Hunt’s new SUB50 Limitless Aero Disc wheels offer “aero superiority and class-beating performance to weight”

Hunt has introduced a new SUB50 Limitless Aero Disc wheelset which, it says, is the fastest road race option out there in a depth of up to 50mm when fitted with either 30mm or 28mm tyres. With front- and rear-specific hookless rim profiles, the option of unidirectional carbon spokes, and a new ratchet hub design, the complete wheelset weighs as little as 1,380g, Hunt claims, while improving on the aero performance of its previous 48 Limitless wheels. 

“Compared to relevant wheels in the mid-depth category, the SUB50 Limitless aerodynamically outperforms the relevant competitor wheels up to and including 50mm in depth when mounted with modern 30mm tyres, and performs similarly to significantly deeper wheels tested,” says Hunt. “When aerodynamic drag-to-weight and aerodynamic drag-to-depth ratios are considered, the SUB50 significantly outperforms [competitors].”

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Hunt says that when it was launched in 2019, its 48 Limitless Aero Disc was “the world’s fastest road disc brake wheelset up to 50mm in depth”. Since then, though, the deeper Roval Rapide II has come along (the front rim is 51mm deep, the rear is 60mm deep) and has a slight aerodynamic advantage over the 48 Limitless, and brands like Vision and Enve have widened the external width of their wheels to 32mm and above.

Plus, there has been a move towards hookless (also called tubeless straight side, or TSS) tech in the road wheel market over the past few years, with some aerodynamic and weight benefits, while the 48 Limitless has hooked rims, so Hunt felt the need to update its offering.

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Hunt says that the SUB50 Limitless, the result of a three-year development project, is “an all-round racing wheelset with drag characteristics among the very best wheels available and a low weight and wide measured tyre profile characteristics that make it excellent for any racing condition, including mountains, cobbles and crosswinds”.

It says the SUB50 Limitless offers performance benefits relating to four key metrics: aerodynamic efficiency, aerodynamic stability, weight, and tyre shape. We’ll take a look at each in turn. 

Before we start, it’s worth pointing out that although we’ve seen these wheels, we’ve yet to use them, so we’re reporting Hunt’s tech claims rather than telling you about our own ride experience.

Improved aero efficiency 

Hunt says that to maximise aero efficiency, it focused on “creating the most efficient rim profile for managing clean airflow at the front of the bike”. 

After looking at possible profiles using CFD (computational fluid dynamics), and testing the most promising shapes in the GST wind tunnel in Immenstaad, Germany, it opted for a front rim that was 49.5mm deep and 34mm at its widest point. 

“Since the rear wheel encounters heavily disturbed airflow affected by the front of the bike and rider, the engineering team saw an opportunity to minimise material in the rear wheel without negatively affecting system aerodynamics,” says Hunt.

Again using CFD and wind tunnel testing, Hunt decided on a rear rim that’s 49.5mm deep, like the front, but considerably narrower at a maximum width of 30mm.

We’ve seen other wheel brands, such as Roval, pair a shallower front rim with a deeper rear rim to reduce drag without affecting handling, but Hunt says its design offers “ample stability and predictability” (more on that in a sec), so it can maximise aero benefits by going for equal depths.

If you want to know precise details about Hunt’s rim profiles and the data and reasoning behind them, we’d direct you to the white paper that accompanies this launch. 

Hunt took its wheelset to the wind tunnel and compared the aero performance with that of key competitors: Roval Rapide CLX II, Enve 4.5 SES, Princeton Peak 4550, Zipp 454 NSW, Zipp 303 S.

With both 28mm and 30mm tyres fitted, Hunt found that the SUB50 had the third lowest aero drag behind the Roval Rapide and Enve 4.5 SES at 45km/h (28mph) – the difference was always less than 1W – but those rivals have deeper rims and are heavier (the Enve 4.5 has rim depths of 50mm at the front, and 56mm at the rear). The Roval Rapide has a claimed wheelset weight of 1,520g while the Enve 4.5 has a claimed weight of 1,511g, compared with 1,380g for the SUB50. Incidentally, the first-generation Roval Rapides were much lighter than the ones that Hunt used in their testing, but they were only suitable for non-tubeless tyres.

“Of wheelsets of a similar depth, the SUB50 stands out clearly from the rest of the sample, having a much more efficient profile for the depth of rim, and with drag numbers close to or exceeding the deeper wheels in the test,” says Hunt.

“With a 28mm tyre, the SUB50 and the Zipp 454 NSW have the lowest drag compared to the wheelset’s weight. This provides versatility: pure aerodynamic performance among the very best tested while also being some of the lightest all-round wheels available.”

Compared with its own 48 Limitless, Hunt says the SUB50 fitted with a 28mm tyre requires 1.4W less to maintain a speed of 45km/h (28mph). 

Of course, all of the data quoted here – and in the white paper – is Hunt's own. Although it was collected by Ernst Pfeiffer at the GST wind tunnel, Hunt gets to decide what it releases, so check out the white paper yourself and see what you make of it. 

Stable performance

Hunt says that the SUB50 Limitless Aero’s stability is all part of its speed story because your ability to predict how the wheel will behave as the wind changes allows you to ride faster. Essentially, you want a front wheel where the steering force you experience in a crosswind is minimised to ensure stable handling. 

“Predictability through variable wind conditions allows riders to comfortably stay in a low, aero position on the bike for longer, which can have a considerable impact on efficiency and expended energy throughout a long road stage or classics race,” says Hunt. 

“This stability is attributed to the wide radius at the rims’ spoke bed, which achieves more consistent and controlled stall conditions, shown on the steering moment co-efficient graph as lower fluctuations around the stall points. Steering moment co-efficient is proportional to side force on the rim.”

If that’s all getting a bit technical, in simple performance terms, stalling means instability. Again, if you want to know why Hunt went for the precise rim profiles it chose, all of the details are contained in its white paper.

Hunt says, “The SUB50, Rapid and Enve wheelsets [fitted with 28mm tyres] share a similar behaviour to each other with lower steering moments up to around 10° yaw, but they do not experience stall until around 16°. This later stall achieves lower average drag and a more predictable change in steering moment as the wind conditions change – albeit with a higher overall steering moment at the highest yaw angles.”

With 30mm tyres fitted, Hunt says, “The SUB50 shows the smoothest behaviour through the stall point which should ensure predictable handling at all yaw angles.”

Reducing the weight

The lightest SUB50 Limitless wheelsets are 130g less than the previous 48 Limitless. Hunt claims a weight of 1,380g per pair for the models with carbon spokes, and we weighed them at 1,382g – so near enough – complete with rim tape, in the road.cc office when Hunt came a-calling.

It’s not one factor that has led to this weight loss; Hunt has been cutting the grams across various wheel components.

For a start, the rims are hookless (more on that below) and that saves a small amount of weight. Hunt first offered road hookless wheels way back in 2016. However, the number of hookless-compatible tyres available at the time was limited, and Hunt eventually updated those wheels to hooked rims. 

Now, though, ETRTO guidelines mean that variances between tyre and wheel manufacturers have reduced, and there are more tyre options out there, so hookless rims are back on the agenda. It looks like they're here to stay this time.

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Hunt also says that recent advancements in composite lay-up capabilities have allowed it “to achieve previously unreachable strength-to-weight ratios in the construction of these new, wide rim shapes, resulting in lighter rim weights”.

Beyond the rims, Hunt uses its existing TaperLock unidirectional (UD) carbon fibre spoke tech for its SUB50 Limitless wheelset (a steel-spoked version is available too). This means the spokes are held mechanically, with no bonding, and can be trued like normal steel spokes.

“The UD carbon spokes offer 6% greater lateral responsiveness compared to steel spoke equivalents with significantly less weight (2.7g per spoke), allowing the design team to reduce the number of spokes used in the system,” says Hunt.

On the carbon-spoked wheels, Hunt goes for 18 spokes at the front and 20 at the rear (full spec details are down below). It says that carbon-fibre spokes also reduce high-frequency vibration to smooth the ride and reduce fatigue.

Hunt has also introduced a new double ratchet hub system at the rear, with a 40-tooth drive ring that’s said to offer “increased engagement surface area while using less shell materials relative to pawl-based systems”. 

The hub shell is made using 6066 aluminium alloy, with a 7075-T6 alloy axle and freehub body with a ceramic-reinforced coating designed to protect against gouging. The carbon spoke version of the Hunt H_Ratchet DBL hubset weighs a claimed 332g.

“Reliably offering 9-degree engagement, the system is designed for high torque load and easy servicing, with tool-free end cap removal and double-sealed main hub bearings,” says Hunt. 

While the Enve SES 4.5 and Roval Rapide wheels offer marginally less drag, Hunt believes that the SUB50’s lower weight – saving 131g and 140g, respectively, according to manufacturers’ claimed weights – provides a significant advantage, as do the lower rim depths and the wider measured widths for a given tyre.

Going hookless... again

Hunt has made the SUB50 Limitless Aero rims hookless, as mentioned above, with an internal rim width of 23mm. The wheels are said to be optimised for both 28mm and 30mm tyres. 

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“Hookless rim technology allows [us] to slightly reduce rim weight, improve manufacturing consistency, and improve aerodynamics at the tyre-to-rim interface by reducing the ‘lightbulb’ effect that inwardly protruded hooks have on the tyre profile,” says Hunt. “A wider hookless bead profile also helps reduce the chance of pinch flats, due to the blunt, flattened profile.”

The previous 48 Limitless wheels were optimised for 28mm tyres but Hunt feels that the market is moving wider still, hence a focus on 30mm tyres too.

“If rims are correctly optimised for wider tyres, the aerodynamic differences between wider and narrower tyres will be reduced and may be eliminated altogether, especially at higher yaw angles where the aerodynamic performance is more dependent on overall rim shape than frontal area,” says Hunt. 

“The wider internal rim width allows riders to take advantage of the rolling resistance benefits that come with wider tyres on all road conditions, but especially on rougher racing surfaces and cobbles.”

Specs and prices

Hunt is offering its SUB50 Limitless Aero wheels in these three versions:
 
Hunt SUB50 Limitless Aero Disc UD Carbon Spoke, CeramicSpeed Bearings
Weight: 1,380g per pair
Internal rim width: 23.0mm
External rim width: 34.2mm front, 30mm rear
Spokes: TaperLock UD Carbon, 18 front, 20 rear
Hubs: Hunt H_Ratchet DBL, 40T, 9° engagement
Bearings: CeramicSpeed, double-sealed
Price: £2,289
 
Hunt SUB50 Limitless Aero Disc UD Carbon Spoke, Stainless Steel Bearings
Weight: 1,380g per pair
Internal rim width: 23.0mm
External rim width: 34.2mm front, 30mm rear
Spokes: TaperLock UD Carbon, 18 front, 20 rear
Hubs: Hunt H_Ratchet DBL, 40T, 9° engagement
Bearings: Double-sealed stainless steel cartridge
Price: £1,849 

Hunt SUB50 Limitless Aero Disc Steel Spoke, Stainless Steel Bearings
Weight: 1,428g per pair
Internal rim width: 23.0mm
External rim width: 34.2mm front, 30mm rear
Spokes: Pillar Wing 20 Elliptical Aero, 20 front, 24 rear
Hubs: Hunt H_Ratchet DBL, 40T, 9° engagement
Bearings: Double-sealed stainless steel cartridge
Pricing: £1,479

The first delivery of Hunt SUB50 Limitless Aero Disc wheelsets is available for pre-order now in limited quantities. Most stock will arrive with riders in late February, with CeramicSpeed wheelsets coming in late April.

For more info, including Hunt’s white paper, head over to www.huntbikewheels.com