Carbon wheels for MTB. Worth it?

I ride a Santa Cruz Hightower and I have an opportunity to pick up a set of their carbon Reserve wheels at a pretty big discount.

I come from a roadie/triathlon background so MTB gear is somewhat new to me and I am wondering if the carbon wheels are actually worth it. I mostly ride XC style trails (I know it’s not an XC bike) and am going to try a couple 50k MTB races this summer.

I currently have the stock Race Face ARC Offset 27 29" Rims on the bike and as far as I can tell the weight difference is pretty minimal. I’m guessing there is more to it then weight so what am I missing?

I have the Reserve 27s laced up to I9 Torch hubs, and I rather like them. I would argue that the benefits of carbon wheels for a MTB may be greater than they are to a road bike. Weight is a pretty big hurdle on a MTB, and there are not many areas where you can get a much bang for your buck in weight savings as in the wheels, imo.

I have carbon rims and race XCO and MTB 100s. If you’re going to lose weight anywhere, the wheels are the best place to do that, expecially since all the reaccelerating in mountain biking. Aside from the obvious weight savings, assuming there are some, below are the other benifits:

  • A major benefit to running carbon rims is their inability to flat spot like aluminum rims do. Over a large sharp impact, aluminum rims have the tendency to flat spot creating unequal spoke tension throughout the wheel.

  • When undamaged, carbon rims will always return to their round shape. Meaning, that when built properly, the spoke tension should not change. This translates to less time spent trueing and re-tensioning spokes through the season or after some big drops or crashes. I’ve rode on my carbon rims for a year, had several crashes and countless washouts and they are as true as the day I got them.

  • Even though all rims can be designed and manufactured very differently, carbon mountain bike rims have the potential to be very strong and stiff while remaining lightweight. This characteristic is much harder to achieve when using aluminum rims. Using a stiffer carbon rim gives you the ability to corner harder and with more confidence, and to accelerate faster out of the turns.

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I have carbon rims on my race wheels and a few sets of alloy rims. Stiffness in corners is an amazing thing! I still ride both and as far as weight, speed, and acceleration I “feel” a negligible difference. There is, however, a very tangible difference in stiffness when cornering. I much prefer the feel of carbon rims in that regard. If I lived in a more rocky place I may stick with alloy rims more, but I don’t, so I’m thinking about a set of reserves to go on my blur this season.

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When I switched to carbon wheels on my XC mountain bike years back, it was one of the biggest game changers for me. Doing long rides on punchy singletrack I saw an immediate impact on Strava times for me. I suspect most of it was the lighter weight coming into play on all the short quick accelerations.

The other big change when I went to carbon was retuning the suspension. The stiff carbon wheels I first switched to (Enve AM’s at the time) allowed be to soften everything up a little and let the suspension handle the dampening.

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Simply… Yes.

You will love them. You WILL feel the difference. The only issue is that you will never want to ride aluminum again. It is a sickness really. I have two sets of Enve (XC and Gravel Bikes), 1 set of Reynolds (140mm trail bike), and 1 set of Profile (road bike).

The spin up so quickly and they have been very durable even on the SoCal choppy trails. I hear really good things about the Santa Cruz wheels. Buy them…

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Durability is one thing. However, I don’t believe the weight argument. There is less than about 100g difference between good carbon and good aluminum wheels. That’s only about 6% of the wheel weight and under 1% of the bike weight. Not to even mention the rider weight. You can do better by careful tire choice. They are cool, though

I’ve been racing Stan’s Valors for years. This season the new CB7. Love them. However, I just love carbon and I want carbon. Personally, I find the ride difference marginal. Modern alu rims are pretty good as well, my training wheelsets are all alu. Of course, this always depends on terrain, system weight and riding style. If money is an issue I would not spend it for carbon rims.

Often the weight difference is minimal between comparable model wheels, but the carbon rim that weighs the same as its alloy counterpart will usually have a better ride quality. Carbon handles everyday stress far better than alloy, so they tend to stay true better as long as you aren’t completely banging the crap out of them, but the alloy rims won’t fare much better in those situations either!

The biggest weight differences in a wheel will be based on how many spokes they use and the types of spokes. I however have not seen or heard of an alloy wheel that can actually handle more than the lightest of off-road conditions that is a comparable weight to the high end Enve’s or Stans Podium. If you run low pressure, that alloy rim will dent pretty quickly.

You’re looking at weight the wrong way.

When referring to the rim, you are taking about rotational weight at nearly the farthest point out (aside from tire) from the bike/rider. So weight has a noticeable difference than when it’s near the low center of the bike or on the rider. The wheels, bike and rider move independently and the constant reaccelerations of MTB make it ever more important.

To experiment yourself (I have), take a 5 pound weight (bottle of sand) and move it from your bottle cage, to your seat post, then to your jersey pocket. Go for a long punchy trail ride and see if you can feel how your bike handles differently in each configuration. Multiply that by the hundreds of accelerations and bike manipulations over obstacles and out of corners. This is why some riders hate Camelbaks or refuse to put on saddle bags, because it affects how they ride or how their bike handles. Now imagine that on the wheels. Where weight IS matters in MTB expecially. Yes, a 100 grams difference per wheel is minimal and could be approaching marginal gains (when you ignore the other benifits of carbon rims), but if you’re in the front pack over a 1:30-2:00 race, that may be the difference in energy savings that give you a little more at the end. In my case I lost nearly half a pound per wheel (200 grams) when I switched to carbon rims. Also, over my 9 hour MTB 100 with 90% singletrack and 10,000 feet of climbing, I am sure my carbon rims assisted both in weight and handling.

Let’s see what science says:

ACCELERATING
An increase in speed means an increase in kinetic energy. Since the kinetic energy depends on both mass and velocity, more mass would mean more energy required to speed up.

La te xi t 1

But does it matter where this mass is located? Does it take more energy to increase speed if you put the mass on the wheel? Yes. First, let’s look at mass on the frame of the bike. If I add something to the frame the total mass increases. This means that I would need more work to increase the kinetic energy. That’s pretty straight forward.

What if the extra mass is on the wheel? In that case, I must do two things to increase speed: increase the kinetic energy and increase the rotational kinetic energy of the wheel. If all of the mass on the wheel is located at the rim, I can write the rotational kinetic energy as:

La te xi t 1

In this expression, m w is the mass of the wheel, R is the radius of the wheel and ω is the angular velocity of the wheel. But if the wheel is rolling and not slipping then there is a relationship between the angular speed of the wheel and the linear speed of the bike (this is how a car speedometer works—or at least the way it used to work).

La te xi t 1

If I substitute in for ω, I can write the following for the total kinetic energy of the bike (translational plus rotational).

La te xi t 1

In the translational kinetic energy, m b is the total mass of the bike (including the wheels) but the rotational kinetic energy only depends on the mass of the wheels.

So let’s say I add 100 grams to the frame. This would increase the value of m b but not increase the mass of the wheel. The translational kinetic energy would increase by some amount and it would require more energy to accelerate (increase the kinetic energy).

Now let’s add 100 grams to the wheel (increasing m w). Since the wheel is part of the bike, this means that the total mass also increases ( m b). Both translational and rotational kinetic energy terms will have a 100 gram increase in mass. You will have double the increase in energy by adding mass to the wheel.

So yes, adding mass to the wheel is worse than adding mass to the frame—but only when accelerating.

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I understand all of the Physics involved. The thing to keep in mind is that it is the total energy input into the system that has to be considered- the energy to accelerate the wheels, the bike, and the rider. The largest mass by far is the rider, then the bike, and then the wheels. Each differs from the other by about an order of magnitude. So the amount of energy I need to accelerate my wheels is way, way smaller than what I need to accelerate myself. My Industry 9 Al wheel SET is less than 100g different than an equivalent Enve carbon wheelset. It is a very marginal gain at best. Especially when you consider that the pair of MTB tires weighs significantly more than the wheels (something not true on the road). I have nothing against carbon wheels. I have them on my road bike. I believe the durability argument. I believe the aerodynamic argument for deeper wheels. I think they are cool. However, as an investment to go faster on a MTB I don’t think they make much difference unless you are within a fraction of a percent of winning already. Or, in a TR perspective, within a few watts of winning. I think you could take the extra $1000 to $1500 you’d invest in carbon wheels and have a bigger weight reduction in other ways.

Then accordingly you should have spent your money elsewhere on your road carbon wheels as they are even more marginal than on your MTB. Also, loss in acceleration of your rotational weight and total weight (translational) is not a 1 to 1 relationship. I can slow and/or temporarily lock up my rotational weight (slipping) through a corner while my total weight acceleration keeps some momentum.

I get that we’re splitting hairs here, but if you have money to burn on bike stuff, carbon wheels is generally the best place to start.

That could vary widely depending on the differences between his old and new wheels. It’s entirely possible he went from a blocky aluminum rim to an aero carbon rim. The range of possible differences are wide and assuming one of them with no info other than material stated is a mistake.

I have carbon wheels on my road bike not at all because of weight. First, they came with the bike. However, these are deep section wheels and the primary, and far largest, benefit is aerodynamic and NOT weight. The thing to remember is that weight on wheels is roughly twice as important as weight on the rider or frame from an energy standpoint. So, 100g on the wheels is roughly the same as 200g on the rider or bike. So, things like a lighter crankset have about the same effect at a way lower cost. Or, even better, lighter tires. Or just losing weight as a rider. Or carrying less junk with you. My point is that the performance improvement of carbon wheels from ONLY a weight perspective makes them a poor investment. Aerodynamics sure, durability sure, but not weight.

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The discussion was regarding the “weight” of the rims in isolation of the other added benefits of carbon…

The discussion has since shifted to discuss the other pros of carbon and points are being made aside from the OP. Obviously one probably shouldn’t decide to buy carbon rims “solely” for weight savings, as there are much cheaper ways to achieve this if one was seeking “weight weenie” goals on a budget. But that’s not the discussion we’re having.

However, when the OP’s question is: Are Carbon Wheels Worth It for MTB? The answer is Yes for all the reasons listed throughout this thread “to include” weight savings, no matter how “marginal” one thinks they may be. It should be “part” of your decision to buy carbon rims, but not necessarily “the” reason.

EDIT:
It’s no different for me now when I’m choosing any new part for my bike. Since I race and I know weight matters, I “consider” the weight of the part as well as the form and function. So all things being equal I will pay a little extra for it to be a little lighter. I optimize my personal weight, my kit, nutrition and my training. So naturally I will do the same with bike parts.

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One thing to consider: If you damage a carbon rim on the trail, it will may be damaged to the point that you will be walking out.

I took a bad line on Porcupine Rim trail this year and the impact badly damaged my aluminum rim (Industry 9). I was able to work the sidewall back into shape enough to keep riding with some duct tape. A carbon rim may have been destroyed and I would have had a long hike out.

Obviously some carbon rims are more durable than others but that may negate any weight savings.