The Polygon Siskiu is a hard hitting 29er trail bike with 135mm of travel and a 140mm fork. Dig a little deeper however, and you quickly discover that this isn’t your typical entry-level full suspension bike that’s been dumbed down for mass production. In fact, it’s one of the best budget mountain bikes out there. 

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Need to know:

• Fox 34 fork and Float DPS shock deliver 140mm and 135mm of travel respectively
• Polygon offers four frame size with a generous 496mm reach on the XL
• Shimano SLX 12 speed derailleur, shifter and cassette, but with a KMC chain
• The in-house Entity components are all top quality.

The Siskiu gets a relatively slack 65.8º head angle for a stable steering response, ultra-short 430mm chainstays to make it easier to loft the front end, and generous reach measurements across the four frame sizes to guarantee a good fit.

And while lots of brands make a big song and dance about custom sizing, but fail to provide short enough seat tubes with adequate dropper post insertion to make it possible to upsize, Polygon has nailed it on the Siskiu T8. With the 430mm seat tube we could comfortably ride the XL bike with the 170mm dropper with room to upgrade to a 200mm post if needed. 

Detailing on the Siskiu frame is also first rate, from the copper highlights under the seat collar that matches the logo on the underside of the downtube, to the one-piece rocker link that adds frame stiffness while maintaining a minimalist, clean look. Even the bespoke chainstay protection looks fitting for a more expensive bike. 

Cable routing on the Siskiu is internal on the front triangle, and thanks to tighter sealing on the entry and exit ports for the cables, there was no noticeable rattle. That’s not to say the Siskiu was a silent runner, however. The large loop of brake hose that’s necessary to prevent it from kinking as it exits the rear brake calliper has a tendency to touch the spokes of the rear wheel after the suspension has been compressed, so it can sound like you have a stick stuck in the swingarm.

Suspension

Getting Fox suspension on a £2k trail bike is quite a boon. And while the 140mm travel Fox 34 Rhythm fork isn’t quite as stout as the 35mm chassis on the RockShox equipped Jamis Faultline, an equivalently-priced bike, it’s only 1mm smaller, so nothing to write home about. The Fox 34 feels responsive and supple off the top, and with a good degree of ramp up it doesn’t bottom too easily on bigger hits.

We measured the rear travel on the Siskiu frame at 136mm, so clearly there’s no rounding up here. The single pivot suspension design is controlled by an inline Fox Float DPS shock. It offers a really usable range of rebound adjustment that will comfortably cover a wide variety of rider weights. Using all of the travel doesn’t require a herculean effort either, so it’s great at soaking up the bigger hits.

You also have a three position compression lever within easy reach. The Siskiu is fairly efficient when pedalling however, so we only used the firm compression settings on really steep climbs to help offset the tipping effect of the super short chainstays. 

Components

From the comfortable Entity Xtent saddle to the copy DMR Deathgrips, the contact points on the Siskiu T8 are totally sorted. The alloy handlebar has a great profile too, while the stubby 35mm stem makes the size XL bike fit more like a size L. In fact, Polygon could probably do with a XXL for riders over 6ft tall.

On paper the Shimano SLX 12-speed drivetrain ticks all the boxes – the wide range 10-51t cassette combined with the 32t chainring easily covering both ends of the speed spectrum. And while the non series two-piece Shimano chainset does not benefit from stiffer hollow forged arms found on Shimano’s higher-end chainsets, you still have the ability to fine tune the bearing preload on the bottom bracket so it should last a little longer. 

One muddy ride was enough to uncover the one box Polygon did not tick when it was completing its Shimano order… and that’s the chain. We know from experience that the 12-speed KMC chains are not compatible with dirt and mud. It doesn’t even need to be that wet for it to feel like you’re constantly pedalling through grit. It’s noisy too, which makes it feel like the chain could explode at any moment.

So rather than waiting nervously for that to happen, we’d recommend spending £20 on a Shimano Deore 12s chain and fit it straightaway. 

The Siskiu T8 is half a kilogram heavier than the Jamis Faultline, and the weight difference is all in the wheelset.  With wide 35mm alloy Entity rims and high volume Schwalbe Hans Damph tyres, they would definitely benefit from going on a diet.

First stop, we’d perform the mtb equivalent of gastric bypass surgery, removing the inner tubes and going tubeless. And while Schwalbe’s SpeedGrip rubber keeps the rolling pace high, simply swapping to our Maxxis control tyres really helped boost traction on sniper roots and rocks hidden under the autumnal blanket of leaves that covered the trails.  

We’d also like to see Shimano brakes added to the original order. And not because the Tektro 4-piston brakes are lacking in power or control. It’s just that if anything does go wrong with them, good luck finding spare parts or a mechanic that’s happy to work on them. 

Performance

After checking the vital stats of the XL Siskiu T8, we were concerned that the short rear end would feel out of sink with the generous 496mm reach…we needn’t have worried. The rear suspension on the Polygon has lots of support at sag, so it helps keep the front end loaded on flatter trails even with the stubby 35mm stem.

In fact, the fit feels really good with this longer reach and shorter stem, so we’d highly recommend upsizing. The flip side of the shorter rear end is that it definitely steps out faster than normal, and while that can be advantageous for snapping the bike around really tight switchbacks, it also highlights the shortcomings of the stock tyres. 

And it’s not just the tyres that limit traction, the rear suspension on the Siskiu isn’t as effective at ironing out bumps as the Vitus, so outright grip and control aren’t as good either. Still, with a relatively long wheelbase and low bottom bracket height, the Polygon feels really stable at speed and you can really smash through big braking bumps without batting an eyelid. 

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