Chris Mehlman’s custom bike for Unbound XL might look like a mountain bike at first glance – because it is, sort of.
It’s a custom drop-bar Pivot Les SL hardtail, decked out with slick 2.1in tyres, a 100mm suspension fork, clip-on aero bars, and a full ultra-racing luggage setup; a mash-up of some of the most forward-thinking gravel tech trends.
Mehlman, based in Colorado Springs, is back to take on Unbound Gravel XL again. Unlike shorter gravel races, the XL is unsupported, requiring riders to carry everything they need across tough terrain and through the night – making water capacity and lighting critical to survival.
Last year’s winner, Sebastian Breuer, finished in just over 20 hours at an average speed of around 17.5mph. Starting at 15:00 means riding overnight, so powerful bike lights are a must.
“It’s 350 miles, a lot can happen, so just trying to optimise for the pretty unique conditions is really important,” says Mehlman, whose bike setup reflects years of experimenting to find the perfect balance of speed, comfort, and reliability.
More Unbound Gravel tech and news
- Everything you need to know about Unbound Gravel – the world’s most important gravel race
- Why XC mountain bike tyres are gravel racing's hottest pro trend
- Who will win Unbound Gravel 2025? Our race predictions and course preview
- “I hope I can finish it”: Thomas De Gendt steps into the unknown at Unbound Gravel
Why ultra-distance gravel?
Mehlman says he realised as a junior XC MTB racer that he was much better at the longer events and enjoyed the adventure element. That led him to MTB marathon events, then in 2022 into gravel racing: “It was definitely a different sport, even back in 2022,” Mehlman says.
“That was my first time doing Unbound XL.”
Mehlman finished fourth that year and fifth in 2023. He skipped Unbound in 2024, but at the Traka, he placed fourth in the new 560km distance.
He’s aiming to win Unbound XL this year, although it’s a distance that’s gaining in popularity. Mehlman is up against a field of 208 starters (up from 71 in 2023) that this year includes 2024 Unbound 200 winner and long distance challenge junkie, Lachlan Morton.
So what attracts Mehlman to ultra-distance events?
“I really like how welcoming ultra-distance is. Elite-level gravel is getting more and more roadie. It’s getting really intense. The Ultra-side is a good community, and I really enjoy being in it.”
Finding the perfect balance: speed, comfort, and reliability
Mehlman’s bike choice for Unbound has evolved over the years he’s competed in gravel races.
“When I first started gravel [in 2022], I was on 40c tyres,” says Mehlman.
“I thought: these are pretty wide. Coming from the mountain bike side, I had no conception of what tyre pressure to run, and I ran high 30s, low 40s [psi]. I didn’t have inserts.
- Read more: Gravel bike tyre pressure explained
Back in 2023, Mehlman says he was limited to 45 or 47c tyres – the widest his frame could accommodate at the time.
Since then, he’s noticed a growing shift towards wider rubber, particularly in the ultra-distance scene. “It’s not just that wider is faster,” he says. “It’s more durable – it’s more comfortable – which is really key.”
"Gravel is changing so fast that brands can’t keep up. 40c tyres used to be big – and 45c tyres were really big – but now every pro is maxing out their gravel bike.”
At Unbound XL in 2023, Mehlman was riding the previous generation Pivot Vault, which had 47c tyre clearance and a more aggressive cyclocross geometry.
The current generation Vault, released in Autumn 2024, follows the recent trends, with longer reach, higher stack and a slacker head angle. The bike also features a suspension-corrected fork and nominal clearance for 50c tyres, although Mehlman says he’s gone wider than that, fitting MTB tyres up to 2.25in.
“It’s been a slow progression of bike set-ups,” Mehlman continues.
“Some aspects have stayed the same, like [using] aerobars, but tyre clearance, geometry and suspension have definitely changed. Even back in 2023, I was like: why would you want suspension on a gravel bike?”
A mountain bike... but not quite
Things have changed massively since then.
That trend towards wider tyres and suspension has led Mehlman to choose a Pivot LES SL hardtail MTB with drop bars for the 2025 Unbound 350. Why an MTB?
“Logan Kasper won in 2023, running a hardtail dropbar MTB with a 100mm travel suspension fork and MTB tyres,” says Mehlman.
Kasper’s decision paid off. In 2023, the conditions were super-muddy, with Unbound's notorious ‘peanut butter mud’. Riders on gravel bikes just didn’t have the clearance and experienced serious clogging, while his hardtail handled the mud much better.
Mehlman says Unbound isn’t technical singletrack – but it is rough terrain.
At night, when fatigue sets in and visibility is limited, line choice becomes almost impossible: “You’re tired, following other riders in a paceline – there are shadows everywhere – and you end up hitting stuff you normally wouldn’t,” he explains.
Back in 2023, limited tyre clearance meant a lot of hiking. “I was running as big a tyre as I could fit,” Mehlman says. “That’s why I moved to a hardtail – I wanted more volume and to still have clearance to spare.”
There’s a big difference, he adds, between tyre clearance and tyre clearance to spare: “Just because you can fit a big tyre doesn’t mean it’ll work when you start picking up mud – not if there’s only 1mm to play with.”
Why a 100mm suspension fork makes all the difference
Mehlman has seen how much of a difference the right suspension setup can make. At the Traka 560, he rode a RockShox Rudy XPLR with 40mm of travel – and says it was a gamechanger.
“For the first time, my hands weren’t numb after one of these races,” he explains. “I was able to descend much faster with more confidence, because it makes things a lot smoother.”
Mehlman runs a 2019 Fox Float Factory SC 32 fork on his Pivot LES SL. It’s a little heavier, but still a solid choice.
“100mm may seem like a crazy choice, but with how rough Unbound is, a sprint finish is unlikely – so maybe it’s not slower overall,” he says.
Switching from a rigid gravel bike to the Rudy fork felt almost strange at first. “It almost feels like the headset’s loose because there’s so little travel,” he laughs. “It’s not suspension you’d notice a ton – it just smooths things out in a way that makes things more comfortable over time.”
With the longer 100mm fork, however, the difference is clear – especially when riding out of the saddle.
“One challenge is I don’t need all 100mm, but I also don’t want to run super-low suspension pressure – that would make it too soft when out of the saddle,” Mehlman says.
“So I’m thinking of adding volume spacers to run a slightly lower pressure, keeping it supple up top but with a really high progression rate. That way it rides more like the Rudy.”
He adds a practical note: “Although you could run the Les SE with a gravel fork, it would completely screw up the geometry.”
"It's the closest thing to lying down in your bed you can get."
Mehlman has decreased his frame size. That’s because when you put drop bars on, the reach is increased, so you have to run a shorter stem. He started off with an XL size frame with a 35mm stem, which is as short as you can realistically go.
He paired that with 40cm wide USE Escape GR 24 carbon bars.
“I found the flare was a little wide, so now I’m running the GR 12 that has a 12 degree flare. It’s enough flare so you get nice control and you can run your hoods tilted in a little bit.
“I’ve gone down from the 46cm, which is a stock width for my height [6’2” / 188cm]. It felt fine, because I came from mountain bikes, but as I’ve understood aero more I’ve slowly narrowed.”
He’s also running USE’s clip-on aero bars with 10mm of spacers. That’s for comfort as well as aerodynamics.
“In races this long, your hands get very tired, so in the middle of the night having that extra position is the closest thing to lying down in your bed you can get.”
Mehlman has chosen RCT Wrap bar tape.
“It’s really thick, that helps to add comfort. It feels like I have more control when I’m running thick bar tape,” he says.
He’s running a mixed SRAM groupset with Force shifters, although he’d prefer the new Red shifters for their one-finger braking. He’s not SRAM-sponsored though and at $675 a pair, the Red shifters are an expensive choice.
He doesn’t tilt the levers in as much as some riders, as he wants to ensure that he can brake properly.
With overnight riding at Unbound XL, Mehlman runs his Exposure Six Pack light on an extender mount, as it’s difficult to mount a light on such a short stem. He also has an Exposure Diablo helmet light and Boost-R Reakt+ Peloton taillight.
Slick, fast, and ready for mud
Mehlman runs XCR wheels from Maple, a small New England brand. These MTB wheels feature Boost spacing and a 29mm internal width, paired with Vittoria Terreno Zero 2in tyres. On the wide rims, the tyres measure around 2.15in.
He highlights durability as a key reason for this choice – the Terreno Zero has one of the thickest casings and robust sidewalls, complemented by Vittoria Air-Liner Gravel Light inserts for extra protection.
Mehlman points out that the slick tread design also helps with grip on rough terrain. “If the rocks are large enough, the tread doesn’t dig into them. The most important thing for grip is contact patch,” he says. The 2.1in width lets him run lower tyre pressures despite the heavy load on his bike.
Mud clearance is another factor – slick tyres have the least surface area for mud to cling to, helping maintain performance in sloppy conditions.
Mehlman has also refined his sealant setup, using a custom latex blend from Parkside in California. It costs around $20–$30 and has more latex than his usual Orange Seal. Though it won’t last long, it stays liquid throughout the 24-hour race, making it a cost-effective way to boost tyre performance.
Crankset conundrums
Mehlman trained on the Les SL with flat bars, progressively increasing his chainring size. “I started out with a 38, then I got a 40 and found I could just fit a 42,” he says.
Paired with a 10-tooth cog at the back, that setup lets him hit 35 mph at a cadence of 110 RPM – his fastest speed in previous Unbound XL races.
His SRAM XX SL crankset, with 170mm cranks, typically fits a 38t chainring – “pretty standard for a hardtail mountain bike.” But for gravel racing, he wanted something bigger. He originally planned to run a Force spider with a Force gravel chainring, but those chainrings have a 6mm offset, so it wouldn't fit his frame.
Instead, Mehlman chose the XX SL crank for its 55mm chainline and 168mm Q-factor, allowing a zero-offset chainring: “If you run a zero offset chainring, you can run something a little bigger.”
He’s now running a Quarq power spider with a Garbaruk 42t 104 BCD chainring – one of the few companies offering such large 104mm BCD chainrings, with options up to 48 or 50 teeth.
To improve clearance, Mehlman added 2.5mm of spacers on the drive side of his crankset to shift the chainline rightwards. It still “just barely clears the chainstay,” he says.
"It feels really weird"
Mehlman says the bike’s handling initially takes some getting used to: “When I first get out of the saddle on this bike, it feels really weird. It feels really floppy, but only for the first five seconds, then it feels natural. You have to get used to that.”
That sensation comes from the bike’s longer wheelbase and slack head angle – features that make it less nimble on tight singletrack but much more stable on fast, straight sections.
“It’s probably not the best bike for really tight singletrack. Because the wheelbase is much longer, it’s not as snappy, but for Unbound, where there are dead straight roads for ten miles, you need something that can eat up chunks in straight lines, and this is perfect for that.”
Mehlman also points to his long seatpost – a monstrous 450mm alloy Woodman GT 2 – which accommodates the smaller frame and his long legs.
He prefers alloy here for its durability over carbon at that length: “The bike is stiff, the frame is stiff, but when you’re sitting in the saddle for 24 hours on rough terrain, having that extra comfort is really important.”
He notes the importance of inserting the seatpost far enough to avoid overstressing the frame, with the post extending below the seat tube–top tube junction.
Carry everything, and then some more
As Unbound XL is unsupported, there’s a lot to carry too: "Unlike the Traka, water is the most important thing at Unbound.”
With plentiful gas stations, it’s pretty easy to get food, Mehlman says, but it tends to be pretty hot. He wants to be able to carry at least 5 litres of water, possibly six.
“It’s a relatively flat race, the hills are short and one of my strategies is to avoid stopping early on, because the early gas station stops are absolute chaos and it’s super-stressful. If you can just keep going a bit longer, that’s a big advantage.”
Mehlman starts off with a 3-litre Tailfin top tube bag, which he rates: “You can tell that they’re designed by people who actually use the bags. They’re stiff, they don’t flip around, they’re easy to open. Every little detail is thought through."
He hasn’t decided whether to run the 2.9 litre wedge frame bag with a hydration bladder and a 600ml bottle on the down tube and a 900ml bottle on the seat tube as well. The alternative is a prototype smaller bag that would let him fit a 900ml down tube bottle.
He’s also running a USWE hydration pack, most likely the Rush 8 litre, with a 3 litre bladder.
“That’s a lot on your back, but I’ve found it pretty comfy. It’s also got the pockets up front to store spares. You can’t stop and just dig through your bags, so for me it’s really important to keep it consistent."
Is this the future of gravel bike tech?
Mehlman sees diversification continuing. Just as for mountain bikes, he sees brands expanding their offerings to suit different consumers. While MTB races tend to be on fairly similar bikes, gravel is much more diverse, and anything goes. It’s just what works for the rider, he says – there’s no right way to do it.
“Gravel is going to trend towards what the pros are doing, but smart brands are going to produce what’s best for the consumer.”
He cites the endurance/all-road category, where brands aren’t just making aero bikes for people who don’t need aero bikes, they’re making bikes that are the right bikes for the rest of us.
“For some people an aero gravel bike might be the right thing, but for a lot of people that’s just not the right choice. The pros are doing something for a certain reason and that may not be the best for the individual.
“I’d love to see brands offer hardtails with slightly different geometry, with shorter reach meant for drop bars, or at least offer their hardtails in a drop bar build. It’s shockingly easy with SRAM to build a mullet/hybrid bike like this.”
"There’s no better feeling"
Mehlman points to the mental challenge as the biggest hurdle. “You’re going to feel miserable at some point. Your body says stop, but you have to push through mentally.”
He also highlights the course’s toughness. “It beats up bikes, it beats up bodies. If there’s mud, you’re hiking.”
The flat, open terrain of Kansas presents a unique mental test. “After 350 miles, it can all feel the same – like you’re going in circles.”
That mental grind is what sets US ultra gravel apart, he says. “The best riders aren’t always the strongest – it’s who’s mentally tough, who can push through setbacks.”
He admires riders like Lachlan Morton for that resilience. “They’re built to deal with that mental challenge.”
But the payoff is huge. “There’s no better feeling than finishing one of these long races.”
Chris Mehlman’s Unbound XL Pivot LES SL bike spec
- Frame: Pivot LES SL, size large
- Fork: Fox Factory SC 32, 100mm
- Shifters: SRAM Force
- Brakes: SRAM Level, 160mm rotors, organic pads
- Crankset: SRAM XX SL cranks (170mm), Quarq 4-bolt power meter spider, 42t Garbaruk ring
- Derailleur: SRAM GX AXS
- Cassette: SRAM GX 10-50t
- Chain: SRAM XO1
- Lube: FAAST drip wax
- Pedals: Shimano PD-M520
- Stem: 35mm or 60mm (still testing)
- Bars: USE Escape GR12 carbon, 40cm width
- Bar tape: ESI RCT wrap
- Wheels: Maple XCR with DT 240 hubs, 29mm internal width
- Tires: Vittoria Terreno Zero 2.0in with Air Liner Light Gravel inserts
- Sealant: Parkside custom blend
- Seatpost: Woodman GT 2 450mm alloy
- Bags: Tailfin 2.7L wedge frame bag, 3.0L top tube bag
- Aero bars: USE TR2 with 40-degree bend extensions
- Lights: Exposure SixPack (bars), Diablo (helmet), Boost-R Reakt + Peloton
- Computer: Hammerhead Karoo
- Pack: USWE Rush Pack (3L bladder) or Outlander Pro (2L), depending on conditions
