Review: Prime Thunderflash - A Standout Enduro Bike

Bred for enduro racing, the Thunderflash rolls on 29” wheels exclusively and employs a 64-degree head tube angle. Full build kits are available in three sizes and two colors, starting at $7,999 with Öhlins suspension. Soon, the direct-to-consumer model will evolve to include a dealer network through Europe, Canada, USA, Singapore, Philippines, and Chile.

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Contents

Frame Details

Arguing that the Thunderflash isn’t striking would just be trolling. Sharp shapes run throughout the frame and it's topped off with a two-tone fade and splatter-finished, hydrophobic paint job.

Prime’s technical expertise came from Cero Designs to build a full-carbon, dual-link suspension platform, and VIP Composites to manufacture the frame. The dorsal-shaped seat mast is a Cero signature touch and can be found throughout their other work, like with Unno and Intense. This one is finished with a clever rubber grommet to seal off gunk from entering the frame, which comes with a lifetime warranty.

Finer linkage details include hidden pivots at the seatstay/rocker link, sealed bolt-heads to shield against water ingress, and double-row bearings on the drive side to increase lateral rigidity. There's even routing for a remote shock lockout that exits below the bottle cage.

Commonplace specifications like a 205x65mm Trunnion mount shock, Boost 148 hub spacing, a threaded bottom bracket, and a 180mm post-mount brake adaptor make component alterations or replacements simple and easy to source.

There’s also plenty of chain damping throughout the rear triangle and a slick fender is tucked between the dual-upright seatstay braces. Under the downtube lies a bolt-on guard and fork-stop bumpers, which double as the housing entry port at the head tube. This particular headset from Acros features a steering lock, although a traditional style could be used, depending on the fork offset and frame size.

Fully guided internal cable routing runs the full length of the frame and takes a convoluted, but secure route, exiting out of the downtube and through the shock basement. The housings are clamped to both the lower link and entry points to the rear triangle. Changing the housing or brake lines requires removing the upper Trunnion shock bolts and holding the rear triangle up and out of way.

Suspension Design

Prime’s SHRED-Dynamics dual-link design equates to a smooth progressive leverage curve that they say works well with either an air or coil-sprung shock. A 65mm stroke shock is used to achieve 165mm of rear wheel travel with a leverage ratio that starts at 3.11 and ends at 2.3.

Special attention is paid to the balance of the bike at sag, which can be tuned to run between 30-40%. In this zone, the Thunderflash earns roughly a 110% anti-squat value in the tallest 50-tooth cog and 30-tooth chainring.

Geometry

Skimming the geometry chart reveals just three frame sizes to accommodate riders between 165 and 202cm. The reach numbers span from 460, 480, and 505mm; all use 445mm chainstays. The size large gets a 443mm seat tube and has ample standover clearance.

Unweighted, the Thunderflash’s head and seat angles seem fairly straightforward at 64 and 77.8 degrees, but Prime devised a dynamic ride balance for the bike, which we’ll discuss later on.

Specifications

Since this is a boutique carbon bike from Europe, don’t expect there to be a budget build or alloy frame option. Two color choices exist in either a blue/black combo or the gray/black test bike. A frame only (excluding the shock) rings in at $3699 USD but includes the Acros headset and an e*thirteen skid plate.

Build kits start at 6,999€ using an Ohlins 38 RXF fork, TTX Air shock, Bike Yoke Revive post, Industry Nine alloy wheels, and a full SRAM GX drivetrain. Oddly enough, all builds are spec’d with some variation of SRAM’s G2 brakes, which were somewhat underwhelming for this big-travel enduro bike.

Our size large S-build costs $7,999 USD and weighs 14.8 kg / 32.6 lb stock with a Maxxis EXO+/DD tire casing combo. Moving up the pricing ladder, the drivetrains graduate to full mechanical X01 and Ohlins TTX 22 M.2 coil shock options for a grand total of $8,999.

Climbing

Pedaling enduro bikes uphill does not have to be a taxing job, especially when you’re on board the Thunderflash. The lightweight build and 500% range, along with a 30-tooth chainring, make that job a breeze; there’s a special balance that keeps it settled without scraping the ground.

Geometry also adds to that zest, placing you in an upright position with a solid perch to sweat out long climbs. The longer chainstays and substantial anti-squat save you from slipping traction and slouching backward, resulting in a strong climbing posture. There’s no need to kiss the stem when the grade increases.

Similarly, cleaning tight switchbacks can be done without exaggerating your weight over the front wheel. Although that’s not where I’d choose to win battles on an enduro bike, the versatility of a moderate 64-degree head tube angle comes in handy in those situations.

I thought that the 25mm of bottom bracket drop and the progressive suspension would make the Thunderflash a ground-hugger through technical climbs, but it actually performs beyond what the geometry states. 170mm length cranks didn't graze the ground too often, despite the Ohlins TTX Air shock having a firm compression lever rather than a full lockout.

Descending

Stance - it’s a word that I’ve mentioned a few times which refers to how the bike sits under the rider’s weight. Prime calls it SHRED Dynamics, but I think they’ve nailed the overall prowess of the Thunderflash.

Often, bikes that are too progressive can feel unsettled through the beginning of the travel and ramp unexpectedly over consecutive square-edge hits. I didn’t find that was true here because I typically prefer a long-travel bike with less progression.

Once I found the optimal balance between enough sag to sit in the bike and not dive into the beginning of the travel, the Thunderflash became one of the stand-out rigs I’ve ridden in the last year. There’s enough small bump compliance that it doesn’t hang up at low speeds, but also doesn’t wallow through the mid-stroke either.

Versatility is one of the Thunderflash's highlights. However, a few numbers had me doubting its all-out downhill capabilities at first, primarily, the moderately slack 64-degree head tube angle and the lengthier 445mm-long chainstays.

Just because the overall weight is on the respectable side for this build, doesn’t mean that the Thunderflash isn’t a burly bike. In fact, it’s quite the opposite. The frame is plenty stiff but the suppleness allows the rear wheel to track rough, rooty, off-camber sections and still hold strong in sharp corners and compressions.

Again, the balance between the axles and actual bottom bracket ride-height kept me confident, descending “in the bike”, yet didn’t sap speed while popping rhythms on flowier trails. I had no issue leaning it into turns thanks to that steady, low center of gravity. You can drive through corners and compressions with your feet because your center of gravity lies low in the bike. That's another reason that the head angle doesn’t need to be overly slack here.

Under braking, there’s no need to hang off the back and upset that centered position and the suspension is still active while on the binders. There’s no sense of firming up or squatting into the travel at all.

Picking out flaws in the Thunderflash requires looking beyond the ride characteristics. There’s plenty of rubber protection against the typical chain oscillations, but on occasion, a large impact would result in the odd “whack”. Debris can build up below the shock, and that cable routing is smart in theory, though tedious to replace when the time comes.

Since it was hard to fault the Thunderflash, I was curious to explore what a -1-degree headset from Works Components would do for two reasons. First, I wanted to shorten the reach and gain some leverage over the front of the bike. Secondly, to see what doors the extra slack Thunderflash would open up on descents by stretching the wheelbase. Basically, this led to geometry very similar to Transition’s Spire, just 10mm shorter in reach - a closer fit for my height.

Those resulting changes led to ride characteristics that I expected. In straight lines, the cockpit of the Thunderflash felt slightly smaller, giving me more strength and range of motion to attack in steep zones. One downside, was that the increased front center length required more planning to navigate hairpin corners and some slight understeer on flat, unsupported corners. As always, there's a trade off to each change and for the purposes of enduro racing, the stock geometry is dialled.

Technical Report

Ohlins 38 RXF Fork: This may just be my favorite fork on the market for enduro bikes. A huge selling feature to me are the two air chambers; one for the positive/negative spring and the second to control the ramp-up without the need to install volume spacers. Fine-tuning between the two chambers can take a little more time to initially set up, so a digital pump is necessary, but the clickers do have fewer indents than other brands. That helps to find the right spring rate first and fiddle with the damper later. The chassis is also much stiffer than the 36 RXF and has a lower axle-to-crown height.

SRAM G2 RSC Brakes: I’m a huge fan of powerful brakes. You spend less time using them and that leads to less arm fatigue and a smoother operating bike. These G2s held back the descending capabilities of the Thunderflash massively and were exchanged early on.

Renthal Apex Stem: Stems don’t have elaborate jobs. They just have to stay quietly in place. Even with some Ti prep paste smeared under the bolt heads, the odd creak would cry out when maneuvering the bike around. I dig the looks of the Apex stem and love how the clamps hold themselves in place on the bar during installation.



How Does It Compare?

Transition calls their 170mm Spire a “nimble bruiser”, and that’s just what the Prime Thunderflash is too. The 29” wheels keep both of these bikes rolling fast over stutter bumps at low speed, the overall weight isn’t a burden uphill, and the geometry holds your center of gravity low and in the middle of the bike.

With a 63-degree head tube angle in the high setting, the Spire does have a slight edge up on the Prime for attacking when the trail tips straight down. On the other hand, the slightly shorter front-center and steeper head tube angle let the Prime dance through switchbacks and pinch points on the trail at a moment's notice.

The Thunderflash’s dual-link design wins out in terms of suppleness too. I found there was less compromise in the setup when it came to balancing and absorbing trail chatter. The Spire either ran a touch harsher off the top with more pressure or sat much deeper in the sag to get that light action at the start of the travel. Another difference that might not be everyone’s cup of tea was the Thunderflash’s stiff frame. I wouldn’t say that the Spire was flexy, though, just slightly softer when loading the bike to dig into a corner.

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Pinkbike's Take

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Posted In:
Reviews and Tech Reviews Enduro Bikes Prime Bicycles Prime Thunderflash