3T Exploro Ultra Boost electric gravel bike review

It’s hard to imagine, given the ever-increasing popularity of gravel riding, that there was a time, not so long ago, when this particular area of cycling was considered niche. To say it’s now established and here to stay would be something of an understatement. That’s why companies like 3T are tilting their traditional gravel bikes, in this case the Exploro Ultra Boost I’ll review here, to have a gentle pedal-assist that will propel your adventures much deeper into the countryside.

Data from Strava shows that gravel cycling was one of the fastest-growing global sports on the platform, with a 55% year-on-year increase in athletes recording gravel rides between 2023 and 2024. During the same period gravel bike sales in the UK rose by 15%, reaching over 30,000 bikes sold. You might be thinking ‘that’s great, but what’s it got to do with the 3T Exploro?’

It’s a fair question. And the simple answer is this: had it not been for the continued growth of gravel cycling, bikes like the 3T Exploro, and many others, simply wouldn’t exist. Rewind a few years and most brands might have offered one or two gravel models at best, and almost certainly not an electric option. Fast forward to today and the 3T Exploro is just one of three different e-bikes the Italian brand now offers.

3T Exploro Ultra Boost review: The headline details

£5,700 | See range

ProsFast and agile handling Aero frame designed for speed without compromising comfort Easy to use assistance button Smooth delivery of assistance on all three support levels Lightweight at under 14kg High frame clearance allows for much wider tyres Excellent range on battery

Cons The seat post clamp is badly designed and not easy to use or adjust.

SpecificationsMotor: Mahle x20 rear hub motorBattery: Mahle iX350 350Wh internalRange: With 171Wh extender, up to 200kmFrame: Unidirectional Pre-preg carbon fibre Weight: 13.2kg Brakes: SRAM ApexGearing: SRAM Apex Eagle Max 52T 12-speedTyres: Pirelli Cinturato Adventure 700×45Wheels: Rody Allloy 700cSaddle: Selle Italia Novus Boost Evo Superflow

3T Exploro Ultra Boost review: On the trail

For the sake of context it’s worth mentioning that I’ve been riding gravel bikes for a number of years now. Not quite as long as those grizzled mountain bikers who claim they were the original gravel riders, but certainly long enough to remember a time when saying you preferred dirt tracks to paved roads would earn you some funny looks at the local cycling club meet-up. So when the opportunity of testing the 3T Exploro came up I was rather eager to see how adding in electrical assistance would change my gravel riding experience.

Let’s start with the frame, as really this is the heart of the bike in every sense of the word. Based on one of 3T’s main gravel bikes, the Ultra, it marries aerodynamic geometry with a road-inspired riding position to offer the same speed, agility and off-road capabilities of it’s non-electrical brother, only with the additional assistance offered by the excellent Mahle X-20 system, more on that later.

With gravel racing very much the modern day trend there are an increasing number of bikes that blur the line between road and gravel bike, with some simply being excellent road bikes with slightly sturdier wheel sets and knobbly tyres to handle the rough stuff. The same is now true of e-gravel bikes, with the 3T Exploro being the perfect example. Not that this is necessarily a bad thing, as after all some of us want to go fast, and others far, and thankfully there are bikes for all tastes and types of gravel.

Yes, you read that right ‘types of gravel’. You see, much like roads, gravel surfaces come in all degrees of roughness and not all bikes are suitable for all of these varying surfaces. Take the Exploro, for example. Given its geometry, it’s a dream to ride on what I call champagne gravel, that is to say hard hard-packed and fairly smooth tracks, whereas once things get a little lumpier, it’s not so much fun. However, with the ability to run 60mm tires, you can always gain a little extra comfort if you’re prepared to compromise on the speed front.

What does add to the fun though, is the 1.39kg rear-hub Mahle X-20 system that provides 55Nm of torque, taking its energy from a 350wh battery and adjusting via feedback from both torque and cadence sensors. This is a smart motor that has AI and machine learning qualities, so it will adapt and improve its pairing to your riding style and environment as you ride with it. If you pair this to the 171Wh range extender, Mahle's estimate is that you could get up to 200km of assisted cycling, albeit that would be in optimal riding conditions with light reliance on the motor.With three different assist levels, all controlled with relative ease through a button on the top tube, it means that you can seamlessly switch from fast, flowing tracks to long mountain climbs without missing a pedal stroke. I was impressed with the responsiveness of the assistance, offering a natural feeling to the pedal stroke even when opting for full assistance.

However, for me the most impressive part of the Mahle X-20 system is what it can do compared to its weight. At just 3kg for the entire system it allows bike manufacturers to offer high-end performance bikes as low as 10kg in weight, which translates to fast and agile e-bikes ideal for those who crave the thrill of speed. For the record, the Exploro starts at roughly 12kg, depending on frame size and your specific components.

Add this to the aerodynamic geometry and what you get is a bike that handles supremely well, remaining agile and responsive on all but then roughest of terrain. The smoothness of the power delivery helps with this. Unlike some e-bikes, where the motor’s boost can feel jerky, the Exploro’s assistance is subtle and natural. And even when you don’t have the system engaged there is a smoothness to the pedal stroke with no feeling of drag to slow you down.

On the topic of being slowed down, there’s no such issue with the Exploro when you do have to take it on the road. Its aero design and stiffness are more in keeping with a road bike in the first place, one of the benefits of that blurring of genres. This ensures that getting to the gravel you crave in the first place is fast and fun, as all riding should be in my opinion, and then once you’re there the bike really comes alive.

There is, however, no such thing as a perfect bike. At least not in my opinion. My biggest issue with this bike focuses on one of the smallest parts, the seat post clamp, and unfortunately, it’s a big enough issue to be a deal breaker for me. It slots into a little space at the front of the seat post in the top tube, making it very awkward to adjust with a multi-tool. 3T uses a self-aligning wedge inside the frame to keep the post straight and apparently this requires a lower torque to secure. Yet, even when tightened to the suggested torque setting, I still had consistent issues with the seat post slipping while I was riding. There’s nothing like having to stop to raise your seat to kill the buzz of an otherwise great ride.

The design is said to use a self-adjusting bolt angle for higher clamping forces with lower torque, while keeping a round seat post, despite the aero seat tube, to allow for more dropper or suspension post options. Personally speaking, if you’re going down the route of dropper and suspension posts, you should be looking at riding a mountain bike anyway, so this mish-mash of designs seems unnecessary and, to my mind, detrimental to the end product.

3T Exploro Ultra Boost review: Who will love this gravel bike?

So the question is this; who is this bike for? Ultimately we all want something different when it comes to riding off-road and thankfully there are now a wide range of bikes to cater to those desires. With its lightweight, aero build, excellent motor system and aggressive tires the 3T Exploro is a fast, versatile e-gravel bike that delivers an exhilarating ride for those looking for fast-paced off-road adventures.

Not only that, but the Mahle X-20 system ensures that it is a more than capable climber as well, opening up a huge range of riding options for those who want to explore far and wide. As the bar tape neatly reminds you, the world is a book and those who do not travel read only one page.

3T Exploro: How about the competition?

Finished our 3T Exploro boost review? Here's a handful more e-bikes in the gravel segment to consider, alongside our dedicated buyer's guide to the category.

Rondo IOON (review)

One of the most striking pieces of bike design we have had the pleasure to ride, the Rondo IOON is another unashamedly premium, lightweight and very capable offering. This time it's the Fazua Ride 60 mid-motor providing a greater grunt than the hub motors can hope to. The IOON also packs a good-sized 430Wh battery in the carbon fibre downtube.

Scott Solace Gravel eRIDE 20 (review)

Alternatively, the Scott Solace Gravel eRide utilises TQ's tiny mid motor, which weighs very little, takes up next to no room and packs a punch. With that small form factor the Solace looks just like a standard gravel bike, albeit one with 50mm wide tyres, making it an expertly capable vehicle for deep countryside exploration. It's a bit more expensive at £6,999, but worth looking at if you're spending in this region.

Merida eSilex 600 (review)

Finally, if you want to shave a ton off of your bill, but still retain a decent capability, Mahle's x30 motor powers the £2,750 Merida eSilex+ 600.We like this bike because it has plenty of on-bike storage, is well specced in terms of components for the lower price and is compatible with a range extender to bolster the included 250Wh capacity.