Factor Ostro Gravel review
Dec 12, 2023
Race-ready, aerodynamic and made for gravel
This competition is now closed
By Warren Rossiter
Published: June 7, 2023 at 5:00 pm
Factor says the Ostro Gravel takes the ‘win-everywhere’ mentality from the brand's Ostro VAM road bike, and applies it to the gravel riding scene.
In keeping with the WorldTour-proven machine, Factor says it has been "developed to dominate its category with incredible aero, superior handling, high stiffness and low weight".
There's no denying the Ostro Gravel is fast, stiff, responsive and very well put together, but the overly aggressive geometry and firm ride mean its appeal could be limited slightly.
You can see the influence of the Factor Ostro VAM in every inch of the Ostro Gravel.
It shares the same aero-optimised fork/head tube interface, and the same aero-shaped down tube and seat tube, along with a common aero-bladed seatpost.
Details on the frame include the cavity in the down tube's underside, which Factor calls a ‘reversing flow energy channel’.
Factor claims this shape completes the flow, starting on the underside of the fork crown, and helps flush out stalled air pulled up from the front wheel to improve aero efficiency.
Its application has simply been broadened to accommodate the Ostro Gravel's 700 x 45c tyre clearance.
Unlike the VAM, the Gravel has a traditional round steerer tube. Factor says the design better copes with knocks, bumps and vibrations thrown up by gravel riding.
The fully integrated routing flows through CeramicSpeed's SLT (Solid Lubrication Technology) bearing system, as found on superbikes such as the Colnago C68.
You might think it's an unnecessary expense, but it's a good choice for a gravel bike destined to spend a lot of time getting dirty because the bearings need far less maintenance.
The bottom bracket uses the T47a threaded standard, which has an asymmetric 77mm-wide shell.
It's claimed to offer the benefits of a press-fit design, but with the quiet (non-creaky) running of a threaded interface. I’ve seen it used by plenty of custom builders, and brands such as Cervélo, Trek and Colnago are also onboard.
The frame and fork finish, called ‘naked grunge’, will divide opinion. Its natural matt carbon with white splatter on the fork legs, down tube, stays and seat tube, has the effect of making your pristine bike look as though it's been pre-ridden.
In my view, the pre-distressed graphics have a mid-1990s Nu-Metal vibe.
Divisive aesthetic aside, every Factor bike I’ve tested has been of the highest quality, and that would appear the case here too.
Factor's aim was for the Ostro Gravel to be the choice of gravel racers. The speeds in gravel racing are increasing steadily, so the need for aerodynamics has shifted higher up the design priority list.
At its simplest, the Ostro Gravel is the Ostro VAM, but with hugely increased tyre clearance.
The geometry has been tweaked over the steep and speedy VAM, but not by a huge amount.
My 56cm test bike sees a relaxing of the head angle by a single degree to 72.3, plus a 3.5mm addition to the fork trail.
The stack is up to 580mm (an increase of 15mm over the VAM) and the reach has been extended to 402mm (from 392mm).
The wheelbase is extended to 1,029mm (from a very short 985mm) to accommodate the larger gravel tyres.
All-in, the Ostro Gravel's geometry has been relaxed somewhat versus the starting point, but if I was quoted such figures for an endurance bike, I wouldn't be raising my eyebrows unduly.
With a SRAM Red AXS XPLR groupset at the heart of the build, the Ostro Gravel is well-equipped.
It includes Quarq's double-sided crank-based power meter.
Value is always relative, especially when you’re dealing with a £9,500 bike, but compared to the BMC Kaius 01 One – which also features Red AXS – the Ostro Gravel is £1,850 cheaper, and the Kaius doesn't have the power meter option.
The chainset runs on a CeramicSpeed bottom bracket to Factor's T47a standard.
The 44-tooth chainring and 10-44t cassette is fast becoming the 1x gravel racing choice, with an ample top end and plenty of range when things steepen.
SRAM's Red hydraulic disc brakes complete the Ostro's drivetrain.
Black Inc, Factor's component arm, provides the integrated handlebar setup. It isn't strictly a ‘gravel’ option, rather the brand's aero cockpit.
It's claimed to offer a nine-watt saving over a conventional bar and stem with external cable/hose routing, thanks to its truncated aerofoil top section and flowing stem shape with matching headset spacers.
My 56cm test bike comes with a 100mm-long and 40cm-wide (centre-to-centre) handlebar. Its road-going, aero design is obvious with the standard (as opposed to flared) drops.
Black Inc's Thirty-Four carbon wheels are, as you’d expect from the name, 34mm deep. The broad blunted profile shapes up at 35mm wide externally, with a hookless 25mm internal width.
The Black Inc hubs come with CeramicSpeed bearings, and the wheel build is completed with a mix of Sapim CX-Ray and CX-Sprint spokes.
The claimed 1,489g weight for a pair helps contribute to the Ostro's low overall 8.12kg weight.
The wheels are wrapped with 700 x 40c Goodyear Connector Gravel tyres with a short, tightly packed knobbled tread, leaning into the bike's racy approach to gravel.
You can certainly feel the road-race roots of the Ostro Gravel as soon as you get on board.
The frame and fork have stiffness in abundance and the oversized bottom bracket shell and generously proportioned chainstays make for a bike that picks up speed with ease.
While the geometry has been tweaked with a higher stack, the reach is still long, so the ride position doesn't feel alien on tarmac.
In fact, it's more akin to a fast endurance bike than the slacked-out angles of a deep-country gravel bike such as Ridley's Kanzo Adventure.
I switched out the wheels for a set equipped with a known 700 x 28c tyre and the Ostro felt every inch a fast, smooth endurance bike in the Cervélo Caledonia or Trek Domane mould.
Reducing the tyre size will effectively reduce the trail figure too, pushing the Ostro Gravel even further into accepted road bike geometry territory.
Off tarmac, the Ostro Gravel is at its best on wider gravel tracks and forest fire roads.
Although it's very stiff, it copes well with jarring vibrations from poor surfaces.
A lot of that is likely down to the Black Inc Aero Integrated Barstem, which though not built specifically for gravel, has an impressive ability to smooth out fatiguing vibrations.
When you venture further off-road into singletrack trails and twisty-turny tech stuff, the road-bike like geometry doesn't do you any favours.
The steering is quick, so you can react and change lines quickly, but it's also bumped off line easily by roots, bumps and cambers.
The Ostro becomes quite a handful at times, and doesn't have the in-built stability of more focused off-road machines.
That said, its responsiveness and the lack of mass (especially in the carbon wheels) makes it a great climber and a speed demon on rolling terrain.
It also impresses when heading downhill on roads and smoother gravel. However, on more technical downhill trails, the Ostro Gravel can prove a handful.
To be clear, if your idea of gravel is byways, un-metalled and fire roads, the Ostro Gravel – much like BMC's Kaius – is one of the best around.
More to the point, if you’re looking for a focused race machine, then look no further.
However, if your gravel riding incorporates more diverse terrain – perhaps a spot of exploration – there are arguably more complete bikes available for your money.
The Ostro Gravel shows itself as very much part of the new breed of gravel racing bikes.
It has road-derived geometry, aero optimisation and enough stiffness to satisfy anyone. Being so focused on the pursuit of speed, it could be said it ventures out of pure gravel and into the realm of all-road endurance bikes.
If your idea of gravel is fast, open, rough roads, you’ll relish the Ostro Gravel. With a switch of tyres, you’ll have a formidable endurance bike to boot.
However, if you want to go deeper into the great outdoors, exploring bridleways, singletrack and some twisty forest routes, the Ostro's tight focus might be too limited.
Each of the bikes selected for our Bike of the Year gravel category was first subjected to a two to three-hour ride at Salisbury Plain in the south of England.
This first fast blast took in wide gravel roads, mountain bike singletrack and forest fire roads, with the ride out using connecting towpaths and bridleways, and the ride back taking in a bit of tarmac.
Next came a 70-mile/113km route over mixed terrain with plenty of elevation changes.
The bikes were then ridden back-to-back over a few weeks to compare the pros and cons of each contender.
I reached my decision on the best-balanced bike, weighing up how well it handles, how well it's equipped, and most importantly how much fun it is.
Thanks to our sponsors, Lazer, FACOM tools and Band Of Climbers for their support in making Bike of the Year happen.
Senior technical editor
Warren Rossiter is BikeRadar and Cycling Plus magazine's senior technical editor for road and gravel. Having been testing bikes for more than 20 years, Warren has an encyclopedic knowledge of road cycling and has been the mastermind behind our Road Bike of the Year test for more than a decade. He's also a regular presenter on the BikeRadar Podcast and on BikeRadar's YouTube channel. In his time as a cycling journalist, Warren has written for Mountain Biking UK, What Mountain Bike, Urban Cyclist, Procycling, Cyclingnews, Total Bike, Total Mountain Bike and T3. Over the years, Warren has written about thousands of bikes and tested more than 2,500 – from budget road bikes to five-figure superbikes. He has covered all the major innovations in cycling this century, and reported from launches, trade shows and industry events in Europe, Asia, Australia, North American and Africa. While Warren loves fast road bikes and the latest gravel bikes, he also believes electric bikes are the future of transport. You’ll regularly find him commuting on an ebike and he longs for the day when everyone else follows suit. You will find snaps of Warren's daily rides on the Instagram account of our sister publication, Cycling Plus (@cyclingplus). ❚