Isaac Boson Disc review

An understated road bike that rides beautifully and balances well

Our rating 
4.5 out of 5 star rating 4.5
GBP £3,000
Isaac Boson Disc

Our review

Great value, understated, very capable ride
Pros: Sweet handling, smooth riding, well equipped
Cons: Understated might not be what everyone wants; saddle isn’t a favourite
Isaac describes the Boson as a bike for big days out and mountainous rides, though when you look at the geometry — parallel, steep 73.5-degree angles, a low (for a 58cm bike) 590.5mm stack and a long 402.1mm reach — the ride position at least suggests something much more race orientated…
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The Isaac Boson Disc is one of our Bike of the Year bikes for 2019. To read reviews of the other contenders and the categories tested across road, mountain and women’s bikes, visit our Bike of the Year hub.

Isaac Boson Disc design and kit

The design of the Boson is refreshingly understated. There’s no talk of aerodynamics, no claims of superlight this or that. It’s just a nicely shaped, honest road bike.

Up front, a slender fork slots into an oversized head tube and big volume down tube. The top tube tapers back to a slim seat tube, with a neatly integrated wedge clamp (with what looks like a guaranteed-not-to-slip 12Nm max on the retaining bolt).

Isaac headset and stem
Headset and stem
David Caudery/Immediate Media

The tight backend blends large, square-shaped chainstays with super-slender bowed seatstays that meet the dropouts with a kink into a vertical junction.

Isaac has followed the well-proven trope of making the head tube, down tube, bottom-bracket shell and chainstays oversized and super-stiff, with a top tube and seatstays that are much more undersized and designed to offer compliance.

Isaac Boson Disc ride experience

When you sling a leg over the Boson, the ride position doesn’t feel overly aggressive, but it does encourage you to give it the beans and go for it.

And while the steeper head angle and relatively short wheelbase (1003.3mm, and short 406mm chainstays) suggest a bike with a fast, almost nervous steering response, what you get is a ride that turns in quickly, but with wonderful balance.

The pick-up to pedal response is solid and rapid, aided by the quality inherent in the excellent DT Swiss hoops and that gives the Boson an edge when it comes to steeper climbs.

The all-up 8.28kg weight is good, but there is plenty of scope to drop more grams with a few well-judged upgrades down the line.

The Boson rides like a lighter bike, thanks to the wheels and fast-rolling Vredestein Fortezza Senso tyres

If anything, the Boson rides like a lighter bike, thanks to the wheels and fast-rolling — and impressively grippy in winter — Vredestein Fortezza Senso tyres.

The Boson’s on-road manners are impressive and the way in which the chassis absorbs vibrations from the buzz and chatter of my familiar test roads is on a par with the best endurance bikes from the big brands.

While the backend is brilliant at killing vibrations, I’m still not a fan of the own-brand Isaac saddle. It’s well-shaped but soft centred and stiff at the wings, so I always felt prominent pressure points on either flank.

slender seat stay
Super-slender bowed seat stays
David Caudery/Immediate Media

I thought I’d get used to it, but four hours into a five-hour ride I found myself looking for any excuse to stand up and away from the saddle.

The full Ultegra groupset and brakes with no omissions is something I always like to see, and there is nothing here that’ll let you down.

There’s slick shifts across the 11-28 cassette and that combined with the 50/34 chainset gives a rideable range for the longest and steepest climbs.

When it comes to descending, the Ultegra brakes are superb, beautifully balanced between power and control, and Isaac hasn’t skimped on the all-important brake rotors, opting for Ultegra’s Ice tech for the best all-round performance from Shimano’s brakes.

Isaac Boson Disc verdict

As you might have guessed, I’m impressed with this bike’s overall qualities. Yeah, I could lose the saddle, but saddles are a personal thing.

In all, the Boson is an understated bike — it doesn’t shout speed, aero, lightweight or any other buzzword, it does, however, go quietly about its business of being a fine bike that’s well priced and rides beautifully.

Isaac Boson Disc specifications

  • Sizes (*tested): 49, 52, 55, 58*, 61cm
  • Weight: 8.28kg
  • Frame: Carbon
  • Fork: Carbon
  • Chainset: Shimano Ultegra, 50/34
  • Cassette: 11-28
  • Derailleurs: Shimano Ultegra
  • Shifters: Shimano Ultegra
  • Wheelset: DT Swiss P1800 Spline
  • Tyres: Vredestein Fortezza Senso 25c
  • Stem: Isaac alloy
  • Bar: Isaac alloy
  • Saddle: Isaac cromo rail
  • Seatpost: Isaac carbon
  • Brakes: Shimano Ultegra

Isaac Boson Disc geometry

  • Seat angle: 73.5 degrees
  • Head angle: 73.5 degrees
  • Chainstay: 40.6cm
  • Seat Tube: 53.9cm
  • Top Tube: 57cm
  • Head Tube: 18.9cm
  • Fork Offset: 4.5cm
  • Bottom bracket drop: 7cm
  • Bottom bracket height: 26.7cm
  • Wheelbase: 1,003.3mm
  • Stack: 59.05cm
  • Reach: 40.21cm
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BikeRadar would like to thank Stolen Goat, Lazer, Northwave and Effetto Mariposa for their help and support during our Bike of the Year test.