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The Kalloy suspension seatpost that came fitted to my mid-priced hybrid cycle broke after a year of light use so I replaced it with the SR Suntour SP6-NEX-D2. The Kalloy was the only suspension seatpost I’d used and I thought it had worked reasonably well until it’s premature demise. How wrong I was! Fitting the SR Suntour seatpost to my bike, together with the existing saddle, revealed just how effective a well-designed suspension seatpost could be.
Suntour seem to produce quite a few variants of this design but they’re all very similar and are likely to have identical performance. I have the SP6 model but the latest appears to be the SP8, which has an improved saddle fixing arrangement and two shorter suspension springs instead of one longer one as in the SP6. Each model is also offered in a choice of two versions: NCX having an aluminium parallelogram arm structure and NEX with some steel arm parts. The NCX versions are fractionally lighter.
The Suntour product I received appears exceptionally well made for under £18, delivered. It looks like a hybrid of a ‘Parallelogram’ and a conventional tube-within-a-tube (linear) design. The saddle rails fix onto a hinged arm that forms the top part of the parallelogram structure. When loaded, the saddle moves backwards and down, forcing a roller (fitted to the arm) onto a hardened top plate that compresses a spring housed within the seatpost tube.
The design introduces a fair amount of leverage in its movement (i.e. the displacement of the saddle is greater than that of the suspension spring compression). Additionally, this leverage increases slightly with load due to the hinged backwards movement of the saddle. I believe this imparts several benefits such as reduced friction effect and a low resonant frequency (which means better isolation) and accounts for the exceptionally smooth, almost ‘floaty’ feel - quite unlike a conventional linear suspension post. The max. vertical travel is quoted as a modest 40mm, same as my previous Kalloy, but it doesn’t require an elephant cycling over Beachy Head (or more precisely, landing after cycling over Beachy Head) to make full use of it. In practice the Suntour feels as if it has much, much more travel than the Kalloy and yet it’s never ‘bottomed out’ on me.
In use with a comfy type saddle, the ride is supple and as smooth as Roger Moore. In fact, I now deliberately aim for bumps and ruts just to test the thing out and the seatpost always does its job magnificently - I arrive at my destination neither shaken nor stirred. There seems to be little of what people are calling ‘sticktion’ – a friction problem associated with conventional (linear) suspension seatposts. Also, there’s no discernable rebound effect (or kickback). All ‘normal’ road bumps/dips are soaked up with ease so you’ll only need to raise a cheek over craters or ‘sleeping policemen’. In fact, the Suntour is so effective on road that I can’t imagine a better performance from any suspension seatpost, irrespective of price (I’d love to try out a selection of the better ones just to see if I’m right - so if any manufacture reads this, I’m willing to act as unpaid tester).
If there’s a slight downside to the design, it’s the weight at 780g for the SP6-NEX model. The SP8-NCX version is slightly lighter (check out the SR Suntour website for details of all models and versions). The solid construction contributes to some of this weight but no doubt this design will always weigh more than the conventional type. If you’re counting the grams then suspension seatposts probably aren’t your thing anyway.
Because of the design, there are a few quirks. There are several linkages within the hinged arm structure that might eventually develop play - time will tell – it’s fine at the moment though. Another distinctive characteristic is the direction of movement under load. Relative to the cycle frame, movement is a downward and backwards arc rather than the downwards and slightly forward linear motion of a conventional design. I am conscious of a slight backwards movement when I first mount up but I don’t detect any additional backward movement after I set off. You’ll need to take this backward movement into account though when fitting the saddle to the seatpost clamp. I needed to pull the saddle as far forward on its rails as possible to get the right saddle position for me. If you currently need to have your saddle as far forward as possible using a standard seatpost, you may find it ends up too far back with the Suntour. Finally, the design is quite tall so the minimum distance from saddle rail to the point where the seatpost enters the cycle frame is a high 115mm.
The only other issue I noticed was that the adjustment afforded by the seatpost’s saddle clamp prevents the user fixing the saddle with much of a front-end upward tilt. I’m guessing that most cyclists prefer the saddle surface to sit at the horizontal - this is fine – and a front-end downward tilt is no problem either. With the saddle I use, I wanted the front-end slightly raised which I just about achieved. (Note that the newer SP8 versions have an improved saddle rail clamping arrangement, which may offer a greater range of tilt adjustment and it looks more secure than the version I have).
According to the instruction manual that comes with the product, the seatpost can be adjusted to suit cyclists in the weight range 65 to 100kg. I’m about 75kg and needed to tension the adjuster plug to suit me. I suspect this seatpost would cope with lighter cyclists than specified, maybe down to about 55 - 60kg. Both softer and harder replacement springs are available for SP8 versions if your weight falls outside the recommended range though. This seatpost appears to be more popular on the continent than in the UK hence you may need to resort to continental outlets for alternative springs if required.
In summary, I highly recommend this product for road and light off-road use, provided you can accommodate the design’s physical characteristics. It’s my best cycling related purchase for years. I just hope it lasts.
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