Factor Ostro Gravel review

Released earlier this year, the Factor Ostro Gravel is a fast-handling, lightweight gravel bike that competitive riders will love.
Using the Factor Ostro VAM road bike as a basis, Factor tweaked features like the bike’s aero tube profiling, tyre clearance and geometry to tune the frame design to suit fast gravel riding.
The innovative frameset design is backed up by high-performance component choices to create a solid package all-round.

While some aesthetic design choices are questionable and the ride quality is on the firmer side of things, the Ostro Gravel is a fantastic proposition for fast gravel riding on easy fire roads, or for having a great time on the road while linking more technical gravel sections together.

Factor Ostro Gravel development

With road-going designs stretching back to the radical 001 and Vis Vires, Factor is a brand with strong racing roots but it was still one of the first names in gravel, releasing the Vista back in 2018.
While that could have been dismissed as an ‘all-road’ bike, which ostensibly sits somewhere between endurance and gravel (or may have even consumed the traditional endurance genre, depending on your viewpoint) Factor’s follow-up to that, the LS, was unequivocally for riding off-road, albeit with a design that could tackle tarmac too with a proficiency befitting Factor’s heritage.
The LS was all about being light weight, having been clearly influenced by Factor’s O2 VAM road bike. Factor’s newest gravel bike, the Ostro Gravel, follows that recipe of inspiration and modification perhaps even more faithfully. It is the off-road counterpart of the Ostro VAM, and both bikes use a design that attempts to maximise aerodynamic efficiency.
‘For the LS we made assumptions that gravel speeds were low enough that we didn’t see a benefit in having an aero frame and we really prioritised light weight instead,’ says Graham Shrive, engineering director at Factor. ‘But working with riders we realised that in gravel races speed is creeping up and being aero is becoming a major factor.’

Factor Ostro Gravel frameset

The Ostro VAM was certainly the basis for the Ostro Gravel’s design, but that doesn’t mean design features have been ported over wholesale. While the cues are familiar from VAM to Gravel, every one has been tuned for off-road use.
For example, the VAM’s ‘Reversing Flow Energising Channel’ – a cavity in the down tube that marries up with the curve of the fork crown, which Shrive says helps flush out stalled air pulled up by the front wheel – is there, but it has been widened so that the transition between the fork, which accepts 45mm tyres rather than the VAM’s 32mm, remains smooth.
The steerer has gone from a D-shape on the VAM to a round one on the Gravel, to ensure the area is able to stand up the harsher impacts experienced during gravel riding over the long term, as well as broaden the compatibility to most aftermarket stems given that finishing component choice on a gravel bike is perhaps a more idiosyncratic mix than on road.

Users may not opt to take advantage of the versatility the Ostro Gravel’s front end offers though, for Black Inc’s (Factor’s components brand) new HB02 integrated bar/stem is said to save 9 watts over a conventional cockpit setup.
Likewise, the tube profiles of the frameset claim to be more efficient than average too, specifically at off-road speeds. They are aerofoil-esque in cross section, yet more sharply truncated.
‘We focussed on the free stream flow, the areas which come in front of the rider and outside of the wheel, so the forks, the head tube and then the handlebar and seatpost,’ says Shrive.
‘At lower velocities, the airflow will detach and at some point it reattaches, but if you can trick that airflow to separate earlier it can then reattach quicker and you get lower performance drag further downstream.’

Staying on the Ostro Gravel frameset but talking about it in the most superficial sense, it is worth discussing the bike’s available paint schemes.
Factor offer it in just two options at the moment: ‘Naked Grunge’ and ‘White Grunge’. Naked grunge is predominantly a clear lacquer over frame’s composite structure. In bright sunshine, this exposes depth and quality of the carbon composite layup and the result is beautiful.
The finish overall is marred in my opinion though by the white paint that speckles the fork, seat tube and chainstays. To me, that looks as if the tyres have had a puncture, sealant has sprayed onto the frame and the rider hasn’t wiped it off.
What’s more, while I genuinely believe that Factor makes some of the highest quality and best performing bikes on the market, the Ostro Gravel’s ‘Never. Status. Quo.’ slogan on the fork legs and top tube is shudder-inducing, reminiscent of a dark time several years ago when brands would festoon their bikes with meaningless, unquantifiable acronyms like UHS and UTSS*.
*For those interested, UHS stands for Ultra Hollow Structure and UTSS stands for Ultra Thin Seat Stay. Both are genuine examples of acronyms found on bikes produced circa 2012.

Factor Ostro Gravel build

The gravel-focussed, 1x XPLR variant of SRAM’s Red eTap AXS groupset (with a built-in Quark power meter) is specced on the Factor Ostro Gravel.
The Ostro Gravel’s resultant asking price is relatively competitive considering its build and the quality of its frame design, but should the prospective customer be looking to reduce the cost, builds with several versions of SRAM’s Force eTap AXS are available, and there’s the option to buy frameset-only or a ‘rolling chassis’ of frameset (which includes the seatpost and bar/stem) and wheels too.

Thanks to SRAM’s eTap AXS 12-speed 10-44 cassette, the Ostro Gravel has a decent spread of gears but ultimately the use of a large 44t chainring means most of those gears are pretty tall for most gravel riding environments.
The bike is built for racing but I can imagine that many customers will want to reduce the stock chainring size to create a bottom gear lower than the 1:1 the Ostro Gravel’s stock guise creates.

The bike follows the lead of Factor’s Lando cross-country mountain bikes by making use of CeramicSpeed’s new SLT headset bearings. In the cavity between balls, cage and races where a regular bearing has grease, the SLT bearings have a solid, self-lubricating polymer that is said to make the bearing maintenance-free because the is no physical space for contaminants to enter the bearing.
In era of integrated cables that often run through the upper headset bearing, and therefore require bar/stem/hose uninstallation in order to service it, this is potentially a great advantage for a bike design (particularly one frequently exposed to grotty conditions) to possess.
Given the relatively brief nature of my test period abord the Ostro Gravel, I can’t comment on the SLT bearings durability, but would say that logically the design should at the very least drastically extend the intervals between necessary bearing service.
The solid polymer used in the bearings unavoidably increases friction versus a grease. I’d say the stiction of the bearings could be noticed when riding no-handed, in that the bike was a little harder to steer with my hips, but in general riding conditions the slightly stiffer rotation was unnoticeable.
Therefore, I’d say the inclusion of the SLT bearings is a valuable addition to the Ostro Gravel and a promising technology for the bike market in general.

The Ostro Gravel also debuts Black Inc’s new Thirty-Four wheels. These are designed to be wide (internal width 25mm, external width 30mm) and robust, but also light too, at a claimed 1,489g.
They are hookless and use high-quality subcomponentry, like Sapim’s CX-Ray spokes and a Black Inc hubset that incorporates CeramicSpeed’s coated low-friction bearings.
While my time on the Ostro Gravel only afforded me a superficial look at the wheels, my impressions were good. They responded promptly to pedalling input despite their light weight, and were notably easy to seat and inflate tubeless tyres on to.
Changing the tyres on the wheelset twice, I completed the task without the need for tyre levers and a regular track pump was sufficient to seat the tyres.

Factor Ostro Gravel geometry and sizing

One aspect of the Gravel tuned for broader applications than gravel racing is its geometry.
It has a higher stack figure to engender a sustainable body position and longer chainstays for a stable ride, but otherwise the Gravel’s figures have more in common with road bikes than traditional gravel machines.
Seat and head tube angles are steep, with Factor selecting a fork offset to create trail figure that sits around 61mm with 40mm gravel tyres on, but reduces to 58mm with 30mm road tyres on (narrower tyres reduce the radius from the wheel axles to the outside of the tyre, effectively making the bike lower). Both figures could be considered nimble in their respective disciplines.

Riding the Factor Ostro Gravel

While the Ostro Gravel does have provisions like plenty of mounting points that widen its riding remit, the bike is clearly geared towards gravel race performance.
That is quickly evident when riding the bike. At low speed, while its fast handling stops it from feeling cumbersome, it certainly thuds over ruts and rocks in a pretty unforgiving manner.

High speed is where the rider gets the best out of the Ostro Gravel. It imparts a similar sense of ease when going fast that aero bikes do in similar situations on the road.
Given that speeds where aerodynamic efficiency even begins to be noticed are far more rarely attained on gravel, generally it was often just a fleeting sensation, but more commonly there was distinct feeling of skimming across the top of broken ground rather than churning through it.
The Ostro Gravel’s road bike-like design made it fun and reactive to ride when back on tarmac too.
It would be reasonable to attribute the Ostro Gravel’s ability to skip over rough surfaces and dart about like a road bike on the tarmac to the stiffness created by the bike’s chunky tube profiles, but also its uncommonly light weight.
There may well only be a few competitors with which to compare it, such as the 3T Exploro Racemax, BMC Kaius, Ridley Kanzo and Cervélo Aspero, but 7.9kg for a size 56cm puts the Ostro Gravel amoung the lightest designs of its type, and as such is quite the feat for Factor to have achieved.

Factor Ostro Gravel verdict

The case for the bike on prolonged sections of easy gravel, as found in places like the US, is clear cut. Given I only have anecdotal evidence and the brand’s word to go on I couldn’t say anything for certain, but providing there is efficacy in the bike’s aero design then the rider could expect to hold an advantage by using the Ostro Gravel in this sort of riding situation.
The rationale for choosing the Ostro Gravel could come across as less valid in places like the UK though, where the gravel riding is often more technical and much slower. It could be said that a rider would be better overall if they opt for a more comfortable bike than the Ostro Gravel in this situation.
However, considering that so much of the time those trails are broken up and linked by stretches of road riding, the bike’s competence on the tarmac makes a solid case for it to be a great choice in that environment too.

• Buy the Factor Ostro Gravel now from viresvelo.com (£8,430)

Factor Ostro Gravel spec

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Factor Ostro Gravel alternatives

Factor LS

The LS was Factor’s first true gravel bike and focusses on light weight. The frameset uses fewer proprietary parts so there is plenty of scope to customise each bike.

• Buy the Factor LS from viresvelo.com (from £5,999)

Ostro VAM

The Ostro VAM served as the starting point for the Ostro Gravel. The two bikes share many of the same features, but the slightly more svelte Ostro VAM is geared towards road use.

• Buy the Factor LS from viresvelo.com (from £8,400)

Pick of the kit

Assos Mille GTS Spring Fall jacket

The Mille GTS exemplifies Assos’s approach of bringing disparate fabrics together in one garment. The front and side panels use Assos’s new Airblock.888 fabric, which feels unusually inelastic, while the back is essentially a light, stretchy mesh.
The arms add a water-repellent fleece-backed fabric to the mix, and the garment they combine to create is superb.
The front blocks out the elements, the back panel ventilates heat and moisture, and the arms are luxuriously soft. It’s an ideal top for autumn and spring.
Looking for your ride? Don’t miss our guide to the best gravel bikes
Photos: Lizzie Crabb