thing made out of metal - even though that's not always the case. And this perception may be part of the reason that carbon wheels have become so popular.