A 40 mm Tire Gamble: Building the Ultimate Endurance Cannondale Synapse

Every component choice on an ultra-endurance bike is a calculated bet. For Felix Smith of BikeRadar, preparing his Cannondale Synapse 4 for the Transatlantic Way – a brutal trek along Ireland's west coast – the biggest gamble is on the rubber. As he puts it, "The big headline with this build though, are the tires."

The choice isn't a chunky gravel tread, but a set of 40 mm Pirelli P Zero Race TLRs. These aren't multi-surface tyres; Pirelli markets them as a "super fast road race tire."

Seeing them on an endurance build for a race with 12,000 metres of climbing over its first 1,000 km is enough to make a traditionalist's eye twitch. It's a bold move, banking on the comfort and vibration damping of a huge air volume to stave off fatigue on rough Irish backroads.

Gearing for Survival, Not Speed

This build is a lesson in pragmatism, learned the hard way. Smith is returning to an event that defeated him once before, citing an overuse injury for his previous DNF.

"I'm coming back because, spoiler alert, I didn't finish it last time," he says. That experience has clearly shaped every decision, none more so than the gearing.

The stock Cannondale Synapse 4 comes with a capable Shimano 105 Di2 12-speed groupset. Smith, however, has jettisoned the stock crankset for a Shimano GRX unit with smaller chainrings. He doubts any aftermarket chainring smaller than a 34-tooth would fit the original crankset, making the swap a necessity.

This isn't a choice born of ego, but of humility. Faced with day after day of relentless climbing, Smith's strategy is about preservation.

"I'm going to walk up the climbs and, yeah, use that easier gear, kind of spin, put less pressure on the tendons." It’s a refreshingly honest approach to ultra-endurance, where finishing is the only victory that matters.

A Frame with Room, and a Few Quirks

The latest-generation Synapse platform provides a solid foundation. As a previous owner, Smith gives it a glowing verdict: "I think the latest version is a fantastic bike."

Cannondale has packed in features for long days, like integrated down-tube storage for a pump and repair kit. The frame also boasts integrated cabling, which provides a clean aesthetic at the cost of more complex maintenance.

Powering through the Irish nights is a new Exposure Revo 5 Dynamo front light. Smith notes it's an upgrade over a predecessor he used for years and found "absolutely bombproof." The new model's larger internal battery can be charged by the dynamo hub in his Hunt 40 Carbon Gravel wheels or via USB-C, adding crucial versatility.

The luggage setup is minimalist. An Apidura saddle pack integrates a mount for his Exposure Boost rear light, while a 2.5-litre Apidura aero bar bag holds a down jacket.

One quirk of the Synapse frame is a lack of mounts on the underside of the down tube. Smith's solution is simple: a strapped-on Tailfin pack to carry tools, another example of the practical mindset that defines this build.

The Verdict

Is this the "ultimate endurance road bike"? For Felix Smith and the specific challenge of the Transatlantic Way, it just might be. It's not a show bike, but a tool heavily modified based on the painful lessons of a previous DNF.

The massive road tyres are a fascinating experiment in comfort, and the super-low gearing is a smart concession to the brutal reality of the course. Every choice here tells a story of a rider who has traded ego for experience, prioritising the finish line over outright speed. It’s a build that respects the distance.

Felix Smith's Cannondale Synapse 4 Build

• Frame: Cannondale Synapse, carbon
• Wheels: Hunt 40 Carbon Gravel
• Tyres: Pirelli P Zero Race TLR, 40 mm
• Groupset: Shimano 105 Di2 12-speed with Shimano GRX crankset
• Lighting: Exposure Revo 5 Dynamo front light, Exposure Boost rear light
• Bags: Apidura saddle pack, Apidura aero bar bag, Tailfin pack