Bike innovation is a tricky thing. Every time a consensus forms, the vibe changes, new trends emerge and that conventional wisdom is thrown out of the window.
In gravel cycling, the last half-decade has seen that process move in double time.
Fueled by rapidly changing knowledge on the efficiency of higher-volume tyres, cycling-wide revolutions in aerodynamics and reconfigured drivetrain tech, the world of gravel is ripe for creative innovation and unique takes in a bid to find a competitive advantage.
With Unbound offering a mid-year crescendo to the gravel season, we spoke to a few athletes and the people behind a newly released bike to discuss the anatomy of gravel bikes in 2025.
From the ground up: wide tyres rule
As trendy as it may be, the topic of wide tyres on gravel bikes is unavoidable.
Knowledge around the efficiency of wider tyres has demanded consideration of innovation around the tyres themselves, gravel wheels and bike frames that are being rolled out to meet the demands of modern gravel racing.
Look no further than the new release from Ventum of an updated GS1 as an example of the importance of volume even in an unapologetic gravel race bike.
“With the new GS1, we're going up to 700 by 56mm in the front and 700 by 50mm in the rear, or that's a flat 2.0,” Sam Gross, the marketing director for Ventum, told BikeRadar.
”We've always had 420mm rear chainstays, which has made our bike feel really, really lively and quick, and allowed us to give it a little bit of a slacker front end without making it handle like a boat.
“The big challenge with more tyre volume isn’t just with width, it's also the height. We solved the width challenge through drop stays, but the height is difficult because with the height of the tyre in the front you hit more geometry constraints. And that's why a lot of other companies go longer in the chainstays to solve that.”
The main geometry constraint from that taller tyre in the front is how the bike tends to have a 'slacker' front end with a taller stack, higher trail figure and longer head tube.
For racier frames, these geometric constraints can be a concern, but for other brands, building around bigger tyres has meant doubling down on the capabilities of the bikes at the expense of a nimble feel.
For certain racers, that skew towards capability over nimble geometry has been factored into sponsorship decisions.
“Part of our decision to seek out support from 3T was centred around being able to run big enough tyres to be competitive in the big American races,” Andrew L’Esperance told BikeRadar. L’Esperance is a veteran of the Life Time Grand Prix and the UCI Mountain Bike World Cup.
L’Esperance and his teammate Sean Fincham are outfitted with 3T bikes on gravel chiefly because of the bikes' ability to handle big tyres. The pair have a long-time partnership with Maxxis and tyre capacity had an outsized effect on their choice.
“I believe strongly that in some of these bigger races with rough, chunky, sharp gravel, like Unbound and Big Sugar, which happens to be 66% of the gravel racing in the Life Time Grand Prix, it's very important to have big tyres," says L’Esperance. "It's going to have a super-positive impact on your performance.”
It is a bit counterintuitive to think about the tyre/bike relationship in terms of finding the right bike to support your tyre of choice. However, with the innovation stemming from Maxxis, it's a massive component of the bike choice of high-level pros such as Fincham and L’Esperance.
“Maxxis has been fantastic as a company in listening to athlete feedback,” L’Esperance says.
"A rider like Keegan [Swenson], who's very detail-oriented, does his own testing, he does his homework, and he relays that information to Maxxis. Sean, myself, and all the other riders on Maxxis are allowed to get feedback. In turn, we also have very specific tyre options that are not available to the public.”
Sneaking aerodynamics where it fits
In road racing, aerodynamics has taken over as the driving force in technology. In gravel racing, most would agree it is secondary. For most, capability is still the number one priority, as evidenced by the importance of tyres.
Nevertheless, ignore aerodynamics at your own peril.
Aerodynamics in gravel has become a tool that works in the margins and can be optimised in the spaces where compliance, durability or comfort are less important.
Within the pro peloton, no one quite attacks these margins like Chase Wark. Wark is a professional on the gravel scene notorious for his unique approach to bike setup. From running a road bike with 32mm tyres during his first venture into gravel at the 2019 Gravel Worlds in Nebraska to his uniquely aero-optimised setup this year at Unbound, Wark has built his career on doing his own thing.
“The first year I did the race was 2022,” Wark says of his evolution as a self-described aero-dork. “I had a CamelBak, aero socks which weren't as popular back then, but I still had them with arrow gloves, a skinsuit, and I think shoe covers that first year.
"I also had aero bars because they were banned the next year and the move to big tyres still didn't happen, but I ran 44mm René Herse tyres, which were big for the time.
“That was the most simple my bike has ever looked.”
With every year that Wark has lined up at the biggest races, more conversation has followed as he continues to push the norm of what is expected of gravel bikes. What started as a regular bike in 2022 morphed into something much more extreme by 2024 when Wark set off as a privateer.
A quasi-disc gravel wheel was just one example of a slew of triathlon-inspired gear that Wark took to the dirt in his quest to find gains others were avoiding, intentionally or otherwise.
“I want to win Unbound, and I know I don't have the power to just stay in the group with a regular skinsuit and standard aero socks, like I was wearing like three years ago. Now, everyone's wearing those, and I can't just do those things and think it's enough. I need to push that technology as much as possible.”
While he has dialled down some of the more extreme water-carrying aerodynamic modes from last year, Wark is back with big tyres on a gravel disc wheel, aerodynamic skinsuits and triathlon calf sleeves. Most controversial is an aero handlebar with the drops chopped off to save weight and lower the frontal area.
Why did he chop off the drops? Wark doesn’t use them. He checked.
At each race leading into Unbound this year, Wark made a mental note of when he would want to go into the drops, if ever. It turns out the answer was never. So off they went.
“If TT base bars had good braking power, I would probably run one of those, but the brakes on those just suck,” Wark says about the choice.
That mentality is at the extreme of gravel racing. Few go as deep into the weeds as Wark. He is quick to point out that most of this is trial and error. However, at the heart of it, Wark is doing it because he knows there is more out there, and he knows few have the same motivation as he does to bring that kind of 'dorky' triathlon concept to pro gravel racing.
“I wish I could be like Dan Bigham, and I can just see aerodynamics. I don't have a degree in this or anything, so I am not really coming up with anything new. It's very much about trying not to fall three to four years behind.”
Even if Wark is the exception, not the rule, he is not alone. Ventum has also had a long history of triathlon experience and has thrown in some of its expertise in aerodynamics to boost the bike around the margins.
“We spent, over the past two years quite a bit of time, actually developing the TT bike, the Tempus, and through that came a lot of lessons learned around aerodynamics in the head tube area,” Gross says. “So this new version of the GS1 takes some lessons from the development of the Tempus.
"We had a really distinct hourglass shape that we put on that bike. This bike also has that hourglass shape. So it's using functional airfoils that blend backwards into the frame, and just helps with aerodynamics.”
Regardless of tyres, wheels, or any other design – an aero head tube is always slightly better than a standard one. For Ventum, it's a margin with no real downside.
Room for debate: one ring or two?
Put all these general agreements aside and what remains is a healthy debate around gravel drivetrains and the split between 1x and 2x options. The main touchpoint of this debate revolves around the SRAM versus Shimano split in technology and theory.
For the last decade, SRAM has been building its drivetrain technology around 1x options.
Historically speaking, SRAM's weak point in the market was front shifting, so it was natural to move in this direction, especially as the capacity of gear ranges and the number of rear cogs expanded.
SRAM’s eTap shifting system has only compounded this movement towards 1x drivetrains, as the simplicity of a single ring and a large-range cassette has matched the simplicity of a wireless shifting system.
Shimano, on the other hand, has been hesitant to ditch its front derailleur. This hesitancy was plain to see during the rollout of GRX Di2 in 2024 without a 1x option.
The company has said it is just matching demand with this choice to retain a front derailleur, but based on the popularity of SRAM and its 1x system, it seems as if it might be more to do with the company and many of its athletes trusting the 2x system and the upside of racing with more gears.
“For Unbound, I am running a 2x setup,” L’Esperance says. “If you're not relying on just a single position for the front chain, 2x can potentially help drivetrain efficiency.
"If I was running a 1x, it would probably be a 48 and then I'd be crosschaining a lot on the steeper stuff, but I can just drop it into the small ring and have a much more efficient chain in those situations.”
Ultimately, at this point in gravel’s evolution, the tide seems to be pointing towards 1x, yet in this regard, tides are susceptible to changes. 1x or 2x itself is becoming a reductive description for shifting systems as products such as Classified’s internally geared hub offer a version of both in one system.
Regardless of perspective, what does seem clear is we are not yet at a paradigm for the right or best approach.