Argon 18 Equation 105 review: a very capable endurance bike with great upgrade potential

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Canada’s Argon 18 has a reputation for an innovative approach to bike design.

The Equation is its most affordable carbon offering (£2,500 / $2,700 / €2,800), all new for 2025 and based on the all-road Krypton – a staple of Argon’s line-up since 2016.

Combining a lightweight frame and fork, generous tyre clearances and a range of affordable models, the Equation looks to be another great option for those seeking a very capable endurance bike.

Argon 18 Equation 105 frameset

The Equation’s front end uses Argon 18’s long-standing ‘3D fit’ system. When being fitted for an Argon 18 bike, the bar height is adjusted by moving the top headset bearing upwards thanks to a range of head tube extending pieces.

That’s unlike a standard road bike, where you add spacers above the headset to raise the stem and, therefore, bar height.

Argon 18 claims this system maintains the stiffness of the head tube at its optimal level. It also gives the bike's front end a much more integrated look.

In theory, no matter what height you need to run your bar at, the Equation will look as good as it does in the catalogue.

The Equation is created with Argon 18’s Topological Compliance System.

This design method combines tube shaping with the physical properties of the carbon fibre to maximse stiffness where needed and introduce more compliance where vibration damping is required.

Explained simply, when drawing an imaginary straight line from the top of the head tube down to the rear axle, everything below that line is maximised for stiffness.

Argon 18 claims this means accurate steering and optimal power transfer. Above the line – the top tube, seat tube and seatstays – everything is designed for compliance.

The brand claims the result is a more comfortable bike that maintains the handling and power transfer of a race bike.

Argon 18 Equation 105 geometry

The Equation’s geometry is optimised for a stable and comfortable ride, all the while staying within Argon 18’s pure racing roots.

It means the Equation gets a taller head tube for a more upright ride position, putting less stress on your shoulders and back for long-distance riding.

On the standard setup, that’s a 166mm head tube on this size-large test bike. Add the 25mm 3D spacer and it rises to 191mm.

The 3D fit adjustment also has a bearing on the stack and reach. In standard trim, it's a 600mm stack on a large-sized bike, rising to 623mm using the 25mm spacer.

The reach as standard is 390mm; with the 25mm 3D adjustment, it grows slightly to 397mm. That’s because the bar height/position is moving in the same plane as the head angle and not just vertically straight as you add head-tube height.

With a 73.1-degree seat angle, a 72-degree head angle and a 62mm fork trail, the Equation is more relaxed than the Surly Midnight Special and Ribble Allroad SL Pro I tested it alongside. However, out on the road, that was less apparent.

The tyre clearance is officially capped at 700x32c tyres (or, slightly confusingly, 34mm measured width).

The wheelbase is extended over race geometry to 103cm to add stability; the bottom bracket height is also lowered, with a BB drop of 75mm on the large bike to improve stability at speed.

Argon 18 Equation 105 specification

At the heart of the bike is Shimano’s latest 12-speed mechanical 105 R7100 groupset, pairing a 50/34T chainset and 11-34t cassette.

Argon 18 has gone with Shimano RT86 rotors with a six-bolt fitting to match the Vision wheelset hubs.

The rotors come from Shimano’s mountain bike line, and I found them less prone to noise in the rain than those on either the Surly or Ribble.

The wheelset is Vision’s alloy Team 30 TC. The 30mm-deep extruded alloy rim is clincher and tubeless-compatible.

With a 19mm internal width, they’re well suited to road tyres, albeit a little narrow compared to the best alloy wheels.

The 30-point engagement freehub gives a 12-degree engagement and they have a claimed weight of 1,920g per pair.

The wheels are shod with Vittoria’s Zaffiro Pro clincher tyres in a 30c width. This is a hardy training/all-purpose tyre for those on a budget, retailing for £23.99, but can be found much cheaper.

Rounding out the Equation’s build is a trio of FSA alloy parts: a Gossamer 27.2mm seatpost, Omega stem and the Vero Compact bar. Contact points are taken care of with Prologo Plaintouch bar tape and a Prologo Akero saddle.

Argon 18 Equation 105 ride impressions

The Equation rides like a bike far greater than its modest price tag.

On the road, it's a smooth operator – the handling is stable without being boring and the slender frame does a great job of keeping road chatter quiet.

It’s the lightest bike of its test cohort, without having any particularly lightweight components.

That makes the Equation a sound basis for upgrades further down the line, if desired.

What you wouldn’t ever need to change is the drivetrain, though. The Shimano 105 R7100 groupset is excellent.

After my first long ride out on the Equation, I needed to tweak the gears and re-tension the cables once everything had settled in – but that’s par for the mechanical course; if you maintain it well, it’ll last years and give slick, smooth shifting and braking.

The gear range offers a wide range for climbing, and a 50-11 combination is more than enough for faster road duties for the majority of riders.

The Equation’s a great companion on big rides; the assured, confident handling and light feel amount to a bike that’s a great place to spend a few hours. The ride position is easy to live with, relaxed up on the hoods, and fast and fun when you use the drops.

The contact points are good, the bar tape is quality, and while the Akero saddle shape isn’t one of my favourites, it’s well-padded and you may fare better than I did.

Getting out of the saddle to climb or sprint, I felt I had a flex-free companion underneath me. Dropping my shoulder into a corner at speed, the Equation stayed on its line with ease.

The Vision wheels are solid performers too. Middleweight they may be, but they’re smooth-feeling. They are, though, finished with some rather uninspiring tyres.

The Zaffiro is Vittoria’s most affordable tyre to feature its proprietary Graphene compound.

They feel more compliant than most budget tyres and the grip is confident on wet roads.

However, they don’t respond with any zip, which is backed up by bench testing that shows the 15.6W rolling resistance is nigh-on treble that of Vittoria’s fastest Corsa Pro Speed TLR (28mm) option.

As soon as the weather improves and the temperature rises, I’d be rushing to replace these with something that would unleash the Equation’s obvious potential.

Argon 18 Equation 105 bottom line

The Argon 18 Equation’s core is very good – the frame and fork feel smooth and snappy, the drivetrain is slick and the braking is exceptional.

The wheelset is as good as you’ll find at this price (albeit worth a future upgrade) and the finishing kit is all solid stuff. However, it could be improved hugely with a set of the best road tyres to unleash the Equation’s full potential.

That way, it’d add up to great value initially and serious fun once the upgrades are dialled in – the sort of equation I like.

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