Isaac Kelvin review

German design meets Taiwanese manufacturing in an ultra-stiff package.

Our rating 
4.0 out of 5 star rating 4.0
GBP £1,754.00 RRP

Our review

Beautifully built, but extreme stiffness counts against it on UK roads.
Skip to view product specifications

Advertisement MPU reviews

The Kelvin combines excellent Taiwanese maufacturing with German design and that classic German pursuit of frame rigidity. It’s stiffer than a very stiff thing, but if that’s your bag, this could well be your bike.

Although Isaac have been based in England since 2001, Isaac frames are designed and developed in Germany to exacting standards and subjected to independent German testing body EFBe’s fatigue testing protocol. However, like many others in this price range (with the exception of Cannondale’s SystemSix), they are actually manufactured in Taiwan. The Isaac Kelvin is one up from their lowest priced Pascal model.


This 2007 Kelvin weighs in at 8.76kg (19.3lb), a little lighter than last year’s model. The frame is manufactured from a mixture of carbon grades and is laid up in the mould entirely by hand. Visible sections under the Isaac graphics and on the fork have a coarse decorative weave. Unusually, to maximise stiffness the fork steerer tube has a larger diameter at the base than at the top – a feature that is only normally seen on some ultra high-end frames. The long head-tube provides a slightly more upright riding position without resorting to using headset spacers, which can rob some of that precious stiffness. The bike is available in six sizes, from 48 to 60cm.


The Isaac would normally come with a ‘standard’ spec based on Shimano 105 for £1,674, though ours had an upgrade in the form of an Isaac-made stem, closely resembling the beautiful, cold-forged and CNC-machined, German-made Tune. The anatomic handlebars give a relatively upright riding position when you’re on the tops or hoods, but the drops are deep enough to provide a low racing position. The gear package, based on Shimano 105, was curiously difficult to index which we later found to have been caused by slight misalignment of the gear hanger – easily corrected in a matter of seconds, once the gear mech was removed, using a Park hanger alignment tool.


Tests have shown that the positive effects of a stiff frame are wasted when it’s partnered with a wheel of insufficient lateral stiffness. So it was a relief to discover that the modestly priced Mavic Aksium wheels work very well with the Isaac, with a remarkable ability to feel lighter than they are when climbing. Having said that, we noticed a further improvement to responsiveness by fitting Fulcrum R1 wheels that set the benchmark for stiffness. The Continental Super Sport 23mm tyres rise to the challenge when exploring the Isaac’s handling limits on descents and grip well on damp surfaces.


While the Isaac Kelvin warms to the kind of smooth road surfaces enjoyed by our German cousins, we found ourselves consciously avoiding any road surface irregularities because both frame and fork react to every blemish. On the flipside, however, the Kelvin feels outstandingly rapid when spooling up the cranks to get up to speed, and the longer than average head-tube helps in part to minimise torsional losses, making it remarkably stable in blustery conditions. Time triallists, however, might wish for a more stretched out, lower riding position.

Advertisement MPU reviews

Isaac are very good at making stiff and efficient bikes and we love the oversized tubing and one of the very best finishes in the business, but we can’t help feeling that they’ve gone too far in their quest for über stiffness with the Kelvin. That said, it’s worth considering if you are tall and heavy and have the need for something as utterly dependable as a frame designed in Germany and built in Taiwan.

Product Specifications


Name Name, 0, 10, Name, Kelvin (07)
Brand Brand, 0, 20, Brand, Isaac

Bottom Bracket Height (cm) Bottom Bracket Height (cm), 2, 0, Bottom Bracket Height (cm), 27
Bottom Bracket Bottom Bracket, 2, 0, Bottom Bracket, 105 Hollowtech II
Brakes Brakes, 2, 0, Brakes, 105
Cassette Cassette, 2, 0, Cassette, Shimano 105 10spd
Chain Chain, 2, 0, Chain, HG 5600
Chainstays (cm) Chainstays (cm), 2, 0, Chainstays (cm), 41
Cranks Cranks, 2, 0, Cranks, 105 Hollowtech II
Fork Fork, 2, 0, Fork, Carbon
Fork Offset Fork Offset, 2, 0, Fork Offset, 4.5
Fork Weight Fork Weight, 2, 0, Fork Weight, 417
Frame Material Frame Material, 2, 0, Frame Material, Carbon
Frame Weight Frame Weight, 2, 0, Frame Weight, 1414
Front Derailleur Front Derailleur, 2, 0, Front Derailleur, 105
Front Hub Front Hub, 2, 0, Front Hub, Aksium Race
Front Wheel Weight Front Wheel Weight, 2, 0, Front Wheel Weight, 1335
Head Tube Angle Head Tube Angle, 2, 0, Head Tube Angle, 72.5
Headset Type Headset Type, 2, 0, Headset Type, Integrated
Rear Derailleur Rear Derailleur, 2, 0, Rear Derailleur, 105
Rear Hub Rear Hub, 2, 0, Rear Hub, Aksium Race
Rear Wheel Weight Rear Wheel Weight, 2, 0, Rear Wheel Weight, 1705
Rims Rims, 2, 0, Rims, Aksium Race
Seat Tube (cm) Seat Tube (cm), 2, 0, Seat Tube (cm), 51
Seat Tube Angle Seat Tube Angle, 2, 0, Seat Tube Angle, 73.5
Shifters Shifters, 2, 0, Shifters, 105
Standover Height (cm) Standover Height (cm), 2, 0, Standover Height (cm), 81.5
Top Tube (cm) Top Tube (cm), 2, 0, Top Tube (cm), 55
Trail Trail, 2, 0, Trail, 6.3
Weight (kg) Weight (kg), 2, 0, Weight (kg), 8.76
Wheelbase (cm) Wheelbase (cm), 2, 0, Wheelbase (cm), 101
Available Sizes Available Sizes, 2, 0, Available Sizes, 48cm 51cm 54cm 55.5cm 57cm 58.5cm 60cm
Front Tyre Front Tyre, 2, 0, Front Tyre, Ultra 2000
Front Tyre Size Front Tyre Size, 2, 0, Front Tyre Size, 700x23C
Rear Tyre Rear Tyre, 2, 0, Rear Tyre, Ultra 2000
Rear Tyre Size Rear Tyre Size, 2, 0, Rear Tyre Size, 700x23C
Year Year, 2, 0, Year, 2007
Sprocket Size Tested Sprocket Size Tested, 2, 0, Sprocket Size Tested, 10spd - 12/13/14/15/16/17/19/21/23/25