Bike Check: Jack Thompson’s Project 1903 custom 2-speed Specialized Roubaix

Jack Thompson rose to fame during the 2021 Tour De France when he not only gave the peloton a 10-day head start in the race to Paris, but after covering 3500km/2175 miles, beat them to the Champs-Élysées by three days, which he called ‘The Amazing Chase’. Since then, Jack has racked up several incredible records, including a 1,000,000m elevation odyssey in 2022, along with a whole host of FKTs (Fastest Known Time) across Australia and Japan.

Now, Jack’s back, and it is another bonkers Tour De France theme challenge for 2025. Jack will be taking on the original and notoriously brutal 1903 route. While only 2428 km/1500 miles, which is short compared to modern standards, Jack will attempt to complete it in the original six-day format, meaning an average of 413km/256 miles per day. Keeping it even more true to the day in which riders would stop to change cogs for the climbs, Jack will be trying to complete that mileage on a custom two-speed Specialised Roubaix SL8.

(Image credit: @inglourious_arnav)

His bike is a relatively stock Specialized Roubaix SL8, which is typically equipped with SRAM Red AXS and a host of Specialized’s in-house carbon components. This includes Roval Rapide CLX II team wheels wrapped in 35mm Mondo tyres, which Jack raves about saying, “I love these tyres, they’re bulletproof and fast”. His saddle is a Specialized Romin, with a carbon seatpost and handlebar combo.

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Visually, what sets Jack’s bike apart from the rest is his custom paint scheme. Jack consistently raises large sums of money for charity during his major challenges, particularly those related to mental health. This time around, he’s sporting the colours of OUTRIDE, a US-based charity whose mission is to “empower all people to experience the social, emotional, and cognitive benefits of cycling.” Chapeau Jake and the team at OUTRIDE.

(Image credit: @inglourious_arnav)

The real headline of this custom build, put together solely for this challenge, is the unusual two-speed gearing setup. Jack originally set out to use a single front chainring for security, paired with a two-speed system in the rear, similar to a traditional derailleur. However, Jack struggled to find much information on how to create such a set-up, or find similar methods employed by others. With the help of a friend, an avid single-speeder and Specialized themselves, they have devised and found workarounds for a single rear cog that shifts on a double chainring setup, to give Jack two gears: 48×16 and 35×16.

Instead of getting lost in the black hole of single-speed ratios and undertaking a considerable amount of testing, Jack employed AI alongside his SRAM AXS data to help him work through all the possible gear ratios, then compare that to what we know the incredibly brave gentlemen would have used back in 1903. His original intention had been to use a 17-tooth cog in the rear, but some last-minute issues on Sunday en route to Paris for the grand départ necessitated an emergency disassembly of a Shimano 105 cassette to get him back up and running.

“The 17T rear cog would have given me a good gear for the flats and a manageable gear to climb on. The 16T is going to be difficult when the road gets steep, but…sometimes we don’t live in an ideal world, haha!”

For anyone inspired by Jack, he notes that the spacing of the rear sprocket on the freehub and the distance the Paul’s Components chain tensioner sits away from it are very important, and proper set-up can only be achieved through trial and error.

(Image credit: @inglourious_arnav)

“Sometimes we overthink things with modern bikes. With a gear for the flats and a gear for the climbs, you just adapt.”

Jack Thompson

Jack mentioned that “while at first it was pretty strange only having two gears, I like the simplicity.”

He added, “sometimes we overthink things with modern bikes. With a gear for the flats and a gear for the climbs, you just adapt.”

He even jokes, “Perhaps I’ll use this setup more often?”

While what Jack says may seem a little blasé, despite his evident cycling prowess, even he didn’t take any risks and did a fair amount of strength and stability in the gym ahead of the challenge.

(Image credit: @inglourious_arnav)

It is an undeniably difficult task for anyone tackling 2500km in just six days with, of course, the mountains being the most daunting part for an effectively single-speeder. However, Jack also has a lot of flat and rolling terrain to cover, which is where Jack hopes to employ something that back then, not even the Wright Brothers had figured out, although they had a much better idea by the December of that year, namely, aerodynamics.

Jack has opted to use Roval Rapide CLX II team wheels, which aren’t the lightest option in the Roval range but feature a reasonably deep 50mm rim. Which, I thought, was a curious choice for someone with a lot of climbing and potential crosswinds to deal with.

Jack said in response to this, “While there are lighter options like the Alpinist and Terra CLX, which I regularly run, I think that the aero advantage over the 6 days will be more critical. I am also more confident in the slightly more robust build.”

(Image credit: @inglourious_arnav)

If all this wasn’t enough, Jack is going to tackle this challenge ‘Self-supported’, which means he’s on his own for the duration of the challenge. Previously, when he’s taken on similarly testing challenges, such as the Tour in 2021, he had a team of five to help ensure he was looking after himself, by fuelling correctly, and he had a team on hand to address any mechanical issues that might arise. This time around, Jack has the added logistics of carrying all his own kit, which not only means weight on the bike, but given that the weather forecast for the next six days across France looks relatively warm, he will need to carry a decent amount of water too.

To do this, Jack has equipped his bike with a range of Tailfin bags, including the highly rated Aeropack. Jack is also a Camelback-supported athlete, so he will utilise their 2L bladder vest to store extra water.

Anticipating very long days in the saddle, Jack is relying on his Garmin 1050 Solar and Garmin Vario for navigation and safety. This is in combination with a much more powerful Magicshine front light than usual, as he predicts he will be riding in the dark regularly to make the distances required.

The best place to follow Jack on his latest challenge is via his Instagram page. @jackultracyclist