Every wheelmaker after the next touts new aerodynamic claims for every different type of road bike. But taking that a bit off-road, are there actually any real aero gravel gains to be had in the fatter-tire, lower average speed world of gravel bike riding & racing? Hunt Bike Wheels was one of the first to quantify more likely real-world aero gains with the wider 28mm tires many roadies ride (and race) these days in their Limitless ‘fastest road wheel‘ project. But could those same lessons make drag saving gains with wider gravel tires too?

Do aero gains make a difference with fat tires on gravel roads?

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

A few weeks back, Hunt sent us their latest engineering research White Paper, where they tried to settle the score on whether aerodynamics really makes any difference for gravel bike wheel design. I’d lead this with the first caveat that: so far, Hunt doesn’t yet make an aero gravel wheelset, so this isn’t really directly trying to sell you a new set of wheels. (With that said, scroll down to the end and you will find a sneak peek at an in-development prototype.)

Hunt isn’t the first to bring up the combine topic of aerodynamics and gravel. Id’ venture to say that the 3T Exploro was the first to seriously pop up on my radar back in 2018, after they put their Sqaero tubing & 3D-printed mud into the wind tunnel.

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

But ever since aerodynamics engineer Luisa Grappone joined the Hunt team, they’ve taken a deeper look into aero gains, and spent more time in the GST wind tunnel. And unlike many companies that keep tight reins over their aero work, Hunt recognizes that they are a relatively small and young wheel company, and is trying to be as open as possible about how aerodynamic study influences their product design & development…

Gravel: Does Aero Matter? – a Hunt engineering analysis

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

So why did Hunt take gravel into the wind tunnel?  Here’s how Hunt’s head of communications put it… “As riders & racers of gravel, we’ve increasingly been discussing (and asked by our customers) whether or not aero is particularly relevant within the discipline. Working with Ernst at the GST wind tunnel and doing lots of number crunching, we wanted to find out if gravel speeds and wide tyres [sic] negated aero considerations.”

They essentially went into the analysis expecting the wider gravel tires to break up airflow so much over a narrower rim, that any end aero benefit would be lost. But with so many iconic ‘gravel’ races from Dirty Reiver to Dirty Kanza, ultra-endurance races from Tour Divide to Atlas Mountain Race, and professional roadies crossing over to gravel racing, it was worth taking a closer look. Plus, there’s just more of us regular recreational cyclists picking new gravel bikes for their versatility.

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

So, what do the numbers say?

Yes. The simple answer is that Hunt’s real-world research and wind tunnel testing say that yes, for gravel, aero really does matter. The full Hunt research white paper (which you can see here) breaks down their assumptions, testing methodology, calculations, results & analysis.

But suffice it to say, comparing 38mm gravel tires set up on wide/deep aero wheels like their own 48 Limitless and ENVE SES AR wheels vs. conventional non-aero (their own 29mm wide external, 19mm deep alloy 4 Season Gravel X-Wide wheels, the reduction in drag across all yaw angles was significant – up to 9W saved.

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

In essence, if you took the 10 hours that Colin Strickland needed to win last year’s 201mi (321km) Dirty Kanza at an average speed of 20mph (32kph), the ENVE SES 4.5 AR wheels with 38mm Schwalbe G-One tires would have been fastest. Hunt’s 48 Limitless wheels would have been a mere 4 seconds behind, the shallower ENVE SES 3.4 AR another minute and 14 seconds back. And the shallow alloy 4 Season Gravel X-Wide wheels would have made the rider almost 7 minutes slower.

The differences aren’t huge, but they are real. And in a race situation it could make things close. Second place finisher Peter Stetina was just 9 minutes behind Strickland after more than ten hours of racing. With increased cross winds, the differences would be even greater.

So do you need to go buy some aero gravel wheels right now? Probably not, unless you are about to race some really long gravel. But if you do race gravel or ultra-endurance events, it is probably worth keeping the idea of aero gravel in the back of your mind from now on.

Sneak Peek: Next gen Hunt Carbon Aero Gravel Disc wheels

Gravel: Does Aero Matter? - a Hunt engineering analysis of the impacts of aerodynamics on gravel bike wheel design and potential drag reduction

So when is Hunt going to introduce an aero gravel wheelset based on these wind tunnel findings? Not surprisingly, they wouldn’t put a date on their development timetable. Yet, they all but confirmed that a next gen Hunt Carbon Aero Gravel Disc wheelset was in the works, and coming relatively soon. We expect it will probably get the Aerodynamicist moniker like the rest of their latest wind tunnel tested wheels, and probably will sell for 1000-1200€ for a set. We’ll be curious how it stands up to the 48 Limitless and those ENVE SES AR wheels when fitted with fat gravel rubber…

HuntBikeWheels.com

35 comments

  1. Martin on

    This sucks really. They will try to bring all the marketing buzz to the gravel field. I do both road and gravel and love them both. But when I ride gravel, aero is the least of my concerns and it should be. It is all about exploring. It can be tough, but this is less about the numbers and more about the venture. I want to keep it that way. If you market a wheel as aero-gravel, you lost me.

    Reply
    • K-Pop is dangerous to your health on

      You need to differentiate between ride or race. Obviously you’re not going to benefit from anything aero if you’re just meandering around and never hit race pace regardless of the surface. The fact that this still has to be explained is becoming increasingly redundant.

      Reply
    • Ollie @ HUNT on

      Hi Martin.

      Cheers for your feedback and totally understand your position – for the record that’s exactly my approach to gravel riding as well. I like to ride fast on the road, and even on the MTB, and then I’ll use my gravel bike for, essentially, ‘downtime’ between the two where I can relax a bit more.

      Saying that, with the proliferation of gravel ‘races’ mostly in the US and (if the rumours are true) UCI-mandated racing in Europe and across the world, aerodynamics is an element of performance that will certainly speak to that kind of gravel cyclist. Enjoying gravel riding at a slower pace, for guys like you and me, isn’t going anywhere I hope.

      Cheers,
      Ollie

      Reply
    • nedersotan on

      @Martin, why does this suck? Just because you are not interested in a product? I don’t think Continental suck, just because they offer a time trial tire and a DH tire, both of which I will never use.

      I also don’t know where you get the idea that gravel is all about exploring? Maybe sometimes it is, but don’t you evergo out for an hour long ride from your house? I do, and after a while, I have covered every possible road and trail. It’s still fun to ride, but it is NOT exploring.

      Lot’s of times riding bikes is about being outside, getting exercise, using skills and enjoying speed. This is equally true on pavement, gravel mtb trails and snow trails. Aerodynamics obviously help with the speed. They even help with exploring, since, if you can travel further in the same amount of time or effort, you can explore more.

      Think about it this way: if you truly only cared about exploring, you’d only ride a fatbike, since it would allow you to explore many more surfaces. I suspect most of us ride our gravel bike instead, because the higher speed on easy terrain, makes it more fun than our fatbikes.

      Reply
  2. Lyford on

    As a counterpoint, my gravel bike sees a lot of mixed-surface rides that combine paved and dirt roads. Being more efficient on the faster pavement sections seems like a perfectly reasonable idea.

    Reply
  3. J'Anky Teal on

    This is interesting I,’d wondered the same. But I have to ask, how much is bladed spokes VS the round spokes on the Gravel Disc X-Wide and Enve wheels? It seems strange not to use the bladed spoke Carbon X-Wides as a baseline.

    Reply
  4. Tom on

    Not buying into this aero is important on gravel business. To be more specific, what tire are they testing? A G one with a super fine tread that would be overmatched in real off road conditions?

    Reply
    • Ollie @ HUNT on

      Hi Tom, cheers for responding and you’re correct in identifying the G-One as our (primary) test tyre.

      We’re testing across quite a few different tread patterns and widths, with mixed results for now. It’s worth noting that Colin Strickland ran a Specialized Pathfinder when he won DK last year, which has even less tread than a G-One so certainly doesn’t overmatch it as you say.

      But it’s definitely a good point, and we’re seeing tyres form an even greater role in the performance of the overall system as you do on the road.

      Best regards,
      Ollie @ HUNT

      Reply
  5. David French on

    Can you buy the rims on their own?

    Obviously the rims are much cheaper than something like an ENVE, so how much difference would it make going for a more expensive rim (more comfort after 6 hours in the saddle perhaps) and hub (something like a King being faster rolling) rather than changing the profile of an inexpensive rim?

    Reply
    • Craig Harris on

      Hunt sell rims alone but a pair of rims costs the same as a full pair of wheels so unless they significantly change pricing in future then it only makes sense to buy full wheelsets.

      Reply
  6. Andrew Loscutoff on

    I don’t know why anyone would argue against innovation and passion to make cycling tech better.

    If you “don’t care” about aero consider other innovations- shifter cables routed under bar tape, helmets (thank you lord) look way better, sleek looking frames, they all improve the sport.

    Hunt is doing a good job at saying here is what we are doing to back up a lot of naysayers which claim “marketing Jargon”

    Reply
    • Velo Kitty on

      > I don’t know why anyone would argue against
      > innovation and passion to make cycling tech better.

      Hi Andrew. I will address your question. Usually new products are promoted with exaggerated claims, often bordering on fraudulent. (Think oversize derailleur pulleys.) Shoddy engineering seems to be way too common in the cycling industry. Also there are usually major trade-offs that the marketers don’t mention. Are the snapped steerer tubes on BMC’s recent Teammachines really making cycling better for customers? All because BMC wanted hidden cable routing. Have you looked at the steering stop setup in Cervelo S5’s?

      Reply
  7. Michael on

    I asked this exact same question on the ENVE AASQ and they said that aero doesn’t matter on any tire that isn’t perfectly smooth and that they would not be making aero gravel wheels. Would love to hear what they say about this study or if they will publish any of their own studies. One question that I have for Hunt is why their internal width is only 22.5mm when their external width is over 35mm. Enve is around 32mm external but 25mm internal, is this all down to hookless beads?

    Reply
    • Weiwen on

      I recall that conversation, and I have a hard time believing what the ENVE rep said. I can buy that a big knobby tire will reduce the benefit of aero rims, sure, but what the rep implied was that a gravel tire would eliminate the benefit, not just reduce it. Perhaps they spoke imprecisely.

      Reply
      • Tom on

        aero is a pretty fine thing. Any tire with significant tread, especially at the sides, will blow out any hoped for aero benefit. So, like most things, you need to read the fine print. Sure, these wheels will be faster than some if you ride fine tread tires with no side knobs, like a G One. To me, that sounds like a pure race tire. If you actually want to have fun on the bike, and not worry about pushing out the front end every time you corner in the the dirt and gravel, you’ll want a tire with side knobs. So no aero benefit.

        Reply
  8. Aerogal on

    Love the ride and quality of my Hunt road wheels and can’t wait to get another pair for my Aspero. Looking forward to see what this research brings to market. And no, I’m not an ambassador/employee/sponsored rider. Keep up the great work!

    Reply
    • J'Anky Teal on

      Are you saying that a YouTube pundit would take issue with a trained aerodynamicist with wind tunnel data?
      Sounds about right.

      Reply
      • Hike-a-bike on

        Hambini is a lead engineer with Airbus with a PhD in Aerospace Engineering and access to the Airbus tunnels for testing. He’s very rough around the edges but knows his stuff.

        Reply
      • edge on

        …and rightly so, since the wind tunnel is not representative if real life. Also he is a pundit that is a more rigorous aerodynamicist than most wheels “manufacturers”.

        Reply
  9. Robin on

    The question was not about marketing but innovation and passion to make cycling better.

    For every case mentioned by you there’s at least one case, possibly more, where your examples don’t exist apply.

    Reply
  10. ben on

    you cannot extrapolate a windtunnel result to a 10 hour race in that way, that’s not how it works. I don’t mind you pretending to be scientific but please don’t make it laughable..

    Reply
    • Tom on

      If you believe Hambini, it’s actually worse than that. Wind tunnels have great signal to noise ratio, which is completely unlike the real world, especially for gravel where speeds are lower than road. Throw in the compounding factor of a tire with knobs, and I’d say aerodynamics are close to worthless, and wind tunnel results even worse.

      Reply
      • ben on

        you can get every result you want from a wind tunel test if you set it up properly. Thats why every brand has ‘scientific’ proof theirs is the most aero. Among other things, Hunt could (and should) have performed the test with different kind of knobby tires. But then again, mayby they did and didn’t like the results.

        Reply
  11. Crash Bandicoot on

    I read the white paper, to quote a common phrase from the pharmaceutical industry looks like more marketing being 10 years ahead of the science. How on earth is a low speed wind tunnel simulating turbulent airflow that is part of not only cycling but is a massive component of gravel riding/racing? Typical cycling marketing bravo Sierra.

    Reply
    • briannystrom on

      The obvious point is that lower drag will allow you to ride faster, so you wouldn’t be riding at the same average speed.

      Regardless, Hunt seems to be honest about sharing their data and as one of their people (Ollie) replied, they’ve had mixed results with tires with more aggressive tread. That sounds reasonable and again, honest. One could reasonably argue with the way the results were extrapolated to a long race and I strongly suspect that the actual difference is smaller and perhaps even insignificant. For the tests to be meaningful, they’d need to be conducted on wheels that are being bounced around on a dirt/gravel road, both vertically and in yaw, which will likely play havoc with aerodynamics.

      Like Martin and Ollie from Hunt who responded to him, I ride gravel for fun, most often on trails and fire roads, so aerodynamics means nothing to me on my gravel bike. Heck, I haven’t even bothered to put aero wheels on my road bikes, because I need light weight for climbing much more than aero for motoring on the flats. That and the fact that I can build light alloy wheels for a quarter of the price of even Hunt’s carbon aero wheels, which are modestly priced by carbon wheel standards.

      If I ever do find myself in the market for aero carbon wheels, Hunt is definitely a brand I’d consider, as their products seem to be a better value than most others in that market. I think they should be commended for that and for at least attempting to quantify whether aero wheels are potentially beneficial for gravel riding, at least under specific conditions.

      Reply
  12. Erik on

    The study is at 32km/h.
    The median customer’s median gravel speed is going to be well under that, and thus the benefits much less.
    Although it is always nice to out coast your buddies down hills.

    Reply
  13. onebiketorulethemall on

    Do you have evidence to back up the claim that side knobbed tires will negate aero benefits? Would a knobbed tire + non-aero rim perform differently from a knobbed tire + aero rim? or are you saying they will perform the same?

    Reply
  14. Will on

    Is there any aerodynamic advantage for 38mm gravel tires when the aero rims are only around 25-28mm at the widest point?

    Reply

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