Takeaway: An aggressive gravel racing bike that shares traits with top-of-the-line aero and lightweight road bikes seen in the pro peloton. It's a no-expense-spared bike built for going fast on gravel.

  • Feels like a road bike with big tires.
  • Cables are hidden to cheat the wind.
  • Factor offers six complete builds of the Ostro Gravel, all with SRAM drivetrains.

Factor Bikes Ostro Gravel SRAM Red AXS

Ostro Gravel SRAM Red AXS

Factor Bikes Ostro Gravel SRAM Red AXS

$10,900 at Factor Bikes
Credit: Thomas Hengge
  • Good tire clearance
  • Lightweight and aero frame
  • Blends the feel of a road bike with gravel capabilities
  • Threaded bottom bracket
  • A little harsher than other gravel racers
  • Electronic shifting only
  • Internal routing can complicate simple adjustments

Gravel bikes are currently the most popular type of bike, and gravel events continue to grow, so it's no surprise to see the segment diversify and specialize. Companies now offer several kinds of multi-surface, drop-bar bikes to fill the varied wants and needs of gravel riders and racers. While some brands prefer to balance utility and performance with their gravel offerings, Factor went all-in on speed.

Factor used its Ostro road bike as a starting point. The Ostro is an aero race bike with all the usual tricks to cheat the wind, like fully-integrated cables and aero tube profiles. These features are not typically found on gravel bikes, but with the growth of gravel racing as a competitive discipline, it's not surprising that the marginal gains philosophy is creeping into more and more gravel bikes.

The Ostro Gravel is a gravel racer's race bike, or maybe it's a road racer's gravel bike, or perhaps it's both. Compared to many gravel bikes, though, the Ostro Gravel feels stripped down, with only the minimal frame mounts required to be successful in a fast self-supported race.

factor ostro gravel
The Ostro Gravel is built for speed on gravel.
Thomas Hengge

As a rider, I fall into the category of those who gravitate toward this kind of gravel bike. I like hopping on my gravel bike and not feeling far off what I'm used to on my daily road bike. Essentially, I want my road bike, but with larger tire clearance and maybe a couple of extra mounts.

The stack and reach numbers of the Ostro Gravel wouldn't look out of place on a road bike, which may appeal to some riders and deter others. The reach is a touch longer and is designed to pair with a slightly shorter stem, a geometry approach many brands employ with their gravel bikes. But Factor doesn't take this to an extreme where it feels awkward or out of place. Riders coming to gravel from a road cycling perspective (those seeking a road bike with big tire clearance) will find that exact bike here. If your idea of a gravel bike is something more versatile, I'd suggest looking elsewhere. This bike is built to go fast.

Frame Details of the Ostro Gravel

The Ostro Gravel uses much of the optimization seen on the Ostro VAM but with a few changes needed by gravel racers. The top tube has mounting points for a small feed bag, and bosses for three bottles, with the third mount placed on the underside of the downtube. Missing are rack, fender, or extra bag mounts, so if bike packing is your primary focus, you probably want to consider a different bike.

The Ostro Gravel tube shapes resemble the Ostro VAM but are tweaked slightly to optimize aerodynamics for the speeds of gravel racing. Black Inc. designed the Ostro's handlebar/stem to integrate seamlessly with the frame and maximize aerodynamics.

factor ostro gravel
The Black Inc bars offer plenty of comfortable riding positions.
Thomas Hengge

Unlike the Ostro VAM, the gravel version uses a round steerer and accepts most traditional stem setups (if you prefer to go that route). Granted, stems with internal routing compatibility will work best, though I was able to test fit an externally routed stem with room for the hoses to sneak into the frame without issue. The downside of the fully-internal cable routing meant I could not quickly swap the stem and bar to get my preferred reach, a common challenge with integrated cockpit designs.

factor ostro gravel
I was particularly impressed with the comfort and shape of the bars when in the drops.
Thomas Hengge

The D-shaped seatpost is proprietary to the frame. This is where I think a little bit of compliance should have been built in, but Factor decided to stick with the chunky aero design seen on its road bike, but with a few changes.

The gravel post features a more traditional cradle design, which helps prevent the saddle from moving when you are bouncing around. It is a bit beefier compared to the one on the VAM. The Ostro Gravel post is built for speed and durability—extra comfort was not on the agenda.

Other gravel bikes I have ridden, such as the BMC URS and Cannondale Supersix Evo SE, have much slimmer seatposts; engineered to flex for a smoother ride over rough surfaces. While the URS is a more endurance-focused gravel bike, the Supersix EVO SE is in the same fast-gravel world as the Ostro and offers a noticeably smoother ride, especially when seated. While the Ostro's large tires do quite a bit to iron out chattery roads, in longer races, every little bit of compliance helps.

The T47 bottom bracket is (mostly) a welcome inclusion. The T47 standard offers compatibility with almost any crank on the market and marries the positives of both PF30 and a threaded system. Factor opts for a Ceramic Speed T47 BB, an enhanced version that saves you some watts and, theoretically, adds more durability. The downside of T47 is the higher replacement cost compared to PF30 and BSA bottom brackets, even if you opt for more conventional steel bearings.

factor ostro gravel
Free speed! Ceramic Speed is seen all over the Ostro Gravel
Thomas Hengge

The drivetrain on our test bike utilizes a SRAM Red AXS XPLR groupset. It features a wide-range 10-44T cassette on the back paired with a 44-tooth chainring up front. The 44x10T offers a large enough gear for high-speed road sections and descents. While the other end, you get a 1x1 ratio for the loose, steep climbs often found in gravel races. Our test bike also included a power meter, but you can skip this option to save some cost.

The wheels were developed (in conjunction with the bike) to be the Black Inc. gravel-specific race wheels. The rims are 34mm deep, have a 25mm wide internal hookless profile, and are optimized for 32 and 43mm width tires. And inside the hubs are yet more Ceramic Speed bearings. With a claimed weight of 1,489g, the wheelset is competitively light.

A claimed frame weight of 900 grams and an impressively light build kit meant that our size 52 cm test bike came to 17.5 lbs with cages, computer mount, and pedals. Weighing under 18 lbs. with accessories puts this bike comfortably alongside many road bikes. If you wanted to go full weight-weenie, you could drop under the 17 lb. mark by swapping to lighter tires and a carbon-railed saddle.

Geometry and Sizing

The Ostro Gravel has six sizes (49 to 61 cm), and Factor kept the handling sharp, as the bike is intended to be ridden fast.

Factor uses a different offset fork on the 49 and 52 cm sizes to maintain similar trail numbers across the entire size range. This keeps the handling uniform regardless of the size you ride. The 54 through 61 cm sizes have 61mm of trail, while the 49 and 52 measure just 1mm longer at 62mm.

When ordering, riders can choose either a 0 mm or a 20 mm offset seatpost. They can also specify their cockpit dimensions, available in lengths from 80 mm to 140 mm, and widths from 360 mm to 420 mm. This level of detail is helpful, particularly on bikes with full-internal cables, as swapping out cockpit parts after purchase can be an expensive headache.

factor ostro gravel geometry chart
Factor Bikes

Models and Pricing

Factor offers customization in its ordering processes that few other brands match. The Ostro Gravel can be purchased as a frameset package (including cockpit and seatpost), for $5,500. For an additional $2,000, buyers can add a set of Black Inc. Thirty Four wheels, with Shimano, SRAM, or Campagnolo freehub options.

Factor has six complete bike builds of the Ostro Gravel, all using SRAM components. Riders can choose between three Force eTap AXS builds. These range from $8,200 to $8,800 with 2x or 1x drivetrain choices and a power meter option. Similarly, there are three Red eTap AXS builds from $9,800 to $10,900.

Ride Impressions

The Ostro Gravel has generous tire clearance (up to 45mm max) and comes standard with 40mm tires. In its proper environment of gravel roads, the Ostro shines. Since the Ostro is purpose-built to go fast, the handling is responsive and precise. It feels perfect for the Ostro Gravel and how the bike is meant to be used.

The trade-off for this efficiency and speed is a slightly harsher ride. The deep aero tubes aren't meant to flex much, and the Ostro Gravel doesn't feel like some other modern gravel rigs. But that's not what this bike is about. For riders who love high-performance road bikes, the Ostro Gravel will easily tug at their heartstrings. I like going fast, so bikes that respond to acceleration are something I seek and want. The Ostro Gravel offers that kind of experience.

factor ostro gravel
Thomas Hengge

While many gravel bikes offer the versatility of doing double duty as commuters or bikepacking adventure bikes, the Ostro Gravel certainly does not. However, it will happily dress up as a road bike when needed, thanks to its speed-focused features. Throwing 35mm slick tires on the Black Inc. wheels transforms the Ostro from a gravel rocket to a double-duty aero road bike, especially with the 2x drivetrain setup.

The Ostro Gravel strikes a good balance of race-like and confident handling. It'll happily dive into a corner but isn't overly twitchy, thanks to a longer front center and stretched wheelbase compared to its road counterparts. When looking at the beefed-up bottom bracket area, you probably won't be surprised that this bike responds to efforts with urgency.

factor ostro gravel
Thomas Hengge

The wide range 1x XPLR groupset worked flawlessly through my test riding. I used every bit of the 10-44T range on the fast, rolling terrain near our Easton, Pennsylvania office. While I found the range perfect for my local roads, some riders might want a bit more. If you live somewhere mountainous, a smaller chainring will offer lower gearing. Or choose one of the 2x builds for the broader gear range.

One gripe I still have with 1x setups on “fast-gravel bikes” is the lack of subtle changes in gearing when rolling at a fast pace. If I needed a slightly harder or easier gear to maintain a preferred cadence, I was forced to choose between two options that weren't quite right. Fortunately for riders like myself, the Ostro Gravel does have provisions for a front derailleur—provided that the FD is electronic.

The Ostro Gravel is only compatible with electronic drivetrains, a trend in high-end bikes that we have lamented on several occasions. Unfortunately, riders looking to build a gravel bike with mechanical shifting will need to skip the Ostro Gravel.

factor ostro gravel
Thomas Hengge

For riders whose idea of gravel riding looks mostly like road riding, just on unpaved surfaces, the Ostro Gravel might be the perfect bike for you. It will also appeal to riders who love the feel of road racing bikes and don't want a gravel bike that strays too far from the familiar. Riders looking for a supremely compliant, comfortable, and relaxed gravel bike—or folks looking to go bikepacking—should consider other options.

Headshot of Trevor Raab
Trevor Raab

Trevor Raab is the staff photographer for Runner’s World and Bicycling, a CAT 1 cyclocross racer, and, occasionally, a product reviewer for the Test Team. He fits the typical “how I got in to bikes” story: his dad introduced him to mountain bikes when he was a kid, then he had a  stint as a skateboarder in high school, and since 2011 he’s been riding every sort of bike he can find.