Trek Domane SLR
Back in 2012, Trek’s Domane revolutionised endurance road bike ride quality with its innovative IsoSpeed decoupler. It was fiendishly simple but tremendously effective. In one fell swoop, the limits of what a carbon road bike was capable of weren’t just expanded, they were rewritten, and beneath Fabian Cancellara, the Domane quickly racked up one ParisRoubaix and two Tour of Flanders victories. Cancellara so loved the Domane’s feel that he raced it all year round, until Trek added IsoSpeed to the current Madone. But the original design’s bumpeating rear end was never matched by its IsoSpeed fork, meaning that your hands and arms felt most of the vibrations that your posterior didn’t.
Trek’s answer to this IsoSpeed imbalance was to equip the head-tube with an evolution of the same technology. Following the principle of permitting only fore and aft flex from the seat-tube, the new front decoupler has an internal rocker cup that’s attached to the head-tube on each side with individual pivots. The upper headset bearing sits at the top of the rocker, and the steerer-tube passes through the whole thing, allowing it to rotate as normal, but also flex fore and aft, independent of the head-tube, and with no lateral movement.
But the changes don’t stop here – Trek have also redesigned the rear IsoSpeed decoupler system and made it user-adjustable. The original system had a conventional seat-tube that sprouted from the bottom bracket but wasn’t woven into the top-tube, but rear IsoSpeed mark two is quite different. From around one-third of its length above the bottom bracket, the rear half of the rounded seat-tube is scooped out up to the top-tube/seat stay junction.
The front half of the separate seatpost is curved to fit the seat-tube recess, and the rear neatly completes the seat-tube’s profile. Below the top-tube it becomes a single round shape, and is pierced by the decoupler pivot. The bottom of the seatpost attaches with an M5 bolt that doubles as the lower bottle cage mount, and is anchored by a flush-mounted nut.
The resulting narrow slot between frame and mast contains a U-shaped plastic slider, with grip tabs protruding on each side. Loosening the lower fixing bolt allows the slider to be moved from just above the bolt almost to the top-tube, altering the seatpost’s compliance. At its lowest point there’s more flex than when the slider is at the top of its travel. Think of it as a plastic ruler held over the edge of a table. Your anchor point on the table’s edge equates to the bike’s lower mount, and the amount of ruler projecting into the air equates to the slider position – twanging a greater length of ruler means greater oscillation.
So there’s the clever stuff. Although it takes some time to explain, there’s very little to see unless you look closely, and you’ll most likely never touch it, unless you adjust the rear compliance. It needs no specialist maintenance, and there’s no weight penalty. The combination of Trek’s 600 series carbon fibre, excellent construction and components bring our 56cm Domane SLR in at an impressive 6.71kg.
Surely then it’s more like a bouncy mountain bike than rapid road machine? Well, no. When it comes
to travelling quickly, the Domane SLR is at least as effective as any fast road bike on the market. Its wide BB90 bottom bracket allows for a huge down-tube and rock solid chainstays, and the oversized headtube area not only provides space for the IsoSpeed unit but maintains massive front-end torsional rigidity. The beauty of the IsoSpeed system is that it has precisely no effect whatsoever on your pedalling action, working only to isolate the rider from unwanted impacts and vibration.
Although not immediately obvious, the cumulative effects of the frame’s inbuilt compliance really delay the onset of muscle fatigue, saving you from countless tiring vibrations and letting you enjoy riding for longer. We set the slider for maximum flex – why wouldn’t you? – and revelled in the magic carpet ride. You still need to avoid potholes on the road, but when faced with a broken section of tarmac that you maybe can’t safely avoid, the Domane happily glides over it.
There are other comfort-inducing factors as well. Our bike came with 28mm Bontrager R3 tyres mounted on Aeolus 3 rims, which are 19.5mm wide internally, producing a generous contact patch. The larger air volume makes it easier to reduce air pressure, so we mostly ran them at 80-90psi. Grip was generally excellent, save for one ride on particularly slimy roads when the rear end stepped out four times, although we suspect most tyres would have done so, and it was immediately brought back under control. The 30mm deep Aeolus 3s ensured that acceleration was always brisk, and maintaining high speeds over everything from rolling hills to false flats was never a chore. Incredible frame compliance plus big tyres allows the bike to remain in contact with the road surface almost all of the time, increasing cornering grip, steering and braking precision, and consequently rider confidence and speed.
With no SRAM direct-mount brake available, Bontrager’s own Speed Stop units are fitted, along with Bontrager-badged Swissstop Black Prince pads. The brake callipers are compact in dimension, but don’t have the smooth look of Shimano’s. Tension adjustment is okay, but not that precise, and after the clamp it is possible for the free cable to rub the tyre unless carefully positioned. But they work effectively, with decent feel and enough power, and the pads remained consistent and noiseless in all conditions.
This Domane SLR’s SRAM eTap was both the icing and the cherry on top, ensuring clean lines, intuitive shifting and almost no maintenance. The compact chainset and 11-28 cassette match its go-anywhere abilities, because as well as dominating tarmac the Domane easily copes with gravel and most surfaces
The cumulative effects of the frame’s inbuilt compliance really delay the onset of muscle fatigue, letting you enjoy riding for longer
this side of cyclocross. With lengthy 42cm chainstays and a slacker than average 71.9 degree head angle wrapped up in a fairly normal 100.8cm wheelbase, the Domane is very stable, plus it boasts generous tyre clearance, helpful for squeezing in even larger rubber or fitting mudguards to the hidden mounts.
Up front, the Bontrager aluminium stem supports an Isocore Pro VR-CF carbon bar, with integrated gel pads for extra comfort and control, and the Affinity Pro carbon-railed saddle is a great addition. Bontrager’s upper seatpost is very satisfying for anyone who dislikes road spray dribbling down their seatpost and looking for a way in to the frame. Because it’s basically a capped tube that telescopes over the flexing seatpost, it’s sealed against filth ingress. The IsoSpeed slider gap can collect grime over time, and you’ll need to keep that mounting nut greased, but we’d readily accept such simple maintenance.
We did test the bike with the slider at its minimum compliance setting too, and although noticeably less bump-absorbent than before, the rear end still subdues rough roads with the feel of the very best competitor endurance bikes. But with that added ability on tap, why not use it? It’s hard to find a weakness in the Domane SLR’s make-up. Yes it’s expensive, but cutting-edge technology doesn’t come cheap and there’s a lot going on in that frame. There’s no weight penalty, at least not in this specification, the bike handles and accelerates as well as anything out there, has excellent grip, stops reliably and tames rough surfaces like no previous fast road bike ever has. The frame even has a limited lifetime warranty.
The Domane doesn’t feel in any way compromised by IsoSpeed or larger rubber. On the contrary, the benefits of both - its predictably secure handling and surprising speed potential - made it our first choice bike whenever there was an option.
Pros Extraordinary comfort, control and performance Cons We’d prefer cleaner looking, simpler brake callipers Verdict With double IsoSpeed and a superb build, the Domane SLR gives enormous rider con idence and truly impressive speed
The Domane gives a magic carpet ride thanks to front and rear IsoSpeed units and big tyres
You can now adjust the seatpost compliance with the updated IsoSpeed decoupler system