Transition Spire Alloy NX review | Enduro Bike of the Year contender

Transition is known for building exciting bikes that are a blast to ride, with something in the line-up to suit just about everyone – from aspiring World Cup racers to those looking to hack about in the woods.

The 170mm-travel Spire is Transition's “nimble bruiser”, delivering the type of pedal efficiency you’d find in a shorter-travel bike, but with downhill rig capabilities when you want to drop into something more challenging.

There are four builds available; two using the pricier carbon frame and two built around the more wallet-friendly alloy option.

The cheapest available is the alloy NX build, as tested here.

As you’ll soon read, this Enduro Bike of the Year contender has proven to be a solid performer in a plethora of different terrain.

Its geometry is up there with the best enduro bikes and makes for a seriously confident ride on the descents, as well as being a surprisingly comfortable climber.

While there’s no getting away from how capable the Spire is, some elements of the spec on the NX build hold it back when you start pushing it hard.

Transition Spire Alloy NX frame and suspension details

The Spire comes with either a carbon or alloy frame and uses Transition’s GiddyUp four-bar linkage suspension system.

This dictates how the 170mm of rear-wheel travel gets doled out. And while all bikes are only available with an air-sprung shock, Transition says the 23 per cent of progression built into the system means the Spire is more than happy being paired with a coil shock, if that’s what you prefer.

If 170mm sounds a like a little too much travel, but you still like the idea of the Spire, you can switch out the 205x65mm stroke shock for a shorter 205x60mm shock, reducing the rear-wheel travel to 160mm.

At the other end of the scale, should you want to get even more extreme with your riding, Transition rates the Spire as dual-crown fork compatible on both the carbon and alloy frames.

Other details of note include 2.6in rear tyre clearance, loads of rubberised frame protection in the areas that matter, a gear accessory mount on the underside of the top tube and the use of SRAM’s Universal Derailleur Hanger. This should help make finding a replacement a little easier, no matter where you are in the world.

Transition Spire Alloy NX geometry details

A flip chip at the lower shock mount enables you to switch between the high and low settings, most notably altering your head and seat tube angles by 0.5 degrees and the bottom bracket height by 7mm.

In the low setting, I measured the head angle to be 63 degrees and front centre a generous 815mm.

This is matched to the long 448mm chainstays at the rear – the longest chainstay measurement within the 2024 Enduro Bike of the Year test. These grow longer on the XL and XXL frame sizes.

With my saddle set to my preferred pedalling height on the medium frame (I’m 172cm), the seat angle measured around one degree steeper than stated on the geometry chart, at 79.9 degrees.

Reach, again in the low setting, is a healthy 455mm.

The low bottom bracket boosts overall stability and is lower than stated on the geometry chart, at 335mm off the floor.

Transition Spire Alloy NX specification

The Alloy NX bike is the cheapest available and, as the name suggests, comes with SRAM’s NX Eagle 12-speed drivetrain.

While you still get 12 gears to choose from, the cassette range isn’t quite as wide as that of the more expensive GX Eagle equivalent, due to the 11-50t spread, versus the 10-52t range you’ll find on GX.

SRAM also supplies its Code R brakes, and it’s great to see Transition has opted for a massive 220mm front disc rotor to try to maximise stopping power.

A Fox Float X Performance shock is paired with a Marzocchi Z1 air-sprung fork up front. This fork uses 36mm upper tubes and a GRIP damper to control the 170mm of travel.

The other three bike builds in the Spire line-up all use forks with 38mm upper tubes, which are generally stiffer.

Tyres come from Schwalbe in the shape of the reliable Magic Mary up front and the Big Betty at the rear. Both use the brand’s ADDIX Soft rubber compound and Super Trail casing.

A Race Face Chester bar and Aeffect stem take care of steering.

It’s great to see the OneUp Components dropper post specced here, even on the cheapest model available. This post has always scored highly in tests and it’s an asset on any bike.

In total, the Spire Alloy NX bike seen here weighs 16.77kg in size medium, without pedals.

Transition Spire Alloy NX ride impressions

I rode the Spire on a wide variety of trails around the South West of England and South Wales.

Conditions ranged from cold and dry through to wet and then even wetter over the course of the test period.

The trails I rode varied more than the weather, spanning everything from natural, hand-cut steep, technical descents covered in roots and rocks through to high-speed jump lines in the bike park – along with everything in between.

Transition Spire Alloy NX setup

Setting up the Spire was a quick and easy affair.

Transition recommends a sag window of 27-33 per cent at the rear. I opted for 30 per cent, which equated to 145psi in the shock’s air spring for my 68kg weight, and left both volume spacers in the shock throughout testing.

Up front, I found 63.5psi in the fork with the adjusters fully open provided a good balance with the rear end. I also ended up leaving the pre-installed fork volume spacer in place.

Transition Spire Alloy NX review climbing performance

As you’d expect from a bike with such a steep seat tube angle, the Spire sits you nice and upright, over the bottom bracket.

This isn’t just comfortable, but feels efficient, too, especially when grinding your way up steeper inclines.

Here, the long back end helps too, ensuring the front end never gets too light or wafty as gradients steepen. This saves you from having to shift your weight forward to counter it – something that can become tiring on long days out.

When seated, as you turn the cranks, the back end of the bike remains nice and calm, with very little suspension bob wasting any of the energy you’re feeding in through the pedals.

It helps that the Schwalbe tyres roll at a decent speed, too. So, while not as tacky as many of the Maxxis tyre combinations found on the other bikes in this category, they help make battling against gravity that bit easier.

As and when you need to make gear changes, the NX drivetrain doesn’t feel as slick as the Shimano equivalent at this price.

I also had numerous indexing issues throughout testing, which came to the fore when scrambling up steep inclines, trying to panic shift at a moment's notice.

Transition Spire Alloy NX descending performance

As soon as you wind the Spire up and unleash it on a high-speed trail, it instantly feels easy to ride fast.

The suspension is supple but balanced, with enough support to ensure it rides lighter and more energetically than the amount of travel and overall weight might have you believe.

Its geometry positively encourages confidence. You’re well centred between the wheels, low to the ground and can tuck in behind the slack front end ready for whatever’s coming your way.

The stance on the bike feels solid and stable, offering a commanding position to feed in small weight shifts here and there when needed, to keep the bike tracking the desired line.

On fast, hardpack tracks, the Spire’s turn of speed makes it an exhilarating bike to ride.

Despite the balanced, supple suspension, though, there’s still quite a direct feel when things get really rough or the impacts become repetitive.

While this might not be an issue on slower-paced, natural technical trails, smashing through rock fields in the bike park provides more in the way of feedback through the bike, especially through the front end.

It’s not harsh or as uncomfortable as some can be, but there’s scope to improve things and extract even more from the Spire.

Switching to a more forgiving handlebar could certainly help take the edge off things here, along with a softer, better-damped front tyre.

Just as I experienced with the Fox 36 Rhythm fork on the Trek, the Z1 here is incredibly comfortable, soaking up chatter and medium-sized hits with ease. Push harder, though, and the Z1 sinks through the second half of its travel a little too quickly.

I played with fork spring pressure and setup to try to resolve this, but ended up back where I started, simply because going too soft limited the support I was after. Going too firm meant comfort deteriorated further, as well as throwing the suspension balance out. This became really noticeable through flatter turns.

There’s plenty of tuning potential with the GRIP damper, though, which will set you back a reasonable £120 for a service and around £50 for a custom tune.

These issues are far from the end of the world, though, and quite easy to forget when you’re skipping, hopping and launching the Spire down the trail.

It helps that it carries speed so well, hammering through nasty sections of track without flinching and firing you out the other side with your momentum almost totally intact, even if your hands might not feel as fresh as they could.

Tipping the balance

Away from high-speed bike park trails, the Spire continues to feel like a surefooted beast of a bike when pointed down something steep and technical. There’s still room for improvement, though.

Although the tread pattern of both Schwalbe tyres works well in the mud, I’d have preferred an even softer rubber compound up front, for better traction on wet rocks and roots, plus improved damping.

It’d also be great to have a tougher, more robust Super Gravity casing rear tyre in place, rather than the lighter Super Trail used here. This would not only give more protection when slapping through jagged rocks, but also better carcass support.

Small changes such as this feel as though they’d unlock even more potential from this bike.

That said, the Spire still feels composed as it tracks through a turn. Tip it over, let the tall shoulder knobs of the tyres dig into the soft mud and you can hold some seriously technical lines – if you’ve got the bottle to commit to them.

It helps that the easy-to-initiate suspension enables each wheel to flutter over trail imperfections, keeping the Spire glued to the track.

The big 220mm front disc rotor helps in this terrain, too, enabling you to be forceful and deliberate with your braking thanks to the power on tap, rather than dragging them unnecessarily.

As confidence in the steeper sections creeps up, the fork’s limitations can become evident here, too, but only when you’re really pushing it.

How does the Transition Spire Alloy NX compare to the Trek Slash 8 Gen 6?

For £50 less, the Trek Slash 8 Gen 6 is a formidable opponent to go up against.

Both bikes use an alloy frame – and both have a Fox Float X rear shock and forks that feature a GRIP damper.

Similarly, both bikes have room for improvement when it comes to tyre selection, although I’d much prefer the Spire’s Schwalbe combo over the Bontrager XR5’s found on the Slash – they’re tougher and far grippier.

As you push the limits of these bikes, the issues highlighted above concerning the Z1 fork are shared with the Fox equivalent on the Trek.

There’s no denying, though, that both bikes are incredibly fun to ride and easy to ride fast. They’re dynamic but still seriously capable when things get rowdy.

I’d take the Slash over the Spire in this specific instance, though. That’s down largely to how impressive the rear end of the Slash performs, and how composed and comfortable it feels at pace on a roughed-up section of trail. The Spire is impressive, but the Trek just has the edge, even with some spec flaws.

Transition Spire Alloy NX bottom line

The Spire is a bike that’s comfortable to ride fast, straight from the off, balancing high-speed stability nicely with a dynamism and playfulness that ensures no trail is ever dull.

Its geometry works incredibly well, while the suspension feels balanced and, for the most part, extremely capable.

There’s more performance to be extracted from this impressive frame, though, and making some slight spec tweaks here and there – as well as getting the fork tuned could elevate this capable bike even higher.

It’s a blast to ride, though, despite the niggles.