IsoSpeed decoupled: Trek bins off comfort-enhancing tech with all-new Domane

Trek has released a brand new generation of its longstanding endurance bike, the Domane, today.

The Domane was introduced back in 2012 as a comfortable, cobbled race machine and featured Trek's IsoSpeed comfort-boosting system, which separated the seat tube from the top tube at the junction of the tubes, along with some bearings and other mechanical parts.

Over the years, this system was made adjustable and also added to the front ends of bikes at the headset to further boost comfort. Disc brake bikes arrived en masse, tyre sizes grew, and the Domane has developed with that technology over the last 14-odd years.

This latest incarnation is the fifth generation of the bike. Over the years, the Domane has been produced with various comfort-boosting features and has long been considered one of the best endurance road bikes.

Now it seems the time has come for Trek to strip things back with this latest release and discontinue the IsoSpeed system.

That's right, as far as we can tell, this is the end for IsoSpeed. Trek hasn't employed it on the new Domane, instead relying on the vibration-damping performance from bigger volume tyres and a new seatpost design wrapped up in a lighter overall package.

We have the technical details below, as well as my first thoughts on the Gen 5 Domane after my first ride with the bike.

I could attempt to sum up the overall design direction of the Domane by saying Trek has dropped the added weight and mechanical complexity of the IsoSpeed system and instead relied on comfort from bigger tyres to do much of the heavy lifting when it comes to smoothing things out.

However, there's a little more to the story than that; this new incarnation of the Domane is interesting and refreshing.

The new frame is lighter and simplified. The IsoSpeed mechanism is gone, as is the storage door in the downtube that the previous gen bike had. Trek says Domane SLR framesets are 305 grams lighter than the previous gen; that's a healthy chunk. Quoted weights for an unpainted frame in M/L size are 835g and 367g for an unpainted fork.

SLR 1x machines are 2.1lbs or just under a kilo lighter than the 'lightest previous generation build'; that is considerable. Where else are we seeing a whole kilo chopped off a new bike compared to the outgoing model?

There's also a new 27.2 round seatpost, designed to flex and damp out vibrations, which is the second piece in the comfort puzzle alongside the bigger tyre clearance of 40mm.

As a result of frame construction, bigger tyres and the new seatpost, Trek says the Domane is within 5% of the previous bike's 'vibrational energy performance' metric when using spec tyres; that's comparing a 32mm tyre on the previous bike wth IsoSpeed and a 35mm tyre on the new frame.

Bikes will come with 35mm tyres, but the frame will have clearance for up to 40mm rubber, an increase over the previous bike's 38mm clearance.

There's also a new 20mm riser handlebar to go with the frame; this may not be so welcome in certain quarters, but for some it might make an already comfy bike even more so, and cleaner-looking if you can drop a headset spacer. There are still full-length fender mounts, and mounting points for top tube and a frame bag.

The carbon-framed Domane SL starts at $2,399.99; 10 models will be available with Shimano and SRAM equipment, rising up to $11,499 for the top-spec SRAM Red / XPLR builds. Trek also claims a very light weight of 6.63kg for the SLR 9 SRAM 1x model with 28mm tyres.

Custom Project One options will also be available, including 124 Project One ICON No. 76 bikes to celebrate the brand's 50th anniversary; that bike comes in at a cool $14,999.

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Trek says the Domane will stay the same and features Trek's 'road endurance' geo. Comparing new geo between Gen 4 and 5 bikes, there do seem to have been some small changes in stack and reach numbers across some sizes, possibly for that new riser bar, and an XS-XL size range has been adopted instead of the Gen 4 47-58cm sizing guide.

The new riser bar also adds 20mm of rise at the hood and has a slight back sweep.

Trek has also specced shorter cranks, like the new Cube road bikes that launched this week. XS/S bikes will have 160mm cranks, M-M/L bikes will have 165mm cranks, and L/XL machines will have 170mm cranks.

The Domane frame has a T47 bottom bracket, is UDH-friendly, electronic groupset only, and has a removable front derailleur mount.

I also asked the brand about what would happen regarding continued support for existing IsoSpeed-equipped machines, and it told me that 'IsoSpeed will still be serviced.'

Trek also provided a white paper on the road to dropping the IsoSpeed tech, saying that increasing tyre volume has 'opened the door' to create a lighter and less complex bike.

The brand's concern for this bike was to reduce weight, improve pedalling stiffness and limit vibration power to the rider. Trek defines Vibrational power as the energy transmitted to the rider over rough ground; let's take that to mean 'feedback' or 'vibrations'.

The brand says the 35mm was 0.9 watts slower in terms of aero, but 1.5watts faster in rolling resistance, assuming compared to a 32mm. We found a similar trade-off in our own CN Labs rolling resistance testing.

Frame layup has been changed; the brand quotes a 6% increase according to the Tour Magazine pedalling stiffness test. This apparently places the bike between the Gen 4 Domane and Gen 8 Madone, with 'notably improved' power transfer versus the outgoing bike.

Trek tested the Domane with a force-sensing saddle and bar to compare the Gen 4 and 5 bikes head to head on a rough surface and at speeds from 7- 20 mph. Tyre pressures were set using the Wolf Tooth calculator.

The Gen 5 Domane tests within 5% of the vibrational power of the outgoing bike. In short, based on Trek's testing, the bike is now lighter with an improved frame layup and, with 35mm tyres, transmits a small amount more energy to the rider.

First ride impressions

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Trek sent me a Domane SLR 7 AXS in a size M, so I got it prepped and headed out for a ride before the bike launched.

The SLR 7 AXS retails at $8,499 / €7,499 and arrived with a 2x SRAM Force groupset, Bontrager Aeolus Pro 51 wheels with 35mm Bontrager Kwaremont RSL tyres that were set up tubeless; I just added a little extra sealant as they were a bit low.

Rolling out, the first thing that struck me about the bike was that it felt short, and in a medium / 54 equivalent, the Domane has one of, if not the shortest, reach numbers I have seen.

Stack and reach numbers for the bike are 575mm and 374mm. Coupled with the 90mm stem, 40/44cm riser bar and a few spacers under the stem, the bike felt super comfortable.

If you want comfort, the Domane geometry will undoubtedly look after you. I like the fact that when it comes to road machines, Trek just offers the Madone, the pure race bike, and the Domane, the endurance bike with very comfortable geometry. Not an endurance bike trying to be as close as possible to the race bike. On my machine, the two-piece bar and stem also means stem swaps would be simple, and I probably would go for a 100mm stem long term.

What the Domane didn't feel was boring and sluggish; it felt light and responsive out of the saddle, and it felt direct climbing at slow speed. I liked the ride quality; it was a lot more engaging and pleasant to ride than the Cannondale Synapse I tested at the start of the year.

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The handling is good, confident, not razor sharp, and I detected a slightly calmer response around a 50kph corner I've ridden my whole life, but it's not slow or sluggish.

On paper, a wider bar with a backward sweep and 20mm rise would not be for me, but it's been executed well by Trek. It works and felt narrower than it was; the rise is also subtle both fit-wise and visually, and I adapted to it very quickly.

At the heart of the Gen 5 Madone, I feel there is quite a zippy, responsive frame. I could also still tuck in and get aero and ended up pondering aero positions and how shorter and taller positions affect them.

The Bontrager Kwaremont RSL tyres aren't a model I'm familiar with, but they use a cotton casing and 320 TPI construction; they felt good. Not dead and boring, which is critical for me on a bike like this. They rolled along nicely and absolutely contributed to smoothing things out; I half found myself imagining how nice they would be in the depths of winter (perish the thought)

On the fact that the IsoSpeed is now gone, I'm totally on board. More than once have I groaned at a corroded, knackered IsoSpeed assembly when working as a mechanic; I like the simplified angle of attack. There's less weight, less to go wrong, and less expense for customers.

Bigger tyres and that more flexible post will be enough, I think, and the ability to tune tyre pressure will bring a lot to the table when it comes to adding comfort.