Xtreme Carbon wheels

Over the last few years, there have been many changes in performance race wheels for bikes. From deeper, to wider and serrated, there seems to be no end to the innovations coming from the big brands in the market. And while these grab most of our attention, occasionally a boutique brand will come out of left field with something that really catches the eye.

Enter Australian company, Xtreme Carbon. Not to be confused with the late 90s, early 2000s wheel company, X-treme (which has long been out of business) this small family business entered the wheel market about 18 months ago and immediately caught our eye. They were different. The wheels looked different. Sure, the depths were familiar with 60, 80 and 90mm all available, but there was more to these wheels. Fast-forward a few months and we were lucky enough to receive a pair of 90s to test.

The box the wheels came in was a visual feast, with the giant ‘Scary Dad’ logo (as my daughter calls it) large and loud across the front. Our test wheel set was the 90mm front and rear Race Grade option. Xtreme Carbon also have a 60mm front and rear Race Grade option and a 120mm rear option in the top-end range available. For the more budget minded, 60mm and 80mm Enticer Grade front and rear options are also offered.

On opening up the box you get a real appreciation for the work that has gone into producing these wheels. Nothing has been left to chance. From the 12K weave of the carbon to the classic decals and high gloss clear coat, not to mention the gold nipples and skewers, these wheels are such a visual delight you would almost be forgiven for missing the hero of the wheel – the hub, which pulls the wheel together. It’s a deep, narrow, alloy aero hub with a carbon axle that essentially hides the spokes behind the rim when looking straight on. Our test wheels were spot on 90mm deep and 25mm wide, as advertised, although not as blunt-nosed as some other offerings out there, and came fitted with Continental GP4000s.

Before we get to the ride quality of the Xtreme Carbon wheels, let’s take a closer look at their development. First of all the designs and moulds are all Xtreme Carbon’s own, in-house designs and are manufactured by Topkey International, in Taiwan. The rims fall somewhere between the straight-line aero shape of a ‘V’ rim and the ‘U’ shape of the more stable rims seen in a lot of wheels today. The shape is the result of basing the development on a rotating aerodynamic object rather than just a rim shape, thus the resulting hub shape – more on that later. They use 12K carbon with a gloss finish on all their rims, and the braking surface and tyre U section (clincher and tubular) are constructed using a 3K weave and high temperature (240 degrees Celsius) resin on the braking surface. All of the Xtreme Carbon wheels are explicitly designed for triathlon and time trial (TT) events, and the forces exhibited by such events. As a result, they have been ratified, legal for all UCI TT and triathlon events. NB: mass start cycling events require depths of 65mm and under, which Xtreme Carbon are working on for future projects. There are also disc brake versions coming down the line, should the current trend become the norm.

Both the front and rear options use 24 J-pull round Sapim spokes. This allows Xtreme to achieve optimal stiffness and reliability. One might expect there to be some deficit with round spokes but Xtreme state that there is no aero data available that confirms that a bladed spoke decreases the aero drag for the wheel. Furthermore, testing undertaken by the AIS track team on round versus bladed spokes revealed that there is ‘no measurable difference’ in the drag experienced between both wheels. So the extra strength of the round spoke wins out. This makes life a lot easier when working on the wheels or when you need a quick change out on the road. This brings us to the hubs.

The hubs are machined from aerospace-grade, single-piece billet Aluminium 6061 T6 in Melbourne, and look spectacular. Just 25mm wide, and with a flange depth of 100m, they came about as a result of the designers realising they needed a hub and axle design that fit precisely with the aero wheel design. Thus, this hub was designed to tuck the spokes behind the rim and reduce the frontal area of the wheel profile resulting in less rotating drag. We checked to see if there had been any failures in the hub. Xtreme reported that through the whole testing period, and in the production time there had been no instances of cracks or failure. Not surprising as the material used is specified for use in aircraft landing gear. Xtreme Carbon top their hubs of with US-based, Enduro ceramic bearings.

Finishing off the look of the wheels are the flashy gold skewers. While they may look bulky, Xtreme assured us they were designed for clamping force, and there is very little aerodynamic penalty. The benefits of a secure wheel, especially when you consider how tight the tolerance is with some modern frames, far outweigh any aero loss.

We received some wind tunnel data from Xtreme highlighting the work they’ve done to ensure that what comes out of their factory has been designed to limit any losses due to drag. The tests were performed at the SAPT tunnel in Arizona, where the protocol was standardised across all tests. The wheels were tested inside a bike to predict more real-life riding, and all variables such as tyres, inflation pressures, wind and wheel speed remained consistent throughout. Yaw angles between 0-10degrees were tested, reflecting conditions triathletes and time trialists might come up against when racing. The data was drawn from testing the Xtreme wheels against several industry-leading wheel brands of the similar depth of 60mm.

The results showed that the Xtreme 60s had around 4.2% less drag than the next best wheel. That equates to saving about 3.2watts at these Yaw angles, which can add up to considerable energy or timesavings over any triathlon course, and especially over 180km. We would like to see how the 60s and 90s perform at higher degrees of Yaw (that you might see in races like Hawaii where a higher Yaw is common). We suspect that the advantages at higher Yaws with these wheel sets may not be as significant because the spokes become more exposed as Yaw values rise. Now, only the 60mm depth wheels were tested. We suspect that the 90mm wheels would offer similar drag reductions or maybe just a little less, as a deeper rim depth will have slightly less spoke profile in the wind.

What we were really itching to test was the 120mm (‘The Godzilla 120’) that has just been released. Unfortunately at the time of testing, this was not quite ready for us. This wheel depth fascinates us, as athletes will typically jump from an 80 or 90mm wheel depth to a disc if they want the gold standard of rears to ride. At 120mm not only is this wheel a great substitute for a disc but can still be legally ridden at Kona, and seems to be the deepest wheel commercially available.

The Godzilla rear wheel is still built with the aero hub and axle system, so there’s the same 25mm distance between the hub flanges, allowing the spokes to vertically align with the rim, as they do with the 60s and 90s. But this is where the wheel becomes more interesting than its shallower brothers or sisters, as Xtreme have designed this wheel to be reverse parabolic like the profile of a sail, and their calculations show that the 120 has the same aerodynamic profile as a solid disc rear wheel through 0-20degrees of Yaw. Adding to that between 30-60 degrees of Yaw (yes, very high Yaw) they have demonstrated that wheel can generate, on average, dependent on wind speed, 1.25% drive or free speed, which equates to around 0.5kph for free speed at 40kph. As Brad from Xtreme tells us, “Sailing mechanics is the new frontier in bicycle wheel design.” This could lead the company to look into different wheel designs and possibly new bike designs too, which can take advantage of the very creature we fight against when racing.

While all of the above is rather interesting the reality is, everything comes down to how the wheels ride. Pulling the wheels out of their box you notice they are a little heavier than a lot of wheels out there, but when it comes to triathlon and time trials, this is not such a big deal. It’s also obvious how stiff the rims themselves are, let alone the whole wheel. Onto the bike – they offer next to no flex, even accelerating out of corners there was no brake rub against a flexing rim, which is a real testament to the build quality. Our first outing on the Xtremes was hitting hot laps around the Melbourne Grand Prix circuit in Albert Park. Through a number of the tight corners, where we often get pushed around by winds, when testing deep rims, they tracked perfectly and returned to speed very quickly – none of the sluggish acceleration you sometimes get with heavier wheels. While it’s hard to notice any real difference from other wheels we have tested when riding with a tailwind, one of the highlights of the wheel set is just how they perform into a headwind. They just want to keep going, riding seems less of an effort than with other wheel sets, and we can only imagine that this is down to the hub and tucked-in spokes. Winds in Melbourne can get moving and, as we have had with almost all brands, there were a few hairy moments with side wind gusts, but overall even in Melbourne you could get away with a pair of 90s for 80% of all races. Having said that we are sure that if you substituted out the 90mm for a 60mm at the front, you could handle any race going around, and have very little aerodynamic loss, so that might be the better all-around option. One area we expected the Xtremes to not perform well in was descending. We expected the narrow pull of the spokes into the hub flange to maybe not spread the pressure through the turns as well as other brands. We were wrong. In fact, they flew down the hills and never gave us the feeling of being on the edge. For the majority of athletes, we would probably recommend going with the 60mm front, and 90mm rear, or even the 120mm – this combination will treat you well from your local sprint race right through to the Ironman World Championships in Hawaii.

When we heard we were getting a pair of the Xtreme Carbon wheels to test, we expected to get a very cool looking and very unique wheel set. What we got ended up being so much more – an Australian brand, ready to go, head-to-head with the industry leaders. At $2000 for a set of Race Grade 90s, they are competitively priced to make an impact locally and internationally. Naturally, we love seeing innovative Australian companies, and can’t wait to see where Xtreme Carbon heads in the future and the products they come up with.



Craig McKenzie and Patrick Legge are The Test Lab. Two guys with an obsession for trialling all things related to swimming, riding and running and telling anyone who will listen what they think. Having 20 years each in the sport, they’ve seen the good, the bad and the ugly, but always loved the innovation triathlon brings to the world stage. Craig raced as a professional triathlete, winning 4 National Duathlon titles, and has worked as an exercise physiologist, osteopath and coach, while Pat has built a career running a personal training, massage and coaching business, working with State, Australian and World Champions, including Australian Olympic and Commonwealth squads whilst competing himself.

Leave a Reply

Your email address will not be published. Required fields are marked *

Sign up for the mailing list

Enter your details below to stay up to date with whats going on.