Wil reviews the Polygon Siskiu D6

In the decade and a half that I spent working in bike shops, one of the general rules of thumb was that if you wanted a cheap full suspension bike, you’d need to spend about a grand more than the equivalent hardtail. That meant it wasn’t really possible to get a decent full suspension bike until you were a few gorillas over the $2,000 mark. Even around that price point though, I’d still recommend that customers consider a hardtail, which would come with decent components that would actually stand up to proper off-road riding. Also, there just really weren’t a lot of $2K full suspension bikes available in the first place. Fast-forward to 2020, and I reckon that advice still stands. Well, I though it did. Then this Polygon Siskiu D6 showed up.

Watch our video review of the Polygon Siskiu D6 here!

Polygon Siskiu D Overview

Amongst the UNNOs, Yetis and Santa Cruz’ of the world, Polygon isn’t the dreamiest of brand names. Rough I know, but you wouldn’t exactly call it bedroom wall poster material would you? That isn’t necessarily a bad thing though – lusting after a bike is one thing, but being able to afford it is an entirely different kettle of fish. And what the Indonesian brand may lack in curb appeal, it more than makes up for in its value-oriented approach.

Putting together well-appointed bikes for less money than its big-name competitors is a game that Polygon plays exceedingly well

Putting together well-appointed bikes for less money than its big-name competitors is a game that Polygon plays exceedingly well, and it’s helped grow the brand’s popularity far beyond its Indonesian-based factories. That value for money is amplified by Bicycles Online, which distributes and sells Polygon bikes direct-to-consumer in Australia, skipping out the middle-man to sharpen the sticker price. And nowhere is the price sharper than with Polygon’s popular entry-level trail bike – the Siskiu D.

Reworked frame & suspension

The Siskiu D is Polygon’s 120mm travel trail bike, and for 2020 its received a significant update with an all-new alloy frame. The overall shape and suspension layout looks similar, but the shock anchors a little further up the downtube, so you can now fit a water bottle underneath it. This has also affected the suspension kinematics, and Polygon says the new bike is more progressive as a result.

Frame geometry receives the usual updates – there’s a slacker head angle, a steeper seat angle, and a longer reach. The chainstays have also been shortened, which has been made possible by a switch to Boost spacing. Whereas the old Siskiu D used quick-release dropouts, the new frame features a sturdy 148x12mm bolt-up axle.

You also get a tapered zero-stack head tube with sealed bearings, internal cable routing through the mainframe, and a threaded bottom bracket shell. All suspension pivots roll on sealed cartridge bearings, except for the dropout pivots that utilise DU bushings. It’s a surprisingly well-finished frame – Polygon has even printed torque specifications on the pivot bearing caps, which is a nice touch.

You get a tapered zero-stack head tube with sealed bearings, internal cable routing through the mainframe, and Boost 148x12mm rear dropouts.

Full suspension for less

There are three models within the Siskiu range ranging from $1,599 AUD to $2,299 AUD. All three models are built around the same alloy frame with 120mm of travel front and rear. The Siskiu D6 we have here is the middle-child, and it’s actually a model that’s specific to the Australian market.

You can get the Siskiu D6 in four sizes from Small through to X-Large. The Small rolls on 27.5in wheels, while the Medium and above use 29in wheels. In terms of spec, Polygon has built the Siskiu D6 with a Shimano 1×10 drivetrain, hydraulic disc brakes, a dropper post and air-adjustable suspension front and rear. Pretty incredible for a bike that has a retail price of just $1,899 AUD.

Even more incredible is that Bicycles Online actually sells the Siskiu D6 for less on its website – $1,799. To put that in perspective, that’s a hundred bucks more than the last suspension fork I tested. Crikey!

There are three models within the Siskiu range – the Siskiu D5 (left), the Siskiu D6 (centre) and the Siskiu D7 (right).

Polygon Siskiu D6 price & specs

Let’s not beat around the bush – this is an extraordinarily cheap bike. For me personally, it’s the cheapest full suspension bike I’ve ever tested. It’s also quite a bit less than many of Polygon’s big-name competitors. Walk into any bike shop on the High street, and these are the entry-level options you’ll see from the biggest brands available in Australia;

• Norco Fluid FS 3: $2,299 AUD
• Giant Stance 29 2: $2,399 AUD
• Merida One-Twenty 400: $2,399 AUD
• Avanti Hammer S: $2,499 AUD
• Scott Spark 970: $2,799 AUD
• Specialized Stumpjumper ST Alloy: $2,900 AUD
• Trek Fuel EX 5: $2,999 AUD

Now I’m not suggesting that all of those bikes are equal, because they’re not. It’s simply a comparison with what else is out there at the lower end of the spectrum from the brands that are available through bricks & mortar shops. The Polygon Siskiu D6 is of course sold online, so that presents a different set of advantages and challenges compared to buying a bike from your local bike shop. If we were to compare it to other bikes you can purchase online, here are three of the cheapest options I could find;

• Marin Rift Zone 1: $2,399
• Canyon Neuron AL 6.0: $2,999
• Commencal Meta TR 29 Origin: $2,999

Again, this isn’t to say that all these bikes are the same. I’ve listed those examples to provide context for where the Siskiu D6 sits relative to other budget bouncers on the market. And the fact that it’s $400 cheaper than the closest competitor listed here highlights just how aggressive Polygon has gone on price. As you’ll read shortly however, compromises have been made to get the price down to that level.

2020 Polygon Siskiu D6

• Frame | ALX Alloy, Link-Activated Single Pivot Suspension Design, 120mm Travel
• Fork | SR Suntour XCR 32 LO R, Air-Sprung, 120mm Travel
• Shock | X-Fusion O2 PRO RL E2, Air-Sprung, 2-Position Lockout, 190×45mm
• Wheels | Alloy Hubs & Entity Double Wall Alloy Rims, 25mm Inner Rim Width, Tubeless Compatible
• Tyres | Entity Spiderbait 2.25in Front & Rear
• Drivetrain | Shimano Deore 1×10 w/Prowheel Charm 32T Crankset & SunRace 11-42T Cassette
• Brakes | Shimano MT-201 Hydraulic Disc w/180mm Front & 160mm Rear Rotors
• Bar | Entity Sport Alloy, 760mm Wide
• Stem | Entity Sport Alloy, 45mm Long
• Seatpost | KS Dropper Post, 30.9mm Diameter, 125mm Travel
• Saddle | Entity Void
• Available Sizes | Small (27.5in), Medium, Large & X-Large (29in)
• Confirmed Weight | 14.55kg
• RRP | $1,899 AUD + Shipping

Polygon has built the Siskiu D6 with a Shimano 1×10 drivetrain, hydraulic disc brakes, a dropper post and air-adjustable suspension front and rear.

Setting up the Siskiu

At 175cm tall, I normally ride a Medium in most brands, and that’s exactly what the online size calculator suggested when I inputted by height, arm length and inseam measurements. A few days later our Polygon Siskiu D6 test bike arrived inside a neat, purpose-built cardboard box at my house. While Bicycles Online offers free shipping to metro areas, a quick calculation shows that shipping to my country town would cost me $29 as a customer.

Building up the Siskiu D6 was straightforward, and there are some useful videos on the Bicycles Online website to help you through the process if it’s your first time. You’ll need to install the front wheel, handlebar, seatpost, and dropper lever. You get a torque wrench included in the box, which you’ll want to use for tightening things like the stem bolts and controls on the handlebar.

Cockpit & Suspension Setup

The Siskiu D6 comes with budget Shimano MT-201 disc brakes, which are smooth, reliable and dish out perfectly adequate power. They feature long 2-finger brake levers, which are good for beginner riders who will use both their fore and index fingers for braking. You can run the levers further inboard to facilitate 1-finger braking comfortably, though unfortunately Shimano’s own Deore trigger shifter doesn’t easily sit outboard of the brake lever clamp. As such, I had to settle with having the brakes in the right spot, and having to move my hand to reach the shift paddles every time I wanted to change gear, which was kind of annoying.

However, it also means you can setup the suspension correctly according to your weight.

Both the fork and shock on the Siskiu D6 use air springs, rather than heavier and less-adjustable coil springs. That means if you don’t have one already, you will need to buy a shock pump to adjust the pressure in each. However, it also means you can setup the suspension correctly according to your weight.

On the X-Fusion shock, I aimed for 25% sag. For my 68kg riding weight, 145psi was the magic number, and I set the red rebound dial a click faster than halfway with 7/12 clicks. After a bit of digging on the Suntour website, I found a handy PDF setup manual, which suggested setting the fork’s air pressure at roughly with your weight in kilos. So 68psi it was for me. There’s also a red rebound dial at the base of the right fork leg, but I ended up winding this off all the way to the fastest setting. More on that in a bit.

Polygon Siskiu D6 weight

While the Siskiu D6 comes fitted with inner tubes, the alloy rims are tubeless compatible. However, you’ll need to fit tubeless tape, valves and tubeless compatible tyres, since the stock Entity tyres aren’t designed to be run without inner tubes. So it isn’t the cheapest or most straightforward upgrade. I decided to leave the bike in its stock trim, and setup the tyres with 23psi in the front and 26psi in the rear.

Aside from having a terrific name, the Spiderbaits have actually been pretty good on my local trails. They’re not exactly Minions when it comes to cornering, and the low-profile tread struggles to clutch onto bigger, looser rubble, but the compound is good and they’re predictable on hardpack surfaces – the kind of stuff that’s typical of modern machine-built trail centres.

But the compound is good and they’re predictable on hardpack surfaces – the kind of stuff that’s typical of modern machine-built trail centres.

Still, going tubeless would be a great upgrade to consider down the line. As well as being able to run lower pressures for improved traction and comfort, you’d also drop some rotational weight since this is a pretty weighty bike out of the box – 14.55kg on the workshop scales for our Medium test bike, without pedals.

Testing the Polygon Siskiu D6

Now before going any further, I want to stipulate that testing a bike like this presents a different set of requirements to the bikes that we typically review. Namely that the type of rider looking at a Siskiu D6 is likely to be newer to the sport, and riding very different trails to a more experienced rider on a bike that costs, say $4,000. Still, I didn’t just want to pootle around on bike paths. I wanted to give the Siskiu D6 a proper test to see how it performed on technical trails, in order to find out what the limits of a sub-two grand full suspension bike really are. With that in mind, here’s how it all panned out.

Great frame shape & handling

Without doubt the strongest attribute of the Siskiu D6 is its excellent frame and geometry. It is thoroughly modern for a short-travel trail bike – there’s a 67.5° head angle, 75° seat tube angle, and a decent 445mm reach on our Medium test bike. Great numbers that some of the big brands could do well to take note of.

The slack head angle and long front centre encourage stability, particularly at speed and on the descents. It inspires confidence, which is exactly what you want for a bike that’s going to be piloted by less-experienced riders. The big wheels have plenty of rotating mass to help you build speed and maintain it, while the long wheelbase keeps the whole bike from pitching too violently when rocking and rolling down the trail.

Overall I was surprised at the effectiveness of the rear suspension. It took a good few hours of ride time for the seals in the X-Fusion shock to bed in, but once they had the Siskiu D6 delivered a relatively comfortable and active ride. Sure it’s not the most supple suspension. The basic shock damper struggles to recover on repeat rapid-fire impacts, and I also found myself wishing for an in-between click on the rebound dial. But it does an admirable job of tracking the ground and insulating you from big square-edge hits, and the added progression means I never encountered a harsh bottom-out. Good stuff.

A dropper post? Yes please!

Another big standout is the KS dropper post, which is an absolute boon for the Siskiu D6. Given the bike’s price, the post itself actually works well, and I love that Polygon has spec’d a proper under-the-bar lever. It may be made of plastic, but it still feels more solid than the floppy alloy levers found on generic droppers like those from Giant, Bontrager, Canyon and TranzX. Of course being able to lower the saddle at the press of your thumb means you can more easily shift your weight around when descending, and that does wonders to the confidence levels.

Unfortunately the bar has a very straight profile that’s virtually sweep-less, which resulted in noticeable wrist fatigue on rides over two hours.

For the most part, you get a pretty comfortable riding position. Polygon has matched the long top tube with a stubby 45mm stem and 760mm wide bars. This keeps the cockpit nice and roomy, without stretching you into a torture-rack position of an angry XC race bike. The short stem does make the steering reasonably light, and it can feel a touch floppy at lower speeds. You could temper that with a longer stem, but I think most riders will appreciate the light steering feel. Unfortunately the bar has a very straight profile that’s virtually sweep-less, which resulted in noticeable wrist fatigue on rides over two hours. I’d love to see Polygon spec something with more sweep, and perhaps a bit more rise too.

Going up

Once gravity’s working against you, the Siskiu D6 isn’t the most sprightly of climbers due to its weight. I’m testing another bike at the moment that is literally 5kg lighter (that also costs seven times as much!), and as you’d expect, it’s chalk and cheese between the two. Still, the Siskiu D6 isn’t totally horrendous, partly because the single pivot suspension design is quite efficient under pedalling. There’s a blue lockout lever on the X-Fusion shock, but the back end is stable enough that I only ever used the lockout while riding on the road.

Furthermore, the steep seat angle places you into a fantastic climbing position. Because the seat tube itself is bent around the rocker link pivot, it does mean that the ‘effective’ seat angle changes depending on how high you run your saddle. For my 70cm saddle height, I measured the effective seat angle to be bang on claimed at 76°, which is great. However, riders with really long legs and lots of seatpost extension will see the saddle sit further backwards over the rear wheel, making the front wheel lighter and more difficult to manage on the climbs. The front wheel is already a bit wriggly due to the very short 45mm stem, so it requires some attention on the steep stuff.

It’s a heavy bike with 29in wheels, and less experienced riders will benefit from lower gearing that allows them to sit and spin for longer rather than grind out their knee caps.

1×10 gearing

Though the shift quality from the 1×10 drivetrain is great, it does have a much narrower range than modern 12-speed systems. Whereas SRAM Eagle offers a 500% range, and Shimano 1×12 offers 510%, the 11-42T SunRace cassette delivers just 381%. Personally I didn’t find it to be a dealbreaker – if anything it just pushed me out of the saddle on the steep climbs. That said, I do think Polygon should spec a smaller 30T chainring up front. It’s a heavy bike with 29in wheels, and less experienced riders will benefit from lower gearing that allows them to sit and spin for longer rather than grind out their knee caps.

While I’m on the drivetrain, I have dropped the chain a couple of times. On both occasions I was putting in a few pedal strokes on a rough descent, and the chain bounced off the chainring completely. I’ve since added a bit more tension to the Deore derailleur’s clutch mechanism, but I suspect the overly long cage, which is really designed for a 2×10 drivetrain, isn’t keeping the chain as taut as it could be. Further evidence can be found on the inside of the driveside seatstay, which is peppered with paint chips from chain slap. A small upper chainguide would be a useful upgrade for to keep the chain more secure.

Further evidence can be found on the inside of the driveside seatstay, which is peppered with paint chips from chain slap. A small upper chainguide would be a useful upgrade for to keep the chain more secure.

The fork-shaped object

That aside, the biggest letdown on the Siskiu D6 by far is the Suntour XCR fork. While it does a great impression of looking like a fork, with its air-spring, adjustable rebound damping and lockout, I’ve since discovered that it’s more of a fork-shaped object.

There is a TONNE of stiction in this thing, which means it’s not too fond of sliding up and down. It will compress if it’s presented with the perfectly oriented obstacle, but hit anything remotely off-axis, or put it under load through a corner, and it binds terribly. I suspect this is a combination of both chassis flex and the quality of the internals. Adjusting the air pressure doesn’t seem to help, and I had to run the rebound on the fastest setting, since the fork already has trouble rebounding cleanly as it is. It also seemed to be quite temperature sensitive, feeling even more sluggish on cold mornings.

At slow speeds it feels sticky and unbalanced alongside the relatively smooth rear suspension. At high speeds it struggles to keep up with the rest of the bike, just as things are heating up. It would be tolerable if it were like this all the time, but you never quite know how it’s going to react. There were times when I was descending on a rocky trail and I’d hit something perfectly square-on at speed, and the fork would suddenly plough through its travel, pushing my weight forward when I wasn’t expecting it. A rigid fork would be marginally less comfortable, but at least it wouldn’t dive as violently.

Whereas the back end of the Siskiu D6 feels solid and responsive, the front is flexy and vague, and that results in understeer on faster corners.

On top of that, there’s a lot of deflection through the steel stanchions and quick release lowers. Whereas the back end of the Siskiu D6 feels solid and responsive, the front is flexy and vague, and that results in understeer on faster corners. A more aggressive front tyre would help improve cornering grip, but most of the blame can be placed on the fork.

The juddery suspension performance hasn’t improved over time. If anything, it’s gotten worse in the couple of hundred kilometres I’ve put onto our test bike, and both of my pulverised scaphoids will attest to this. Any ride beyond 20km was incredibly fatiguing, partly because of that very straight handlebar, but mostly because of the choppy Suntour fork.

And I think it speaks volumes to the quality of the geometry on this bike that I’ve been able to ride the trails I have even with a near non-working fork on the front.

On the plus side, I never needed to use the lockout lever because the travel is so stiff already. And I think it speaks volumes to the quality of the geometry on this bike that I’ve been able to ride the trails I have even with a near non-working fork on the front. Yes, the poor fork performance does upset the Siskiu D6’s overall balance, and it’s held me back from seeing exactly what the rear suspension can do. But overall the geometry pulls this bike through a lot.

Is it really that bad?

It’s pretty bad. The thing is though, Suntour does make good suspension. I’m also testing a Giant Stance 29 2 at the moment, and that comes with a Raidon 34 fork that is significantly more supple and responsive on the trail. I know it would lift the sticker price of this Siskiu D6, but I can only imagine how much better it would ride if Polygon had spec’d a Raidon instead.

Perhaps I’m being too harsh on this fork though. Harsher even than it’s been on my wrists. Maybe I’m just being an ungrateful bike tester who’s been spoiled by $10K superbikes and forks that cost the same as this whole bike? Well, yes and no.

Sure this is a cheap bike, and there have to be concessions somewhere to get the price below that $2K barrier. And perhaps the rider who’s looking at a full suspension bike at this price point is only going to ride the buffest of singletrack and the smoothest of dirt bike paths. Maybe the only mountain bike they’ve ridden is a rusty twenty-year old K-Mart special. In which case this Suntour fork, and the whole bike, will feel absolutely amazing in comparison. Certainly on smooth machine-built trails it’s perfectly mediocre, and lower riding speeds are less likely to reveal the limitations of its twangy chassis.

Still, is a full suspension bike the smartest tool for that rider who’s cruising on green trails and bike paths?

Still, is a full suspension bike the smartest tool for that rider who’s cruising on green trails and bike paths? I’d argue that rider will likely be better off looking at a hardtail instead. Something like Polygon’s own Xtrada 8.0, which is a 27.5+ hardtail that that sells for about the same money as the Siskiu D6, would be a terrific option. As well as having significantly better components, it’s also lighter and it’ll be cheaper to maintain in the long run.

How about a fork upgrade?

You could do that, and the frame is certainly worthy of it. And on that note, there’s tuning potential here, since the Siskiu D frame will take up to a 130mm travel fork and it’ll fit 2.6in tyres for those who want to beef it up as their riding progresses.

However, the stock fork uses a tapered steerer tube with quick-release dropouts – a slightly awkward combo that isn’t hugely available in the aftermarket. RockShox does offer the Judy Gold RL in such a configuration for $599, and the X-Fusion Slide RL2 can be had for a similar price. Alternatively, the enterprising Siskiu D6 owner could also scour the 2nd hand market for an older Reba, or even a Fox 32 or 34. And there’s always that person in the riding group who’s upgrading their bike all the time – you could do well to get chummy with them and benefit from some hand-me-down parts.

Polygon Siskiu D6 vs D7

But I’d still say that if you’re looking at upgrading the fork, then you should really, really consider the Siskiu D7. The RRP is $400 higher (though at the time of writing, Bicycles Online has the Siskiu D7 listed on sale for $2,099), and for the extra cash you’ll upgrade to a RockShox Recon fork with thru-axle lowers, WTB tyres and a Shimano XT 1×11 drivetrain. For growing your skills and riding a broader variety of trails and terrain, the Siskiu D7 has more potential and capability built into it from the get-go.

Flow’s Verdict

Testing the Polygon Siskiu D6 proved to be an eye-opening experience for me. Aside from the fact that it’s really, really cheap, there’s actually a lot to like about this bike. It has a great frame with modern, well-considered geometry, and as a result it offers the rider plenty of confidence for tackling varied terrain. The rear suspension is actually quite good, and Polygon has done well to spec quality brakes and a dropper post on a bike at this price. Aside from dropping the chain, nothing came loose or broke throughout testing.

However, the fork totally lets the whole bike down. Indeed it’s bad enough that for any riders who are looking at doing actual off-road riding that involves riding over rocks and roots, I would highly recommend looking at the Siskiu D7 instead. Otherwise have a long, hard think about whether you really need a full suspension bike, or whether a hardtail could be a better match for your riding.

If you must have a full suspension bike though, and you want to spend less than two grand, then there really isn’t anything on the market that competes with the Siskiu D6. It’s living proof that cheap doesn’t have to mean bad geometry, and providing you can accept the fork’s limitations, you’ll enjoy a durable and vibrant entry point into the world of trail riding that has plenty of upgrade potential.