2026 Polygon

Siskiu D5

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.  Best mountain bikes: the ultimate trail, enduro and XC bikes 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 …Continue reading »

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