Polygon builds on the success of the popular Siskiu T series analogue trail/enduro bikes, by going all in on a sleek new e-bike version with the same progressive geometry and ride-hard attitude. There are currently only two models in the range and we are testing the top-end Siskiu T7E. But can £4k really get you an enduro worthy e-bike? And is it worthy of a spot on our list of best budget e-bikes? Time to find out.

The Polygon Siskiu T7E was lower and slacker than claimed, not that we’re complaining.

Polygon Siskiu T7E Need to know

• Enduro ready e-bike with a Shimano EP801 motor
• Shimano 630Wh removable battery
• 29in wheels as standard
• Geometry flip-chip for MX wheel conversion
• Fully adjustable SR Suntour suspension
• 150mm travel fork, 144mm travel frame
• Four-piston Shimano SLX brakes
• Shimano SLX 12-speed drivetrain
• Weight 24.62kg (54.28lb) size L

Frame and geometry

The burly aluminium Siskiu T7E frame is designed around Shimano’s excellent EP801 motor and 630Wh removable battery. It comes stock with 29in wheels, but the frame also sports a flip-chip to correct the geometry for an MX setup with a smaller 27.5in rear wheel.

The high shock position corrects the geometry for a 27.5in rear wheel.

Now, given that Polygon offers the Siskiu T7E in four frame sizes, S to XL, and that the flip chip is such a great feature, we’d like to see Polygon deliver the size small and medium bikes with the 27.5in rear wheel as standard, as this would offer shorter rider more room to get off the back of the bike on steeper descents without buzzing the rear tyre.

No expense spared. Shimano’s EP801 motor powers the Siskiu T7E

With a short 435mm seat tube, our size L test bike had plenty of standover clearance. It also had considerably slacker and lower geometry than claimed – 2º slacker at the head tube and 12mm lower in BB height! It was also the only bike in test with a relatively short 445mm chainstay length. Taken together, the Polygon instantly felt like a modern enduro e-bike. No bad thing, right? And that wasn’t the only anomaly. We couldn’t find the claimed frame travel for the Siskiu T7E anywhere on Polygon’s website, but seeing as we measure all of our test bikes, we know for sure that the Siskiu T7E pumps out 144mm of vertical rear wheel travel.

The Polygon needs a longer chainstay protector to reduce chain slap and paint chips.

Overall, the details on the alloy frame are neat. The bridgeless seatstays offer stacks of mud clearance, but we’d like to see the chainstay protector extend all of the way along the chainstay, like on the Decathlon Rockrider in this group test, because even after a couple of rides the paint was chipped next to the chainring where the chain had been hitting the frame. Not only would this protect the frame finish, it would also ensure an overall quieter ride.

Suspension

Most entry-level e-bikes don’t come with all of the top-end suspension bells and whistles. That’s clearly not the case with the Polygon, the SR Suntour suspension offering both adjustable rebound and compression damping and then some. The piggyback Suntour TriAir2 3CR rear shock features rebound adjustment and a three-position compression lever to firm things up for climbing.

There’s a second air valve on the shock piggyback for adjusting the  IFP pressure. The what?

And if you want to get really techy, you can change volume spacers in the air can and adjust the pressure and overall damping curve, by playing with the air-spring backed IFP. If you don’t know what the IFP (internal floating piston) does, don’t fret, as you don’t need to adjust it, but be aware that it has to be kept within an operating pressure range of 170-200psi for the shock to function correctly. Now, given that most high-end shocks don’t allow riders to mess around with the IFP pressure – because riders are prone to messing it up – it’s probably not a good idea to have it on an affordable e-bike.

With a 35mm chassis, the 150mm travel Suntour Aion fork is plenty stiff enough.

Up front, the Suntour Aion 35 RC fork has 150mm travel, and again it is air sprung, and comes with rebound and compression adjustment. Out of the box the fork feels really smooth and composed. Maybe not as buttery smooth as the RockShox Lyrik on the Yamaha Moro 07, but definitely more composed than the basic RockShox 35 on the Giant Stance E+1 when you get into faster, choppy terrain, where the fork has to recover quickly from each successive impact.

The 15mm Q-Loc axle is fast and easy to use, once you know the correct technique.

As the name suggests, the Aion 35 fork has 35mm upper tubes and it also gets a 15mm Q-Loc axle to improve chassis stiffness and steering precision. Just be aware that there’s a specific technique for the Q-Loc axle, so read the instructions, as it’s really fast and easy to use once you know how it works. It’s also worth removing the axle and greasing it regularly, just so it doesn’t seize into the hub or dropouts.

Components

When an e-bike weighs the best part of 25kg, and has geometry akin to an enduro rig, you need really good brakes. Thankfully, the 4-piston Shimano SLX units on the Polygon deliver. They didn’t exhibit the variable bite point that Shimano’s XT and XTR units are prone to, instead we were treated to ample braking power and good modulation with just one finger covering the lever.

Shimano’s 4-piston SLX brakes are a great set of anchors.

And this is important, as it leaves three fingers and a thumb to form a tight grip with each hand on the handlebar for improved control. Best of all, any bike shop will be happy to service or bleed Shimano brakes, while the same is not always true of the Tektro brakes on the Rockrider and Giant in this group test.

Schwalbe’s Super Trail casing is great, but the Polygon needs softer compound tyres.

In fact, the speed modulation limiter on the Polygon is ultimately the harder compound 2.6in wide Schwalbe Hans Dampf Evo tyres. If you’re into mile-munching, then the hard compound will extend the life of the 630Wh battery, but given the attitude of the Siskiu T7E, it really needs softer compound tyres as standard to unlock the bike’s full potential.

In a blind test, Shimano SLX feels just like XT, minus the double-downshift feature

We’re not convinced that e-bikes really need 12-speed drivetrains, but it is really useful to have the wide-range 10-51t cassette on the Polygon, especially when you’re in Eco mode trying to eke out the miles. That big 51t cog is also really handy for conquering crazy steep climbs in Boost mode. All of the Shimano SLX kit worked flawlessly, but we suspect that the KMC chain will cause problems when it starts getting muddy.

The short stem puts the rider in complete control.

The cockpit on the Polygon is totally dialled. The stubby 35mm stem, 780mm bar and 170mm dropper post are all on point. Even the imitation DMR Deathgrips are excellent. And while the cool kids and park rats like to have the nose of their saddle pointed up, be sure to run the saddle on the Polygon flat, as this makes seated climbing that much more comfortable.

Performance

Some test bikes you simply gel with straight away. The Siskiu T7E was one such bike. With progressive geometry, composed suspension, a great specification, and a Shimano EP801 motor, the Polygon Siskiu T7E looked set to be the runaway success in our Affordable E-bike test.

Climbing

With the Shimano EP801 motor delivering 85Nm of smooth, controlled torque, the Polygon does not shy away from the steepest climbs. It has limitations, though. Namely, the harder compound Schwalbe Hans Dampf rear tyre struggles to maintain traction in both wet and dry conditions. Also the distinct lack of overrun with the Shimano EP801 motor makes it more difficult to navigate really technical climbs.

Getting the power down is easy, maintaining traction, less so.

Basically, when you stop pedalling the Shimano motor cuts out, rather than powering you forward a little longer, like on the Brose and Yamaha motors in this test. So, if you momentarily stop pedalling to hop up over a rocky step or fallen tree, you don’t get that extra push from the motor, which can be really helpful to get you up and over any awkward sections. Especially on a heavy e-bike. Also, because the frame geometry of the Polygon is considerably slacker and lower than claimed, you’ll probably want to run the flip-chip in the high setting, even with the 29in rear wheel, if you live anywhere with rocky, techy climbs, as you’ll be forever clipping pedals in the low geometry setting.

Descending

If you spin up fire roads to access the best trails, you will not be complaining about the lower/slacker geometry of the Siskiu T7E, because it strikes a really good balance between stability when going flat out, yet it’s still agile enough for low-speed tech. Yes, you’ll also moan about the harder compound tyres within the first few turns, but even the distinct lack of traction wasn’t enough to prevent us from having a total blast on the Polygon. From the smooth, loamy trails of the Surrey Hills to the white knuckle runs at BikePark Wales, the Polygon impressed us with its composed handling and dialled geometry. At least until it all went pear shaped…

Strap in. The Polygon Siskiu T7E offers a blisteringly fast ride.

Jumping into a rooty section of trail at BikePark Wales, our biggest e-bike fear became reality; the 630Wh battery pulled the ejection cord, dropping out of the down tube and hitting the front tyre before bouncing down the trail. Our first thought was ‘lucky it didn’t happen on a big jump’. Then we thought, maybe we hadn’t located the battery properly in the frame, so we slammed it back in and continued riding. Then it happened again in another jarring section… and again.

Belt and braces. We ran a tool strap around the battery for extra security.

So we left the battery in the van and jumped back on the uplift. The bike felt completely different now, and we quickly realised that all of the damping in the Suntour TriAir2 shock had disappeared. So that was it for that day of testing. Pedalling back to the van we were reminded how the Shimano EP801 motor has very low pedalling resistance when you have no assistance from the motor, and it was probably the only time during the test that we were thankful of the faster rolling Schwalbe tyres.

The Polygon Siskiu T7E does it all, and more of it too, thanks to the 630Wh battery.

Go Outdoors promptly sent us a replacement shock, and a Shimano tool to check that the battery latch had been fitted and adjusted correctly. It wasn’t, which explains why the battery was falling out on bigger impacts. Still, we used a Velcro tool strap around the down tube on subsequent test rides just to ensure that the battery wouldn’t part ways with the frame again. We also noticed on social media that some Polygon riders have adopted a similar approach. Better safe than sorry, right? Especially given that we could ride the Polygon way harder than any other bike in this test.

With better tyres, the Polygon Siskiu T7E could have bagged a 10/10 rating