Syntace P6 Carbon HiFlex review

Flexible seatpost for extra comfort

Our rating 
4.0 out of 5 star rating 4.0
GBP £140.00 RRP

Our review

One of the most attractive ‘flexy’ seatposts available, with a 10-year warranty too
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The HiFlex is the latest version of Syntace’s excellent P6, retaining all the key features that made it a favourite: the 53mm long bottom clamping plate for excellent support, the 30mm long upper clamp plate that allows a lot of fore and aft seat rail movement, and its two micro-adjust bolts angled to be as in-line as possible with the loads placed on them, for adjustability and strength. 


It’s classic carbon P6, with an integrated carbon head. It uses 50mm long cold-forged alloy (7075) lower rail plates and deep-head titanium bolts to give 30 degrees of saddle tilt, plus maximum rail support – great for lovers of carbon-railed saddles or riders who bend regular rails.

Its party trick is that Syntace have laid the fibres in such a way that the seatpost is able to flex backwards under load, increasing riding comfort without any unwanted sideways movement. 

The main post and the head section is a single piece of uni-directional carbon fibre. The material is thicker at the front and back than at the sides, and it’s this that allows the post to flex. The result is a post that really does take the edge off bumps if you’re on a road bike. 

The benefits also extend to mountain biking. If you’re sat in the saddle hammering a hardtail up a bumpy climb, a conventional seatpost and saddle force you to lift your weight slightly from the perch. You’re not standing or sitting, but hovering. That’s a tiring position to ride in. With the P6 HiFlex you can remain seated over the stutters and ripples in the trail, letting the engine (that’s you) and chassis (the frame) work happily together applying power to the rear wheel. 

The maximum level of movement at the saddle clamp is around 2cm, though you’ll be using nearer 1cm most of the time. It’s enough to do the job and the effect of using it is clear and distinct. It’s not suspension, but it is comfy and raises the performance of both bike and rider.

More importantly, it does so in a manner that feels controlled. It doesn’t have a ‘springy’ feeling to it, and there’s no sudden kickback after hitting bigger bumps. The drawback is that there is less flex available with less exposed seatpost. After some load/deflection testing we concluded that if you have 150mm or more of exposed seatpost then you are going to benefit from the HiFlex – anything less and you’re essentially riding a very high quality lightweight post and not seeing enough flex to feel the extra comfort.

The P6 is available in 27.2, 30.9, 31.6 and 34.9mm diameters, 300, 400 and 480mm lengths and accepts seat rails up to 11mm tall – so it will fit any conventional railed saddle. Our 31.6mm/400mm post weighs a reasonable 206g.

The P6 comes with a 10-year warranty. And while the Syntace tuned-flex seatpost isn’t the first to market, contendors come from more esoteric brands, so it’s likely to be the one you actually see in the shops. 

Syntace p6 carbon hiflex:
Russell Burton

This product was originally reviewed in Cycling Plus and What Mountain Bike magazines, available on Apple Newsstand and Zinio.

Product Specifications


Name P6 HiFlex seatpost (12)
Brand Syntace