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Specialized Roubaix SL4 Double review

23 Nov 2015

Are the Zertz inserts on the Specialized Roubaix SL4 a gimmick? We're not sure but it's one of the most comfortable bikes we've ridden.

Cyclist Rating: 
Very comfortable
Same fork rake regardless of the size

Specialized released the first generation Roubaix in 2008 and it’s been winning races ever since. The Roubaix name comes from the infamous Paris-Roubaix race that cuts across the landscape of northern France, covering 253km with approximately 53km of that taking place on rough cobbled roads. But how effective is their frame design and is it all just a gimmick?

To read our first ride review of the new 2017 model, click here: Specialized Roubaix 2017 first ride review

The frame

The Roubaix SL4 has been designed with one thing in mind: comfort. The frame is constructed from Specialized’s own blend of carbon, FACT 8r, but the frame’s uniqueness comes from the Zertz inserts placed into the seatstays and fork. These inserts are made from a viscoelastic polymer that act as dampers, so they absorb vibrations from the road before they reach your body. The idea being that this increases comfort and reduces fatigue so that you can ride faster and longer. A good look at the geometry chart and you can see this carried through. The top tube is on the shorter side and the headtube is quite tall at 16.5cm (2.5cm taller than the equivalent Tarmac, Specialized’s out-and-out racing platform). The head angle is quite slack at 71.6°, so the steering remains relaxed. The bottom bracket is quite low too, which, when combined with the 415mm chainstays, gives the bike a longer-than-usual wheelbase, making for a very stable ride; perfect for the rough roads the bike was designed for.

Specialized Roubaix SL4 zertz

Despite all the comfort focus, cornering on the bike remains fun and precise thanks to the full-carbon tapered fork and the oversized, hourglass-shaped headtube. There is clearance for 28mm tyres too, if you want to make the ride really plush. The spread of sizes on the frame is good, and Specialized make a point of altering the chainstay length and BB drop through the sizes to keep the ride feel the same, although the jumps are a little large at either end of the spectrum. What is disappointing to see is that the same fork rake (49mm) is used throughout the range, so the smaller sizes have a whopping 59mm trail but the 61cm has just 53mm, which is really short and nippy – not really the sort of thing you want a cobbles bike.


The Roubaix SL4 Double comes with a 9-speed Shimano Sora groupset and it’s pretty much all there. The only exceptions to this are the brakes, but they’re better than the Sora units. The braking power is excellent and they’re fitted with cartridge pads so replacing them is easy and cheap. The Roubaix comes with an 11-32 cassette so you’ve got a huge spread to take on almost anything. We have two complaints and both are related to the front shifting: we had to give the lever a few hard presses to get it to shift down onto the little chainring. The same little lever also had a bad habit of getting stuck behind the brake lever, which sometimes made shifting impossible until it was pushed back into the correct position.

Specialized Roubaix SL4 sora

The finishing kit is all own-brand and does the job just fine, but the standout star has to be the seatpost. The CG-R seatpost is a clever bit of kit; the top of it is built into a dog-leg shape with a Zertz insert to fill the gap. The result is a seatpost that has 18mm of suspension and it’s great to ride. When pedalling along normally, it doesn’t bounce, and you can’t feel any loss of power usually associated with suspension, but go over a big bump or pothole and you can feel it flex and absorb the impact. The only constraint is that it’s only available in one setback so the resulting saddle position might not work for everyone.


Money has to be saved somewhere and the wheels and tyres are fairly basic Axis items. They’re quite heavy but appear strong enough to withstand most things you could throw at them and they remained true throughout the test. The tyres are Specialized Espoir Elite. They have a low thread count so they’re not especially supple or fast rolling, but they’ve got a folding bead, which makes swapping out inner tubes that bit easier when you get a puncture.

The ride

Specialized Roubaix SL4 seatpost

Going off the numbers, there was a danger that the bike would feel a little pedestrian but there’s nothing to worry about – it’s a complete pleasure to ride. Travel across some badly kept roads on the Roubaix and you’ll barely notice they were there. The handling is predictable, so you can corner and descend with confidence, knowing that a few little bumps in the surface won’t upset the whole bike. It also means you can forget what’s going on underneath you and just enjoy the ride. The bar tape is thick and spongy too, so it’s comfortable at the front end as well as the back. It’s fair to say that it’s not the stiffest bike under acceleration, but it doesn’t claim to be, so you can let it off for that. By the end of the ride you still feel fresh – it’s one of the most comfortable bikes we’ve ever ridden. Overall, it’s a do-it-all road bike with a frame that is well worth upgrading with better wheels and, eventually, we’d be looking at a 105 drivetrain. 


Well designed to fit the 'all-day comfort' brief - 8/10


Excellent brakes and the Zertz seatpost stand out - 8/10


Strong but heavy, although the tyres let them down - 7/10

The ride

A real pleasure to ride - comfortable but not dull - 9/10


Geometry chart
Claimed Measured
Top Tube (TT) 548mm 544mm
Seat Tube (ST) 495mm 498mm
Down Tube (DT) 596mm
Fork Length (FL) 376mm
Head Tube (HT) 165mm 165mm
Head Angle (HA) 72 71.6
Seat Angle (SA) 73.5 73.3
Wheelbase (WB) 1000mm 1003mm
BB drop (BB) 71.5mm 72mm


Specialized Roubaix SL4 Double
Frame Specialized SL4 FACT 8r carbon, FACT carbon fork
Groupset Shimano Sora
Brakes Axis 1.0
Chainset Shimano Sora, 50/34
Cassette Shimano Sora, 11-32
Bars Specialized Comp Shallow
Stem Specialized Comp Multi
Seatpost Specialized CG-R, FACT carbon
Wheels Axis 1.0
Tyres Specialized Espoir Elite, 25c
Saddle Specialized BG Toupe Sport

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