Isaac Sonic review

With a name inspired by the work of 17th century mathemetician and physicist Isaac Newton behind it, this Anglo-German company promises much. Big on its frame testing protocol

Our rating 
4.5 out of 5 star rating 4.5
GBP £5,299.00 RRP

Our review

Superb handling but hard ride and price limits appeal for this beautifully built racer
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With a name inspired by the work of 17th century mathemetician and physicist Isaac Newton behind it, this Anglo-German company promises much.


Big on its frame testing protocol, the company is keen to point out that the quality of an Isaac is more than skin deep and that each frame has passed the stringent German EFBe fatigue tests.

Isaac is still some way behind the big names on brand perception, but since the company started in 2001, it has gone on to develop nine road models, starting with the Shimano 105-equipped Pascal at under £1,300, and headed by the Sonic that, weighing 13.3lb, is one of the lightest as well as one of the most expensive Shimano Dura-Ace-equipped bikes that we’ve seen.


Stiffest frame we’ve tested yet

Paul puts the Sonic through its paces
BikeRadar ©

Isaac’s carbon frames are built using the standard practice of mitring the tubes and wrapping them where they join. This ‘streifband’ (wrapped) method, as it is called, produces lighter frames than if lugs were used. The outwardly similar 2007 version of the Isaac Sonic is currently doing the rounds at various international bike shows; it uses a lighter, more fragile layer of carbon in areas of low torsional stress, to reduce weight to a claimed 860g for the 55.5cm size. The 2006 version tested here, at 20g less than a kilo, is still far lighter than its supersized appearance suggests.

There are six frame sizes and all have a very slight slope in the toptube, ranging from a drop of 30mm to 45mm fore/aft on the 60cm sizes. This combines the modern look of a compact with the traditional appearance of a level top-tube. There were no qualms with the frame geometry across the sizes and the Isaac catalogue includes a handy reference to help work out the frame size required. More advice can be found at the website

Judging by our recent visit to the Eurobike show, the industry is split over whether to paint carbon or not. Isaac do both but there’s no paint on the Sonic instead a painstakingly applied decorative layer under a translucent blue lacquer. We would also like to have seen a chain pick-up plate, as featured on a lot of carbon bikes these days, to reduce the likelihood of damage to the bottom bracket in the event of unshipping the chain.

Looking at the back of the bike, the chainstays and seatstays are massively oversized and the gear hanger is a replaceable type to stop the frame being rendered scrap in the event of a fall.


Uncompromising race-day tool

RBS, Isaac’s UK distributor, are always keen to point out that Isaac bikes are exceptionally stiff, and so it proved on test with a level of stiffness that has to be experienced to be believed. The Sonic is certainly one of the best bikes we’ve tested for riders who like to give it everything in a sprint. This has a lot to do with the Sonic’s massively oversized fork crown and fork blades, and the cigarshaped head-tube that also worked to such good effect on aluminium bikes such as the Danish Principia bikes of old.

We expected a frame of this calibre to handle confidently on corners and we weren’t disappointed. Aided by an enviable level of lateral stiffness, the Sonic is fantastic at responding to fast direction changes when following a line of riders in a criterium.

The Lightweight wheels have a huge influence on the impression of speed and can change the whole feel of a well known training route, but it’s their climbing ability that sets them apart. Their low weight, at just 1,841g including the tyres and cassette, gives the rider a clear advantage on long, steep climbs. However, it does take an experienced hand to coax the bike down longer and more technical descents because the brake blocks have a tendency to heat up and grab during long periods of braking. In the hands of a novice this anomaly will negate the advantage of a rapid ascent, but with an experienced rider the Lightweights are the single most performance-enhancing product you can fit to a bike, and they complement the Sonic perfectly.

Several manufacturers have managed to balance comfort and stiffness successfully, but the Isaac has been criticised for being on the harsh side. Some will warm to the direct nature of the ride that transmits every nuance of the road surface through to your fingers and backside, but a couple of testers said they would be too uncomfortable with the Sonic for more than 50 miles.


Superb in almost all areas

Componentry and finishing kit on our Sonic is about as exotic as it gets. Mind you that doesn’t guarantee comfort, the hard Gipiemme saddle combined with the stiff frame to butt battering effect. The full-carbon Isaac handlebars are well made and are a comfortable shape though, held in place with a Tune stem. This has been forged and then CNCmachined before being anodised in When it comes to leverage on the climbs and spinning ability on the flats, the 172.5mm Dura-Ace cranks strike a nice balance. We would also like to have seen a compact non-series Shimano or FSA compact chainset option for those who intend making full use of the Sonic’s exceptional climbing ability. This would improve their standing considerably in tough rides such as the Etape.

The setback-type carbon seatpost means you can adjust the saddle through a useful range, though it did slip down a couple of times and we had to apply some Tacx carbon-prep to the mating surfaces, which fixed the problem.

The Gravity Research brakes are just a little over half the weight of the competition, but they had less feel when feeding the brakes out of a corner and around five per cent less power than a Shimano Ultegra calliper fitted with carboncompatible brake blocks. The inner brake cable also had a tendency to pull through the cable clamp unless it was very tightly secured. At around £275 we would give them a miss.


Sensationally fast but compromised in blustery weather

The German-made Lightweight wheels combine low weight with the aerodynamic benefits of a deep section rim. They are produced in limited numbers and are built using a technique that is kept very close to the manufacturer’s chest. From what we can glean, though, the spokes are in fact hoops of Kevlar that fold around the loadbearing profile of the rim and hubs, thus doing away with the need to true them during the manufacturing process or indeed their lifetime.

The rims are flat in section, but wind tunnel tests have shown that a lenticular (lens)-shaped section is preferable in terms of aerodynamic efficiency, borne out by the Lightweights’ tendency to catch the wind in blustery conditions. While they are primarily intended for competition use, this highlighted their unsuitability for general cycling. On busy roads for instance, it had the alarming effect of turning the steering towards passing lorries. Not what you want cycling to work in the morning…


The Lightweight wheels are shod with Tufo tubular tyres, and while clincher tyres are on a par performance-wise, there is a healthy argument in favour of tubs because they are, on average, 10 per cent lighter than the combined weight of the lightest clincher wheel and tyre. Although the Tufos aren’t the best tyres that we’ve come across for grip, tending to skate a little at high speed, this was predictable enough and never gave us cause for concern.

The pricey but beautiful Isaac Sonic
BikeRadar ©

Product Specifications


Name Sonic
Brand Isaac

Frame Model Aluminium
Frame Weight 980
Headset Type Integrated
Weight (g) 6190
Weight (kg) 6.19
Colour Black
Available Sizes 19 Inches 20 Inches 21 Inches 22 Inches 22.5Inches
Chainrings Brand Shimano