Factor has officially announced its Ostro lightweight and aero race bike that has already seen action with Israel Start-Up Nation in the Tour de France. The new model is available exclusively for disc brakes and electronic shifting and, like most new race bikes these days, it comes with fully internal cable routing. Factor sees the Ostro as “the ultimate all-rounder” for mixed terrain and, with clearance for tyres up to 32mm wide, even cobbles.
“The Ostro concept was born from my long experience working with pro teams and riders, especially at Paris-Roubaix,” said Factor’s Director of Engineering Graham Shrive.
“Every year there would be a couple of riders who wanted to use their aero bikes to get that advantage, no matter how poorly suited they were to the cobbles. Plus, of course, pros have always wanted an aero bike with no weight penalty, or a super light bike with no drag penalty in the valleys, as the climbers might see it. Instead of battling to get them on a bike made for the cobbles, we decided to build them what they wanted, and it turns out to be a hell of a bike."
Factor says that every element of the Ostro is optimised for aerodynamics. The frame uses medium-depth tube profiles that are derived from NACA (National Advisory Committee for Aeronautics) shapes, orientated horizontally (in line with airflow) and truncated – meaning that the trailing edge is cut off square rather than tapering off gradually. This is usually the case in the bike industry, the idea being to make the airflow behave as if it followed a complete airfoil.
“The critical element to the performance of a truncated airfoil is the tight radius at the transition or cut point, but this is challenging to manufacture in carbon fibre,” says Factor. “Owning our factory allows Factor to use a more expensive and time-consuming process to achieve the optimum shape without passing on that cost to consumers.”
The fact that the tubes are truncated aero sections also reduces drag in crosswinds and makes for better handling, and accommodates bottles well.
“In designing the Ostro, Factor considered every aspect of the frame and applied the optimum aero profile, with particular regard to the transitions between frame sections (eg down tube to seat tube, fork and head tube to down tube) and to performance across a full range of effective wind angles,” says Factor.
The Ostro’s fork features what Factor calls a ‘Reversing Flow Energising Channel’. That requires an explanation!
“Both the channel and the fork’s wide stance address the aerodynamic challenge of incoming airflow meeting the ‘reversing flow’ of air carried by the wheel and tyre moving forwards through the fork,” says Factor. “This reversed flow stagnates behind the fork and disturbs airflow around the outside of the fork onto the down tube.
“To solve this, Factor designed a converging nozzle into the fork crown to accelerate the reversed flow out of this area, significantly reducing the pressure changes met by the relatively clean air travelling over the outside of the head tube and fork legs, and thereby improving laminar flow and cutting overall drag.
“Additionally, by significantly increasing the width of the fork legs, the fork legs and the wheel rim are each able to operate in airflow that is undisturbed by the other, allowing the aero profiles to function at optimum efficiency.”
The fork is aerodynamically optimised for use with a 26mm tyre although there is enough clearance to go up to 32mm on a rim with a 21mm internal width.
The Ostro also features a one-piece Black Inc combined handlebar/stem – Black Inc being Factor’s in-house brand – that is also designed to reduce drag.
“Fully internal cabling brings further gains and [we have] achieved this while maintaining a 1 1⁄8in top headset bearing for optimised frontal area, whereas many other brands increase the head tube size to accommodate internal cabling, cancelling out the benefits,” says Factor.
The lower headset bearing is 1 3/8in.
The Ostro is also compatible with separate handlebars and stems, the cables entering below the stem.
Factor claims a weight of 780g for a 54cm Ostro frame (painted) and says that this easily builds into a 6.8kg complete bike (the UCI’s minimum weight for racing) with a power meter and mid-depth aero Black Inc Forty Five wheels (see below) fittee.
“It achieves its remarkable lightness in three ways,” says Factor. “The tube profiles were carefully developed to balance aerodynamics against weight. The down tube, for example, has almost exactly the same cross-section as that of the O2 VAM.
“Also shared are the exceptionally high grades of carbon fibre material used and the industry-leading manufacturing techniques employed to get the very best from them, all made possible because Factor owns its factory and can pass considerable efficiencies to the customer.”
Factor lists the Ostro’s frame as using a mix of TeXtreme, Toray, and Nippon Graphite pitch-based fibre, the same as the O2 VAM.
“Finally, the new integrated cabling system, which debuted recently on the revised O2 VAM, is weight neutral, which is to say it doesn’t add a single gram,” says Factor.
The brand says that it has managed to achieve a low weight while maintaining a high level of frame stiffness. It must be said, we hear that claim a lot. Factor doesn’t offer any figures but says that the “stiffness levels are at or above those of the O2”.
We’ve not ridden the Ostro but Factor claims that it offers a smooth ride, partly because of its ability to take 32mm-wide tyres. Obviously, any bike that can take tyres this wide will benefit in the same way.
Slim seat stays are designed to absorb road noise and cushion bumps, and the fact that they join the seat tube low is intended to help here.
Factor also says that it was able to refine the carbon layup during the Ostro’s R&D phase “in order to achieve a high level of frame compliance without sacrificing any of the power transfer efficiency”.
The Ostro’s geometry is identical to that of Factor’s existing O2 and O2 VAM.
“This is the optimum racing geometry for confident handling and that is unchanged by this bike’s broader role,” says Factor. “Consistent geometry makes it easy for our pro riders to switch bikes and for our customers to choose based on the riding that they do.”
Three different fork offsets (the distance the front hub is offset from the steering axis) are used across the range – 43mm, 48mm and 53mm – to “ensure optimum handling characteristics across all frame sizes”.
Factor’s mid-depth profile seatpost is available in 0 and 25mm offset options (the offset being the distance the clamp sits behind the centre of the post).
We’ve seen both Trek and Specialized move back towards threaded bottom brackets recently, and it looks like Factor is shifting in the same direction by using the T47 standard on the Ostro.
First introduced by Chris King and Argonaut Cycles, T47 bottom brackets thread into a wide shell. They offer a secure fit and straightforward maintenance.
We see the resurgence of threaded BBs as A Good Thing.
Factor sees the Ostro as the all-rounder in its range, for those who want one bike for all kinds of racing and terrain.
The Factor One is designed “for riders looking for the fastest and stiffest road bike to race on flatter terrain and criteriums”.
Factor sees the O2 VAM as the best option for climbing.
The Ostro is available to preorder now.
Frameset: £5,400 (frame, fork, seatpost, bar/stem, CeramicSpeed bottom bracket, headset).
Factor’s Black Inc sub-brand has also announced a new Forty Five wheelset.
“The Forty Five is designed with an optimal balance of aerodynamic performance and lightweight for riders who want a single wheelset to do everything from high mountain gran fondos to flat road races to long training days, and everything else in between,” says Factor.
It’s a disc-only, tubeless-ready wheelset with a rim profile derived from the NACA 0018 airfoil and an internal rim width of 20.7mm. Factor says that the rim is designed to work best with tyres from 25mm to 28mm.
“It’s optimised for real-world conditions, where consistent effective wind angles rarely exceed 10°,” says Factor. “It’s true that riders may experience gusts of wind well beyond this angle, but the sudden and brief nature of a gust means that virtually every aero profile would stall anyway (15° is generally the limit for maintaining laminar flow) and that it is not a lasting condition.
“Therefore, a consistent effective wind angle above 10° is very rare and not a use case for which performance in other conditions should be compromised. Whereas other brands have made the mistake of pursuing ever higher angles of flow attachment as a point of differentiation, Factor focused its attention on creating a wheel that performs best where our customers and pro riders need it to - the real world. The transition point between stalled and unstalled flow conditions is tuned to be less abrupt, which will lessen the buffeting effect in crosswinds and provide more predictable handling.”
The Black Inc HU-07 (24/24 spokes) hubs feature oversized flanges and CeramicSpeed bearings.
The Forty Five wheelset features on complete Ostro bikes (see above) and will also be available separately for £2,170.
Get more info at factorbikes.com
Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now pushing 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.