Cannondale Synapse vs Boardman SLR: the winner stole my head and heart – it has everything I want from an endurance bike 

Endurance bikes have switched up a gear for 2025.

The trend towards all-road bikes we’ve seen over the last few years seems to be over, thanks to the emergence of fast, lightweight, all-road capable gravel bikes such as Specialized’s Crux, Cervélo’s Áspero 5 and many others.

The good news for endurance bike fans like me is that these road bikes, built for non-racers, have become slicker, more road-focused and purer in design – arguably kicked off by the latest Giant Defy, which won our overall road Bike of the Year title in 2024.

This year, I’ve been impressed by new endurance bikes from Cervélo (Caledonia 5), Ribble (Allroad SL R), 3T’s Strada Italia, Cannondale’s Lab71-issue Synapse and the Parlee Ouray.

We’ve seen the endurance category bring some seriously good value too, with Cube’s Attain C:62, Ribble’s Allroad SL and Argon 18’s Equation.

We’ve even seen more traditional materials make a proper comeback here. Surly’s stylish Midnight Special and Ribble’s 3D-printed Ti incarnation of the Allroad both piqued my interest.

Our two endurance bike finalists for Bike of the Year 2025, however, are Boardman’s newly updated and improved SLR in a value-packed special edition and Cannondale’s Synapse Carbon 2 SmartSense, which brings race-bike handling and endurance comfort along with a tech spec few (if any) endurance bikes can match.

Introducing the Boardman SLR 9.4 LTD

The original Boardman SLR was very much a race bike, but as the model has matured, it has moved further into the endurance sphere. A more accommodating ride position and geometry, plus lots of practical touches, have made it a more rounded machine.

At the same time, Boardman has integrated more aerodynamics and kept the weight low, with claimed weights for the frame and fork of 995g and 450g, respectively. The aero improvements are claimed to be worth a 24-second saving over 20 miles at 31 miles per hour (that’s 32km at 50kph, for fans of the metric system). 

This is impressive for a bike that can accommodate 36mm-wide tyres, or 32mm rubber with mudguards installed.

Introducing the Cannondale Synapse Carbon 2 SmartSense

It’s a similar story with the Synapse, which was originally conceived as Cannondale’s specialist bike for the cobbled spring classics. It was a bike designed to bring comfort in a raceable package.

The latest Synapse has already seen success, but not in the traditional racing sense. It’s the bike Lachlan Morton used for his record-breaking lap of Australia, covering the 14,200km in 30 days, nine hours and 59 minutes, and averaging more than 450km per day.

The Synapse comes equipped with integrated lights and a rear radar light, along with practical details such as class-leading tyre clearance of 42mm, mudguard/fender eyelets and a down tube storage compartment that also houses a central battery. This powers both the lights and the SRAM AXS drivetrain. 

The Synapse combines these practical elements with a new frame design that brings much of the aero thinking from the SuperSix Evo race bike, and the compliance from its racing gravel bike, the SuperX.

While Cannondale should be applauded for equipping the Synapse with its down tube storage, I’d also add a round of applause for Boardman’s simple solution to adding more storage. Rather than a complex storage compartment on the SLR, it supplied a third set of bottle bosses on the underside of the down tube. 

For testing, I added another bottle cage here and rode with a tool can. It’s a much better option than a saddle pack in my eyes, and it doesn’t take up valuable water-carrying capacity.

Builds to beat the competition

The Boardman’s build packs value that we haven’t seen from a mainstream bike since before the double whammy of Covid and Brexit (not to mention US tariff uncertainties).

The £3,100 price tag gets you SRAM’s latest Rival AXS groupset, a value-packed drivetrain in itself, along with Boardman’s own 50mm tubeless-ready carbon wheels shod with Goodyear Eagle tubeless-ready tyres.

The icing on the cake is Vision’s Metron 5D carbon cockpit, which can be seen on pro bikes raced at the highest level, and which has an aftermarket price tag of over £600 / $650 / €660 on its own. Throw in a quality saddle, and Boardman hasn’t cut corners to get the SLR 9.4 LTD to this price; it’s by far and away 2025’s best-value road bike.

Boardman has gone non-standard with the drivetrain, bringing a tighter cassette from SRAM’s Force group into the Rival AXS mix. That gives a gearing pairing of 48/35-tooth chainrings with a 10-33-tooth cassette.

Read more: Best endurance road bikes in 2025: our pick of the best bikes for speed and comfort

That’s a similar set of ratios to a more race-ready setup, such as a Shimano 52/36 and 11-28t cassette, but importantly, taller gearing than you’ll find on the Synapse. That’s great if you want to keep pace on rolling terrain with a fast club ride, but not quite so accommodating if your goal is heading for the lengthy climbs of the European peaks.

The Synapse Carbon 2 SmartSense also has a superb specification, albeit not offering the same value for money as Boardman.

However, it’s no slouch value-wise when compared to similarly priced rivals – Cervélo’s equivalent Caledonia 5 (with Ultegra Di2) is £150 more at £7,400. Specialized’s Roubaix SL8 Pro with Ultegra Di2 is still more at £8,000. Trek’s Domane SLR 7 with Force AXS is £7,450, although that gets you the power meter upgrade.

The Boardman SLR 9.4 LTD doesn’t have any rivals for value.

Trek offers the Gen 4 SL7 Domane at £3,900 with Shimano 105 Di2. The Specialized Roubaix, at £3,250, gets a 1x SRAM Apex AXS groupset and alloy wheels. Cannondale’s Synapse Carbon 5, at £2,995, has alloy wheels and mechanical Shimano 105. Canyon comes close with the Endurace CF 7 with Shimano 105 Di2 and DT Swiss carbon wheels for £150 more.

Even master of value Ribble can only offer the Allroad SL with Shimano 105 Di2 and alloy wheels for similar money. 

The Boardman is built around SRAM’s Force AXS groupset, which offers shifting and braking performance that is Red’s equal, but weighs only 141g more. For significantly less money, I’ll leave Red to the pro tour and stick with Force every time.

The Synapse rolls on a combination of solid-performing Vittoria Rubino TLR tyres wrapped around Reserve’s 42/49 Turbulent Aero carbon wheels.

A great saddle from Fizik sits on top of a carbon seatpost and, up front, the stem integrates seamlessly with the frame, holding a well-shaped, comfortable alloy bar. The Synapse is built from good, solid stuff.

What sets the Synapse apart, however, is SmartSense, which I think is worth every penny.

The system combines with Cannondale’s app to enable you to register your bike (for both warranty and security), alter setup preferences on the lights, radar and wheel-mounted speed sensor, and monitor the system.

It’ll show you battery levels on both bike and speed sensor, let you know what settings you’re running on the lights and radar, and identify any connectivity issues. I’m fully onboard with the idea of using the SmartSense lights for daytime-running duties. 

We all have daytime-running lights on our cars, so why not do the same when it comes to bikes? We are inarguably more vulnerable road users. The same goes for the rear radar. I’m a full convert to using a radar on the road – having an indication of vehicles approaching on my GPS screen is a real safety boon. 

The SmartSense rear radar gives you a real-time graphic of vehicles approaching from the rear, with colour coding to represent the speed of their approach. It makes riding on the road safer, adds confidence, and I’m not sure I’d want to be without one for road riding on busier routes.

The beauty of SmartSense, when it’s integrated this well, is there are no cumbersome brackets to fit, or misplace when it comes to fitting lights for winter. There is only a single battery to charge, either on the bike or off. 

Combine the SmartSense data with SRAM’s data-rich AXS ecosystem and the Synapse Carbon is a bike born of the 21^st century.

Winning rides

Both bikes have geometries that take huge influence from racing, with Boardman going further into race-ride position with a longer reach and lower stack than its predecessor.

The 577mm stack and 394mm reach are lower than the Synapse’s 610mm, but only a single millimetre longer than the Synapse’s 393mm, comparing my large SLR test bike with the 58cm Synapse on test.

The Boardman’s 72.5-degree head angle is steeper than the Synapse’s 71.3 degrees, although the trail on the Synapse comes in a millimetre shorter than the Boardman at 61mm.

Both bikes deliver impressive comfort levels, and both get a lot of that from the shift towards larger-volume tyres – 30mm on the Boardman and 32mm on the Cannondale. 

It’s worth noting, though, that the Synapse’s tyre width comes out broader than the 32mm printed on the tyre, at 35mm, thanks to the progressive internal width of the Reserve rims.

When it comes to on-road smoothness, the Synapse has the edge, but that’s not down solely to the tyres. I tried switching the wheelsets over on the bikes (because they’re both SRAM-equipped) and, even with the skinnier rubber, the Synapse had a more refined ride quality, both through the bar and the saddle. 

That does the Reserve wheels something of a disservice, because they are undoubtedly the superior offering. The differential depths (and widths) aid crosswind stability while keeping the weight down, with Cannondale using a front wheel that’s 42mm deep compared to the Boardman’s 50mm. It means a noticeable difference when it comes to how light and controlled the steering feels on the Synapse, especially in more adverse conditions.

It’s not that the Boardman is harsh – it certainly isn’t – it’s just that bit firmer, which becomes noticeable on poorer road surfaces.

The Boardman’s handling is very nimble; it’s a fun bike to put the hammer down on, such is the feeling of stiff efficiency through the pedals, and it’s a great companion when it comes to downhill cornering. The tyres deliver bags of grip when you need it. The stiffness through the drivetrain is also a boon on climbs, although I could induce a bit of front brake tick as the fork flexed.

The cockpit on the Boardman is superb. The Vision Metron 5D has a great shape that feels ideal down in the drops, with a top section that’s aerodynamically designed and, as a bonus, tactile to hold.

The Synapse has a more modest bar, although also from the Vision stable, so it shares the same excellent mid-drop shape and subtle flare. It has a similar tactile, comfortable top section, although without the panache of the slick carbon one-piece unit on the SLR.

The Synapse has handling that’s quick, yet stable. It inspires confidence when the going is less than optimal – on broken tarmac and undulating surfaces, the bike is very surefooted. This is matched by comfort levels that set the standard for the modern endurance bike. 

Here, when riding on the limit, the Synapse edges the Boardman, with the more refined road manners making for a more confident bike.

The Synapse has quickly become one of my favourite bikes to head to the hills on, too. For out-of-the-saddle attacks on steep ramps, it feels race-bike responsive. Yet when you sit in and concentrate on cadence, its smoothness translates into an overwhelming sense of efficiency; it feels as though all my efforts are driving through the rear wheel, with nothing going to waste. 

The Boardman’s efficient power delivery makes it a solid climbing tool, too. However, with the racier gearing, only stronger climbers will get the full benefit. The rest of us will likely want the extra lower range the Synapse can offer.

Cannondale Synapse Carbon 2 SmartSense vs Boardman SLR 9.4 LTD bottom line

If our endurance Bike of the Year title was down solely to value for money, Boardman’s SLR 9.4 LTD would romp home. The £3,100 price tag, with this specification and this ride quality, is unbelievably good in such price-sensitive times.

Before the disruption we’ve seen over the last decade, with a global pandemic and Brexit on UK shores, the 9.4 LTD would have been exceptional value.

Boardman deserves huge praise for the package it has managed to put together here. If you’re tempted by the value and performance, I wouldn’t hang around because I can’t see this special-edition ‘LTD’ spec being in stock for long.

The Synapse, however, won both my head and my heart. It brings everything I want in a complete endurance bike to the fore.

It handles with the swiftness of a race bike, but layers on stability thanks to the smoothness of the frame and fork. It cossets the rider brilliantly, while not giving any sense of being isolated. It’s involving, while being comfortable. It’s exciting to ride fast, while being surefooted when the surface is less than optimal.

The ride quality sets the Synapse apart from its rivals. The addition of the clever SmartSense tech, with its powerful integrated front light, radar-equipped rear and practical central battery, makes the Synapse a taste of the future of bike technology.

Most importantly, it’s a forward-thinking piece of design that’s all about the rider experience.

It confidently combines aerodynamics, ride quality, comfort, practicality and safety-enhancing tech. That it does all of this with a dynamic, exciting ride proves that you can have it all, with a panache that’s unbeaten in 2025, earning the new Cannondale Synapse our endurance bike title, as well as being crowned our overall Road Bike of the Year.