I’m something of a Trek fan. There are several reasons for that, and IsoSpeed is an important one. My Domane, the bike on which I got to know the system, has IsoSpeed, and so does my Checkmate. On the new Domane, Trek has dropped it. I understand why, first and foremost weight. I still think it’s a shame.
What IsoSpeed does
IsoSpeed decouples the seatpost from the frame. On a regular road bike, the post sits in the seat tube and is clamped tight at the top. Frame and post form one rigid unit. With IsoSpeed, a carbon tongue at the junction of top tube and seat tube holds the post instead. So the post is neither rigidly fixed in the seat tube nor at the top tube, it sits in this separate, flexible element.
It’s not suspension with a damper and travel, and nothing bobs when you pedal. The frame itself stays stiff, only the post is allowed to give, and only in the direction the hits come from. So you don’t feel IsoSpeed as travel. You feel it because cobbles, roots and gravel no longer go straight into your back. After 300 km, that makes a big difference.
I got to know the system on the Trek Domane Gen 4, Trek’s endurance bike. I also came to really appreciate IsoSpeed on the Checkmate, the gravel racer. The Checkmate is only approved for 45 mm, but I run 50 mm. To make that work, I trimmed the outer knobs on the rear tyre, and combined with IsoSpeed it’s incredibly comfortable, and therefore fast too.
The Rev 4 clamp
I’ve never had problems with the clamp on the Domane Gen 4. That said: I took the mechanism completely apart, greased it and used carbon paste on the seatpost. If you buy a used Domane, I’d recommend doing the same. Anything older than the Rev 4 clamp, I would upgrade.
Where IsoSpeed helps me
On the long days. Over 300 km, the small hits add up, and those are exactly what IsoSpeed takes out. And off-road: gravel, forest tracks, anywhere the Domane can also go with wide tyres.
The new Domane
In August, Trek launched the fifth generation. IsoSpeed is gone, and a round 27.2 mm seatpost sits in the frame instead. According to Trek, the frame is around 300 g lighter, and that’s probably what it’s mainly about.
The round post has one real advantage: you can fit whatever you like, for example Ergon’s CF Allroad Pro Carbon leaf-spring post, in my view the best post there is when it comes to compliance. Trek also offers its own round post with plenty of flex.
Trek’s reasoning makes sense. IsoSpeed comes from a time when a wide tyre meant 25 mm. Today 40 mm fit in the frame, and the tyre does a large part of the work.
| Domane Gen 4 | Domane Gen 5 | |
|---|---|---|
| IsoSpeed | yes | no |
| Tyre clearance | 38 mm official, 40 mm fit easily | 40 mm |
| Seatpost | Trek KVF Aero Carbon | round, 27.2 mm |
| Frame weight | around 300 g lighter, according to Trek | |
| Geometry | Endurance | largely carried over |
Tyres and IsoSpeed, not either or
The thing is: I already run 40 mm tyres on the old Domane. Officially, 38 mm is the limit, but 40 mm fit easily, even with a 2x drivetrain. So I have both, the tyre and IsoSpeed. For me it was never an either-or question.
One detail from Trek’s own white paper I find quite interesting. It puts the new Domane within 5% of the old one with IsoSpeed in terms of comfort. However, the test ran the new bike on 35 mm tyres against the old one on 32 mm, with the wider tyre at 10% lower pressure. So with the tyre advantage, the new Domane gets close to the old one. To me, that speaks for IsoSpeed rather than against it.
What I’d really like to know: 40 mm with IsoSpeed against 40 mm without. New frame, new post, same tyres, same loop. Maybe I’d be convinced afterwards. If anyone from Trek is reading: I’d love to try it 🙂
Why Domane
IsoSpeed aside, the Domane is the ideal bike for me because of its geometry. Very high stack, short top tube. That’s in contrast to almost every modern race bike, which is built long and low.
I believe this geometry would suit many road cyclists better than they think. And the good news: Trek has largely carried it over to the new Domane. So the most important part stays.
The verdict
The Domane stays my bike, and Trek stays my brand. IsoSpeed plus 40 mm tyres is the most comfortable combination I know on a road bike, and I’ll miss it when my Domane eventually retires. Until then, I’ll keep riding it.
