Cyclist0108

Let's say for the sake of argument everything is the same (weight, tires -- let's pick something cushie and road-insulating like 38mm Compass, hubs, bike, rider). The only difference is the composition of the rims. "Aero profile" is the same. Number of spokes is the same. Also, assume both have the same disc brakes, so we aren't talking about rim brake differences.

I recognize all of these assumptions are a bit artificial and might be hard to realize, but the point is if you could control for everything else, could you feel a difference with carbon rims due simply to their composition? If so, how would you describe the difference in ride quality?

woodcraft

There's now way to have a deep section alloy rim that's not heavy, and 38mm tires make the aero profile largely irrelevant.

You could also try to figure out if there was a difference between apples & oranges, if you made size, color, taste, etc, the same.

I do have an alloy wheelset with slender bladed spokes & an aero-ish profile that feel pretty fast. I don't actually use them but maybe I would if I rode clinchers.

Marcus_Ti

Which is a set of assumptions you'll never ever see in real life, short of finding some (primitive) 20 year old CF rims from the Good Old Days. The CF rim will always be stronger at the same mass, and lighter at the same shape AKA extrusion.

Cyclist0108

Hence, I anticipated this objection:

The main point is whether carbon per se feels any different, or whether it is the secondary effects -- lighter weight, ability to make aero rims, etc, that make the claimed difference?

Teamprovicycle

it will feel different when it cracks over a bump and explodes lolol,

its something thats nice to have but , i doubt you will ever truly feel a difference at the casual level , maybe it will absorb bumps better than metal , ive beaten pledy of dudes that have 1,000 carbon aero wheels on metal non aero wheels ?!

Wildwood 

With a 38mm tire = all you feel is tire&air.
IMHO.

dmanthree

I've ridden both, and while they do feel different, you may or may not experience speed gains. That said, I've never ridden Zipp 808s, so maybe they do provide some benefit. Just watch for crosswinds.

Phil_gretz

Wait. You've invented an aluminum alloy that is as light and strong as resin impregnated carbon? Yay! Does it also cost less? If so, you have permanently won the internet!!! Champion! Champion!

Cyclist0108

So can we infer from this that there is no inherent advantage to using carbon as a material, but that instead the advantage derive indirectly from (miniscule) weight-savings, and the ability to put on cowling that enables display of colorful decals?

indyfabz

Subscribed.

Phil_gretz

Nope. Carbon permits an aero profile that can be achieved without a substantial weight penalty, actually incredibly light weight. Or else aluminum aero rims would already be a thing.

AlmostTrick

I've never cared for or wanted CF rims for many reasons... I'm only here to see if all the wisdom posted can make me change my mind. Good thread!

Cyclist0108

So you can play dumb, but I can't?

• Santa Cruz Reserve 700C rims: 358g (what I would consider, albeit lacking in decorative cowling, but has the merits of a small decal and lifetime warranty)
• HED Belgium Plus 700C rims: 469g (what I have now, which are heavy, robust aluminum rims)

mass difference = 111 g water = 111 ml water = 7.5 tablespoons of water = 1 swig from water bottle

My wife's (Specialized) bike came with what we derisively refer to as "fake carbon" rims, i.e., they have the (allegedly) aero shape that catches cross-winds. From what I can tell, it is essentially a decorative, hollow-shell aluminum cowling.

So back to the question: is there any inherent difference to the ride-quality of carbon rims (say, in the way that there are claimed differences in the dampening properties of carbon handlebars vs. aluminum), or is it simply the ability to form pretty shapes and display brand loyalty with colorful decals?

Phil_gretz

Sorry about that. I was using internet shorthand speak, and it came off as smart alecky.

From what I've read from researchers, reviewers and testers, carbon rims tend to be on the stiffer side rather than the more compliant side. At any rate, the more substantial wheel flex would more likely be due to the spoke pattern and tensioning rather. But modern wheels are pretty stiff laterally.

I've encountered aluminum semi-aero radially-spoked front wheels that have substantial lateral flex under power (like climbing or sprinting). So much so, that I've had to open the front caliper a hair to give more room to prevent rubbing. These are true wheels, properly tensioned, with no slop in the hub. Just flex.

I think that the weight savings is key. The greater volume of material needed to create the deep aerodynamic shape doesn't weigh substantially more than the lightest lower profile aluminum alloy rims, to the benefit comes from the shape.

There are data out there (I can't reach out and link it easily) where numerous shapes and sizes (brands) were tested for their aerodynamic benefit as a function of speed. We're talking a handful of watts, but that matters. So does having an aerodynamic posture, and having an aerodynamic helmet. After those, the watt savings diminish.

If there's research on the "compliance" feel of carbon rims, I haven't stumbled across it. Not saying that it doesn't exist, I'm just not familiar enough with the subject. There are experts who might chime in, but it's a pretty technical subject. I'm not experienced enough, by any stretch, as this is a relatively new area. In fact, I likely know less than most who actually race regularly and are sponsored and have had several of the top competing carbon wheelsets.

Why not get a mid-level quality set and try them out?

subgrade

I reckon the inherent difference might be the same as with other components - allowing for some flex in desired direction while maintaining stiffness in others. The Zipp single wall MTB rims are specifically designed wit that in mind. https://www.zipp.com/wheels/3zero-moto-rim/

Cyclist0108

Thanks. That is MUCH more helpful!

The divorce lawyer will still charge the same.

The two I would consider:

• Santa Cruz reserve 700C
• November's GOAT carbon option

hagak

Just to note neither of those are deep section rims. As such the benefit of carbon vs al is probably not that great. When you start getting to 40-50mm deep rims is where you see difference in weight and aero. A 28mm deep rim will not have that much of an aero benefit versus a low profile light Al rim.

As already stated to reason for carbon rims is more about being able to get an aero profile without weighing a ton. If you just want lightweight there are many low profile Al rims that will be very light even compared to a carbon rim. But if you want aero, you need to go to carbon.

You have mention larger cowling for a fancy logo multiple times in this thread, that larger cowling is for aero purposes and is not just for logos.

WizardOfBoz

Not sure if this can be answered via reasoning and opinion. You need field tests or engineering analysis (e.g. Finite Element Analysis) or both to answer the question and to know why the field tests gave you the answer they did.

But hey, lack of relevant data never stopped me from speculating before, so ...

One aspect of carbon fiber composite (CF) is that it can have directional stiffness and strength if you use oriented fiber layup vs random discontinous fiber. So, not only can you make stuff that's really strong and stiff in the exact direction you want, but you don't have the extra weight added in for strength in directions that aren't stressed. To get an "apples to apples" comparison (e.g. rims the same weight) you'd have to use massive amounts of CF material, which would be massively stiff. So for equal weight I think you'd have the stiffest wheels in the universe.

As others have mentioned, tires take up a lot of the shock of stiff wheels and frames, so would this stiffness matter?

I've been thinking about spokes and reading some of the wheelbuilding books (Brandt, Schraner, Musson...). So I'm thinking that with a very stiff, strong rim you'd have less deflection of the rim in the area where the tire touches the road. This means that you probably could get away with less spoke tension. My reasoning here may be flawed: If a rim deflects an amount d, then to avoid a spoke of length D going slack you have to have it stressed to at least mT = E * A * d/D, where mT is minimum spoke tension, E is the spoke Young's Modulus, and A is the spoke cross-sectional area. So, one question for folks with more CF experience than I is whether my theoretical speculation observed in reality.

If so, again, would this matter? In general, most of what I've read is that, within a range, spoke tension doesn't affect ride much. You hit a bump, this applies force to the spokes, and they stretch an amount that doesn't depend upon the original tension.

What would I do? Right now, I use alloy rims because I'm a big guy and have rim brakes. But if I had a bike with disc brakes I'd probably go for CF. Lighter, stronger, more rigid. Plus, it's what the cool kids have.

Cyclist0108

Many people, who (like me) have nothing aero about them, like deep-dish wheels for aesthetic reasons, and even I admit they do look kind of cool. For me, my abilities, riding condition, and blubber status, the only thing deep aero rims will do is make me more vulnerable to cross-winds. Apologies for the hyperbole, but maybe this would be a better way to formulate the question:

For lower-profile (shallow) rims like the Reserve and November's GOAT and RCG36 options, is there any inherent advantage to carbon as a material? I'm getting the impression that it might be minimal. (Even November's web page says their rims are "as good as" the Belgium Plus.) I have head the rims stay round and true more than aluminum, but in five years I haven't has an issue with my HEDs.

hagak

Yeah if you are looking at low profile carbon you probably won't see much benefit over Al, as long as the Al is of similar weight.

Note good modern deep carbon wheels really won't have the cross-wind issue you speak of particularly if you are not light. Manufacturers have done a good bit of wind tunnel work to minimize the cross-wind issue. I have 50mm Roval and ride in heavy cross-winds all the time (10-15mph) and have no noticeable issue with it. I weigh 180 pounds.

Trakhak

I don't even notice any differences in ride comfort between my steel, aluminum, and carbon race bikes, let alone wheel sets, and I've been riding racing bikes for 55 years.

fietsbob

I found the feel of the few carbon rim wheels on the TransAm race-tour bikes, in the shop last week,

does feel different to the touch , ... the braking surface textured, a bit,

than the aluminum rimmed ones on all the bikes the locals use JRA..

if that's what you wanted ... (I don't recall the rim brands)







...

Cyclist0108

I can feel differences between my two steel road bikes. (One has SLX tubing, which is rather stiff in a small frame.)

Cyclist0108

Disk brakes ...

WizardOfBoz

Ah, wg, I can identify. Nothing in my riding remotely related to the Greatest Of All Time. So I'm looking for a firm that will, instead of "GOAT" rims, formulate "WALRUS" rims. With good salesmanship*, these would be popular rims.

BTW, a flat tire on my CF (Domane) bike forced me to ride my steel (Lemond Zurich - 853) last weekend. I was a bit slower (possibly due to the seat being a half inch lower) but the steel did not absorb the bumps as well. But the Domane has that shock absorber setup in frame near the seatpost, and the saddles were different. In any case, I'm thinking of swapping out the hard plastic-shell Bontrager RXXXL? set for a Brooks Professional. Point is, you can set CF up to be more flexy, and steel to be more rigid. There are material traits that limit this, but its materials, design, the roads to be traveled, and ... being "blubber challenged". All affect ride.

*I remember an adipose-gifted comedian once relating his experience in buying a suit. "Ah, yes sir, a suit for you. Would we be looking at a dirigible size, sir? Or perhaps Zeppelin?" So its all in the sales pitch.